Alternator / engine room fan thermostat

[geem]

The new system will be using the large cockpit locker as a "heat sink" so air flowing past the alternator will be cooler than before

That is a very inefficient way of doing things. The cockpit locker will heat up. Once everything is hot you won't have a heat sink. You will only be reducing the temperature of the air over the alternator by a small amount if any.

 

[geem]

But it's still bolted to the 80 degree C engine. How do you imagine that the alternator can be any cooler than that ?

If you can get cold outside air piped directly to the alternator then it will work. My alternator actually has a flange connection for a cold air inlet. It was manufactured by Prestolite to do this. The alternator is off a bus

 

[GHA]

and you have peace of mind. great!

Completely agree, feeling good is important, even if the physics isn't so clear cut.

Would be interested to have the results after a reasonably long period of motoring.

Probably more important is what is in control of the power output - the batteries!
Never seen my alternator get more than a degree or so different to the engine, but the batteries never get really discharged so just won't accept enough amps to push the alternator hard.

And.... bit of searching, always assume your memory is wrong!!! , alt temperature is lower than engine >

 

[PaulRainbow]

If you can get cold outside air piped directly to the alternator then it will work. My alternator actually has a flange connection for a cold air inlet. It was manufactured by Prestolite to do this. The alternator is off a bus

Of course, if you're getting cold air in, but the OP isn't.

Worrying about alternator temps of 60-80 C is pointless, anything up to 100 C will be fine.