New battery in car alternator started to smoke

[Paul Howl]

Hi just put new battery in my car and the alternator started to smoke do I need  to get a new alternator. Focus 1.6 tdi

[AndyDC]

If it started to smoke before you turned on the ignition etc, then I'd suggest you double check the connections are on the right way round (without turning the ignition on). It is possible that there's a problem with the alternator or its rectifier, and the battery and connections are fine, but putting a battery on backwards could damage lots of things including an alternator.

[jonj1611]

Yes I would agree you need to make sure the battery terminals are attached correctly.

Some batteries do not have the positive and minus in the same places, a lesson I learned myself some years ago when I bought a replacement battery and they were switched around

[mjt]

It should be quite difficult, but perhaps not impossible, to get the connections wrong because the battery posts are different sizes.

 

[isetta]

what diagnosis did you do to establish you needed a new battery. I am wondering if the original problem was the alternator and not the battery (faulty alternator was flattening the battery).

the alternator has the rectifier built into it. The alternator produces AC current, the rectifier converts it to DC for the car battery. But something else the rectifier also does (it is made up of a few diodes) which is important, it acts as a 'valve' . It only lets current pass from the alternator to the battery and stops the current flowing from the battery back to the alternator when you turn the engine off.  Although not common, the rectifier can go faulty and let current drain back through it into the alternator (draining the battery) and smoke and burnt out. 

 

[Ennvoqation]

2 hours ago, isetta said:

Although not common, the rectifier can go faulty and let current drain back through it into the alternator (draining the battery) and smoke and burnt out. 

 

That happened on my old car, the alternator burnt out requiring it to be replaced and also some of the wiring looms in the bay. Caused a bit of panic for the driver when smoke started coming out from under the bonnet and into the cabin. The engine warning light was on and was being driven to the garage at the time!

It might be worth pulling the logs from the car to see what error codes you're getting, and getting someone handy with electrics to test voltages/circuits.