200 AMP Battery Isolator HOT

[passerby]

Doing spring maintenance cleaning chassis grounds, battery levels, chassis lube, etc.
Took it to fill up and smelled something hot, just thought maybe engine cleaner. Smelled it again, opened rear battery switch bay and felt the Isolator and it was HOT. The alt is 3 years old and I cranked down on connections, but will double check. Help from this knowledgeable group would be appreciated.
Thanks
Bill

[DtBt]

It can get warm. If it is cooking enough to smell there is an issue. It is supposed to charge both battery banks with the alternator and is essentially two big diodes with the anodes tied together and connected to the alternator so the alternator output can charge both banks while maintaining isolation between the banks.
Start engine, get a meter and check voltage at the three terminals. It both banks are charged the center lug should be 14.1V and the end terminals should be about 13.8V if it is functioning. If one bank is low then the center lug (Alternator output) will be lower as well as the end lug associated with the "low" bank.

[passerby]

I checked the Isolator today.
Center post 18+V
Top post 17.8V
Lower post 13.4V
Chassis battery Lower post
Checked the ALT 19.8V
Top post house batteries boiling and the Battery isolator is hot.

[twinboat]

9Your alternator is running with a bad regulator or low voltage feedback to your regulator.

There should be a chassis battery wire to a "sense" or dulvac terminal on the alternator.

This issue usually appears when the wrong alternator is installed on MHs with diode isolators. They stopped using isolators in the early 2000s.

Look for it and make sure it is connected.

There may also be a wire that gets power from the key, but that's not important right now.

A test to see if the regulator has failed would be to jump the alternator terminal to the chassis terminal, on the isolator.
If the volts go down to 14.2 or so, the alt is ok but not seeing battery voltage. You can also jump from alt. to the house terminal as a test.

If it works correctly, jumped, you need to look for the sense wire.

Alternators with internal regulators need to see battery volts to know how to regulate. Diode isolators block that voltage so they came up with the " sense, delvac " terminal on the alternator.

Also make sure the wire from the chassis terminal to the chassis battery is clean and well connected.

[passerby]

I took the Alternator to a repair shop and he tested and it was ok.
We think it's the isolator and I ordered a new one, should be here tomorrow.
Will see.
Alt to chassis reads 13.4

[twinboat]

I hope that fixs it.

If you jump all three isolator terminals together, it should confirm it being bad by seeing the same voltage at both batteries.

Alt. to chassis being 13.4 is low for a 14 volt alternator.

If it is only seeing 13.4, it will keep trying to produce 14 volts.

That is why it is outputting the high voltages to the house bank.

One of the small wires should go directly to the chassis battery. Any resistance in the connections will screw up the system.

Check the red wire carefully.

Here is a wire diagram.


http://www.prestolite.com/literature..._4800-4900.pdf

[passerby]

It turns out it was the battery isolator. Installed a new Cole Hersee 200 Amp battery isolator and things went back to normal.
Alt reading 15.13Volts
Chassis 14.29Volts
House 14.29Volts
Thanks for the help