Hot Alternator Xanti HDI

[charentejohn]

Any thoughts anyone, I read this thread http://www.frenchcarforum.co.uk/forum/v ... alternator" onclick="window.open(this.href);return false; which had some general comments on voltages so just checked mine.

Readings are taken at the battery terminals. Before starting (but after car had run for 5 mins earlier) battery showed 12.94V. Started car and read 14.4V at battery, after about a minuts this dropped to 14.15V.
From the sound of it this is all correct, so why does the alternator get hot ?

I just replaced it after the old one failed in clouds of smoke and a was making the enging stutter and stall, so was affecting control gear etc.
The new one is a 150A as was the original, new not recon from a good supplier but is their own brand.
After about 4-5 mins it gets hot, just ok to touch it but hot enough, engine is lukewarm at this point.
Normally I wouldn't notice but was just checking around after installation. Do they generally get this hot ? Hard to tell at the moment as hands are freezing so I don't like touching it for too long as by the time I register it is really hot I could be stuck to it.
No noises or burning smells I so far. I don't want to be far from home when it bursts into flame and goes bang

[Xantidote]

Well the voltages you quote are what I'd expect, suggesting alternator is functioning correctly (and so it should, being new)

Can't help on the hotness of it - alternator temperature is the sort of thing we take no notice of, until we get a problem, and then we start think all sorts of terrible things. It will obviously heat up after start-up, because of the high current being generated to recharge the battery. Always going to be hot once the engine's been running a while of course

[RichardW]

I think it's normal for it to be hot just after a cold start - 150A @ 12V is 1.8kW after all, a bit of inefficiency in the alternator and it will make some heat! It has a big fan on the front of it for his reason!

[charentejohn]

Good point as this was all done on tickover after starting up after alternator change. Would make a difference when spedded up as generating easier.
I should know these things being an ex electrician. Generation is always a problem as the generator acts as a motor at the same time and so resists the turning of the generator. Hence being quite inefficient really. Any resistance generates lost energy as heat.

I will take it for a run and then see how it compares with general engine bay heat.
I used my new car stethoscope on it, neat thing really but scary as you hear all sorts of wierd noises. I have a problem with my right ear so don't hear stereo any more, very frustrating working on cars.
Front and rear sounded like normal whirring bearing noises, placed on the centre it was harsher. May be the metal cores touching slightly ? but bearings seem ok and any touching will soon wear off (if that is what it is.

So I will reserve judgement as the voltages seem spot on, and see how it is after a run.