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Alternator hot to touch with boost switch on

December 21, 2017, 04:49:53 pm

The coach is in storage plugged in to shore power for the past several days. I was working in back checking fluids, etc. when I put my hand on the alternator and noticed it was hot to the touch. I checked all the wires and connections and found everything secure and the batteries were showing 13.1v. they should be about 12.8 so i went forward and found that the boost switch was on. I turned it off. A while later i checked the alternator again and it had cooled down.

Is this normal? has anyone run into this before? what would cause the alternator to get hot when the boost switch is on and the coach is on shore power?

Thanks

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Re: Alternator hot to touch with boost switch on

Reply #1 – December 21, 2017, 04:51:36 pm

Do you still have the OE or OE style diode-based battery isolator?

If so, see if the center lug (B+ to alternator) has voltage with/without boost.

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Re: Alternator hot to touch with boost switch on

Reply #2 – December 21, 2017, 05:51:05 pm

Mis-wiring around the isolator or a bad isolator, could put 12v on alternator output and maybe short out alternator.  Since it only happens with boost, it could imply the start battery post of isolator is back-feeding to isolator's center alternator post.

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Re: Alternator hot to touch with boost switch on

Reply #3 – December 21, 2017, 11:27:23 pm

Thanks. I'll check it tomorrow.

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