Repairing Old School Power Supply?

[Noitoen]

If that has a split secondary winding, then it's possible to have a grounded wiper making contact with both coils at the same time. That would change the number of turns being put into the circuit on both coils simultaneously. Essentially it becomes a typical battery charger where a center tapped coil is used so that only two rectifiers are needed. In this case the center tap is varied for both coils at the same time. That's my latest guess on how this thing works.

The voltmeter should read anytime the thing is on, and the ammeter should read only when a load is connected to the output.

As far as the rectifiers, if these are good then so be it. If they are bad, then swap in a pair of high current diodes and get on with it. I'm curious now- what has the latest troubleshooting revealed?

That is what I've drawn in post 48

[darryl]

If that has a split secondary winding, then it's possible to have a grounded wiper making contact with both coils at the same time. That would change the number of turns being put into the circuit on both coils simultaneously. Essentially it becomes a typical battery charger where a center tapped coil is used so that only two rectifiers are needed. In this case the center tap is varied for both coils at the same time. That's my latest guess on how this thing works.

The voltmeter should read anytime the thing is on, and the ammeter should read only when a load is connected to the output.

As far as the rectifiers, if these are good then so be it. If they are bad, then swap in a pair of high current diodes and get on with it. I'm curious now- what has the latest troubleshooting revealed?

[BCRider]

Gazz, you should be able to look down into the gap where that arm is located and see if there's any dimples or other wiper that slides along the bared windings of the secondaries. Or if there is some linkage or cam action that moves a magnetic coupling control of some sort.

As power supplies go this is the most basic of basic. And given that it's intended for plating I'm thinking that the knob will primarily adjust the current and the voltage will be whatever it is from the resistance of the plating tank and surface area of the item being plated.

As for other uses? As it is now it could be used for a totally dumb battery charger. Just don't leave it or it'll overcharge. Or it could be used to sort of run a DC motor as a test? But it likely wouldn't be all that great for that either. As for use as a power supply to run anything more than that I suspect it would need a lot more added to it than you want to deal with. That is unless the look of the case has you captivated. It does have that early "arts and crafts" look of old electronics which was and still is very cool looking for many of us. Perhaps the meters and dial could live on with new modern guts and regulators added inside? Depends on how well it cleans up I guess.

[Noitoen]

The company exists and have a modern version

[J Tiers]

Not the same one. OP has 10V / 20A max. Look at the meters.

[Bob Engelhardt]

Did a quick search online and that same power supply is quite common under different brands. Gesswein Electro Plater model D

That's an interesting power supply: 30A (!) & 20v. Probably not 600w, but maybe. Yeah ... probably not 30A, either - that's a lot. I'd like one for testing DC motors.

$175 +- $25 from various sources.

[Noitoen]

Did a quick search online and that same power supply is quite common under different brands. Gesswein Electro Plater model D

[macona]

All this discussion of selenium rectifiers has got me worried about my mig welder's health. I has a big (4") square selenium rectifier in it and it has been replaced once.

Miller makes a generic drop in replacement rectifier that you can fit in there somehow. It's in their general parts catalog.

[darryl]

Can't believe I just saw it now- that transformer IS the variac. I was wondering why it was mounted so close to the front panel- now it makes sense.

Here's a nugget from my past experience which I just thought of- I had a unit in one day which wouldn't power up. The fuse checked ok, power cord ok, plug ok, and power switch ok. No power to the transformer. In this case the fuse holder wasn't passing the juice. A little unusual, but it happens. Fast track the troubleshooting and see if the transformer energizes before you get too deep into the wiring.

[Noitoen]

There is no sign of overheat on the transformer so, with the exception of those rectifier bolts, everything could be disassembled and cleaned to restore good contact between the connections.

[Noitoen]

It could be a variable magnetic shunt transformer, where the coupling between primary and secondary is adjusted by a moving iron yoke, or shunt. Similar to the following:

https://nationalmaglab.org/education...magnetic-shunt




https://patents.google.com/patent/US3622868A/en

Those regulate the current and not the voltage. You will only see the voltage change under load

[J Tiers]

Those have been used in welders, and in automatic regulators for street lighting. I don't think this one is that fancy.... the layout of the magnetic circuit is just wrong-appearing for it.


A [ic more straight down on the front part of it would show for sure.

[chipmaker4130]

Thanks for that, Paul. It's a neat concept. I'd had something similar going through my head for the power supply but couldn't quite put it together. I'm NOT an EE!

[PStechPaul]

It could be a variable magnetic shunt transformer, where the coupling between primary and secondary is adjusted by a moving iron yoke, or shunt. Similar to the following:

https://nationalmaglab.org/education...magnetic-shunt




https://patents.google.com/patent/US3622868A/en

[J Tiers]

So that is interesting, just what does the knob on the front panel do? It looks like there is some sort of swinging arm so maybe contacts on the secondary, or is something happening in the magnetic circuit?

Just as I suggested, and Noitoen drew. It's a fonky variac, but it is one. Yes, tapped secondary..... a variac just has a LOT of taps.

Taps may go to ground, that would be mechanically simple to implement. but is functionally identical to having them more directly in series with the rectifiers. Primary presumably wound under each secondary.

Very simple setup, low voltage, one rectifier cell each side. Cells see double the peak voltage, so presumably that is under 12V by jut enough.