HHO power supply question

[keiththevp]

OK, I have built a new power supply that can output 0-150v DC 25 amps from a variac and bridge rectifier on one side and can output 0-15v DC 120 amps from 3 transformers on the other side. I want both power supplies to output to the same positive and negative leads to load. I have installed relays to turn on/off the power to each side of the power supply. But I do not want the power from either source back feeding into the other source, so ....

How would I wire in the diodes and in what direction in order to stop current from passing from one power supply to the other and instead just going to the load? The best I could find are 40 amp diodes (since I could not find or afford a 120 amp one) so I will have 3 positive and 3 negative leads coming from the 3 transformers that will need diodes. I have attached a rough drawing of what I am trying to do.

Thank you for any help electric gurus!!!

Keith

[Philldpapill]

Put a bridge rectifier on the output of EACH transformer, then tie the outputs of the rectifiers together. You really should have diode capacity of at least 3 times the rated current that you want to use. In other words, each diode on the output of a transformer should be rated for 120A minimum. If you get on the ST.com site, they actually offer "free samples" of some beefy diodes. I have some rated for 200A. They are normally a $45 part, but.... well, I love free samples.

[keiththevp]

I already have 2 50 amp bridge rectifiers on each of the 3 transformers to turn them into dc. What I was wondering is if I had to put diodes on as well or will the bridge rectifiers stop the current from one supply going to the other?

[keiththevp]

Forgot to add that the bridge rectifiers only have a positive out the neg comes from the transformers.

[keiththevp]

Should I try to hook the negative up to the BR and remove from the transformer? Also here is a more detailed drawing of the current wiring config

[H2OPWR]

Should I try to hook the negative up to the BR and remove from the transformer? Also here is a more detailed drawing of the current wiring config

Keith, From your drawing it looks like you have the transformer output going through the variac. Is that the case or am I just looking at it wrong? If that is the case this set up will not work.

Larry

[keiththevp]

No, the 110v ac goes into the variac. Then out of the variac you have two sets of leads, one set goes to a bridge rectifier then out to the load. The other set goes to the three transformer inputs. Then out of the transformers into the Brs hot leads only, and a positive comes out of the Bridge rectifiers while the neg comes directly from the transformer. This pos and neg join with the pos and neg out of the other power supply as sown in the diagram so that I can have one pos and neg output on the power supply. This enables me to have anywhere from 0 to 150v dc 25amps or 0-20v 120 amps dc. Does it make more sense now or did I just make it more confusing. I wish I knew how to make a wiring diagram.

[H2OPWR]

No, the 110v ac goes into the variac. Then out of the variac you have two sets of leads, one set goes to a bridge rectifier then out to the load. The other set goes to the three transformer inputs. Then out of the transformers into the Brs hot leads only, and a positive comes out of the Bridge rectifiers while the neg comes directly from the transformer. This pos and neg join with the pos and neg out of the other power supply as sown in the diagram so that I can have one pos and neg output on the power supply. This enables me to have anywhere from 0 to 150v dc 25amps or 0-20v 120 amps dc. Does it make more sense now or did I just make it more confusing. I wish I knew how to make a wiring diagram.

Keith, Yours is very similar to mine. Mine is just wired a little different. The normal setup is to have both AC leggs going to the bridge but with the way those transformers are wired up I had to use several large diodes to pull it off.

Larry

[keiththevp]

Larry the only difference between your setup and mine is that I split the output of the variac into two places one the transformers for LV DC and the second to a straight BR for HV DC applications, all in one power supply. I thought that would be a good idea and only added an extra BR to the build. However I think the way I have it setup is fine, since you can setup two battery chargers on the same load and have one off and one on. My setup is just like that. But I just wanted to make sure it was safe first by some of the people here that know way more then me rather then risk blowing one or all of my transformers.

The heart of my question is this, if I take the variac out into a BR then the positive of this BR into positive on the BR coming off the transformers. Then Neg from BR (on Variac) to neg LEAD ON TRANSFORMER (not on the BR from transformer) Will I get magic smoke or flames???

I know that if I had a BR with pos and neg coming out on both the variac side and transformer side then connected them together NOTHING would happen since the two BRs are going to stop the current from going backwards. But these transformers do not hook up like that, you can only run the positive from the BR the neg has to come from the bottom back side of the transformer, just like it is setup in the original battery charger.

[H2OPWR]

Larry the only difference between your setup and mine is that I split the output of the variac into two places one the transformers for LV DC and the second to a straight BR for HV DC applications, all in one power supply. I thought that would be a good idea and only added an extra BR to the build. However I think the way I have it setup is fine, since you can setup two battery chargers on the same load and have one off and one on. My setup is just like that. But I just wanted to make sure it was safe first by some of the people here that know way more then me rather then risk blowing one or all of my transformers.

The heart of my question is this, if I take the variac out into a BR then the positive of this BR into positive on the BR coming off the transformers. Then Neg from BR (on Variac) to neg LEAD ON TRANSFORMER (not on the BR from transformer) Will I get magic smoke or flames???

I know that if I had a BR with pos and neg coming out on both the variac side and transformer side then connected them together NOTHING would happen since the two BRs are going to stop the current from going backwards. But these transformers do not hook up like that, you can only run the positive from the BR the neg has to come from the bottom back side of the transformer, just like it is setup in the original battery charger.

As for the dual high/low voltage set up I am not the right person to answer that question. Others here are way more electronically minded than I am. As for the way you have the bridge rectifiers hooked up. You are getting the positive DC out of the rectifier and the negative directly from the other AC leg on the transformers. I do know that is the way the battery chargers were origionally wired. I beleive we used almost identical battery chargers to get the transformers from. It is far and away cheaper than just buying the transformers. The reason the battery chargers are wired that way is to lower the cost. They do not care about the ripple in the DC because the battery being charged smoothes it out better than capacitors could. If you want to check and see how smooth the DC out is then hook up a multimeter to the DC after the capacitors you have in the wiring. Then check for voltage on the AC setting and compare it to the DC setting. You should have very low readings on the AC setting. It shoule be in the milivolt range. If you are reading volts then you may have too much ripple.

Now the million dollar question that I do not have an answer for. Does some ripple in the DC even make any difference? If it does not then who cares and you save some money by not buying those expensive high amp diodes that you will have to use to wire it the way I did. I would have done the same as you if I did not already have them gathering dust in my supply box.

I think you will like your power supply. It will be adjustable all the way from just millivolys up to about 21 volts and very stable. You will be able to provide over 100 amps to your device and at whatever voltage you desire at fractions of the cost of a decent high amp variable voltage DC power supply. I would love to see a video of your setup in action.

Larry