Check out my new PSU!

Got it from my chem teacher... kinda
he said it didn't work and that he wouldn't notice if it went missing, good enough for me

I have a hunch that it's the capacitor, those old cardboard ones didn't last.
2000uF, 25V, and the 'lytics I'm replacing it with are like 1 twentieth the size.

Looks like rectifier is an old selenium one, check. Is it wired as a half wave rectifier? Is the transformer for line isolation, 1:1 ? Nice find.

Wow, is that a tiny variac for the variable output?

ooo nice. You going to upgrade it at all?

magnet18 said:

Got it from my chem teacher... kinda
he said it didn't work and that he wouldn't notice if it went missing, good enough for me

I have a hunch that it's the capacitor, those old cardboard ones didn't last.
2000uF, 25V, and the 'lytics I'm replacing it with are like 1 twentieth the size.

Click to expand...

Magnet18,

The finned component appears to be a selenium rectifier. Please be careful with it since it can give off toxic fumes if it overheats and fails.

hgmjr

As I recall, when the selenium rectifier goes, it makes RED smoke!

Yes, I was informed that I should replace it with diodes as necessary, I'm not sure how it's wired, but it has four wires going into it and a 250 ohm power resistor.

and yep, that's a tiny variac, 0-120 volts, 2.5A (wish it was more current, can these be paralleled?) It also controls the DC.

I'm going to upgrade the cap and the finned thingy, other than that I'll try to keep it original unless I can get more out of it, I like the classic look

and I honestly can't tell at a glance for sure if that's an isolation transformer, but I think it is.

[EDIT]
I think I might drill out all the rivets and replace them with bolts... make things easier.

So the selenium is definitely wired fullbridge, any special rules for replacing it or will any high current, low voltage diode do?

What is the rated current?

0-2 Amps
0-12 V

The front panell says 12v @ 2Amp max, By the look of the size of the transformer i wouldnt be exceeding that. Silicon rectifiers will certainly be more efficient.

Wait, I thought they were old, inefficient, and prone to failure?

[EDIT]
nevermind, you said silicon, for a second I thought you said selenium

Strip it and get ready to rebuild a more effective one.

Looks like the 12V is isolated and the 120V isn´t, but be sure to check anyway.

It looks like the 120V output is variable. Neat.

It would seem that the variac controls the 0-120V, and the transformer is a 1:10 step down for the 12V output.

That explains the "use only one variable output at one time"; otherwise, you could overload the variac.

R!f@@ said:

Strip it and get ready to rebuild a more effective one.

Click to expand...

I have three now!
one works fine, so I'll leave it as is

the second doesn't work at all, so I'll update it quite a bit, and the third (the one I posted on here) I'll see if it works with the replaced caps, if not I'll replace the silicon.

unless I can find some chokes so I can parallel them...

kubeek said:

Looks like the 12V is isolated and the 120V isn´t, but be sure to check anyway.

Click to expand...

Right you are.

tom66 said:

It looks like the 120V output is variable. Neat.

It would seem that the variac controls the 0-120V, and the transformer is a 1:10 step down for the 12V output.

That explains the "use only one variable output at one time"; otherwise, you could overload the variac.

Click to expand...

Spot on, the top 120V outlet is a direct mains outlet, 10 A breaker
the bottom is variable, 1A

the transformer steps it down to the selenium, which leads out to the 12VAC and 12VDC

Ima make a schematic here in a bit.

magnet18 said:

Spot on, the top 120V outlet is a direct mains outlet, 10 A breaker
the bottom is variable, 1A

the transformer steps it down to the selenium, which leads out to the 12VAC and 12VDC

Ima make a schematic here in a bit.

Click to expand...

Very cool. I'm jealous.

I wonder what devices would do on 60 VAC instead of 120 VAC. I heard some small TVs work down to 30 VAC!

Nah, but it needs an over-range mode, 0-240VAC! Actually, around me that would probably be dangerous.

Well, I found out that the low voltage ac will put out 5 amps before it kicks the breaker, bit more useful than 2 amps...

magnet18 said:

Well, I found out that the low voltage ac will put out 5 amps before it kicks the breaker, bit more useful than 2 amps...

Click to expand...

Maybe true, but the variac is rated to 2.5A. Don't exceed that for too long, or you could burn out one of the windings in it, and that would make for a difficult, if not practically impossible repair.

That was with one of the working ones in chemistry
Using a ammeter to measure the current and measuring the time it takes to create 50ml of gas, from that were supposed to determine the faraday and the charge of an electron... finally, labs I understand.

It's fun because everyone just looks at me when they look at the lab handout

[EDIT]
I also got a analog ammeter, I think I'm going to put it on this for quick reference, and maybe a volt meter.