Voltage doubler using PSUII?

[Brit01]

Attempting to use PSUII to create a voltage doubler.

I have to 28V (3 amps each) trannies I will put in series and use a voltage doubler.

I calculate 28+28= 56 volts
56 *1.4 = 78.4

78.4 * 2 = 156 volts.

I cannot seem to get a simple circuit to work from 78.4 volts.
Maybe I'm expecting too much from the draw of 800 mA of current needed.
I tried using low resistors and high capacitance but the psuII drops negatively and gives me around 20 volts! What am I doing wrong?

Better to work it out manually?

Can I get 100-150 volts to supply 800 mA from these 2 trannies?

Maybe better to buy a new 110V tranny. But...$$$

 

[piano3]

Hi, I'm not sure that putting transformers in series,rather than separate windings on the same one is recommended.

 

[piano3]

If you want to get high voltage from 2 low volt secondary transformers then run the low voltage secondary of the 2nd one as a primary from the low voltage secondary of the first one. I often use transformers backwards without any problems so that I can get nearly 400V from an off the shelf control panel transformer. You can expect that the V out will not be quite as high as the V in. If you want to reduce it further then use a low value reservoir cap(a microfarad or so) so as not to waste power. Or, you could then use a doubler if you wanted.

 

[Brit01]

If you want to get high voltage from 2 low volt secondary transformers then run the low voltage secondary of the 2nd one as a primary from the low voltage secondary of the first one.

220/28- 28/220 = 220V.
How much loss would I expect?

Think I'll be looking for a used 220/110 step down tranny. These are common and supply high amps.

Great to run 6080 and 6AS7 @ 100mA with 100volts or so at the plate.
This would dissipate 1 watt of power no through a 100 ohm? So a 2 watt 100 ohm cathode resistor should be fine I think.

Looking to start my first OTL. Will start with 1 channel and a couple of tubes first.

Maybe a modified futterman with floating power supplies as used in the M-60. Not sure how I will implement it yet but ....

 

[piano3]

The loss is a bit difficult to predict and I presume mainly comes about because of a resistive drop on a winding which is not usually a source.Ask one of the big guys;I find DF96 very helpful. If the transformer is high VA I would expect the problem to be less. Where exactly are you? You seem to have a great problems sourcing transformers!

 

[Merlinb]

I just tried it in PSUII without problems (see attached).

Using 470uF capacitors, at 800mA load current the DC voltage is 131V with 8Vp-p ripple. The ripple current in the transformer is 3Arms, which nicely matches your real transformers.

 

[Brit01]

Yep I'm down in Uruguay.
I even get strange looks in the electronics shops when I ask for 400V caps!!
Have to source most of my parts from ebay. 80% get through customs in small packets.

There are some locals that make power transformers but at ridiculous prices and I and dubious about their amperage ratings.

There are some good power rated step down trannies made for playstations etc.

I see in the atmosphere M-60 power supply they use a 50+50 tranny with RCCCCC set up for the floating supplies. 1 x 1ohm resistor and a series of high value capacitors in parallel following but unfortunately PSUII does not allow me to do this. 'Illegal operation" it says.

 

[piano3]

Uruguay! Goodness,that really is exotic. Must be fun though!

 

[Brit01]

Goodness,that really is exotic

Lol. Not quite. Don't imagine Brazil!
It's way down south.

Some palm trees around but with British like winters!!

Must be fun though!

And boring. Nothing to do here. (but build valve amps!)

 

[leadbelly]

#1 I have to emphatically disagree with piano3: it is far preferable to use 2 identical transformers with secondaries in series than to do a back-to-back with those same identical transformers. Back-to-back is best done with dissimilar transformers, so that the larger one can handle the extra magnetizing current.

#2 Using a 3A rated transformer with a doubler and expecting only 800mA is quite reasonable. As for why it isn't working in PSUDII; have you really gone over all the settings you have in PSUDII? Are you focusing on the start up transient too much? Maybe we should be focusing on that?

 

[Brit01]

have you really gone over all the settings you have in PSUDII? Are you focusing on the start up transient too much? Maybe we should be focusing on that?

thxs leadbelly.

Having trouble choosing the right values here. Never designed a voltage doubler before.

Could you assist?

Lets say I need max 1 amp.
2 x 28v trannies @ 3 amps each.

Looking for around 100+volts output.

No chokes, just resistors and caps.

 

[piano3]

#1 I have to emphatically disagree with piano3: it is far preferable to use 2 identical transformers with secondaries in series than to do a back-to-back with those same identical transformers. Back-to-back is best done with dissimilar transformers, so that the larger one can handle the extra magnetizing current.

#2 Using a 3A rated transformer with a doubler and expecting only 800mA is quite reasonable. As for why it isn't working in PSUDII; have you really gone over all the settings you have in PSUDII? Are you focusing on the start up transient too much? Maybe we should be focusing on that?

leadbelly,I am keen to learn; I have never seen transformers used in series in schematics and I always assumed that the reason for this was that there might be small phase differences between them which might mess things up. Is this not the case?
I have not actually implemented back to back myself-just set it up and noted that the output was a bit lower. What is the reason for extra magnetizing current?
I have used them backwards many times, however, and given that Brit1 has difficulty obtaining what he wants then this may help him out in future projects.
Unfortunately my poor computer skills have stopped me from successfully using PSUD11. I just calculate from first principles and then tweak the supply under test!

 

[SY]

Either the transformers will be in phase (2x voltage) or out of phase (0 volts and possibility of smoke). Nothing in between. It's safe to test them without a load to verify the proper connection.

 

[leadbelly]

thxs leadbelly.

Having trouble choosing the right values here. Never designed a voltage doubler before.

Could you assist?

Lets say I need max 1 amp.
2 x 28v trannies @ 3 amps each.

Looking for around 100+volts output.

No chokes, just resistors and caps.

Sure, I can have a look at it tonight maybe (Wed is wing night here). The thing with a voltage doubler is that your AC ripple is also doubled, but you can use SS diodes and big caps to smooth that. Also, you just barely meet 160VDC rating, which helps a lot with the cost of big caps (also, if you are a recycler you can pull a lot of 200VDC caps out of PC switching supplies). You can try something like a CRC filter with 2 1000uF/160VDC caps and a resistor in between.

Personally, at 160 VDC or less I would use a LM317 regulator (without protection) to smooth things out, but I know that is generally frowned upon by this forum and the collective recommendation would be to consider a Maida regulator.

 

[piano3]

Either the transformers will be in phase (2x voltage) or out of phase (0 volts and possibility of smoke). Nothing in between. It's safe to test them without a load to verify the proper connection.

Thanks Sy; so small discrepancies in wire resistance or eddy currents will not effect things in any significant way? This is good news to me! Is it then possible to use two in a centre tapped manner?

 

[Brit01]

Many thxs.
In fact I have some big 6800/10000 caps at ~200v and others from a SS amp recap I did and an old pc psu.

Also I have a few LM317's.

No rush. Let me know when you can assist.

Cheers

 

[Brit01]

Either the transformers will be in phase (2x voltage) or out of phase (0 volts and possibility of smoke). Nothing in between. It's safe to test them without a load to verify the proper connection.

I tested 2 in series the other day with no load and got a good 56 volts from the 2 28v trans. Maybe I was lucky.
50/50 chance.

 

[SY]

so small discrepancies in wire resistance or eddy currents will not effect things in any significant way?

Nope, the transformers don't even have to be the same. I've used this trick a few times in amps where I wanted to decrease or increase the B+ slightly by wiring one of the heater windings in series with the primary- in one direction, it's a buck, in the other direction, it's a boost.

 

[piano3]

Nope, the transformers don't even have to be the same. I've used this trick a few times in amps where I wanted to decrease or increase the B+ slightly by wiring one of the heater windings in series with the primary- in one direction, it's a buck, in the other direction, it's a boost.

I hope many DIYers will read this as I am sure that the difficulty of getting suitable mains transformers bugs everyone from time to time. I had often mused on this possibility but because I never actually saw anyone doing it I had naturally assumed that there was a problem. From what you are saying it should be possible to create any B+ that you want from freely available inexpensive transformers. I am sure that not many DIYers are so encumbered with cash that they want to order a special transformer every time they want to try something!

 

[leadbelly]

I hope many DIYers will read this as I am sure that the difficulty of getting suitable mains transformers bugs everyone from time to time. I had often mused on this possibility but because I never actually saw anyone doing it I had naturally assumed that there was a problem. From what you are saying it should be possible to create any B+ that you want from freely available inexpensive transformers. I am sure that not many DIYers are so encumbered with cash that they want to order a special transformer every time they want to try something!

While I understand that this post is meant in a very positive way, it actually irks me. What underlies it is the tendency of newcomers to refuse to search on a topic of discussion. These tricks have been discussed ad nauseam on this forum over the years and even the most half hearted search would have uncovered countless examples.