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'[PIC]: Direct LED connection?'
2002\10\29@155148 by Brooke Clarke

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face
Hello:

Old Business:
Thanks to a number of people who pointed out the RA4 is an open collector in
response to my last post.

New Business:
I inadvertently connected an LED directly to RC5 with no current limiting
resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port can only
source about 25 mA and that's about right for a bright LED.  Other than the
current draw is there any down side to driving the LED directly?

Thanks,

Brooke Clarke

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2002\10\29@160313 by Bob Blick

face picon face
> I inadvertently connected an LED directly to RC5 with no current limiting
> resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port can only
> source about 25 mA and that's about right for a bright LED.  Other than the
> current draw is there any down side to driving the LED directly?

According to Kurt Kuhlmann of Microchip, running an LED directly from a
PIC pin and ground, power supply voltage up to 5 volts, is perfectly OK.
It will not draw more than 25 mA.

Connecting the LED from PIC to +5, on the other hand, is likely to draw
more than 25 mA and is not recommended.

That's because the PICs output MOSFETs have different on-resistances, the
high side being P-channel types.

Cheers,

Bob

P.S. use a resistor anyway :)

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2002\10\29@161523 by Herbert Graf

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:
> I inadvertently connected an LED directly to RC5 with no current limiting
> resistor.  It is flashing brightly at 1 Pulse Per Second.  The
> PIC port can only
> source about 25 mA and that's about right for a bright LED.

       No, the PIC output is speced to source a max of 25mA, that doesn't mean it
is limited to 25mA, you are likely drawing more then 25mA which is out of
spec for the PIC and will damage something.

> Other than the
> current draw is there any down side to driving the LED directly?

       Yes, for the above reason, the PIC outputs are NOT current limited by
design, and certainly don't limit themselgves to only 25mA. TTYL

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2002\10\29@164016 by Bob Blick

face picon face
On Tue, 29 Oct 2002, Herbert Graf wrote:
>         Yes, for the above reason, the PIC outputs are NOT current limited by
> design, and certainly don't limit themselgves to only 25mA. TTYL

But when you say that, you make it sound like there could be infinite(and
damaging) current flow.

Let me point out that the PIC has internal resistance (which varies
depending on power supply voltage and pin polarity, among other things)
which does, in fact, lead to a predictable limit on output current.

If you connect a PIC output to ground and try to drive it high, excessive
current will flow. However an LED connected to ground is not ground. The
voltage drop of the LED and the PICs resistance will limit the current to
under 25 mA.

-Bob

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2002\10\29@165925 by Russell McMahon

face
flavicon
face
> I inadvertently connected an LED directly to RC5 with no current limiting
> resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port
can only
> source about 25 mA and that's about right for a bright LED.  Other than
the
> current draw is there any down side to driving the LED directly?

'tis somewhat naughty and you really should check the current to be certain.
This will change with LED type also - eg white LED at 3.5v odd is much nicer
to PIC than red LED at rather less forward drop.

Doing this risks holding the PIC pin at near mid rail where interesting
internal effects may happen. While this is normally more of a concern for
inputs it's not overly wise here.

All that said - this definitely works OK in practice SOMETIMES. YMWV. If
this is for a one off non mission critical application for fun and you don't
mind it self destructing and size is all critical (eg in a brooch or badge
etc) then do it. Otherwise, addition of a resistor is recommended.



       Russell McMahon

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2002\10\29@184738 by Herbert Graf

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> On Tue, 29 Oct 2002, Herbert Graf wrote:
> >         Yes, for the above reason, the PIC outputs are NOT
> current limited by
> > design, and certainly don't limit themselgves to only 25mA. TTYL
>
> But when you say that, you make it sound like there could be infinite(and
> damaging) current flow.

       Not infinite, but it could be damaging. I personally err on the side of
caution and assume that if I exceed the posted current draw I'll kill the
part. A little cautious perhaps but it has served me well (expect for those
times where I ignored my own rules and a puff of smoke resulted... :) ).

> Let me point out that the PIC has internal resistance (which varies
> depending on power supply voltage and pin polarity, among other things)
> which does, in fact, lead to a predictable limit on output current.

       True, but would you count on that for a production design? Unless Microchip
officially says "the output current is limited to 25mA" I wouldn't. For
experimenting sure.

> If you connect a PIC output to ground and try to drive it high, excessive
> current will flow. However an LED connected to ground is not ground. The
> voltage drop of the LED and the PICs resistance will limit the current to
> under 25 mA.

       Until Microchip changes something and doesn't tell us... they can do that
since that is not part of the spec sheet. TTYL

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2002\10\30@160139 by Olin Lathrop

face picon face
> I inadvertently connected an LED directly to RC5 with no current
limiting
> resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port
can only
> source about 25 mA and that's about right for a bright LED.  Other than
the
> current draw is there any down side to driving the LED directly?

This is a bad idea as the PIC port is only specified to provide at least
25mA at a certain minimum voltage.  There is no guarantee it won't supply
more, at the LED voltage.  You could end up damaging both the PIC and the
LED.


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2002\10\30@162030 by Olin Lathrop

face picon face
> Let me point out that the PIC has internal resistance (which varies
> depending on power supply voltage and pin polarity, among other things)
> which does, in fact, lead to a predictable limit on output current.

No, not predictable.  Show me how to calculate this from spec sheet
values.  It might be predictable for any one chip that was explicitly
measured, but may change drastically next die shrink or even next
production batch.

> If you connect a PIC output to ground and try to drive it high,
excessive
> current will flow. However an LED connected to ground is not ground. The
> voltage drop of the LED and the PICs resistance will limit the current
to
> under 25 mA.

Not according to anything guaranteed in the spec sheet.


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2002\10\30@231738 by Brett Walach

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> > I inadvertently connected an LED directly to RC5 with no current
> limiting
> > resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port
> can only
> > source about 25 mA and that's about right for a bright LED.  Other than
> the
> > current draw is there any down side to driving the LED directly?
>
> This is a bad idea as the PIC port is only specified to provide at least
> 25mA at a certain minimum voltage.  There is no guarantee it won't supply
> more, at the LED voltage.  You could end up damaging both the PIC and the
> LED.

Also, if the LED is not destroyed, it will most likely appear to be a
different color, usually dimmer than before. Returning to a safe current
will also not fix the LED once its been "roasted" ;)

Sincerely,
Brett

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2002\10\31@171022 by Bob Blick

face picon face
On Wed, 30 Oct 2002, Olin Lathrop wrote:
> No, not predictable.  Show me how to calculate this from spec sheet
> values.  It might be predictable for any one chip that was explicitly
> measured, but may change drastically next die shrink or even next
> production batch.

Easy. From spec sheet, .7v at 3mA, from Ohm's Law .7/.003 = 233 Ohms.

I'm not just spouting lies, this use (connecting LED directly from PIC and
ground) is blessed by Microchip FAE Kurt Kuhlmann regularly at Microchip
seminars.

Cheers,

Bob

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2002\10\31@203153 by Roman Black

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Bob Blick wrote:
>
> On Wed, 30 Oct 2002, Olin Lathrop wrote:
> > No, not predictable.  Show me how to calculate this from spec sheet
> > values.  It might be predictable for any one chip that was explicitly
> > measured, but may change drastically next die shrink or even next
> > production batch.
>
> Easy. From spec sheet, .7v at 3mA, from Ohm's Law .7/.003 = 233 Ohms.
>
> I'm not just spouting lies, this use (connecting LED directly from PIC and
> ground) is blessed by Microchip FAE Kurt Kuhlmann regularly at Microchip
> seminars.


So at what point are Microchip going to back him
up by putting the "constant current source" spec
in the datasheet?

Is this the same guy that wrote the infamous Microchip
app note showing 120vac connected directly to a PIC
input via a resistor?? <grin>
-Roman

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2002\10\31@210403 by Sean Alcorn - Avion SYD

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Roman,

> Is this the same guy that wrote the infamous Microchip
> app note showing 120vac connected directly to a PIC
> input via a resistor?? <grin>

Cool! Where is that app note? Is there one for connecting to 240VAC?
Although, they'd probably run a little hotter on 50Hz :-)

Cheers,

Sean

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2002\10\31@212400 by Roman Black

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Sean Alcorn - Avion SYD wrote:
>
> > Is this the same guy that wrote the infamous Microchip
> > app note showing 120vac connected directly to a PIC
> > input via a resistor?? <grin>
>
> Cool! Where is that app note? Is there one for connecting to 240VAC?
> Although, they'd probably run a little hotter on 50Hz :-)


I believe it's the "ac mains zero crossing detector"
application note that was discussed here on the
list a while back. :o)
-Roman

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2002\10\31@213343 by Russell McMahon

face
flavicon
face
> > Is this the same guy that wrote the infamous Microchip
> > app note showing 120vac connected directly to a PIC
> > input via a resistor?? <grin>
>
> Cool! Where is that app note? Is there one for connecting to 240VAC?
> Although, they'd probably run a little hotter on 50Hz :-)

It was a test input for a measuring instrument.
AFAIR the device concerned won a design contest. It was a clever piece of
work by a competent designer but that didn't make this particular aspect
'right'.

It was potentially able (no pun intended) to both pump up the whole power
supply and violate the PIC operating specs. This was pointed out to uChip
but the answers I saw posted seemed to indicate that the respondent did not
understand the question or the problems. There's no reason that everyone at
uChip or anywhere else has to be a rocket scientist or that they will pass
something they don't understand on to somebody who does. In this case they
CLEARLY didn't. <<Flame suit? Who needs a flame suit.>>



       Russell McMahon

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'[PIC]: Direct LED connection?'
2002\11\01@070449 by Sean Alcorn - Avion Sydney
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Hi Roman,

> I believe it's the "ac mains zero crossing detector"
> application note that was discussed here on the
> list a while back. :o)

Well that's different! I misread your original post as supplied from
the AC.

But I have seen this zero crossing detect in a number of places. It's
in two circuits on pages 11 and 89 of "50 things to do with a PIC" by
Paul Benford - a 6M8 resistor is connecting GP5 of a PIC12C508 to the
"neutral" and a simple capacitor/resistor supply not unlike a circuit
one that I have used to supply PICs in a couple of commercial products.

In the text he says;

"The PIC devices are very good at handling high voltage. The majority
of I/O pins have clamping diodes both to Vdd and Vss. This means that
any voltage appearing on the I/O greater than the supply or less than
ground will be clamped to Vdd or Vss respectively. The instantaneous
current rating for these diodes is 20mA. This does not mean that they
will be happy sinking that current forever. The maximum continuous
current rating is 500uA. Therefore before applying any large voltage to
an input ensure that there is a current limiting resistor in series."

He then goes on to say;

"The value of the input resistor needs to be less than 10Mohms. [he
does not explain why] It needs to be high [enough] though to limit the
current to less than 50uA. This provides a safety margin of 10 over the
maximum continuous rating. The calculations fall out easy with:

Vpeak = V2 x 240 = 339.5 Volts
Resistance = Vpeak/Ipeak = 339.5 Volts/50 uA
= 6.8 MOhms"

A similar circuit also appears on page 100 of "The Greatest Little PIC
Book" by Gordon Macnee. This circuit has the neutral connected to GP4
of a PIC12C508 via 2 x 4M7 resistors.

Also on page 84 of the "PIC Cookbook - Volume 1" by Nigel Gardner and
Peter Birnie, a circuit shows Pin RA3 connected to neutral via 2 x 1M
resistors.

I was quite seriously considering such a technique in my next project.
Can I assume that you do not think this is wise?

Regards,

Sean

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2002\11\01@075952 by Olin Lathrop

face picon face
> Easy. From spec sheet, .7v at 3mA, from Ohm's Law .7/.003 = 233 Ohms.

That is either a minimum guaranteed current at that voltage or the maximum
guaranteed voltage at that current (the exact reference wasn't supplied,
so I didn't chase down the particular spec sheet line).  Nothing says that
the current at 700mV couldn't be considerably higher.


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2002\11\01@085422 by Olin Lathrop

face picon face
> I was quite seriously considering such a technique in my next project.
> Can I assume that you do not think this is wise?

I don't see a problem with connecting a PIC input to mains power via a
suitably large resistor (several Mohm), but you should note the following:

1  -  This does not apply to analog inputs.  I have noticed small Vdd
protection diode current cause significant errors on the remaining analog
channels.  I'm guessing this is because the internal reference voltage
gets messed up.

2  -  I would keep the protection diode current well under the specified
maximum.

3  -  This topology should never be used if any part of the PIC circuit
goes anywhere near where humans can touch.  It would never get regulatory
approval, and is safety hazard in any case (imagine a little dirt or
moisture on the resistor).  It is fine if this circuits in encapsulated
inside a grounded metal box on the primary side of a power supply, for
example.

4  -  Unless this is a very high volume product where every cent matters,
I would spend a few extra resistors and diodes to make it just a little
more failsafe.


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2002\11\01@091525 by Sean Alcorn - Avion Sydney

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Olin,

> 1  -  This does not apply to analog inputs.  I have noticed small Vdd
> protection diode current cause significant errors on the remaining
> analog
> channels.  I'm guessing this is because the internal reference voltage
> gets messed up.

No. Only digital I/O necessary to detect zero cross.
>
> 2  -  I would keep the protection diode current well under the
> specified
> maximum.

Yes. As the writer says - 50uA - just 10% of the MAX.
>
> 3  -  This topology should never be used if any part of the PIC circuit
> goes anywhere near where humans can touch.  It would never get
> regulatory
> approval,

I do not agree. What's the difference if 240VAC is on the resistor when
the triac on the same board is at the same potential? Provided the
circuit is enclosed, what is the difference?

> and is safety hazard in any case (imagine a little dirt or
> moisture on the resistor).

You fry the PIC?

> It is fine if this circuits in encapsulated
> inside a grounded metal box

A lot of our stuff is encapsulated, but this project will probably not
be. But we never encapsulate in grounded metal boxes - always in
plastic.

> 4  -  Unless this is a very high volume product where every cent
> matters,
> I would spend a few extra resistors and diodes to make it just a little
> more failsafe.

Well yes, it is high volume, and every cent does matter, but what would
you suggest? An opto is over-kill and is not necessary when the entire
circuit can be assumed to be at mains potential, and is therefore
always out of human contact - either double insulated or encapsulated.

Regards,

Sean

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2002\11\01@094326 by Michael Rigby-Jones

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> >
> > 3  -  This topology should never be used if any part of the PIC circuit
> > goes anywhere near where humans can touch.  It would never get
> > regulatory
> > approval,
>
> {Original Message removed}

2002\11\01@095143 by Roman Black

flavicon
face
Sean Alcorn - Avion Sydney wrote:
{Quote hidden}

No I don't like it at all. A series resistor does
NOT isolate voltage. Now 2 resistors maybe.
A resistor into a zener of known and testable
properties yes. Add a capacitor across the zener
and even better.

I the Microchip lab which probably has isolation
transformers and nice SMOOTH 120v ac mains it
will probably work forever with just the resistor.
Here in Australia with some of the dirtiest 240vac
in the western world I wouldn't even consider it.

People will argue that the PIC internal diode clamps
the pin to never exceed 5.5v or so. This is AFTER
the diode has properly turned on and saturated.
With dirty mains you will get spikes of very high
Dv/Dt and the pin voltage will rise to unknown
high levels BEFORE the diode has fully turned on
as that takes a finite time.

Much better than a clamp diode is an external 5v
zener, this will "break down" to provide the
clamping, and I would always add a capacitor
across the zener to further provide RC time
constant so fast spikes no longer are an issue.
Also remember resistors have a max voltage and
when you get regular spikes into the kV range
you need 2 or more resistors to be reliable
with 240v systems. I've replaced a lot of "start"
resistors in TV sets, typically 2 or 3 resistors
in series about 470k each. With age these change
value and the carbon ones especially do strange
things. :o)
-Roman

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2002\11\01@100739 by Micro Eng

picon face
I've used the AC direct to PIC via resistor for years now...granted its 6VAC
not 120VAC...but it works well to determine if I have a 50Hz or 60Hz
mains...






{Quote hidden}

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2002\11\01@102008 by Chris Loiacono

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> > I was quite seriously considering such a technique in my
> next project.
> > Can I assume that you do not think this is wise?

I followed a project where a guy try out the ap note that has one connecting
the AC to inputs with series resistors, without, and in every manner
imaginable. It was rather sad to find that he had gone through an insane
number of PIC's before giving up. He had a particularly noisy AC line.

I suppose the idea would work if you could count on a clean AC line.
Transients on even a 120V line (such as a cheap lamp dimmer, noisy motor
nearby, etc..) will kill the PIC in a heart beat. Even the projects reported
on in this thread that worked were probably not analzed with a multi-channel
anlyzer or DSO with one analog channel tracking the Ac simultaneously. I
have seen very brief hits that show up on the PIC's RST pin that coincide
directly with captured line transients. Interestingly, the operation of the
PIC seems to continue with only minor hitches (a single bit may flip or a
register value may get garbled) and if the system includes a control loop
that will recover the hiccup may not ever be noticed. If I hadn't seen this
with my own eyes, I wouldn't report it here.

So I guess people would say that this method has worked for them, but it
always scoped as I described  - too sloppy for me. These are the products
that you can get signed off, but then have hi failure rates in the field.
No thanks....not for me.

Chris

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2002\11\01@102424 by Chris Loiacono

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My point exactly. Same situation in SE U.S.
Nicely put, Roman. I'll add just a few more words: "it's like russian
roulette"

CL

> No I don't like it at all.
> I(n) the Microchip lab which probably has isolation
> transformers and nice SMOOTH 120v ac mains it
> will probably work forever with just the resistor.
> Here in Australia with some of the dirtiest 240vac
> in the western world I wouldn't even consider it.

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2002\11\01@102624 by Spehro Pefhany

picon face
At 08:54 AM 11/1/02 -0500, Olin wrote:

>1  -  This does not apply to analog inputs.  I have noticed small Vdd
>protection diode current cause significant errors on the remaining analog
>channels.  I'm guessing this is because the internal reference voltage
>gets messed up.

I think it is because of the way currents flow in the protection diodes,
isolation tubs etc.- the current ends up flowing *out* of remaining inputs
in the port. If so, you can expect the error to increase with increasing
input impedance.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\11\01@123608 by Olin Lathrop

face picon face
> > 3  -  This topology should never be used if any part of the PIC
circuit
> > goes anywhere near where humans can touch.  It would never get
> > regulatory
> > approval,
>
> I do not agree. What's the difference if 240VAC is on the resistor when
> the triac on the same board is at the same potential? Provided the
> circuit is enclosed, what is the difference?
>
> ...
>
> Well yes, it is high volume, and every cent does matter, but what would
> you suggest? An opto is over-kill and is not necessary when the entire
> circuit can be assumed to be at mains potential, and is therefore
> always out of human contact - either double insulated or encapsulated.

I think we agree anyway.  By "near where humans can touch" I meant things
like user buttons, etc.  These things should be isolated from mains by
some sort of dialectric to several thousand volts as required by various
regulations.  If your PIC is part of the circuit on the "hot" side, then
there is no problem as long as it is isolated from where a human could
touch.


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2002\11\01@123627 by Bob Blick

face picon face
> > Easy. From spec sheet, .7v at 3mA, from Ohm's Law .7/.003 = 233 Ohms.
>
> That is either a minimum guaranteed current at that voltage or the maximum
> guaranteed voltage at that current (the exact reference wasn't supplied,
> so I didn't chase down the particular spec sheet line).  Nothing says that
> the current at 700mV couldn't be considerably higher.

With a red LED that amounts to 15 mA at best. Say the spec is very
conservative and you get "considerably higher". You're still likely to be
less than 25 mA.

We're talking PICs here, OK? Not mil-spec, the only time you'd do this is
if you wanted a bright LED and no resistor. Otherwise you'd have to use
some active component to boost the current.

Please let me pose a question. What would you do to get 15 mA into a red
LED when the PIC output is positive and it's supplied with 5 volts or
less? I don't see any way to do it with a resistor, you won't get enough
current.

Cheers,

Bob

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2002\11\01@140352 by Olin Lathrop

face picon face
> Please let me pose a question. What would you do to get 15 mA into a red
> LED when the PIC output is positive and it's supplied with 5 volts or
> less? I don't see any way to do it with a resistor, you won't get enough
> current.

Let's say the LED drops 2V at 15mA, which would be reasonably typical of a
standard red LED.  The spec sheet doesn't give a maximum guaranteed
voltage when sourcing 15mA, so you should calculate the resistor assuming
the worst case which is that it stays at 5V.  (5V - 2V) / 15mA = 200 ohms.

Of course that guarantees not to exceed 15mA, not that it will always be
15mA.  If you want to get a higher current, then substitute 20mA (the
assumed LED maximum current) into the equation above and use a 150 ohm
resistor.  If the LED can take more current, then the limit is the 25mA
allowed per PIC port pin, which results in 120 ohms.

So there are three choices depending on what you want to make sure you
don't exceed.  If you cared more about the exact LED current, then using
the PIC port to sink rather than source the current would be better
because the low side drivers are known to be stronger.  If you want a
guaranteed 15mA +-5% thru the LED, then driving it directly from a PIC pin
isn't the answer.  Some things are just not guaranteed.


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2002\11\01@185153 by Sean Alcorn - Avion Sydney

flavicon
face
Olin,

> I think we agree anyway.  By "near where humans can touch" I meant
> things
> like user buttons, etc.  These things should be isolated from mains by
> some sort of dialectric to several thousand volts as required by
> various
> regulations.  If your PIC is part of the circuit on the "hot" side,
> then
> there is no problem as long as it is isolated from where a human could
> touch.

OK. Thanks for clarifying. I took it as it would never get regulatory
approval simply because the high voltage was on the PIC and/or the
resistor. Yes, we most certainly agree. I have had a lot of experience
with UL and other approvals, and we always design to the most stringent
rule - whether we need to get approval or not.

One interesting point in all these circuits (that I have seen) is that
they always seem to drive from the neutral. In Australia, we use a MENS
system - where the neutral or "cold" of the AC line is actually tied to
Ground at the point of supply entry into a building.

Theoretically, the neutral is as good as ground and you can grab onto
it - although have sufficient lack of faith in Australian electricians
that I do not make a habit of this without testing first! :-) However,
my point being that since these circuits have there power supplies
configured to provide 5 volts above neutral - then there is no way we
are ever going to see the 339.5 volts on this line.

I know in "my world" - the circuit contained inside the confines of my
little plastic box - I can not assume that we are on an equivalent of
an MENS system and also can not assume that it will be wired correctly
(see previous note), but assuming that it is correctly connected to the
neutral, would this not rule out any transients etc. raised by Roman
and others? And is this perhaps the reason they have chosen the
neutral? The books are published in the UK, and I am not sure if the
neutral is tied to ground, but I assume that it is.

Cheers,

Sean

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2002\11\01@190031 by Sean Alcorn - Avion Sydney

flavicon
face
Mike,

>>> 3  -  This topology should never be used if any part of the PIC
>>> circuit
>>> goes anywhere near where humans can touch.  It would never get
>>> regulatory
>>> approval,

> Presumably you won't be letting the user touch the triac either?  Olins
> point is perfectly valid.

No. Without the clarification he has since provided, it was not. In a
separate sentence he declared "It would never get regulatory approval"
- he didn't say that it would not get regulatory unless... etc. I
simply do not agree that such a circuit could not attain such approvals.

Cheers,

Sean

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2002\11\01@190500 by Olin Lathrop

face picon face
> One interesting point in all these circuits (that I have seen) is that
> they always seem to drive from the neutral. In Australia, we use a MENS
> system - where the neutral or "cold" of the AC line is actually tied to
> Ground at the point of supply entry into a building.

Almost the same here in the US, at least for individual houses.  There is
a transformer near your house that is fed from one of the three power
phases.  The secondary is center tapped with each half creating 110V AC.
The center is grounded usually right where the power enters the house.  In
my case there is a large copper rod driven into the ground right by the
breaker box.  Half the circuits in the house are between one end and the
center tap (neutral) and the other half between the other end and the
center tap.  Special 220V circuits like for dryers and electric ranges are
accross both ends of the transformer secondary.  Three wires are run for
each 110V outlet, hot, neutral, and ground.  The neutral and ground are
eventually connected back to the ground point, but the return currents are
all intended for the neutral and ground is for safety.  "Ground fault"
circuit breakers check for current in the ground line and trip if more
than a few mA are found.


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2002\11\01@191952 by Jim

flavicon
face
>  I can not assume that we are on an equivalent
>  of an MENS system and also can not assume that
>  it will be wired correctly ...
>  The books are published in the UK, and I am not sure
>  if the neutral is tied to ground,

Yikes!

Just imagine what the effects  could be if
a *small* amount of AC leakage current were
to occur from the HV power distribution
transformer's primary to the secondary
winding if there were not a 'neutral'
connection ...

(And not to mention the effects that strong,
charged thunderclouds have on non-one-side-
grounded secondary distribution lines ...)

This leakage current could easily cause both
sides of the line (termed "common mode") to
reach voltages of, well, what ever the
secondary was ...

I think experience with (and accidents with) power
distribution systems over the years has lead to
one-side-grounded power distribution practices
all over the world (funny how physics reveals flaws
in man's 'systems' like this sometimes - regardless
of location!) ...

RF Jim

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2002\11\01@195742 by Sean Alcorn - Avion Sydney

flavicon
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Hi Olin,

{Quote hidden}

Yeah, That's pretty much how we have always done it. Except we have no
need for the transformers - since our 3 phases are 415V each, we tap in
at 240VAC

Residual Current Circuit Breakers or Ground Fault Breakers that trip at
30mA are pretty much standard now.

So you guys finally caught up? :-)

Cheers,

Sean

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2002\11\01@200308 by Sean Alcorn - Avion Sydney

flavicon
face
Jim,

I am referring to as separate connection from neutral to ground at the
consumers board. Then from there, the consumer's ground distributed
throughout the building. And no, this is NOT done all over the world.

A relatively recent introduction in North America, if I am not mistaken.

Regards,

Sean

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2002\11\01@200324 by Bob Ammerman

picon face
----- Original Message -----
From: "Olin Lathrop" <EraseMEolin_piclistspamEraseMEEMBEDINC.COM>
<snip>
> "Ground fault"
> circuit breakers check for current in the ground line and trip if more
> than a few mA are found.

Actually, "ground fault" circuit breakers are designed to detect any current
flowing from the hot that does not return on the neutral. They use a
differential sensor to do this (counterwound coils, IIRC). This causes them
to trip when current runs thru either a fault in a device insulation or an
external path (like you) to ground.

Bob Ammerman
RAm Systems

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2002\11\01@200506 by Bob Ammerman

picon face
----- Original Message -----
From: "Sean Alcorn - Avion Sydney" <spamBeGonesdalcornspamKILLspamAVION.COM.AU>

> Yeah, That's pretty much how we have always done it. Except we have no
> need for the transformers - since our 3 phases are 415V each, we tap in
> at 240VAC

I am sure you use higher voltages than 415 for neighborhood distribution,
don't you?!? Otherwise you'd use an awful lot of Cu or Al.

> Residual Current Circuit Breakers or Ground Fault Breakers that trip at
> 30mA are pretty much standard now.

I believe GFIs in the US are supposed to trip at 7 or more ma.

Bob Ammerman
RAm Systems

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2002\11\01@203628 by Sean Alcorn - Avion Sydney

flavicon
face
Bob,

> I am sure you use higher voltages than 415 for neighborhood
> distribution,
> don't you?!? Otherwise you'd use an awful lot of Cu or Al.

I have a delightful 11000 volts in the corner of my front yard. I'll
wait until the garden overgrows for a little camouflage before I put it
on the market. On a quiet night, I can hear a distant buzz! :-)

So yes, we have 33kV and 11kV transformers scattered around the place.
I can not remember what it originates at the stations - it's been far
too long. I was simply referring to the common supply lines.

> I believe GFIs in the US are supposed to trip at 7 or more ma.

I have often wondered about this. I have done some paramedics training,
and from memory - doesn't the heart start to fibrillate at about 25mA.
I've often thought it cruel that - if my memory is correct and it is
indeed 25mA -  our RCCBs are set at 30mA :-)

Even at 30mA though, I know that electricians (in Aus) will run
separate unprotected circuits for refrigerators and airconditioners. My
brother recently refurbished his kitchen and his refrigerator is on a
protected circuit. He said it has tripped twice in say, 6 months. 7mA
is incredibly low. I reckon everybody on this list has had more than
that! Nothing like a little heart starter! :-)

Regards,

Sean

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2002\11\01@204045 by Olin Lathrop

face picon face
> Yeah, That's pretty much how we have always done it. Except we have no
> need for the transformers - since our 3 phases are 415V each, we tap in
> at 240VAC

I'm a bit skeptical about not having a transformer locally.  That's just
asking for some very nasty problems with lightning strikes anywhere near
either the house or where the ground is.  One good reason for a transformer
is so that everything can be grounded in one place.  That way when lightning
strikes nearby and glitches the local ground, it is all common mode noise to
the house wiring and the inhabitants inside.

> Residual Current Circuit Breakers or Ground Fault Breakers that trip at
> 30mA are pretty much standard now.
>
> So you guys finally caught up? :-)

Maybe not.  Most circuits even in new houses do not have ground fault
circuit breakers.  Usually just for outlets over sinks and outdoors.
Bathroom outlets often have the ground fault interruptor built into the
outlet and a normal breaker down in the basement.


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2002\11\01@204252 by Jim

flavicon
face
part 1 4067 bytes content-type:text/plain; (decoded 7bit)

 "A relatively recent introduction in North
  America, if I am not mistaken"

Ahh .... I *don't* think so ... we've had 'grounded'
sytems in use since I came into contact with home
wiring systems (60's as a kid) ...

From my 1922 (yes, nineteen twenty-two) "Standard
Handbook for Electrical Engineers" pg 1116 I find:

+ + + + + + + + + + + + + + + + + +

128. Alternating-current, low-voltage, secondary circuits mubt be grounded.
This is the recommendation of the Code rule 15b and is the practice of
progressive central-station companies. Grounding ininimizes accidents to
persons and damage, by fire, to property. If some point of a low-voltage
secondary circuit is grounded, no point of the circuit can rise above its
normal potential (except under unusual conditions) in case of a breakdown
between primary and secondary windings of the transformer, or of other
accidental connection between the primary and secondary circuits. See the
Code for further information regarding.grounding.

The ground connection should be made at a neutral point or wire if one is
accessible. Where no neutral point is accessible, one side of the secondary
circuit may be grounded (Code rule 15b). Fig. 26 illustrates how f3orne of
these connections are arranged with commercial transformers. The neutral
point of each transformer feeding a two-phase, four-wire secondary, should
be grounded, unless the motors taking energy from the secondary have
interconnected windings. Where they are interconnected, the center or
neutral point of only One transformer is grounded.

No primary windings are shown in the illustration and the secondary winding
of each transformer is shown divided into two sections, as in commercial
transformers. 129. All metal conduit and metal raceway systems must be
grounded (see Fig. 27), by attaching an approved clamp (there are many on
the market) to a conduit or raceway of the system and connecting it with a
ground wire to-i6nother clamp attached to a water pipe on the street. side
of the meter. The wire must be soldered in the clamps. All parts of the
conduit or raceway system must be in good electrical contact.

In an ungrounded system of conduit, "sneak" currents are possible. These
leak from one wire to the conduit through an abrasion of insulation and
reach the other side of the line through another ground. The resistance of
the path may be sufficient to hold the "sneak " currents below the line fuse
capacity, and yet these currents may be sufficient to start a fire.

Grounding the conduit also eliminates the possibility of electrical shock to
persons coming in contact with the conduit. In combination fixtures the gas
pipe should be in thorough electrical contact with the conduit or raceway
system at each outlet box. Wire for grounding ordinary conduit or raceway
runs must be of copper or of other metal which will not corrode excessively
(Code Rule l5Aj) at least No. 10 A. W. G. gage, where the largest wire
contained in system is not greater than No. 0 A.W.G. gage; it need not be
greater than No. 4 A.W.G. where the largest-wire contained in conduit is
greater than No. 0 gage. Service-conduit ground wires shall be not less than
No. 8 gage copper. All ground wires must be protected from mechanical
injury.

+ + + + + + + + + + + + + + + + + + + + +

As I said before - there are SERIOUS reasons *why*
secondary distribution systems are 'grounded'.

RF Jim

{Original Message removed}
part 2 22901 bytes content-type:image/jpeg; (decode)


part 3 136 bytes
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2002\11\01@204937 by Sean Alcorn - Avion Sydney

flavicon
face
Bob,

> Actually, "ground fault" circuit breakers are designed to detect any
> current
> flowing from the hot that does not return on the neutral. They use a
> differential sensor to do this (counterwound coils, IIRC). This causes
> them
> to trip when current runs thru either a fault in a device insulation
> or an
> external path (like you) to ground.

That's how I understood them to work, and I took it that Olin does too
- 'caus he's a pretty smart cookie! :-)

If Olin has ever seen one, he would know that he simply has not worded
his sentence correctly, as an RCCB or GFI makes no connection to the
ground at all.

Roman and I appear to have taken this thread on a rather bizarre
tangent! Anyone would think we were still talking about LEDs! :-)

Cheers,

Sean

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2002\11\01@204948 by Olin Lathrop

face picon face
> I am referring to as separate connection from neutral to ground at the
> consumers board. Then from there, the consumer's ground distributed
> throughout the building. And no, this is NOT done all over the world.
>
> A relatively recent introduction in North America, if I am not mistaken.

Depends on what you mean by recent.  Some very old systems actually ran one
wire and used the earth as the other conductor.  Apparently rare instances
of these survived until the 1980s in remote areas, but new systems haven't
been installed that way since long ago (back when Australians were referred
to as "inmates" <g>).


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2002\11\01@205155 by Olin Lathrop

face picon face
> > "Ground fault"
> > circuit breakers check for current in the ground line and trip if more
> > than a few mA are found.
>
> Actually, "ground fault" circuit breakers are designed to detect any
current
> flowing from the hot that does not return on the neutral. They use a
> differential sensor to do this (counterwound coils, IIRC). This causes
them
> to trip when current runs thru either a fault in a device insulation or an
> external path (like you) to ground.

Yes, you are absolutely right.  I noticed that my statement was a bit
misleading right after I sent it and wondered if some wiseass would bother
point it out <g>.


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2002\11\01@205353 by Olin Lathrop

face picon face
> I believe GFIs in the US are supposed to trip at 7 or more ma.

It must be that Aussies have thicker skulls or maybe the extra current gets
shunted thru all the beer in the bloodstream <g> <duck> <don asbestos
underwear>.


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2002\11\01@210431 by Sean Alcorn - Avion Sydney

flavicon
face
Jim,

> Ahh .... I *don't* think so ... we've had 'grounded'
> sytems in use since I came into contact with home
> wiring systems (60's as a kid) ...

Well ditto to that, as far as experience goes. But I have never seen a
2-pin outlet in Australia. A 2-pin plug in a double insulated appliance
- yes, but never an ungrounded socket. I welcome other Australians to
correct me, but I have worked on installations (almost) as old as
electricity itself. I have somewhere a history of our 3-pin outlet. Not
sure if it is as old as your 1922 standard though! :-)

However, I have seen many 2-pin (ungrounded) outlets in my travels
around the United States. Did I imagine these?

Regards,

Sean

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2002\11\01@211255 by Ashley Roll

flavicon
face
Hi Guys,

Could be the thicker skulls, I mean being upside down on the earth, all the
blood is rushing to our heads all the time.. Maybe this effect means that
our hearts are stronger to counter this problem :)

The other alternative is that the standard was written between rounds at the
pub. ;)

Ash.

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> {Original Message removed}

2002\11\01@213408 by Jim

flavicon
face
 "Some very old systems actually ran one wire and used the
  earth as the other conductor."

Maybe in the case of some runs of a single-phase REA
(Rural Electification Administration) lines out to the
boonies- but then a few hundred ohms of real earth
resistance weren't a factor to currents measuring in
the 100's of millimaps range on that HV circuit ...

RF Jim

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2002\11\01@214032 by Sean Alcorn - Avion Sydney

flavicon
face
You guys,

> It must be that Aussies have thicker skulls or maybe the extra current
> gets
> shunted thru all the beer in the bloodstream <g> <duck> <don asbestos
> underwear>

I did some work at Pine Gap - a highly secretive joint Aussie/American
installation out in the outback of Australia which is presently in the
news a lot with protesters against Australia's support for the US
making a nuisance of themselves. This base is complete with a massive
Russian Antonov that comes every Wednesday with supplies. I don't know
if was always an Antonov (I assume not), but this flight is still
affectionately known as the "Mac flight" as inside it's belly of
precious cargo were frozen Big Macs for all the expat Americans who
just needed a fix! There is now a MacDonald's in town, so they no
longer pine for the beloved flavours of their homeland. :-)

However, I will never forget going into this boardroom where there was
a bank of VCRs, a large monitor and host of other similar appliances.
Under each device was a large (200mm cube - er, sorry 10" cube)
transformer powering each device. I said (quietly - I'd only just
arrived) to my host "don't they know that we have VCRs and TVs here?" -
to which he replied "Oh no. They all seem to think we still live in
grass huts!" :-)

Later in the day, I asked for a soldering Iron. I got the same Weller
soldering station that I had on my bench (at the time) back in Sydney.
I started to walk away and they yelled out "Hang on, you need this!"
and I saw them getting out that same bloody transformer I had seen in
the board room earlier that day! I had to carry that bastard over a
kilometre to where I was working!

Lovely people, and I was treated like royalty. At no time did I feel
that I was in such a sensitive environment. But no, there is no point
to flame you over such comments when even the United States military
has such high opinions of a small, but important ally! :-)

I saw a US military (propaganda?) film about "US boys on R&R downunder"
made during WWII - a very sore point for most Australian men of
fighting age during WWII  - but there was a classic line that I never
forget - referring to Sydney - "Our boys feel right at home here - they
even have tall buildings!"

Not much has changed - as far as opinions go - we have even taller
buildings now though! :-)

Sean

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2002\11\01@215054 by Sean Alcorn - Avion Sydney

flavicon
face
Ashley,

> The other alternative is that the standard was written between rounds
> at the
> pub. ;)

Taking work to the pub? Fair go, mate. How Australian is that? More
like the standard was going to press at 2:00pm on a Friday and they
pulled the number out of a hat - just to get to the pub!

But seriously though, if the US is running at 7mA and we use 30mA and
still see trips on refrigeration equipment, does it come down to our
dirty power that Roman already pointed out? Or is this simply due to
inherent operating characteristics of refrigeration equipment? I am
curious if they run refrigeration compressors through protected
circuits without nuisance trips in the US.

Cheers,

Sean

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2002\11\01@215253 by Olin Lathrop

face picon face
> However, I have seen many 2-pin (ungrounded) outlets in my travels
> around the United States. Did I imagine these?

2-pin yes, but not ungrounded.  These were the norm until the 1960s(?) when
all new house outlets had to be 3-pin.  There are still many in houses that
were built before this requirement.  My mother's house was built in the late
1950s or early 1960s and all original outlets were 2-pin but new ones added
since then are 3-pin.  My house was built in 1985 and is all 3-pin.

My office is in a building originally built in 1880 (before electrons were
invented) and there are some very strange looking power outlets that I've
never seen anywhere else in a few places.  Fortunately none of these seem to
be live.


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2002\11\01@220414 by Olin Lathrop

face picon face
> But seriously though, if the US is running at 7mA and we use 30mA and
> still see trips on refrigeration equipment, does it come down to our
> dirty power that Roman already pointed out? Or is this simply due to
> inherent operating characteristics of refrigeration equipment? I am
> curious if they run refrigeration compressors through protected
> circuits without nuisance trips in the US.

Funny you should mention that.  When we moved into our new office in April
(a freshly rennovated attic in an old building, totally new wiring) I
plugged the refridgerator into an outlet that it turns out was on the same
GFI interruptor as the outlets by a sink.  The fridge kept tripping the GFI
interruptor.  I moved it to a different outlet and the problem went away.  I
asked an appliance guy a while later and he acted like that sort of problem
was well known.  The fridge is grounded with a 3-prong plug, but I still
don't see why it needs to leak that much current to the ground.


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2002\11\01@220620 by Olin Lathrop

face picon face
> I don't know
> if was always an Antonov (I assume not), but this flight is still
> affectionately known as the "Mac flight" as inside it's belly of
> precious cargo were frozen Big Macs for all the expat Americans who
> just needed a fix! There is now a MacDonald's in town, so they no
> longer pine for the beloved flavours of their homeland. :-)

That's funny since there was a scandal around here a few years ago about
MacDonalds using kangaroo meat in their burgers instead of the beef they
advertised.


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2002\11\01@220717 by Tim Tapio

flavicon
face
Well, you all "down under" shouldn't feel too bad.  We still have folks in
the eastern states that think the west is still filled with cowboys and
Indians....

Tim


{Original Message removed}

2002\11\01@221224 by Sean Alcorn - Avion Sydney

flavicon
face
Olin,

> 2-pin yes, but not ungrounded.

But they may as well have been ungrounded right? The ground could not
have been connected to the chassis of the appliance? AFIK, the pins
were not polarised - although I have seen some plugs with one pin
slightly larger than the other - so the plug could very easily be
reversed and the 'hot' applied to the chassis?

>   These were the norm until the 1960s(?) when
> all new house outlets had to be 3-pin.  There are still many in houses
> that
> were built before this requirement.  My mother's house was built in
> the late
> 1950s or early 1960s and all original outlets were 2-pin but new ones
> added
> since then are 3-pin.

So according to what Jim says, your mother was out in the boonies (at
that time)?

> My office is in a building originally built in 1880

Very nice (I assume - if it's been maintained well)

> (before electrons were
> invented) and there are some very strange looking power outlets that
> I've
> never seen anywhere else in a few places.  Fortunately none of these
> seem to
> be live.

So you have a kerosene powered PC? :-)

Sean

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2002\11\01@221841 by Jim

flavicon
face
> The fridge kept tripping the GFI interruptor.
> ... but I still don't see why it needs to leak
> that much current to the ground."

Couldn't be the arcing from the fridge thermostat
contacts opening and closing that drives the GFI
nuts - could it?

I have a self-designed electronic thermostat that
drives a contactor on my 'fridge - and I have an
appliance off a wall-wart on the same circuit that
sometimes gets reset when that contactor cycles on
or off (it's easy to tell when this appliance gets
reset - it starts to make a loud squawk) ...

RF Jim



{Original Message removed}

2002\11\01@222257 by Jim

flavicon
face
>But they may as well have been ungrounded right?

No.

THEY simply did not have the third 'safety' grounding prong ...

This is a far cry from an UNGROUNDED system which would NOT
meet eletrical code (you didn't read any of the fine historical
and technical material I dutifully scanned and posted?) *and*
represent a SIGNIFICANT DANGER to human users ...


RF Jim


{Original Message removed}

2002\11\01@222504 by Sean Alcorn - Avion Sydney

flavicon
face
Olin,

> That's funny since there was a scandal around here a few years ago
> about
> MacDonalds using kangaroo meat in their burgers instead of the beef
> they
> advertised.

It was 1980~81 and I remember it well. My family did a tour of the West
Coast of USA. We were in Lake Tahou and we got a front row table to see
Sammy Davis Junior. 'Surf & Turf' Australian Lobster and beef
(American, I hope - now that I think about it) was served and we had a
magic night.

We were walking back to our hotel and some of us wanted a coffee. We
stopped in at one of those American joints that sell doughnuts until
the wee hours of the morning and we were greeted with the typical West
Coast American service. Nice guy, recognised that we were "oRsees" and
got chatting to us. Then he asked the question that all traveling
Aussies fear - "So you guys have many kangaroos around where you live?"
and before any of us could respond, my father replied - quick as a
flash "No, you bastards ate them all!" - you should have seen the guys
jaw drop! It was a classic moment, but he also had a good laugh, and
then we got talking about the scandal! :-)

Apparently it is very healthy! Far less fat than beef! :-)

Cheers,

Sean

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2002\11\01@222919 by Sean Alcorn - Avion Sydney

flavicon
face
Jim,

> This is a far cry from an UNGROUNDED system which would NOT
> meet eletrical code (you didn't read any of the fine historical
> and technical material I dutifully scanned and posted?) *and*
> represent a SIGNIFICANT DANGER to human users ...

Yes, I did. But I gotta go guys. It's been great chatting with all of
you today, and I am sure that we have opened a few more cans of worms
today. I am sure that you guys are getting ready for the sack soon in
your part of the world anyway!

Cheers,

Sean

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2002\11\01@223538 by Dale Botkin

flavicon
face
On Fri, 1 Nov 2002, Tim Tapio wrote:

> Well, you all "down under" shouldn't feel too bad.  We still have folks in
> the eastern states that think the west is still filled with cowboys and
> Indians....

Ha.  Try living in "flyover country" like me.

I'd have moved this OT, but Olin wouldn't see it...  but it *is* time for
that, you know.

Dale

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2002\11\01@230251 by Jim

flavicon
face
I should add - that single REA line that ran out
to the boonies was in the thousand-volt-plus-range,
and stepped down (via transformer) for use around
the farm in the home!

RF Jim

G'nite all ...

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2002\11\01@231127 by Bob Ammerman

picon face
I'm pretty sure that US spec GFIs are required to meet an 'inverse time'
spec.


IE: Trip in X ms at 7ma

Trip in Y<X ms at Z>7ma

etc.

ie: the higher the current the quicker the trip

Bob Ammerman
RAm Systems

{Original Message removed}

2002\11\01@233029 by Bob Ammerman

picon face
Olin,

I'll readily accept the 'wise', not sure about the 'ass'.

Bob

----- Original Message -----
From: "Olin Lathrop" <spamBeGoneolin_piclistKILLspamspam@spam@EMBEDINC.COM>
To: <PICLISTspam_OUTspam@spam@MITVMA.MIT.EDU>
Sent: Friday, November 01, 2002 8:50 PM
Subject: Re: [PIC]: Direct LED connection?


> > > "Ground fault"
> > > circuit breakers check for current in the ground line and trip if more
> > > than a few mA are found.
> >
> > Actually, "ground fault" circuit breakers are designed to detect any
> current
> > flowing from the hot that does not return on the neutral. They use a
> > differential sensor to do this (counterwound coils, IIRC). This causes
> them
> > to trip when current runs thru either a fault in a device insulation or
an
{Quote hidden}

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2002\11\01@233041 by Bob Ammerman

picon face
Um....

Have aliens inhabited Olin's body or something. This is something on the
order of the third or fourth witty/joking response from him in the past
couple of days.

Bob

{Original Message removed}

2002\11\02@035331 by Roman Black

flavicon
face
Bob Ammerman wrote:
>
> Um....
>
> Have aliens inhabited Olin's body or something. This is something on the
> order of the third or fourth witty/joking response from him in the past
> couple of days.


Maybe he has discovered the famous shire weed;
Creativity++
Productivity--

<grin>
-Roman

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2002\11\02@040035 by Roman Black

flavicon
face
Sean Alcorn - Avion Sydney wrote:

> But seriously though, if the US is running at 7mA and we use 30mA and
> still see trips on refrigeration equipment, does it come down to our
> dirty power that Roman already pointed out? Or is this simply due to
> inherent operating characteristics of refrigeration equipment? I am
> curious if they run refrigeration compressors through protected
> circuits without nuisance trips in the US.


I think with refrigerators the motors draw a
very heavy start current and the motor is submerged
in an earthed can (compressor) with liquid freon
etc as a dialectric between the motor power and
the earthed can. Add the obvious contact arcing
etc.

One point with the "dirty power" 240vac as I have
mentioned before in the light bulb thread is that
with 240vac you get MUCH bigger inrush currents
into cold light globes, water heaters and stalled
motors etc compared to 120vac mains.

My lights here dim and brighten at many times
during the night sometimes subtle and sometimes
quite nastily. I also live near a steelworks and
copper smelter, and yes the i'm on the other side
of where the power comes from. :o)
-Roman

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2002\11\02@040047 by Roman Black

flavicon
face
Sean Alcorn - Avion Sydney wrote:

> > MacDonalds using kangaroo meat in their burgers instead of the beef


> Apparently it is very healthy! Far less fat than beef! :-)


And is tough as leather and tastes very ordinary.
As an exotic meat it makes great pet food. ;o)
-Roman

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2002\11\02@052118 by David Duffy

flavicon
face
> > MacDonalds using kangaroo meat in their burgers instead of the beef

Sean:
> > Apparently it is very healthy! Far less fat than beef! :-)

Roman:
>And is tough as leather and tastes very ordinary.
>As an exotic meat it makes great pet food. ;o)

You must have got a tough 'Roo. We bought some from Woolworths
(supermarket) a while ago and it was cheaper than beef at the time.
The flavour was a little stronger IIRC, but the kids never even noticed
that they were eating Skippy until we told them later! A friend of ours
buys Kangaroo & Crocodile meat quite often. You just have to eat it
before it jumps right off your plate!!  :-)  Hmmm... I wonder just how
far we can stretch this LED thread out? I got it! We could design the
worlds first 'Roo meat quality tester. (with LED readout of course!)
David...

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2002\11\02@061321 by Peter L. Peres

picon face
On Sat, 2 Nov 2002, Sean Alcorn - Avion Sydney wrote:

*>But seriously though, if the US is running at 7mA and we use 30mA and
*>still see trips on refrigeration equipment, does it come down to our
*>dirty power that Roman already pointed out? Or is this simply due to
*>inherent operating characteristics of refrigeration equipment? I am
*>curious if they run refrigeration compressors through protected
*>circuits without nuisance trips in the US.

Not from the US but really dirty power can trip GFIs. A common mode AC
filter before the panel (!) will cure this. Refrigeration equipment has
on/off cycles of compressors (with lots of turn-on current), contact
arcing and all the rest, like condensation bridging insulation
temporarily. If a particular piece of equipment on a circuit causes all
the faults then it could have bad insulation. GFI trip current is between
15 and 30mA in most parts of the world. 30mA is not supposed to go
directly through someone's heart, it's the total fault current. I can
witness that up to 150mA will not start fibrillation, although it can be
very painful afterwards ;-) Maybe in the US the liability issues are
larger (i.e. someone once injured his spine by tripping on a marmalade jar
while being electrocuted with 7.2 mA of mains from a partly dismantled
electric knife with which he was trying to cut off his left ear, and sued
successfully - so the authorities decided GFI current will be 7.0mA).

Incidentally the resistance required to pass 7mA peak at 120V is about
24k, 30mA peak at 240V is under 11k. The 'hand to hand' resistance of a
normal man is usually over 50k when not wet etc. So you can't fib from
touching with both hands (at least in theory). Right now I measured 200k
between left and right hand.

Otoh there are noGFI interrupters on high voltage power supplies and
inside valved equipment ;-)

Peter

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2002\11\02@080428 by Olin Lathrop

face picon face
> > 2-pin yes, but not ungrounded.
>
> But they may as well have been ungrounded right? The ground could not
> have been connected to the chassis of the appliance? AFIK, the pins
> were not polarised - although I have seen some plugs with one pin
> slightly larger than the other - so the plug could very easily be
> reversed and the 'hot' applied to the chassis?

Even if you don't connect the chassis to the ground, having one side
grounded is useful.  It guarantees no large common mode voltage with
respect to a nearby water pipe or whatever.  If the secondary were
floating, nothing would prevent it from picking up a high voltage from
static electricity, lightning, leakage from the transformer primary, etc.

The "newer" (1960s ?) standard for 2 pin outlets is the neutral side a
little larger than the hot side.  Some appliances use polarized plugs to
make use of this, although I don't think you are allowed to connect the
neutral to anything a human would touch.  These appliances have one prong
larger so that they only fit one way into a polarized outlet, and don't
fit at all into an old unpolarized 2 pin outlet.  All 3 pin outlets are
polarized.

> So according to what Jim says, your mother was out in the boonies (at
> that time)?

Not at all (Salem Massachusetts actually).  Her house was built to code in
the early 1960s or late 1950s with 2 pin outlets.


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2002\11\02@080838 by Olin Lathrop

face picon face
> Couldn't be the arcing from the fridge thermostat
> contacts opening and closing that drives the GFI
> nuts - could it?

Hmm, interesting hypothesis.  That seems to fit the observations, and is
something the average appliance guy wouldn't understand.


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2002\11\02@081254 by Olin Lathrop

face picon face
> We were walking back to our hotel and some of us wanted a coffee. We
> stopped in at one of those American joints that sell doughnuts until
> the wee hours of the morning and we were greeted with the typical West
> Coast American service. Nice guy, recognised that we were "oRsees" and
> got chatting to us. Then he asked the question that all traveling
> Aussies fear - "So you guys have many kangaroos around where you live?"
> and before any of us could respond, my father replied - quick as a
> flash "No, you bastards ate them all!" - you should have seen the guys
> jaw drop! It was a classic moment, but he also had a good laugh, and
> then we got talking about the scandal! :-)

ROTFL.

When that scandal hit it made me wonder what kangaroo meat tasted like,
and I had heard it was better for you.  I went into a MacDonalds and
specifically requested a kangaroo burger.  The girl behind the counter
didn't know what to say.  The manager overheard this and basically threw
me out without me saying another word.


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2002\11\02@091813 by Sean Alcorn - Avion Sydney

flavicon
face
Hi guys,

It's very late here, and we have been officially slapped on the wrist
for this thread, but I have just got to say that if I got a "ROTFL" out
of Olin, then it must have been worth the bandwidth.

I also have to say, his reply made me laugh too! I've never managed to
get myself thrown out of a McDonalds! David Duffy's comments on roo
meat seem to ring true to what seems to be the general public opinion.
I can not offer my own opinion, as I have never tried it. But from what
I do know, Roman must have got a tough piece - one that John West
rejected perhaps? I also need to add that as clearly as I remember that
roo meat scandal, I don't remember McDonalds being involved! :-)

But my variation of this thread did start of quite serious though. My
next project is a Triac based speed control for 240VAC and I do have to
detect the zero crossing point of the AC wave. Before anyone suggests
the obvious, I do not have a transformer. So far, I've got "2 resistors
are better than 1" and Olin's "the more parts the merrier" :-) - then
we just started getting silly.

I will draw the circuit which I believe Roman's original comments were
about and post it or a link to it on Monday. I've never posted a file
to the list. Is there any maximum size, format, etiquette to obey? I
should focus this question to Olin only - as he won't hold back with
his opinion! :-)

Any thoughts on why this technique should or should not work, is or is
not safe and would or would not pass regulatory approvals will be
interesting and most appreciated.

Regards,

Sean

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2002\11\02@101946 by Alan B. Pearce

face picon face
>Even at 30mA though, I know that electricians (in Aus) will run
>separate unprotected circuits for refrigerators and airconditioners. My
>brother recently refurbished his kitchen and his refrigerator is on a
>protected circuit. He said it has tripped twice in say, 6 months. 7mA
>is incredibly low. I reckon everybody on this list has had more than
>that! Nothing like a little heart starter! :-)

I do not know what the trip current rating of earth fault current breakers
in the UK is, but my wife periodically trips ours using the iron with steam
on. It is a real pain as the "standard" UK method of wiring house appliance
outlets is a single ring main, so you lose absolutely everything except the
house lights.

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2002\11\02@161241 by Dwayne Reid

flavicon
face
At 12:34 PM 11/2/02 +1100, Sean Alcorn - Avion Sydney wrote:

>>I believe GFIs in the US are supposed to trip at 7 or more ma.
>
>I have often wondered about this. I have done some paramedics training,
>and from memory - doesn't the heart start to fibrillate at about 25mA.
>I've often thought it cruel that - if my memory is correct and it is
>indeed 25mA -  our RCCBs are set at 30mA :-)

Articles that I have read in the distant past suggested that 50 Hz is MUCH
less likely to induce ventricular fibrillation than 60 Hz - IIRC, the most
susceptible frequency is somewhat above 60 Hz.  I don't recall the specific
details but I'll try to look it up later this weekend.

dwayne

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2002\11\02@185759 by elect phys

picon face
----- Original Message -----
From: "Peter L. Peres" <KILLspamplpspam.....ACTCOM.CO.IL>
To: <spam_OUTPICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Saturday, November 02, 2002 9:01 PM
Subject: Re: [PIC]: Direct LED connection?


{Quote hidden}

sort of related

A guy I was working with, made contact with 415v 400Hz while
voltage checking in a distribution panel. Went across the chest.

Straight after had a ecg and other tests, while rather shaken up
tests found no damage.

Three months had a medium heart attack. The doctors
couldn't explain why. They said there was nothing
they could find which could have caused a heart attack.

Had a few zaps myself, but nothing across the chest,
I always do the old keep one hand in the pocket
or only hold one lead and use a clip on the other.

Most painfull I've ever had was from rf equipment,
200w HF amp, one of the joints on the test rig hadn't been done up properly.
This was the only zap I've had that left a burn mark and it
took a few weeks to heal up.

Even though 8000VDC can be reasonably painful.
First electronics kit I was ever given was a negative ion generator.
Rather dodgy Dick smith electronics one.

It had no isolation and plugged straight into 240v.
A certain smart arse 14 year old changed the current limiting resistors,
used high rating caps and diodes.
If you took the end cap off a hobby dc motor
you could get the rotor to shoot about 15 feet
or if attached it to a cooper coil fire ball bearings
or small lumps of iron up to 30 feet.

A real safe kit for parents to give as a first electronics kit :-)

Talking about dirty power, my old mans business partner
lives outside Perth (WA)
has had horrendous problems with both
brownouts and overvoltage.
Measured volatages range between 140VAC and 400VAC
on a single phase 240V system.

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2002\11\03@153352 by hard Prosser

flavicon
face
My guess is that the 'fridges & aircon units have suppressor caps to
minimise spike generation on turn on & off.
These present a useful leakage path to earth that trips the interruptor. -
especially under switching conditions.
Richard P





> The fridge kept tripping the GFI interruptor.
> ... but I still don't see why it needs to leak
> that much current to the ground."

Couldn't be the arcing from the fridge thermostat
contacts opening and closing that drives the GFI
nuts - could it?

I have a self-designed electronic thermostat that
drives a contactor on my 'fridge - and I have an
appliance off a wall-wart on the same circuit that
sometimes gets reset when that contactor cycles on
or off (it's easy to tell when this appliance gets
reset - it starts to make a loud squawk) ...

RF Jim

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