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'[EE]: 120AC to 5V no transformer'
2001\03\22@220506 by Richard Sloan

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Can you make a power supply that outputs 5V at 50-100ma that connects to 120AC line with no transformer, the idea needed is for a very cheap device. It would need to be at least CSA/UL approvable.

What comes to mind is a cheap 100ma 78L05 5V reg, but whats needed between it and the AC?

What about isolation issues?

Lots of issues here I am sure.

Thanks,
Richard.

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2001\03\22@224531 by Robert A. LaBudde

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At 10:07 PM 3/22/01 -0500, Richard wrote:
>Can you make a power supply that outputs 5V at 50-100ma that connects to
>120AC line with no transformer, the idea needed is for a very cheap
>device. It would need to be at least CSA/UL approvable.
>
>What comes to mind is a cheap 100ma 78L05 5V reg, but whats needed between
>it and the AC?

A bridge rectifier, series resistor and a 24-30V zener diode that will
stabilize and drop the input voltage to within the upper range of the 78L05
regulator. A capacitor post-zener will filter out the zener noise.

>What about isolation issues?

That's the price you pay! If you don't want a transformer, you don't get
the isolation. Make sure you have a fuse on the mains side (input to bridge).

>Lots of issues here I am sure.

Not really: just the lack of isolation and the maximum power/current
through the zener.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam@spam@lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\03\23@030840 by Bob

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Take a look at http://us.st.com and look up the VB409.  This is a five pin chip
(VI Power Pentawatt) made in a TO-220 like package (except for the extra two
pins), and it's even available in a dip version.   It can put out 5VDC 5%
regulated at up to 70ma (but you'll need a heatsink then), and another 12~15VDC
unregulated at up to 400ma peak (but for only 10ms).

It only requires a rectifier (half or full), two resistors, and a capacitor to
operate (although a small inductor is recommended for more efficient operation,
and line spike protection).  They even have a small circuit design parameter
program you can download for it.  It is MUCH more reliable than the standard
X-cap Zener circuit that you may have seen around, and it also has several
internal fail-safes built into it.  I've been running one for a 4~5 months now,
and I ain't even seen it even hiccup yet (and I get line spikes & transients
like crazy here).

The biggest problem with this part is finding a distributor that stocks it (is
only being marketed to the "white market", aka "appliances market" currently).
Let me know if you find one.  I see that Arrow has them priced at $1.23, but
don't show any in stock (special order item).

Hope this helps,

Bob.


{Original Message removed}

2001\03\23@070645 by mike

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On Thu, 22 Mar 2001 22:44:47 -0500, you wrote:

>At 10:07 PM 3/22/01 -0500, Richard wrote:
>>Can you make a power supply that outputs 5V at 50-100ma that connects to
>>120AC line with no transformer, the idea needed is for a very cheap
>>device. It would need to be at least CSA/UL approvable.
>>
>>What comes to mind is a cheap 100ma 78L05 5V reg, but whats needed between
>>it and the AC?
>
>A bridge rectifier, series resistor and a 24-30V zener diode that will
>stabilize and drop the input voltage to within the upper range of the 78L05
>regulator. A capacitor post-zener will filter out the zener noise.
That would be a rather big resistor - it would dissipate 14 watts, and
the regulator another 2W - that's a LOT of heat.
You could us a capacitive dropper, but you're looking at a few uF,
which is big and expensive (more so than a small transformer)
>>What about isolation issues?
>
>That's the price you pay! If you don't want a transformer, you don't get
>the isolation. Make sure you have a fuse on the mains side (input to bridge).
>
>>Lots of issues here I am sure.
>
>Not really: just the lack of isolation and the maximum power/current
>through the zener.
oh, and heat!
>================================================================
>Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam.....lcfltd.com
>Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
>824 Timberlake Drive                     Tel: 757-467-0954
>Virginia Beach, VA 23464-3239            Fax: 757-467-2947
>
>"Vere scire est per causas scire"
>================================================================

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2001\03\23@070655 by mike

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On Thu, 22 Mar 2001 22:07:53 -0500, you wrote:

>Can you make a power supply that outputs 5V at 50-100ma that connects to 120AC line with no transformer, the idea needed is for a very cheap device. It would need to be at least CSA/UL approvable.
>
>What comes to mind is a cheap 100ma 78L05 5V reg, but whats needed between it and the AC?
>
>What about isolation issues?
>
>Lots of issues here I am sure.
>
>Thanks,
>Richard.
At this current level a transformerless PSU is not really practical -
small transformers are very cheap, and will be cheaper than any other
method except maybe a HUGE resistor and a lot of heat.
Using a transformer will also save a lot of approval costs.

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2001\03\23@080334 by t F. Touchton

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part 1 2070 bytes content-type:text/plain; charset=us-asciiOne common way is to use a capacitor to give you a voltage drop, then rectify,
filter and clamp with a 1W or larger zener.  If you skip the zener, then you may
hurt your circuitry since the voltage drop across the capacitors reactance is a
function of the current drawn.  This can then be passed to a simple linear
regulator.

Harris used to have a chip (1988 or thereabouts) that you hooked 120AC to 2
pins, added a couple of caps, and you got 5V @50mA or so out of it.  I don't
remember the part number.  But I do remember my boss blowing most of them up!
That's why we went with the idea above.

Hope this helps.


|--------+--------------------------->
|        |          Richard Sloan    |
|        |          <rsloan@THEMINDFA|
|        |          CTORY.COM>       |
|        |                           |
|        |          03/22/01 10:07 PM|
|        |          Please respond to|
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 |       Subject:     [EE]: 120AC to 5V no transformer                        |
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Can you make a power supply that outputs 5V at 50-100ma that connects to 120AC
line with no transformer, the idea needed is for a very cheap device. It would
need to be at least CSA/UL approvable.

What comes to mind is a cheap 100ma 78L05 5V reg, but whats needed between it
and the AC?

What about isolation issues?

Lots of issues here I am sure.

Thanks,
Richard.

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part 2 2448 bytes content-type:application/octet-stream; (decode)

part 3 154 bytes
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2001\03\23@153453 by Lawrence Lile

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I was hoping someone would suggest the dropping capacitor.  Take apart any
steam iron with AutoShutoff,  X-10 module, hair dryer with autoshutoff, etc.
and you are likely to find this type of supply.

You have to full-wave rectify after the capacitor, or it won't work right.
Place a 22 ohm 1 watt resistor on the hot side, as well as a fuse if you can
afford it.  We actually use the 22 ohm resistor as a fuse (cheaper).  I
never regulate the output with anything other than a load.  Usually use a
resistor-zener power supply to step down to 5V.  Everything between the
rectifiers and the step-down resistor may see 24V, may see 50V, who knows?
I usually am driving a relay in there, with a transistor rated at least 150V
(2n5551 = US$0.05) and a capcitor rated 63V, 75V surge.    Once the relay
turns on, I can rely on 28VDC +/- 5v (which is good enough for a 24v relay).

Now there are many people who will begin flaming me, saying this type of
power supply is unreliable, cheap, problem-prone, cheeesy, etc. etc.  They
are right!  This is only a useful design in an under US$20 appliance with
heavy cost pressure and a high allowable failure rate.  No isolation, no
regulation, lots of ripple, and the whole thing costs about US$0.25 -
everything a person could want in a power supply!

Advocating this type of supply, is like advocating use of a soap-box go-cart
in the Indy 500.  But you know, if you are racing on Cost-Per-Mile, the
go-cart would win!

-- Lawrence Lile




{Original Message removed}

2001\03\24@015640 by Roman Black

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Lawrence Lile wrote:
{Quote hidden}

A cap reactive supply can be good. A 1uF poly cap
is about 3200ohms at 50Hz and 2700ohms at 60Hz if
I remember properly. Xc = 1/ 2pi f c

So at 120v 60Hz a 1uF cap will supply average
current of say 110v/2700= 41mA.
This is with full wave rect bridge and a 10v load.
With a half wave rect, as per the Microchip
"transformerless" appnote, you only get 20mA.

Some good design tips, always use a series resistor
between active and the cap, about 5% of the Xc ohms
value, so 120 ohms is good for 1uF cap. A 1.5 megohm
resistor across the cap is a good safety measure and
is required for UL listing also.

Then important stuff!!
Capacitor quality is everything, I prefer the 630v
polyester caps, these are great especially if you can
get the blue "milspec" ones. With a 120v mains you
might get away with 250v poly caps. Always use a zener
on the output or voltage can climb to full mains
volts.

The full wave bridge rect gives double the current
for the same size cap, but BEWARE all parts of your
load circuit will swing to full mains potential. Be
real careful with buttons, etc that someone might
touch of get finger sweat etc.

My preferred type is the two diode half-wave example,
with this type your load has it's neg lead at the
mains neutral potential, normally 0v. Much better
if you have buttons etc attached. I have a Ni-Cd
charger built like this that has given many years
good service, as a constant current supply with
a meter and two alligator clips.
-Roman

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2001\03\24@150333 by Bill Westfield

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   A cap reactive supply can be good. A 1uF poly cap
   is about 3200ohms at 50Hz and 2700ohms at 60Hz if
   I remember properly. Xc = 1/ 2pi f c

And it has to dissipate as much power as a 2700ohm resistor, right?
A bit of a problem, since caps are rarely rated for power dissipation.


   Capacitor quality is everything, I prefer the 630v
   polyester caps, these are great especially if you can
   get the blue "milspec" ones.

Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say, close to
transformer sized?

Actually, a shaver I took apart recently looked like it had a particularly
interesting circuit involving a resistor in series with the primary of a
very small transformer.  (It didn't actually have this, but it sorta looked
like that originally.)  Can you do this in reality - limit the primary
current to allow a smaller transformer?

BillW

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2001\03\24@180820 by Jinx

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> Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say,
> close to transformer sized?

A 1uF 250V X2-rated cap is 31 x 24 x 14mm, about 1/2 the size
of a small mains Tx. And a lot more common than Tx's in gear
available for parts-stripping (eg PSUs) by the frugally-inclined

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2001\03\24@200441 by robocat

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On Sat, 24 Mar 2001 12:03:38 PST, Bill Westfield <@spam@billwKILLspamspamcisco.com> wrote:

>    A cap reactive supply can be good. A 1uF poly cap
>    is about 3200ohms at 50Hz and 2700ohms at 60Hz if
>    I remember properly. Xc = 1/ 2pi f c
>
>And it has to dissipate as much power as a 2700ohm resistor, right?
>A bit of a problem, since caps are rarely rated for power dissipation.

No.  Capacitance is reactive; as far as it is a good capacitor it doesn't
dissipate power.  Of course real parts have loss in the resistance of the
leads, in the dielectric, etc. and do dissipate some small amount.

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2001\03\24@210557 by Olin Lathrop

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>     A cap reactive supply can be good. A 1uF poly cap
>     is about 3200ohms at 50Hz and 2700ohms at 60Hz if
>     I remember properly. Xc = 1/ 2pi f c
>
> And it has to dissipate as much power as a 2700ohm resistor, right?

No.  Ideal capacitors are incapable of dissapating any power.  This is
because their current and voltage are 90 degrees out of phase.  Energy is
only temporarily stored in one part of the cycle, then released in another.
This why a capacitor coupled power supply can be so efficient.

Real capacitors do dissapate power because the dielectric material
dissappates energy in the process of storing and releasing the charge.
Fortunately this isn't much of an issue at 60Hz.

Back in college I once made a small radio transmitter at about 1MHz that fed
its signal into the AC line.  I had a push-pull class C output circuit
driving an LC tank.  Each half of the L had an adjustable slug and a .1uF
ceramic capacitor accross it.  I would tune it by adjusting the slugs for
maximum output on an oscilloscope.  I noticed that I had to keep re-tuning
it for the first few minutes after switching it on.  I figured it was
settling thermally, but the drive transistors stayed pretty cool the whole
time.  Then I accidentally touched one of the tank caps and almost burned
myslef!  I was amazed that the capacitors were that inefficient at 1MHz.
Then I calculated the current and realized I was dumping over 3A RMS thru
them.  It was a great lesson on real world versus theoretical electronics.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, KILLspamolinKILLspamspamembedinc.com, http://www.embedinc.com

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2001\03\24@213746 by Bill Westfield

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   > Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say,
   > close to transformer sized?

   A 1uF 250V X2-rated cap is 31 x 24 x 14mm, about 1/2 the size
   of a small mains Tx.

So how much bigger is the recomended 630V cap? :-) I have sitting next to
me a 32 x 26 x 21 mm 1.5VA PCB mount transformer with a 15V 0.1A secondary
(more power than the original poster needed, although transformer vendors
tend to keep the same size and power rating constant as they change their
secondary voltage, so this doesn't mean you can easilly get a smaller 6V
0.1A transformer.)  This particular transformer comes stamped with a bunch
of safety approvals, BTW...  This makes it a close race, size wise.


   And a lot more common than Tx's in gear available for parts-stripping
   (eg PSUs) by the frugally-inclined

There is that.  From the things I've stripped recently, it takes a pretty
honking big power supply to rate a 1uF filter cap, though...

I wonder if there's likely to be a bunch of low current "stand-by" power
supplies created as part of the "green appliance" push?  I vaguely recall
seeing such a thing (5V 50mA supply in a 1 inch cube?) in a "new products"
section of some magazine recently, but I don't recall the vendor or
magazine.  (Since these tend to be aimed at computers, copiers, TVs, and so
on, they DON'T run "cheap" when new, but it'd be neat to be able to start
digging them out of scrapped equipment and/or have them show up as surplus
from companies that didn't make it.)  OTOH, such things tend to get cost
reduced as economies of scale come into play...

I've been wondering if you can't do something along the lines of a lamp
dimmer circuit (triac or SCR), charging your filter cap for the last 5% of
the (occasional?) sine wave.  Ripple would be pretty gross, but filter and
regulator ought to clip that off, right?  It'd be somewhat analagous to
those micropower switching regulators that skip pulses when the power drain
is low...

BillW

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2001\03\24@222259 by Jinx

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> A 1uF 250V X2-rated cap is 31 x 24 x 14mm, about 1/2 the size
> of a small mains Tx.
>
> So how much bigger is the recomended 630V cap? :-)

A 0u22 630V I have is about the same size as the 1u X2. A 1u 630V
I'd imagine would be of a size sufficient to stun a small apprentice if
aimed accurately

> I have sitting next to me a 32 x 26 x 21 mm 1.5VA PCB mount transformer
> with a 15V 0.1A secondary (more power than the original poster needed,

The only reference book I have is the RS catalogue. The smallest 1.5VA
I can see is a little larger than yours. The price though, NZ$17, is enough
of a deterrent to consider a transformerless circuit. Especially when there
is a never-ending supply of dead SMPS to envulturate (new verb)

> And a lot more common than Tx's in gear available for parts-stripping
> (eg PSUs) by the frugally-inclined
>
> There is that.  From the things I've stripped recently, it takes a pretty
> honking big power supply to rate a 1uF filter cap, though...

Mostly I come across 0u22 or 0u47, occassionally 0u68 or 1u

> I've been wondering if you can't do something along the lines of a lamp
> dimmer circuit (triac or SCR), charging your filter cap for the last 5% of

You could be back to the cost issue, for the low-volume constructor
anyway

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2001\03\25@003618 by Roman Black

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William Chops Westfield wrote:
>
>     A cap reactive supply can be good. A 1uF poly cap
>     is about 3200ohms at 50Hz and 2700ohms at 60Hz if
>     I remember properly. Xc = 1/ 2pi f c
>
> And it has to dissipate as much power as a 2700ohm resistor, right?
> A bit of a problem, since caps are rarely rated for power dissipation.

Not so, no current flows through a cap, only charges built
up on it's plates. A good poly cap will run more efficient
and cooler than one of the micro-transformers you mentioned.


>     Capacitor quality is everything, I prefer the 630v
>     polyester caps, these are great especially if you can
>     get the blue "milspec" ones.
>
> Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say, close to
> transformer sized?

Nope. I have buckets of them that the apprentices strip
from old TVs and such. You can get some smaller than others,
1uF about 30 x 16 x 7mm are the ones I use. You can get 0.33uF
in the same size package, just depends on the manufacturer.



>
> Actually, a shaver I took apart recently looked like it had a particularly
> interesting circuit involving a resistor in series with the primary of a
> very small transformer.  (It didn't actually have this, but it sorta looked
> like that originally.)  Can you do this in reality - limit the primary
> current to allow a smaller transformer?

I had one of those shavers too, a rechargable one with its
own charger built in. I pulled it apart too! I think it
is some type of saturation transformer system, so the NiCd
being charged acts like a short circuit and overall current
is limited by the resistor and special cored transformer,
dumping max and constant 100ma or so into the NiCd.
Fairly unconventional, and real messy when the NiCd
eventually fails.
-Roman

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2001\03\25@004656 by Roman Black

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William Chops Westfield wrote:
>
>     > Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say,
>     > close to transformer sized?
>
>     A 1uF 250V X2-rated cap is 31 x 24 x 14mm, about 1/2 the size
>     of a small mains Tx.
>
> So how much bigger is the recomended 630V cap? :-) I have sitting next to
> me a 32 x 26 x 21 mm 1.5VA PCB mount transformer with a 15V 0.1A secondary



I am going to risk being unconventional here, but I have
a capacitive reactance supply here that uses two electro
caps back to back, reversed. 2.2uF 400v. These caps are
quite tiny compared to a poly or non-polarised cap suitable
for 240vac use.

It has worked fine for a few years, of course it has a
series resistor dropping about 10% of the mains voltage.
I build supplies like this all the time for testing
things with a constant current like leds, and for trickle
charging NiCds that a lot of our multimeters and test
equipment use in the workshop. You can use a switch to
switch different caps in and out of circuit to adjust
total current, and my main system is to build them in
old analogue multimeter frames, using the rotary
switch to adjust current and the meter to display the
current/voltage etc. The Xc supply is small and cool
enough to do this even in those small cheap boxes.

My favorite one is a zener tester, it injects 2mA
to 50vdc and 0.4mA to 200vdc and will test zeners
in-circuit most of the time, and show their zener
voltage on the meter.
:o)
-Roman

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2001\03\25@113558 by Oliver Broad

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I've seen the consequences of this type of supply in some timer modules used
in some equipment I was involved in installing. Fault logging was poor on
the site but I believe two units failed in under a year. I got hold of one
for examination and the series capacitor was half melted. I find it hard to
believe the parts were intrinsicly flawed but I believe they are unusually
vulnerable to surges. Looking back I believe the surges originated in a
contactor coil every time it shut off, but I'm not aware of any design rules
on mixing timers and coils on the same circuit, especially as similar timers
are sold as relay accessories.

A transient suppressor might have protected it.

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2001\03\25@115006 by Roman Black

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Oliver Broad wrote:
>
> I've seen the consequences of this type of supply in some timer modules used
> in some equipment I was involved in installing. Fault logging was poor on
> the site but I believe two units failed in under a year. I got hold of one
> for examination and the series capacitor was half melted. I find it hard to
> believe the parts were intrinsicly flawed but I believe they are unusually
> vulnerable to surges. Looking back I believe the surges originated in a
> contactor coil every time it shut off, but I'm not aware of any design rules
> on mixing timers and coils on the same circuit, especially as similar timers
> are sold as relay accessories.
>
> A transient suppressor might have protected it.


I absolutely agree, to make this kind of circuit
reliable you need a decent series resistor. This
reduces surge currents from high slew-rate spikes,
which ALWAYS occur on the AC mains.

I use 5% volts drop resistor with the nice
milspec 630v polyester caps, and about 10%
volts drop resistor with any other caps. I have
built some with 250v rated caps and used on 240v
AC mains, with the 10% drop resistor, and they
have worked well for years. With some fast and
peaky spikes the relative AC freq can be very
high, and the Xc of the cap just a few ohms.
So gives high currents and resulting cap destruction.
Adding a 220ohm (etc) resistor in series with
the cap doesn't affect power efficiency that
much, but can reduce spike current to hundreds
of times less.
-Roman

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2001\03\25@131306 by dpharris

picon face
Hi-
I'd be interested in a schematic for such (and any other useful instruments :-)
Maybe in the PICLIST archives?
Thanks, David


Roman Black wrote:

{Quote hidden}

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2001\03\25@163700 by Peter L. Peres

picon face
> A 0u22 630V I have is about the same size as the 1u X2. A 1u 630V
> I'd imagine would be of a size sufficient to stun a small apprentice if
> aimed accurately

FYI there is a scrappable capacitor of suitable value in nearly every
color TV and monitor. It is used in the HOT circuit to connect the HD coil
to the HOT stage. Common ratings are 2-10uF 250-400Vac and more. The next
time you go past a thrown out chassis or TV pick it up ;-). Beware that
these are not X2 rated but they should do the job in a hobby circuit and
have much higher current ratings than X2 caps. Always use fuses and a
thermal fuse too if you want to be safe.

Peter

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2001\03\25@163934 by Peter L. Peres

picon face
>    A cap reactive supply can be good. A 1uF poly cap
>    is about 3200ohms at 50Hz and 2700ohms at 60Hz if
>    I remember properly. Xc = 1/ 2pi f c
>
> And it has to dissipate as much power as a 2700ohm resistor, right?
> A bit of a problem, since caps are rarely rated for power dissipation.

No, it shifts the phase so it does NOT dissipate any power except what the
capacitor losses dictate. Draw one of them vector diagrams for RC
circuits. Zc is vertical so it does not dissipate power. The load is a R
and it does dissipate (it has a horizontal vector in this representation).

Peter

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2001\03\25@191638 by Jim Windgassen

flavicon
face
The company that makes that 1" cube power supply is called Bias Power
Technology.  Their web page is:  http://www.biascompany.com/

They told me that they were about 10$ each.  Check them out.

Jim
{Original Message removed}

2001\03\25@210254 by Jinx

face picon face
> FYI there is a scrappable capacitor of suitable value in nearly
> every color TV and monitor. It is used in the HOT circuit to
> connect the HD coil to the HOT stage. Common ratings are
> 2-10uF 250-400Vac and more.

That's one I was talking about, big brown thing. Usually stuck
down with that yellow crap that eventually goes dark and makes
trouble

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2001\03\25@232717 by Roman Black

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face
Jinx wrote:
>
> > FYI there is a scrappable capacitor of suitable value in nearly
> > every color TV and monitor. It is used in the HOT circuit to
> > connect the HD coil to the HOT stage. Common ratings are
> > 2-10uF 250-400Vac and more.
>
> That's one I was talking about, big brown thing. Usually stuck
> down with that yellow crap that eventually goes dark and makes
> trouble


Gorilla snot. Yep, that's what it's called,
even in the technical manuals we get for
TV fault finding. Serious. :o)
-Roman

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2001\03\26@002603 by Jinx

face picon face
> Gorilla snot. Yep, that's what it's called,
> even in the technical manuals we get for
> TV fault finding. Serious. :o)
> -Roman

Anyone nose who picked that for an adhesive ?

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2001\03\26@004714 by Dan Michaels

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face
Captain Jinx wrote:
>> Gorilla snot. Yep, that's what it's called,
>> even in the technical manuals we get for
>> TV fault finding. Serious. :o)
>> -Roman
>
>Anyone nose who picked that for an adhesive ?
>

IIRC, it was Cyranose.

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