Alternator - How Hot?

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Jeva

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I've just fitted a Stirling alternator regulator to my existing 120A Bosch Alternator. It works fine, putting out loads of current, but runs very hot -up 100 degs C at the front but only about 50-60 degs at the back end. I can't find anything on the web as to what the safe operating temp of an alternator is. Does anybody know?
 
How much current? Have you an ammeter or battery condition gauge to measure amps?
First thing to check is a slipping drive belt.
100 c is too hot.
 
Just had a look in the Balmar 614 manual, where an alternator temp sensor is fitted the field current will be reduced and an error flagged at 108c by default.
 
Jeva said:
I've just fitted a Stirling alternator regulator to my existing 120A Bosch Alternator. It works fine, putting out loads of current, but runs very hot -up 100 degs C at the front but only about 50-60 degs at the back end. I can't find anything on the web as to what the safe operating temp of an alternator is. Does anybody know?
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Your 100C temperature is high but not sufficiently to start melting the field winding lacquer.
Most alternators will run hot when really having to work but cool down as their output drops. If running an alternator really hard it's best to have an external fan.
The temperature difference between front and back suggests most of the heating is probably due to belt friction.
Use a heavy duty, toothed belt and make sure the belt is tensioned to give about 10mm side play at its greatest span.
 
I had a similar problem two years back. I had a new Volvo D130F with a 115 A Alternator. The alternator got so hot that it set of the fire extinguisher placed above the engine. I added thermocouples to monitor its temperature and the air surrounding the unit which both reached about 100 C. I cured the problem by improving circulation with a couple of 12V computer fans that run when the alternator runs. The older Volvo engine that it replaced has a much lower output alternator which did not require as much cooling. The unit was fitted in an area of low air flow so the ambient temperature was high to start with.

The issue is that at 110 A the unit is delivering about 1.5KW and will not be 100% efficient the lack of efficiency will result in a requirement to cool the alternator.
 
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cliff said:
Or bush
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Alternators usually have bearings ( ball races ?) at both ends don't they ?

IIRC dynamos had a ball race at the drive end and a bush at the other end which you used to have to put a drop of oil in at service intervals.
 
Thanks for all of the input. First, the alternators producing about 40-60 Amps depending on the battery state and reducing accordingly. Second, the alternator was recently serviced, so I'm fairly sure there's not a bearing/bush problem. Third, the belt is a multi Vee type so it's not slipping, but because the pulley isn't keyed it may be slipping on the alternator shaft, so I'll look at that again.
Thanks again for the input.
 
Jeva said:
And P.S. - Just out of interest, how hot can an alternator run before it's defined as too hot?
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The only reference I can find is in a US aviation paper, the figure quoted is 280F. However that has more to do with the point at which the alternator output starts to degrade significantly.
I've found alternators with external fans seem to run cooler than those with a small internal one alone.

When you say it's multi-V are you referring to a PolyBelt (Nitta Coporation) or a serpentine belt as used on modern cars to drive multiple ancillaries.
In which case it's not slip and you need to urgently duct some cooling air to the alternator.
 
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