I have toroidal transformer with 4 x 110V (0,9A) sec. For one my new project I need 500V DC. Can I use this transformer? Any schematic?
Given sufficiently good insulation 4 x 110V AC RMS will give you offload DC voltage of about 400V (choke input) or 600V (cap input). Adding some load will drop the voltage a bit. How accurate does the 500V have to be?
If you need a schematic then maybe this sort of mains PSU is not for you. Safety requires understanding, not just following rules.
If you need a schematic then maybe this sort of mains PSU is not for you. Safety requires understanding, not just following rules.
I need 380mA. I understand safety. I build several tube amps (10+), some of them with 450V B+, but I had transformers with one secondary.
I just can not find how to connect wires or diodes with 4 secondaries to get one DC.
If you are willing 3 full wave bridges cap loaded and floating stacked on top of each other ( neg of first bridge as ground with a cap positive of first bridge to second neg and so on ) then the 4th one stacked on top choke loaded about 560 volts . Or two and two 150 plus 150 then 99 and 99 giving about 500. This also gives you taps at about 150, 300, 400 approx. and at about 980ma . A schematic would be of great help. Tektronix used that method in it's power supply circuits book. The insulation value is no not as important because each section is seeing only 110 ac to the bridge .
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No, the top section still sees high voltage to the frame. It may be OK, but we can't assume that.
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That only between the output of the bridge and ground(or) earth the winding it self has only 110 ac on it. If it is an American ul listed transformer it need to have at least 600ac rating for ul labs. That deduction was based on this tranny being legal for sale in the USA . Most likely a 1k volt rating to be safe is often seen . I do not know the EU standard on insulation. Given that Slovenia used the 220 to 240 main voltage and the cee7/4 plug the insulation should be rated to at least 600v if not 1k . This should if it is a legal tranny be a total non issue. Regards.
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The top winding has 110V AC across it. When the diodes conduct the bottom will be connected to about 400V DC so the other end will be at about 550V. As you say, the insulation may be OK for this but it does considerably exceed 110V.
A four secondary toroid will almost certainly have a quad-fillar wound secondary. i.e. all four wires will lie next to each other.
Any one winding can touch any other of the four particularly at the overlap section in the middle of the toroid.
The ONLY insulation between these windings is TWO layers of enamel. Don't expect infinite insulation resistance for the enamel, particularly if one coating has been scratched or kinked (cracked around the bend).
Any one winding can touch any other of the four particularly at the overlap section in the middle of the toroid.
The ONLY insulation between these windings is TWO layers of enamel. Don't expect infinite insulation resistance for the enamel, particularly if one coating has been scratched or kinked (cracked around the bend).
Given that it does not bode well for a stack job in my view. Given less than a amp of current (984ma) How much of a problem might that be ? If it is a tested EU legal tranny then the section where tested for isolation from each where they not ? The toroids I have had each section (2) wound one at a time . I have no real reason to disbelieve that a quad-fillar winding would not be used for 4 sections that would be cheaper to make. What are you thoughts on easy testing for that problem ? Regards
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Unfortunately the only *real* test for insulation is destructive, as to applying 1.5 to 3KV secondary to secondary and check it holds .... or not 🙁
That's what certification labs do.
Now you can use a more hobbyist oriented system
1) visually check whether 4 secondaries are quadrophilar wound .
or
2) short each winding ends together and measure capacitance to another winding, same conditions.
Then as a reference measure from each of them to primary (which by definition, *is* insulated from them).
Compare capacitances.
You are not measuring "insulation" but "overlapping", but that's a hint.
That's what certification labs do.
Now you can use a more hobbyist oriented system
1) visually check whether 4 secondaries are quadrophilar wound .
or
2) short each winding ends together and measure capacitance to another winding, same conditions.
Then as a reference measure from each of them to primary (which by definition, *is* insulated from them).
Compare capacitances.
You are not measuring "insulation" but "overlapping", but that's a hint.
I'm with Triodethom here.....
this type of psu has been done before, no big deal imho.....
Champ 1000 Watt Tube Amp
Champ CBA-1000 Amplifier - Schematic Diagram
this type of psu has been done before, no big deal imho.....
Champ 1000 Watt Tube Amp
Champ CBA-1000 Amplifier - Schematic Diagram
If your fear isolationprobs there is a possible solution by using a fullwave voltagemultiplier. If the secundaries are all wound together connect them in parallel and feed it to a bridge. Stack a second bridge (- on +)on it and then a third bridge on top.
Feed the ac inputs of the second (200Vcaps) and third bridge with electrolytic caps (400Vcaps) from the paralelled secundaries. You can also feed the third bridge from the ac-connections of the second bridge (has the advantage that all caps use the sam voltage, disadvantage that you have to double the capacitance of the caps feeding the second bridge, but in the end it is the same VC-product that is needed). The caps really have to have sufficient capacitance to keep voltagesag to a reasonable value. I know it sounds award but I have done that sometimes in cases where I needed multiple/higher voltages or would have had to stack the caps anyhow.
Offcourse a proper transformer may be a better choice, lots of unnecessary currentshifting
in your case, but if for example high power low voltage and also low power high voltage is needed it works like a charm.
Feed the ac inputs of the second (200Vcaps) and third bridge with electrolytic caps (400Vcaps) from the paralelled secundaries. You can also feed the third bridge from the ac-connections of the second bridge (has the advantage that all caps use the sam voltage, disadvantage that you have to double the capacitance of the caps feeding the second bridge, but in the end it is the same VC-product that is needed). The caps really have to have sufficient capacitance to keep voltagesag to a reasonable value. I know it sounds award but I have done that sometimes in cases where I needed multiple/higher voltages or would have had to stack the caps anyhow.
Offcourse a proper transformer may be a better choice, lots of unnecessary currentshifting
in your case, but if for example high power low voltage and also low power high voltage is needed it works like a charm.
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may be good to mention, in your case, it may be best you stack two 100V/4700uF to
get the odd 200V required, put some resistance (dissip. at least 5 times leakage current) to each cap in paralellel to equalize voltages. 100V is generally the voltage electrolytcaps can be built with the least tradeoffs.
get the odd 200V required, put some resistance (dissip. at least 5 times leakage current) to each cap in paralellel to equalize voltages. 100V is generally the voltage electrolytcaps can be built with the least tradeoffs.
or you can simply series connect all of the 100 secondaries, then a FWB and be done with it....i would favor a hybrid tube/silicon combo...plenty plenty for your 500v dc goal...
you don't know this for sure....better to check with the torroid vendor to be sure....
that's why I posted "almost certainly".
I don't know, nor do you.
But in my opinion it is better to be aware and take steps to reduce the risk.
Given a current need of 380ma approx. A power supply with lots of ripple reduction to it should be easy . As well as good lower noise bridges made from 4 diodes with out costing too too much . Given less than an amp and low voltage differences from each section taking standard hv safety protocal this will work.
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