How do you test a Selenium Rectifier?

I still have, and use, an "antique", Big, Honkin' 50 amp 12/6V battery charger -- and it uses selenium rectifiers. It's out in the bitterly cold, dark, detached garage ATM -- or I would quote from it's metal name tag. A hand-me-down from my father ... and maybe even, his father.

In the past I was able to start my old, dilapidated, hardly-any- compression Jeep with no onboard battery!

Still have the charger -- not the Jeep. :-)

Jonesy

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Reply to
Allodoxaphobia
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** But silicon diodes like 1N4004s or 1N4007s you see everywhere have a similar voltage drop - about 1V at 1 amp.

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** But the *REAL* reason is the low reverse voltage capability - 25V per diode rather than 400V or even 1000 volts.

FYI: Silicon diodes are remarkable devices - a finger nail size, 4 diode bridge is adequate for a 1kW DC supply using only the PCB foil as a heatsink.

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amp bridge

Think there is another reason too in that Selenium diodes cannot be allowed to run as hot as Silicon, or their life span is drastically shortened.

... Phil

Reply to
Phil Allison

The big plates are heatsinks. Further in are the smaller selenium plate rectifiers.

NT

Reply to
tabbypurr

I plan to leave it on the chassis for looks, but replace it. My voltage is real low, so it seems it's weak or worse....

Reply to
tubeguy

In a selenium rectifier the big plates are BOTH rectifiers and heat sinks! Seen the hugh vacuum chambers in which the were made. CP

Reply to
MOP CAP

and about to go into toxic fumes mode.

Reply to
tabbypurr

forward/back resistance with a basic ohm meter should be around 100:1 or better as I recall, and you might have to use a resistance bridge of some kind (or other measuring circuit) with a voltage potential of several volts for the higher voltage selenium rectifiers.

Selenium rectifiers might have a voltage drop of several volts during normal operation. So maybe a test circuit would work better...

You could drive normal AC power through it, into a (safe) resistive load (no capacitors), and then look at the downstream waveform on an o-scope. It should be half wave AC at a reasonable peak voltage, into a reasonable resistive load (let's say a 10k or 20k several-watt resistor).

I assume it's for a radio that runs on 110V [or maybe 220/240V for EU and AU radios]. So you'll see a half-wave 50/60 cycle waveform that peaks at around 1.4 times the input voltage.

If you look at it with an o-scope and see too much on the negative cycle, you'll know it's bad. Otherwise it should be ok to use it as long as the resulting output voltage is correct.

--
(aka 'Bombastic Bob' in case you wondered) 

'Feeling with my fingers, and thinking with my brain' - me
Reply to
Big Bad Bob

right they'll probably short out when they fail and blow the filter caps.

You could try a resistive load (10k-20k, several watt resistor) and disconnect it from the filter capacitors when you do it. Then look at the waveform. (I suggested this in a different post already, just summarizing)

--
(aka 'Bombastic Bob' in case you wondered) 

'Feeling with my fingers, and thinking with my brain' - me
Reply to
Big Bad Bob

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