Considering building a brute force, high current, adjustable linear bench supply

[GamerAndds]

I have an aluminum chassis and I put an aluminum plate ontop of the transformer, when I tried to ground that plate to the chassis through 3 14 guage woes they started to smoke. I don't know if it applies to you because ur using smaller ones, but for me that was a real scare!!! I'm pretty sure it's the plate, since that happened I switched out the metal plate for a plexiglass one and everything was fine, perhaps it was the bolt causing the major amps. The 3 14 guage wires were grounding the plate to the chassis and that's why they were hot, it was the weak link I'm the chain, they were no where bear the transformer

[johansen]

I have an aluminum chassis and I put an aluminum plate ontop of the transformer, when I tried to ground that plate to the chassis through 3 14 guage woes they started to smoke. I don't know if it applies to you because ur using smaller ones, but for me that was a real scare!!! I'm pretty sure it's the plate, since that happened I switched out the metal plate for a plexiglass one and everything was fine, perhaps it was the bolt causing the major amps. The 3 14 guage wires were grounding the plate to the chassis and that's why they were hot, it was the weak link I'm the chain, they were no where bear the transformer

looking at your signature you have a rather large transformer, probably on the order of 1 volt per turn.
so when you short out the "aluminum plate" you are forming a shorted turn and you've got 1 volt dropped across whatever.
so of course it glows red.

OP: i have the pass transistors from two 0-36v 0-30 amp keptco power supplies if you want them. shipping from seattle area, they probably weigh 2 kilograms for a set, i can throw in the fans if you want, they will be sufficient for a 0-50 volt 0-25 amp supply.

[AmmoJammo]

Thanks for the offer, I've pretty much figured out what I'm going to do (I think).

[sprocket]

Hmm..

Have you considered paralleling LDO's? Or perhaps incorporte som power transistors to take some of the load of the LDO's. You could for an exsample use a 2N4399, I think it can handle 30amps or so.

You could potentially use LT1083/LT1084 or LT1085.. I have not reallly read the spreadsheets carefully. But they can handle some thing like 30 volts input, dish out about 7amps per LDO.

Best of all you can request free samples from liniar technology and have a few of them to play around with for free. I think it take about a week or so for you to get the samples. I have some in transist now I want to play around with for a similar project like yours.

Though my project is going to be more modest and less lethal. 15volt 30amps CC and CV ajusted by an arduino and a OLED display of some sorts.

Oh and you might seriously think about some sort of short circuit protection. I'm always super careful when it comes to high amp equibment. I have been zapped more times by high voltage circuits then I care to admit, but as unpleasant as that is, it's always been a circuit with barely any amps in it. 

[AmmoJammo]

Plan is four separate, "floating" adjustable supplies, one per transformer.

LM317 with five external MJE3055 transistors each.

Four separate switches too, one per transformer

By having four supplies, I can connect them all in series, or parallel, or parallel series, or tie the positive output to ground for negative rails.



Transformers "mounted" it all has to come apart again, as I'm not sure in what order I need to assemble it...

[calexanian]

Does this work instead of the original design?

Yes. That is the preferred method.

[AmmoJammo]

Plan is four separate, "floating" adjustable supplies, one per transformer.

LM317 with five external MJE3055 transistors each.

Plans changed again!

LM723 regulator! same external transistors, but this regulator can easily do adjustable current limiting...

[AmmoJammo]

Switched! and, of course, I snapped a drill bit, and smacked the drill into the front panel.... ah well! not overly worried about it.

[AmmoJammo]

Any potential issues with this layout?

Bottom row of binding posts will be grounded.

[AmmoJammo]

Well, that's the layout I went with!

Seeing as nothing has arrived yet (binding posts, voltmeters, transistors, resistors, shunt resistors, knobs, pots, etc?) I'm using ebay specs for the cutouts... and hoping they're right! 



The bottom row of binding posts line up with the lip on the aluminium plate, so they will be grounded straight to that... no stuffing around with terminals and links
(hence the drilling holes with the case half assembled, so they line up properly)

Oh, and I bought a crusty, cheap(ish) second hand drill press.

[AmmoJammo]

Two runs of 7.5amp cable from the back of the socket... one side of the socket says 10amp, the other says 15amp 







Really can't do anything else with it till all the other bits arrive!
I've got a heatsink being bent up at the moment, hopefully it works out.

All up, its going to weigh about 20kgs...

[AmmoJammo]

[AmmoJammo]

I've decided to go with mains powered fans, operated by thermal switches mounted to the heatsink.

Of course, this means I need to change the mains wiring again... planning ahead? no, not me!

Decided to use three 120mm fans, centre will come on at a low 40 degree Celsius, and the other two will be 60 degrees... No point in running things hotter than they need to be!