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Brian Whatcott Brian Whatcott is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 813
Default How Hot should an alternator get?

On Fri, 14 Jul 2006 21:02:47 -0400, "GBM"
wrote:

We have a 55A Hitachi alternator on our 2 cyl 13HP Yanmar. It is charging 2
banks of batteries - 200AH in house and 100AH in Starting.

Today, I had an alarm sound when I started the engine (turned out to be low
oil level!), but it caused me to check the engine belts etc.

The alternator belt was loose, so I adjusted it - it had been slipping. I
noticed that despite only having run for about 5-10 minutes at low rpm
(~1200), the alternator was quite hot to the touch - I would guess in the
50-60 deg C range (120-140F), so I would keep my hand in contact with it.
The engine block was not nearly as hot - I could put my hand on it
anywhere - just warm.

There is a combiner, so both banks MAY have been connected. Refrigeration
was running at time. Batteries were not fully charged - maybe just below
12v. I don't have an ammeter, so don't know what amps are being put out.

Should the alternator run that hot?

Would low speed caused by slipping belt cause overheating?

If not, what could cause be? Or is it normal?

GBM


Any electronic equipment you can place your hand on for 30 plus
seconds should have a good service life. The electronics in question
would be the rectifier banks, if built in. A slipping belt
provides heating to the belt and pulleys.
An alternator reaches charging voltage sooner than an old time
generator, but self heating is roughly proportional to charging
current, which is lower at low speed.

This situation you describe does not seem specially iffy, but if you
are this anxious, get a spare alternator and a spare belt and sleep
sound

Brian Whatcott Altus OK