Advice needed - smoking battery charger.

[PeteHall]

I'm sure someone on here will know, but my electrical engineering is rather rusty, so hopefully someone can help me out.

My question relates to a lead-acid car battery charger, but I'm sure the guts will be identical to my lead-acid Oldham charger, so vaguely caving related...

I've not used the charger for a couple of years snd when I switched it on, it started smoking.

Taking the cover off, I can see that the transformer is mostly wound with thin wire, but the outer windings are a thicker wire. The thin and thick wires appear to be separated by a plastic layer.

The smoke is coming from this plastic layer, but there is no sign of any other components having got hot.

Is there anything I can do to better diagnose the fault?

Is it likely that the charger can be repaired?

Is it likely to be safe/effective to carry on using it? Presumably the smoke will stop once all the plastic has burnt off

Thanks in advance

 

[Ian]

It means the transformer is probably overheating. For safety I wouldn't continue to use it since the plastic is there for safety.

 

[Fjell]

It’s buggered. It’s also a prime candidate for giving you a nasty shock, let alone cause a fire. Take to tip. It’s also over-rated for your average 70 amp.hr car battery If that is what you want one for, a 10 amp with a plastic case would do fine.

I have a 25 amp multi-stage charger for a 250 amp.hr battery. One of it’s features is being waterproof so it doesn’t go rusty like yours. Despite running at 14.4V on bulk, the current drops off at 80% charge as the battery won’t accept it. Big chargers for a car or truck battery are a con.

 

[Flotsam]

It's either a rectifier failure or a transformer failure.
To diagnose, disconnect one output leg from the transformer. When plugged in again, if the transformer stops smoking, it's the rectifier. You need to check If there's still some output from the transformer, use a car bulb, should light. If the transformer has failed it's scrap. The rectifier can be replaced with minimal cost.

 

[Ian Ball]

I've often wondered why car battery chargers are rated by engine size. If they are all lead acid 12v then surely a 14.4 v charger is fine just a case of how long it takes to charge when using a smaller rated machine?

 

[PeteHall]

It's either a rectifier failure or a transformer failure.
To diagnose, disconnect one output leg from the transformer. When plugged in again, if the transformer stops smoking, it's the rectifier. You need to check If there's still some output from the transformer, use a car bulb, should light. If the transformer has failed it's scrap. The rectifier can be replaced with minimal cost.

Thanks for the advice.

Based on these diagnostics, the transformer is fried.

Will strip for useful parts and scrap the rest.