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Alternator

Today my chassis batteries were down to 11.5 v. After being off the charger and driven around locally getting service done. Alternator voltage at pos/neg post reads 15.5v.  The voltage isn't getting to the batteries. Is there something online between alternator and batteries that would cause this problem.? All cables are right.
Jody and Juli
1997 U320 40ft. Cummins M11 400hp
Build #5028
Master Mariner Unlimited Tonnage
USNR Lt. Commander (ret)
Texas A&M Maritime (me)
Baylor (wife)

Re: Alternator

Reply #1 –
Sure, you have a diode-based BATTERY ISOLATOR. 

Check between good ground and the middle lug (directly from battery B+) and then to the two outer lugs (one to each battery bank).

They DO fail.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Alternator

Reply #2 –
I'm with Brett check the isolator, I've had one fail.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Alternator

Reply #3 –
Quote from: jelfert –
Is there something online between alternator and batteries that would cause this problem.?
In your Owner Manual set there should be a B-2126 Automotive Wiring Diagram.  Referring to this diagram is helpful when trouble shooting the 12 volt system.  Copy below (from our excellent Forum library).

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator

Reply #4 –
Good chance that you can bypass the isolater and connect the bat cables on the same stud to get you down the road.
Unhook when landed

Re: Alternator

Reply #5 –
So where exactly is this battery isolator? Part number replacement?
Jody and Juli
1997 U320 40ft. Cummins M11 400hp
Build #5028
Master Mariner Unlimited Tonnage
USNR Lt. Commander (ret)
Texas A&M Maritime (me)
Baylor (wife)

Re: Alternator

Reply #6 –
Most are on the front bulkhead of the engine compartment.  Raise the bed to access.

PLEASE use your voltmeter to diagnose before spending $$ on what may/may not be the problem.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Alternator

Reply #7 –
Quote from: jelfert –
So where exactly is this battery isolator? Part number replacement?
OEM location on a '97 was just inside the door behind the left rear tires mounted on the frame rail. Some owners have relocated them to where Brett as mentioned.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Alternator

Reply #8 –
The isolator is fried.  Burn marks, separation  around the post.
Jody and Juli
1997 U320 40ft. Cummins M11 400hp
Build #5028
Master Mariner Unlimited Tonnage
USNR Lt. Commander (ret)
Texas A&M Maritime (me)
Baylor (wife)

Re: Alternator

Reply #9 –
Quote from: jelfert –
The isolator is fried.
If you wish to retain the stock factory configuration, the Victron Argo FET isolator is one excellent replacement to consider.

FET based (more efficient than diodes) and has alternator energize input in case you ever want to upgrade to a Delco alternator.

Amazon.com: Victron Energy Argo FET Battery Isolators 200-2AC (2 Batteries...

https://www.victronenergy.com/upload/documents/Datasheet-Argofet-Battery-Isolators-with-alternator-energize-input-EN.pdf


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1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"