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Rectifier unit in charger how does it work ?

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b.james

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I attach a picture of a charger I intend to replace a transformer in . I see three wires out of the secondary and assume perhaps a center tap middle wire with an output wire each side fed to a rectifyer . I don't understand how this works and wonder if anyone can explain its operation for me please.

The rectifyer has 4 plates

It has a switchable high/ low out put and on the front panel has a plug for 12 Volt and a plug for 6 Volts
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That's about as basic as it can get. Certainly looks like a selenium rectifier, which I've always considered as just about bullet proof.

Transformer has obviously gotten quite toasty :woot:...
 
It had a bi-metalic overcurrent cut out and it physically fell apart so I replaced it with a polyswitch but I didn't get that right so it overheated the transformer which I wish to replace now .

So how would I wire up the new transformer to the present rectifyer? do you think I would be best to switch to a diode bridge type .? I'd like to keep it fairly original if I can . I prefer to use the old equipment if it will still work
 
That's about as basic as it can get. Certainly looks like a selenium rectifier, which I've always considered as just about bullet proof.

Yes, 100% a selenium (metal) rectifier - however, I certainly wouldn't call them 'bomb proof' :D

I've replaced huge numbers of them in old TV's, radios, record players etc. - it was a VERY, VERY common fault (incidentally, the technique was to replace them with a silicon rectifier and a wirewound resistor in series - to give a similar voltage drop to the original).

As already mentioned, they common stink when they fail - and badly :p
 
And the stink, Selenium Dioxide if I remember correctly, makes you feek sick.

A bit like welding zinc plated (galvanised) steel. The fumes from the burned zinc can make you feel quite sick.

JimB
 
The selenium rectifier doesn't appear to have been overheated, a sure sign of failure. As they say, if it ain't broke...

What is the range of the ammeter? That will give you an idea of the current specs needed to replace the transformer (which appears to have a center tap on the secondary).

The "bi-metalic overcurrent cut out" (or its equivalent) should be replaced as well.

Although I admire your desire to rehabilitate the charger, unless you can find some used replacement parts, especially the transformer, the cost(s) are going to surprise you.
 
This is probably the same charger which ive had since around 1976. It gets used a lot & the extra circuit board is an SCR voltage regulator which I built years ago & added to it, & it now is only used for 12V battery charging & is used fairly regularly. It is rated at 2.5Amps continuously. The circuit diag is the original circuit. I wouldn't be keen to use it with out the thermal over load, as if a battery is fairly flat it is capable of about 4 Amps & get fairly warm.
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It's probably more likely to be a copper oxide rectifier, they seem more common in battery chargers than selenium.
 
Thats the one thanks for the circuit and pics debe ,Very helpful I'd like to save it
 
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