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'[PICLIST] Transformerless PSU'
2001\07\25@205039 by Alexandre Domingos F. Souza

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       Dear guys,

       I think it's a basic one, but maybe fits the list

       I designed a circuit with a PIC (12C508) that turns on and off a relay, controlled by an external source. The power to this circuit (around 120mA) is a small transformer. I'd like to build a transformerless PSU into this circuit. But EVERY scheme I found on the internet was unusable. I saw something on the Embeeded Control Handbook from Microchip, but it only goes to (if I'm not mistaken) 45 mA. Maybe someone can help me to develop (or at least learn to) a simple transformerless PSU that can give me 12vcc / 120 mA???

       Thanks for any info! :o)


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Alexandre Souza
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2001\07\25@211345 by Spehro Pefhany

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At 09:52 PM 7/25/01 -0300, you wrote:
>        Dear guys,
>
>        I think it's a basic one, but maybe fits the list
>
>        I designed a circuit with a PIC (12C508) that turns on and off a
relay, controlled by an external source. The power to this circuit (around
120mA) is a small transformer. I'd like to build a transformerless PSU into
this circuit. But EVERY scheme I found on the internet was unusable. I saw
something on the Embeeded Control Handbook from Microchip, but it only goes
to (if I'm not mistaken) 45 mA. Maybe someone can help me to develop (or at
least learn to) a simple transformerless PSU that can give me 12vcc / 120
mA???

I'd suggest not doing it. This kind of power supply has marginal
reliability in many cases, and
transformers are not that expensive in volume. If you must, then go to as
high a voltage DC relay
as possible to reduce the current. 24V at least. Keep in mind that without
isolation any input or
output is a potential source of DEATH to the user at any time in the
future, over the life of each
unit that you make. A typical 24VDC 360mW relay draws only 15mA. If you
don't know how to scale the
one shown in the MChip data then all the more reason to steer clear...
transformers not only are more
reliable but they are usually very effective at filtering noise and
transients out of your circuit.

A (bad) example of these is the crappy China-made IR light switches that
sell for about $7 US retail
on special (including die cast and molded housing, two CSA/UL light
sockets, PCB, relay and IR sensor,
supposedly weatherproofed, several pots and with a 4-color printed carton.
These things last about
one season around here.

Best regards,
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2001\07\25@222722 by Edson Brusque

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Hello Alexandre and Spehro,

   Alex, you don't want to use a transformer because of it's costs or to
save weight and/or space?

   If cost isn't your problem, I would suggest you to buy a transformerless
suply for 24V and step-it-down to 5V with a swithed-regulator like LT1173.
You can use an small transistor to switch the relay from the PIC output and
use the output from the LT1173 to power a 5V circuit up to about 300mA.

   LT1173 isn't cheap at about US$3.40 in Brazil.

   Best regards,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\07\25@225713 by Alexandre Domingos F. Souza

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>    Alex, you don't want to use a transformer because of it's costs or to
>save weight and/or space?

       It's a matter of space. Note the circuit is completely isolated from the operator (optocoupler).

>    If cost isn't your problem, I would suggest you to buy a transformerless
>suply for 24V and step-it-down to 5V with a swithed-regulator like LT1173.
>You can use an small transistor to switch the relay from the PIC output and
>use the output from the LT1173 to power a 5V circuit up to about 300mA.
>    LT1173 isn't cheap at about US$3.40 in Brazil.

       Nah, I need it to be as small and CHEAP as possible :o( Any sugestions? ;o)


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2001\07\25@231653 by Spehro Pefhany

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At 11:59 PM 7/25/01 -0300, you wrote:

> Nah, I need it to be as small and CHEAP as possible :o( Any sugestions? ;o)

If you insist, you can scale the supplies by simply increasing the capacitance
and beefing up the other parts.

But first try to reduce the current your circuit requires as much as
possible.
The higher the series resistor you put in there, the more heat you get, but
the more resistant to transients your circuit will be. To get 100mA from a
240V 50Hz supply, you'd need a couple of uF rated for across the line
operation
(preferably 630VDC rating or UL/CSA X type if you want it to be relatively
trouble-free). That means a fairly large film capacitor. They are fairly
cheaply
available (polyester).

A transformer is usually better unless your product is throw-away cheap and
dirty.

Best regards,
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2001\07\25@233121 by Gennette, Bruce

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If you are trying to save space you're on a loser here.  The 600V+ rated
capacitor required to give >100mA in a transformerless power supply is
*MUCH* bigger than than a transformer.  *AND* about twice the price.

Bye.

{Original Message removed}

2001\07\26@014830 by Chris Carr

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Presumably you are using a relay with a low voltage coil. Why not ease the
low voltage current requirements by using a relay with a high voltage AC
coil.

If my presumption is correct then you will probably reduce your current
consumption on the 5 volt rail to 45mA or less. Use a small Triac or
thyristor to switch the relay.

Regards

Chris Carr

> {Original Message removed}

2001\07\26@051543 by Roman Black

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Alexandre Domingos F. Souza wrote:
>
>         I designed a circuit with a PIC (12C508) that turns on and off a
>relay, controlled by an external source. The power to this circuit (around
>120mA) is a small transformer. I'd like to build a transformerless PSU into
>this circuit. But EVERY scheme I found on the internet was unusable. I saw
>something on the Embeeded Control Handbook from Microchip, but it only goes
>to (if I'm not mistaken) 45 mA. Maybe someone can help me to develop (or at
>least learn to) a simple transformerless PSU that 120mA.


Hi Alexandre! This can be done if you REALLY want
to do it. The Mchip app note shows 45mA, and that
is with a half-wave rectifier (two diodes).

Just change to a proper rectifier bridge, this will
double the current to 90mA. Then using a 30% larger
value of the main Xc cap will give you 120mA.
This web page has Traffic.PDF sent by Richard Ottosen
which shows a larger current Xc supply with a
full-wave bridge:
http://centauri.ezy.net.au/~fastvid/tube4w.htm

IMPORTANT! using a full wave rectifier will give
lethal voltages at ALL points of your 24v circuit.
You no longer have a reference ground! I know you
said you were using an optocoupler but remember at
all times this circuit is dangerous...

Some handy points, you can get reliable relay
operation at half the hold current usng the old RC
trick, which gives it full current for pull-in
but only half current under hold. Costs one resistor
and one 470uF electro. Maybe this would get you
down to 60mA circuit current. I have used this trick
down to about 25% hold current.

Remember the Xc supply ALWAYS runs full current,
so if your 120mA relay is OFF, something else
(large zener?) must be drawing the 120mA. Have a
serious think about this. Xc supply is best for
circuits that always draw the same current.
:o)
-Roman

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2001\07\26@055235 by Bob

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If the relay is a simple single pole on/off type, and not too many amperes are
going through it, you could replace it with a triac and a zero crossing triac
optocoupler interface (as low as 5ma current draw).  If the load is inductive,
you will need to add the proper snubber circuit too.

You could then use a VB409 (from ST microelectronics) which is rated at 70ma out
of its 5vdc 5% regulated pin (which should be more than enough to drive the
triac opto and the pic), but I think it can kick out a bit more out of the
12~15Vdc unregulated pin (something like 140ma for 10ms max).  Like the X cap
setup, this part does run your circuit at line potential.  Unlike the Xcap
setup, it don't care if your not drawing anything from it, but it may need a
heatsink if your drawing more than 40~45ma.


{Original Message removed}

2001\07\26@061525 by Vasile Surducan

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I've done one, some time ago, see
http://www.geocities.com/vsurducan/c520.htm
at the bottom of the page, up to 150mA, but I don't recommend such power
supplies for production devices ( maybe on 120V mains, only )
Note that in my design, the supply don't like to remain without load...
Vasile

On Thu, 26 Jul 2001, Roman Black wrote:

{Quote hidden}

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2001\07\26@064931 by Spehro Pefhany

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At 12:10 PM 7/26/01 +0300, you wrote:
>I've done one, some time ago, see
>http://www.geocities.com/vsurducan/c520.htm
>at the bottom of the page, up to 150mA, but I don't recommend such power
>supplies for production devices ( maybe on 120V mains, only )
>Note that in my design, the supply don't like to remain without load...
>Vasile

If you use something like this (and I don't recommend it..) be sure to
put a resistor in series with the capacitor to reduce current surge and
in *parallel* with the capacitor .. because there is a good chance
if it is unplugged near the peak line voltage the capacitor may hold as
much as +/-300V charge .. that's enough energy in a 4.7uF cap to give
someone a goodly shock, and they can get it quite easily without
opening the case, if you see that?

Best regards,

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2001\07\26@071458 by Vasile Surducan

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Yapp, thank's for the point, I knew it ( it's more than 300V, it's 316V
usual and much more on spikes or mains failure ) but this one was intend to work
plugin forever , and exactly like this is working continuously from about
two years...with same capacitor.
But needs a VERY GOOD capacitor and I must admit, I had search something
for it. (any cap or xcap like you named it, who make a delicate noise,
almost imperceptible, will die soon )
About the current surge, you have right, there is a series resistor  which
seems is missing in the picture.
Vasile

On Thu, 26 Jul 2001, Spehro Pefhany wrote:

{Quote hidden}

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2001\07\26@072342 by mike

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On Wed, 25 Jul 2001 21:52:50 -0300, you wrote:

>        Dear guys,
>
>        I think it's a basic one, but maybe fits the list
>
>        I designed a circuit with a PIC (12C508) that turns on and off a relay, controlled by an external source. The power to this circuit (around 120mA) is a small transformer. I'd like to build a transformerless PSU into this circuit. But EVERY scheme I found on the internet was unusable. I saw something on the Embeeded Control Handbook from Microchip, but it only goes to (if I'm not mistaken) 45 mA. Maybe someone can help me to develop (or at least learn to) a simple transformerless PSU that can give me 12vcc / 120 mA???
>
For that current, a transformer will be the cheapest, and probably not
far off the smallest solution.
Can you change the relay? - some types of relay are readily
availalable with 48v coils, so you immediately reduce your current
requirement by a factor of four, making a transformerless solution
more practical.
Another possibility is to use a mains-coil relay, and a small (TO92)
triac, or MOC3020 opto-triac to drive it. The PIC can be run from a
small transformerless 5V supply  
Of course if you REALLY wanted to do it as small as possible, and have
a strong nerve, you could use the PIC to PWM or phase-control the
relay current to get 12v avarage from the mains, using the relay's
inductance to limit peak current, but make sure think very carefully
about what would happen if the software crashed!

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2001\07\26@093203 by Roman Black

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Vasile Surducan wrote:
>
> I've done one, some time ago, see
> http://www.geocities.com/vsurducan/c520.htm
> at the bottom of the page, up to 150mA, but I don't recommend such power
> supplies for production devices ( maybe on 120V mains, only )
> Note that in my design, the supply don't like to remain without load...
> Vasile


Hi Vasile! Great web page! But that picture power.gif
scares me a bit! The only thing limiting the voltage
across C5 is the current drawn by the load!!
Maybe you could put a 8v 1w or larger zener diode
across it. Would improve safety a lot!
:o)
-Roman

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2001\07\26@094431 by Spehro Pefhany

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At 11:32 PM 7/26/01 +1000, you wrote:

>Hi Vasile! Great web page! But that picture power.gif
>scares me a bit! The only thing limiting the voltage
>across C5 is the current drawn by the load!!

The regulator or C5 will break down before it gets to 50V,
most likely. ;-)

Best regards,

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2001\07\26@095636 by Roman Black

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Spehro Pefhany wrote:
>
> At 11:32 PM 7/26/01 +1000, you wrote:
>
> >Hi Vasile! Great web page! But that picture power.gif
> >scares me a bit! The only thing limiting the voltage
> >across C5 is the current drawn by the load!!
>
> The regulator or C5 will break down before it gets to 50V,
> most likely. ;-)


Ha ha! You could design TV sets! ;o)
-Roman

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2001\07\26@135805 by Steven Bakaletz

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Download the application note from MicroChip for a dimmer using the 12C508
www.microchip.com/Download/appnote/category/rdesigns/40171a.pdf
Strip off everything but the triac part, and use that to drive a 120V AC
relay.
You don`t need the zero crossing  just a high or low to the triac drive.

Works I've used it.

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2001\07\27@063108 by Vasile Surducan

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Like usual you have again right, but as I said already ( and test on about
100 hours with my measuring tools and more than 2 years just with my
eyes...) it's no need any zenner on load or resistor across the capacitor
if:

- never plug on the supply without computed load connected ( and no other
load ! )
- use a best quality polyester or PMP capacitor with nominal voltage 2 or
3 times greater than maximum voltage you may have (have big size ! )

I other condition I use a 5W 12V zenner as you've mentioned, but I don't
like this sort of supplies (I've repaired many supplies like this,
produced at Ganz-Hungary in some energetic equipment, here the capacitor
was protected with a varistor who crashed frequently, also the
protective zenner diode crashed ...), it's easy to develop a
comutation supply up to
100W with only one power transistor, an a cheap UC344 or TL494, a little
transformer, some fast diodes and some capacitors.
You don't need to know only Faraday's low and some tricks about projecting
a good pcb. Maybe in my next web page...

Cheers, Vasile



On Thu, 26 Jul 2001, Roman Black wrote:

{Quote hidden}

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2001\07\27@063111 by Vasile Surducan

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The regulator input never gets here more than 15V because I have a serious
load on the unregulated section ( connected directly to the filtering
capacitors ).
Knowing this potential is a projecting rule for this kind of garbage
supplys. Also you must know which is the whole variation domain for cos_fi
on your local mains ( it's important to know if you have a more inductive
or more capacitive loads connected on the same mains ) The capacitive
reactance for pure resistive loads or for inductive loads is not the same
(thinking from the capacitor life point of wiew ) and must be computed both
for maximum voltage variation and supply cos_fi variation.

Probably my last english phrases will be dificult to understood...
Cheers, Vasile


On Thu, 26 Jul 2001, Spehro Pefhany wrote:

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2001\07\27@085324 by Ned Seith

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Vasile,

Your series capacitance voltage divider circuit has certainly received
criticism.
So I hope that I'm not kicking a dead horse.
While a transformer would definitely be the safest approach for the typical
hobbyist, I'm glad to see that there is someone who is willing to be more
intimate with the electrons.
The concept and configuration of your series capacitance voltage divider
circuit is fine.
I have designed industrial applications which have provided several amps of
current at low voltages from 220 Vac and 277 Vac mains using a series
capacitor. Industrial equipment and machines frequently use a series
capacitor instead of a transformer for providing lower voltages.
A few points:
I would not add a resistor in series with the capacitor (C9) as this will
vary the effective capacitance reactance which is providing the desirable
voltage drop and will also dissipate heat.
I would not add a resistor in parallel to the capacitor (C9) as this will
vary the effective capacitance reactance which is providing the desirable
voltage drop. This resistor would also dissipate heat.
I would not be too concerned with the capacitor (C9) remaining charged as
the approximate 6 mA current consumption from the voltage regulator will
quickly discharge the capacitor. UL and TUV stipulate that the voltage
potential on an unplugged power cord must diminish to 1/3 of the mains
voltage within 10 seconds. So, If I wanted to increase the rate at which
the capacitor discharges, I would place a resistor in parallel to (C5) on
the low voltage side of the circuit.
I would want a 1/4 amp fuse between the 220 Vac main and the series
capacitor (C9).
I would also want the series capacitor (C9) rated for 800 V to 1000 V.
If the series capacitor (C9) is getting warm at all, then the voltage
rating should be increased.
I would want the diode rectifiers voltage rating increased to 800 V to 1000
V (1N4006, 1N4007) to assure that there is not any brief reverse conduction
during the delay of the capacitors charge cycle.
Otherwise, looks good to me.
Just a few comments from an old engineer.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
G O T    G A R L I C ?
GILROY GARLIC FESTIVAL 2001 !
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

At 12:10 PM 7/26/01 +0300, you wrote:
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2001\07\27@091026 by Roman Black

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Ned Seith wrote:
{Quote hidden}

Hi Ned, I find these type of supplies very interesting,
and have been playing with them for many years. Since
before they were legal. :o)

I'm really interested in your "several amps" applications,
can you give any more info? Size/cost of the capacitors?
Or custom built capacitors? I've made some medium supplies
with the 630v poly types, pref the blue milspec ones.
They are still going good now after many years. Never
been brave enough to sell one though, just for personal
use in my workshop.

Do you have any specific tricks for handling current
under-loads or spike conditions? Regulation? Sorry to fire
questions at you. :o)
-Roman

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2001\07\27@092025 by Eisermann, Phil [Ridg/CO]

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> -----Original Message-----
> From: Roman Black

[sni[]

>
> I'm really interested in your "several amps" applications,
> can you give any more info?

and please share your wisdom with the list. I'm also interested in this sort
of application.

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2001\07\27@093726 by Spehro Pefhany

picon face
At 05:46 AM 7/27/01 -0700, you wrote:

>I would not add a resistor in series with the capacitor (C9) as this will
>vary the effective capacitance reactance which is providing the desirable
>voltage drop and will also dissipate heat.

It is the only thing limiting current when voltage transients appear at
the input (as at turn-on). All production circuits will include this
resistor.
Consider the surge current rating on the metal film capacitor if nothing
else...
the current at switch-on is otherwise limited only by the impedance of
the mains and the connections to the capacitor, which can blow the
thin metalization right off the dielectric, creating holes and eventual
failure ('self healing' notwithstanding). Needless to say, it also
whacks the diodes with a surge, though diodes are fairly tough, I don't
like to see the circuit dependent on external factors (such as whether
the customer has plugged it into an extension cord or not) to be reliable.

>I would not be too concerned with the capacitor (C9) remaining charged as
>the approximate 6 mA current consumption from the voltage regulator will
>quickly discharge the capacitor. UL and TUV stipulate that the voltage
>potential on an unplugged power cord must diminish to 1/3 of the mains
>voltage within 10 seconds. So, If I wanted to increase the rate at which
>the capacitor discharges, I would place a resistor in parallel to (C5) on
>the low voltage side of the circuit.

This will do nothing- the capacitor is in series with the low voltage
side when the plug is removed from the socket and the voltage will remain
too long to meet any kind of safety standards without a parallel resistor.
You won't see an approved design without it, or some equivalent.

>I would want a 1/4 amp fuse between the 220 Vac main and the series
>capacitor (C9).

A flameproof fusible resistor can probably be used to avoid the need for
that...
it has to be a high surge current type anyway (not metal film, but MOF
or wirewound).

>I would also want the series capacitor (C9) rated for 800 V to 1000 V.

Preferably with an AC rating > maximum line voltage.

>If the series capacitor (C9) is getting warm at all, then the voltage
>rating should be increased.

Yes, a film cap should never get warm.

Have you gotten your "several amperes" supplies inspected by any
safety approval agencies?  Are there any power factor specifications
that cause problems?

Best regards,
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2001\07\27@112421 by Ned Seith

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Roman,

I had the good fortune, in the early 1990's, of consulting with Ralph Kerrigan, the Chief Capacitor Design Engineer with Sprague Electric due to the quantity of capacitors that I was ordering. I will share a few things that I learned from Mr. Kerrigan. At that time, the high voltage capacitors manufactured by Sprague were available with either a "foil" conductive material or with a "metalized film" conductive material. Mr. Kerrigan indicated that the "foil" conductive material had a superior reliability for handling "higher currents" while the "metalized film" conductive material had a superior reliability for "voltage transients". The "metalized film" also had a "self healing" characteristic allowing for recovery from minor transient voltage damage. At that time, the Sprague high voltage capacitors were also available with a "polyester" film dielectric material,
a "polypropylene" film dielectric material or a "polycarbonate" film dielectric material. The "polypropylene" film was superior to the "polyester" film and cost 150% more than the "polyester" film.. The "polycarbonate" film was superior to the "polypropylene" film and cost 650% more than the "polyester" film. After weighing all the pros and cons, I decided to go with the "metalized film" conductive material with the "polypropylene" film dielectric material. This combination was available off the shelf in voltage ratings from 400V to 2000V in standard capacitance values. However, I had to special order because my specification of 1.68uF was not a standard value. I could have used an off the shelf  1uF and a 0.68uF combination, however, that would have doubled the cost and the physical space required. The body of these capacitors was approximately 1" in diameter and 3" in length. These capacitors had the typical oval geometry, typical white body and typical yellow outer wrap. In quantities of 10,000 the capacitors were $3.90. These capacitors were used to replace malfunctioning solid state controllers that provided 120 Vac to "Exit Lamps" from a 277 Vac main in all the international airports throughout the free world! Prior to this project, I didn't know that the typical international airport has 2,000 "Exit Lamps".
The capacitors that you have are probably "foil" and "polyester" film which are fine for non critical applications. You should be able to purchase small quantities of "metalized" "polypropylene" film capacitors from a capacitor manufacturer's distributor and might even acquire "free" engineering samples!
It should be noted that a 1,000 V "foil" and "polyester" film capacitor will provide a similar level of reliability as a 630 V "metalized" film and "polypropylene" film capacitor. This is why I emphasized raising the voltage ratings of the capacitors. The most important thing is that the voltage rating is more than adequate and that the capacitor is not generating heat. The capacitors surface temperature should never be allowed to reach 75ºC. The "Exit Lamp" capacitors while enclosed in the lamp fixtures experienced a maximum  increase in surface temperature of 3ºC after 72 hours of continuous operation.
I eventually upgraded the "Exit Lamp" design with SIDACs (SYDACs) that were manufactured by RCA and Motorola at that time. The SIDAC is a very interesting thyristor that has many useful applications. A simple but inaccurate description of the SIDAC would be that it is a two terminal TRIAC (DIAC) that must be activated by the application of a voltage that is greater than the typical 130 Vac main. Placing a SIDAC in series with a 120V lamp on a 120 Vac main will accomplish nothing. However, placing a 120V lamp in series with a SIDAC on a 277 Vac main will illuminate the lamp!

One last bit of advice and hocus pocus . . .  When ever dealing with high voltages, I sincerely think that it is best to be in a Nikola Tesla state of mind!
Good luck with the killer volts!

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
G O T    G A R L I C ?
GILROY GARLIC FESTIVAL 2001 STARTS TODAY!

At 11:10 PM 7/27/01 +1000, you wrote:
{Quote hidden}

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2001\07\27@115727 by Douglas Butler

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> malfunctioning solid state controllers that provided 120 Vac to "Exit
> Lamps" from a 277 Vac main in all the international airports
> throughout the
> free world! Prior to this project, I didn't know that the typical
> international airport has 2,000 "Exit Lamps".

What an odd voltage!  I design stuff for seaports all over the world but
I have never run into 277Vac.  Is this some derivative of airplane
wiring?

Sherpa Doug

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2001\07\27@120157 by Eisermann, Phil [Ridg/CO]

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sounds like the phase voltage of a three-phase 480V Y-connected supply....


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2001\07\27@122928 by Spehro Pefhany

picon face
At 10:59 AM 7/27/01 -0500, you wrote:
>sounds like the phase voltage of a three-phase 480V Y-connected supply....

Yup. 480/sqrt(3). I think mostly used in the USofA.

Best regards,

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'[EE]: Transformerless PSU capacitors'
2001\07\27@130928 by Roman Black

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Ned Seith wrote:
{Quote hidden}

Hi Ned, wow thanks for the info. I have saved your
post for prosperity! :o)

I'm an old hardware guy too, and have played with lots
of caps, but generally i'm using the milspec polyester
ones for size vs capacity.

Let me say I really appreciate you sharing your experience
here, like others I was a bit sceptical about your first
post re not using the series resistor, as this is required
by some certification standards, and series resistors
always appeal to me as a TV repairer, i've seen what mains
spike do to hardware! :o)

I have a lot of polyprop caps, but generally don't use them
as the 630v polyester are smaller and cheaper, but like
I said before I don't sell HV cap products. I have seen
some polyprops used in personal defence (electric discharge)
products. And i've never seen one fail.

Please keep sharing any wisdom you have on this matter,
the whole Xc deal interests me a lot, I don't see why
Xc should be any less respected than Xl but that always
seems to be the case. In the future I see big improvements
in caps but not much changing in inductors, and after being
abused by my lecturer many years ago about my 45mA Xc supply,
then seeing them become the modern standard some 15 years
later, i'm now keeping an open mind as to where the future
is headed. Capacitive transformers anyone??
-Roman

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2001\07\27@140128 by Ned Seith

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Spehro Pefhany,

You are clearly well educated, however, I have an entirely different view
of the situation.
I do not consider resistors to be surge protectors. A 1,600 V inductive
spike will have a DVDT that can not be suppressed by any RC circuit. If I
was trying to implement surge protection I would employ an appropriate
surge protector such as a Raychem over current surge protector.
In my view, we are trying to get as much electrical current as possible
from a high voltage source. As we are trying to "get" current, we don't
want to "limit" the current whatsoever as that becomes counter productive,
is inefficient and generates heat. In my view we want the impedance as low
as possible. Voltage transients due to current in rushes are proportional
to the resistance (impedance) of the circuit so that a higher resistance
(impedance) will contribute to a higher transient voltage (I x R or I x Z).
The majority of power line transients are due to "inductive" (not
capacitive) voltage spikes caused by the collapsing electromagnetic fields
of inductors which have experienced a removal of power. The power line's
ability to kill equipment occurs when a motor or solenoid is deactivated at
the moment of peak line voltage resulting in an inductive spike that is
7.07 times greater than the line voltage. The second most problematic
source of voltage transients is from arching and ring oscillation in power
switches and relay contacts which generates bursts of pulses with on times
approaching RF frequencies. The switches and relay contacts also contribute
to inductive voltage spikes of the inductive apparatus on their circuits.
Turning off inductive equipment causes transients not turning inductive
equipment on. As for power factor, the capacitive current of 150 mA in this
application or a few amps in my applications is not of any significance to
the utility companies local distribution transformer with a 10,000 amp
capability. It should also be noted that if there was the introduction of a
massive capacitive load to the power line that the line voltage would
actually dip due to the current demand. The notion that capacitors are
frail and can not withstand power line behavior is unsubstantiated.
Capacitors have been used for decades as filters in equipment and directly
connected across the power line. Utility companies employ capacitors for
filtering and power factor compensation directly to the power lines.
Selection of the proper composition of capacitor with a conservative
voltage rating will assure reliability in conjunction with the power lines.
For maximum reliability the capacitor should be rated for the electrical
environment and not for just the working voltage. Excluding lightning
strikes, when capacitors fail it is because the electrical environment
exceeded the capacitor's rating. It should also be noted that a capacitor
with a 2kV rating will absolutely not be harmed by the maximum inductive
spike of 1,600 V produced on a 220 Vac power line.
Of course lightning strikes require spark gap and/or MOV  technology and
there are no absolute assurances with lightning.
I really honestly believe that Vasile should be commended for his circuit
and encouraged.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
G O T    G A R L I C ?
GILROY GARLIC FESTIVAL 2001 STARTS TODAY!



At 09:39 AM 7/27/01 -0400, you wrote:
{Quote hidden}

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2001\07\27@141836 by Ned Seith

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Phil,

The 277 Vac is taken from 3 phase transformers and used to power
fluorescent lights in extremely large facilities such as airports, high
rise buildings, sports arenas, etc. Most extremely large facilities have a
277 volt bus that powers the entire facilities lighting. The 277 volt
scheme presents a tremendous cost savings as individual lamp ballasts are
not required. Other benefits include centralized power factor control and
other power saving controls. LSI Lighting / Prescolite of San Leandro,
California, USA is the world leader in 277 V bus power control technology.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
G O T    G A R L I C ?
GILROY GARLIC FESTIVAL 2001 STARTS TODAY!
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
At 10:59 AM 7/27/01 -0500, you wrote:
>sounds like the phase voltage of a three-phase 480V Y-connected supply....
>
>
> > {Original Message removed}

2001\07\27@152718 by Eisermann, Phil [Ridg/CO]

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       Right. And each phase is 277V. Now take three phases, 120 degrees
(electrical degrees) out of phase, and connect them in a 'Y' with a common
neutral. If you then measure the voltage between any two terminals (other
than neutral), you'd get 480V. In other words, you're measuring the voltage
between any two phases. Or am I misunderstanding you here?

> {Original Message removed}

2001\07\28@013608 by jeethur

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Looks like the main power hog in your circuit is the relay.
Why not use a Solid state Relay or better yet build one
using MOC3041 Triac Opto Coupler and A good old Triac ?
An added benifit of this circuit is that MOC3041 gives you
Switchover at Zero Crossing. Of course, I'm assuming that
You want to switch AC mains. If not, forget this Idea.
I've had the same problem with a PIC16f84A. And I'm using MOC3041

Reagrds,

Jeethu Rao

> {Original Message removed}

2001\07\28@041837 by Graeme Zimmer

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> The concept and configuration of your series capacitance voltage divider
> circuit is fine.

It isn't fine. It relies absolutely on the Mains being clean AC with no
harmonics present.

If you are on a solid feed, it will probably work just fine.

If you are on the end of a poorly regulated line, any AC hash will
dramatically increase the current through the Capacitor.

These things are a big headache for the Solar Power people. Imagine what
will happen when someone tries to run it off a squarewave inverter.

Zap !!!

............................. Zim

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2001\07\28@142755 by Alexandre Domingos F. Souza

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       Ops, far away from home, now I'm back ;o)

>Presumably you are using a relay with a low voltage coil. Why not ease the
>low voltage current requirements by using a relay with a high voltage AC
>coil.
>If my presumption is correct then you will probably reduce your current
>consumption on the 5 volt rail to 45mA or less. Use a small Triac or
>thyristor to switch the relay.

       It would be great IF finding 110v coil relays could be found here in Brazil. We are in a country that your project has to be easyly changeable, since the component distribuitors bring to the market whathever they fit in their bills, and not always what the customer wants. Oh, so nice to live in a third world...


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2001\07\29@101720 by Chris Carr

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>        Ops, far away from home, now I'm back ;o)

>>Presumably you are using a relay with a low voltage coil. Why not ease the
>>low voltage current requirements by using a relay with a high voltage AC
>>coil.
>>If my presumption is correct then you will probably reduce your current
>>consumption on the 5 volt rail to 45mA or less. Use a small Triac or
>>thyristor to switch the relay.

>It would be great IF finding 110v coil relays could be found here in
>Brazil. We are in a country that your project has to be easyly
>changeable, since the component distributors bring to the market >whatever
they fit in their bills, and not always what the customer wants.

>Oh, so nice to live in a third world...

Everywhere has it's advantages and disadvantages.
.

As you have not knocked back my supposition that the relay is the major
consumption of power then I will assume that the supposition is correct.

The use of a Relay with a 110 volt coil is not an option due to
unavailability.

OK, presumably Relays with 5 volt, 12 volt or 24 volt coils are available.
So why not energise them directly from the rectified 110 supply .

Just apply pulses of 155 volts to the relay coil instead of a continuous
5,12 or 24 volt.

Regards

Chris Carr

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2001\07\29@224633 by Alexandre Domingos F. Souza

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       Learning, and learning, and learning...

>Just change to a proper rectifier bridge, this will
>double the current to 90mA. Then using a 30% larger
>value of the main Xc cap will give you 120mA.
>This web page has Traffic.PDF sent by Richard Ottosen
>which shows a larger current Xc supply with a
>full-wave bridge:
>http://centauri.ezy.net.au/~fastvid/tube4w.htm

       Interesting, one more bit of knowledge, thanks ;o)

>Remember the Xc supply ALWAYS runs full current,
>so if your 120mA relay is OFF, something else
>(large zener?) must be drawing the 120mA. Have a
>serious think about this. Xc supply is best for
>circuits that always draw the same current.

       This is something I didn't know

       I'm looking now for another approach: Using 2 relays of 24VDC in series (so, 48VDC) and using a wire wound power resistor and a diode. It will be activated thru an opto-triac. I think it will work. I'll test tomorrow ;o)

       Thanks anyway!


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2001\07\29@231830 by Alexandre Domingos F. Souza

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>> I've done one, some time ago, see
>> http://www.geocities.com/vsurducan/c520.htm

       Vasile, I tried it but got no pictures, anything wrong?


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2001\07\30@011601 by Vasile Surducan

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Ned, we are on the same wavelenght !

Cheers, Vasile

On Fri, 27 Jul 2001, Ned Seith wrote:

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2001\07\30@012454 by Vasile Surducan

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On Fri, 27 Jul 2001, Spehro Pefhany wrote:

>
> >I would also want the series capacitor (C9) rated for 800 V to 1000 V.
>
> Preferably with an AC rating > maximum line voltage.


Here we could talk a little... I don't know exactly if you have other
technology for large value capacitors in AC usage, but here the only one
I know is made by aluminium folia, shieleded by oil imersed, paper folia.
And trust me, this one is not good because it has a large leakage current,
this sort of capacitors are used only for filtering the mains and NOT for
voltage dividers ! If you have PMP capacitors in AC range, this is
different...
Best regards, Vasile

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2001\07\30@071145 by Alexandre Domingos F. Souza

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>rise buildings, sports arenas, etc. Most extremely large facilities have a
>277 volt bus that powers the entire facilities lighting. The 277 volt
>scheme presents a tremendous cost savings as individual lamp ballasts are
>not required. Other benefits include centralized power factor control and

       Fluorescent lamps? No ballasts? Could you give more info? ;o)


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