Transformerless Power supply

tvtech · Oct 7, 2011

carbonzit said:
Amen to that last statement. (My emphasis added.)

So true. Keep up the good posts carbon

Cheers,
TV Tech

VaughnX5 · Oct 7, 2011

OK, never mind, I got my answer. Thanks for your input guys.

I did it without zener got 111-130vdc 43ma, with zener 18vdc 17ma.

tvtech · Oct 7, 2011

VaughnX5 said:
OK, never mind, I got my answer. Thanks for your input guys.

I did it without zener got 111-130vdc 43ma, with zener 18vdc 17ma.

Good Luck. Hope it lasts

carbonzit · Oct 7, 2011

VaughnX5 said:
OK, never mind, I got my answer. Thanks for your input guys.

I did it without zener got 111-130vdc 43ma, with zener 18vdc 17ma.

Mind showing us a schematic of exactly what you did? Some of us are curious.

alec_t · Oct 8, 2011

I just wanted to know if this HV 2100VAC .90uf can handle being C1 without issues

Is the cap X2 rated? If so, it should be ok.
I assume the X2 rating takes factors other than voltage into account (can anyone confirm that??), e.g. flammability of the dielectric and cap coating, self-healing properties of the dielectric. If your cap is not X2 rated it may, therefore, be unsafe to use even if its voltage rating is adequate.

tvtech · Oct 8, 2011

alec_t said:
Is the cap X2 rated? If so, it should be ok.
I assume the X2 rating takes factors other than voltage into account (can anyone confirm that??), e.g. flammability of the dielectric and cap coating, self-healing properties of the dielectric. If your cap is not X2 rated it may, therefore, be unsafe to use even if its voltage rating is adequate.

Hi there alec

X2 mains rated caps are designed to be permanently connected to the mains. Stringent procedures are followed with their manufacture and subsequent testing.
Here is what I use from Jimson. The data sheet does not list their 2.2MF 275VAC cap yet...but hopefully the spec sheet will show you what hell these Caps are put through to ensure they are safe.....

Check the endurance spec

Cheers
TV TECH

dr.power · Oct 8, 2011

Hello Guys,

Sorry but I got a question while I was reading this thread.
Is the below circuit isolated from the mains? Can we use it as a supplier in low current application while it has 2 incoming caps?

Thanks

ericgibbs · Oct 8, 2011

dr.power said:
Hello Guys,

Sorry but I got a question while I was reading this thread.
Is the below circuit isolated from the mains? Can we use it as a supplier in low current application while it has 2 incoming caps?

Thanks

hi,
No its not isolated

dr.power · Oct 8, 2011

ericgibbs said:
hi,
No its not isolated

Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!

tvtech · Oct 8, 2011

dr.power said:
Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!

To give you an idea...

A transformer isolates. Keeps you safe from Electrocution.

An X2 Cap cannot do that. All it does is limit the currrent in said circuit. Does NOT isolate.

It is up to good design to make all work well. Application for application. They vary greatly.

For example: Philips are well known for their electric shavers. I have owned a couple of them...They isolate the Mains with a miniscule little SMPS transformer.....

What is the point???

Wet is wet. If you have 220 Volts coming in and a small casing and all is wet....you have a problem.
Choppper Transfomers dont help then. Isolation needs space to work. Seriously.

That's my take

Thank you
TV TECH

KMoffett · Oct 8, 2011

dr.power said:
Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!

If you touch the output side the cap connected to the "hot" side of the power line, and then touch neutral, ground, or the output side of the cap connected to neutral you will pass a lot of current through you body, limited only by the impedance of the cap and the impedance of your body. If you touch either the + side or the - side of the rectifier circuit (or anything attached to it), then touch "neutral" or ground you will pass current through your body. With an isolating transformer you can touch either side of the secondary winding and then "hot", neutral, or ground on the primary site and not get shocked.

Give it up...it's not safe.

With the the current and voltages you talking about, just get a switch-mode wall wart charger. They are small, efficient, safe, and usually in the regulated voltage range from 3.5 to 12VDC and currents from 0.5-2A. I find them all the time in thrift stores for as low as 39 cents. Or, check with your friends. Seems like everyone has old cell phone chargers in their junk drawers.

Ken

carbonzit · Oct 8, 2011

dr.power said:
Thanks, But whats the reason?!
We all know that both plates of a capacitor are separated to each others and there is a gap (air or anything else) between them. So I am not able to see any reason why the said circuit is not isolated from the mains!

Keep in mind that when we speak of isolation when referring to a power supply, we're not speaking so much in an electronic sense as we are in a safety sense.

You could say, with some justification, that both capacitors and transformers isolate the downwind part of the power supply from line voltage; in one case, you have a dielectric, in the other case, insulation between any part of the output side and the line.

However, in a safety sense, a transformer is a good isolator, while a capacitor isn't.

dr.power · Oct 8, 2011

Thanks all guys, for your inputs,
But actually I should say that it does not make any sense tome, Is there any math or something so to prove your sayings?
To make it very simple, suppose that I take one pin of a capacitor by my finger and put its rest pin to the Phase of the mains, Are you thinking that I am in hazards? If so what's the real or mathematic reason while the cap's plates inside the capacitor are insulated to each others??. I myself think that by doing so,my body acts as a resistor for the phase-cap=ground. But I am suspect if there would be any HIGH volatge across my body...

carbonzit · Oct 8, 2011

Well, come on: you're a smart person, and you have some electronic knowledge, so you tell us: calculate the voltage across your body if you touch the other size of a capacitor connected to your power line (230/240 volts?). ASS-U-ME that the other side of your body is connected to the opposite side of the line (i.e., grounded).

KMoffett · Oct 8, 2011

carbonzit;1009279...capacitors and transformers isolate the downwind part of the power supply from line voltage; in one case said:
No, capacitors isolate DC with the dielectric...but they "pass" AC. That's why they are not considered to provide "isolation" in a line powered AC circuit. A capacitive circuit like the one shown merely puts the load in series with the capacitive impedance, across the line. In a transformer isolated circuit the only potential difference at the secondary is between the two ends of the secondary. There is no potential difference between the secondary and the line-feed primary.

However, in the real world, with some poorly designed transformers, there can be a small amount of inter-winding capacitive coupling between the wire in the primary and the wire in the secondary that can cause a measurable AC "leakage current". https://en.wikipedia.org/wiki/Isolation_transformer

Ken

dr.power · Oct 8, 2011

KMoffett said:
No, capacitors isolate DC with the dielectric...but they "pass" AC. That's why they are not considered to provide "isolation" in a line powered AC circuit. A capacitive circuit like the one shown merely puts the load in series with the capacitive impedance, across the line. In a transformer isolated circuit the only potential difference at the secondary is between the two ends of the secondary. There is no potential difference between the secondary and the line-feed primary.

However, in the real world, with some poorly designed transformers, there can be a small amount of inter-winding capacitive coupling between the wire in the primary and the wire in the secondary that can cause a measurable AC "leakage current". https://en.wikipedia.org/wiki/Isolation_transformer

Ken

Good Point Ken.
So You are talking about COMPLETE isolation which is commonly achieved by the transformers. You do not accept a low volatge at the output which I GUESS can be achieved by 2 caps in the both sides of the mains as I show in my pic. Certainly my pic is not isolated for WHOLE voltages, But I think there is no hazard by such a connection, Am I right?

Ok to be honest, I did the math for an input capacitor of say 1uF, a body resistance of say 10KHz, and with a mains of say 220V, 50Hz.
The voltage across the said body resistance as I calculated was 166V, which is yet dangerous.

carbonzit · Oct 8, 2011

dr.power said:
Ok to be honest, I did the math for an input capacitor of say 1uF, a body resistance of say 10KHz, and with a mains of say 220V, 50Hz.
The voltage across the said body resistance as I calculated was 166V, which is yet dangerous.

There's no better person to convince you of something than yourself.

dr.power · Oct 8, 2011

carbonzit said:
There's no better person to convince you of something than yourself.

MrAl · Oct 9, 2011

Hi OP,

The circuit in question is quite common and used in lots of stuff like lamp dimmers. The key is to make sure there is no way that the user can ever come into contact with any part of the circuit. This means it is definitely possible, plausible, doable, and has been done, used, and reused countless times in circuits.

If on the other hand you have the idea that the circuit is "isolated", then you could find yourself in series trouble. It's indeed isolated, but only for DC not AC, and certainly not for transients.
For example, call one side of the line 'live' and the other side 'ground', connect a small capacitor (rated for AC voltage usage) that hasnt been used in a week and connect it to the power line 'live' side. Connect a 100 ohm resistor to the cap. Using a switch, switch the open end of the cap to ground. As the switch is closed, there could be more than 1 amp peak in the cap and resistor for the time it takes to charge up to some DC level. Some time after that the circuit will function like an AC circuit, but still wont be isolated.
The voltage from the zener to ground is only say 12v, so touching that and ground may not give you a shock. But if the AC input connections are reversed (as they often do become) then the live side is 'ground' and touching the top of the zener and earth ground (wet grass, damp floor, cold pipe, etc.) and you get more than a 100v shock.

So yes, this circuit is doable and usable and has been used for a long time and is still being recommended by lots of big companies, but only for people who know how to deal with the isolation problem and know for sure that there definitely is no isolation that could be taken as pure isolation like that you get from using a transformer with an isolated secondary.

That said, you can use the circuit once you understand how and why it is NOT truely isolated, but until then you really should not do it. Best bet is to purchase a wall wart. If you insist on using the cap, it may give you the proper current level or it may not depending on the load and cap value, but you should be aware that there is definitely a concern for safety with this kind of circuit.

From your opening statement you seem to be aware of the *possible* problem, but you should really be taking this as a *definitive* problem that needs very strict attention to detail.

tvtech · Oct 10, 2011

MrAl said:
Hi OP,

The circuit in question is quite common and used in lots of stuff like lamp dimmers. The key is to make sure there is no way that the user can ever come into contact with any part of the circuit. This means it is definitely possible, plausible, doable, and has been done, used, and reused countless times in circuits.

If on the other hand you have the idea that the circuit is "isolated", then you could find yourself in series trouble. It's indeed isolated, but only for DC not AC, and certainly not for transients.
For example, call one side of the line 'live' and the other side 'ground', connect a small capacitor (rated for AC voltage usage) that hasnt been used in a week and connect it to the power line 'live' side. Connect a 100 ohm resistor to the cap. Using a switch, switch the open end of the cap to ground. As the switch is closed, there could be more than 1 amp peak in the cap and resistor for the time it takes to charge up to some DC level. Some time after that the circuit will function like an AC circuit, but still wont be isolated.
The voltage from the zener to ground is only say 12v, so touching that and ground may not give you a shock. But if the AC input connections are reversed (as they often do become) then the live side is 'ground' and touching the top of the zener and earth ground (wet grass, damp floor, cold pipe, etc.) and you get more than a 100v shock.

So yes, this circuit is doable and usable and has been used for a long time and is still being recommended by lots of big companies, but only for people who know how to deal with the isolation problem and know for sure that there definitely is no isolation that could be taken as pure isolation like that you get from using a transformer with an isolated secondary.

That said, you can use the circuit once you understand how and why it is NOT truely isolated, but until then you really should not do it. Best bet is to purchase a wall wart. If you insist on using the cap, it may give you the proper current level or it may not depending on the load and cap value, but you should be aware that there is definitely a concern for safety with this kind of circuit.

From your opening statement you seem to be aware of the *possible* problem, but you should really be taking this as a *definitive* problem that needs very strict attention to detail.

Hi Mr Al

I am wondering now: What if a Manufacturer puts an X2 cap in series with BOTH the N and L. Two Mains rated X2 caps. One on Live. One on Neutral. Surely this arrangement would prevent swapped Neutral and Live being a problem ??

All should be reasonably safe.....I think??

Cheers

Transformerless Power supply

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