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Alternator replace question - Isolator


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Long story short, new 96 Monaco Windsor 8.3 Cummins DP. First trip Speedometer starts stop working. Charge gauge on dash showing 17v. Get home chassis batteries dead. 
Had ongoing issue chassis battery would die overnight if disconnect left on. 
Opened up battery compartment. What a mess. Top tray had 1 house battery. Too tall for that position. That battery had electrolyte an inch over plates. 
bottom shelf held the chassis battery and another big house battery. Same electrolyte situation as on house top house battery. both showing full 13.5 v charge.   The chassis battery electrolyte level was below the top of the plates and read 8v. I filled it to cover plates and put 2A charge on it for 24 hrs. Filled with distilled water and leaving in charge for a couple days. 

Used one of house batteries to crank up. Charge gauge in dash shows 17v. I go outside and see battery overflowing. Quick check of voltage is 17v. So shutdown and disconnect. 

I have removed the alternator a 2800JB rated for 160A. I noticed I have a HD PSI 33-43 Isolator rated for 190A. Is that a problem?  Does alternator need to be sized at isolator rating?

I am planning to have alternator rebuilt at local shop, but I don't want to burn it back out if it's not powerful enough. 

Help and advice appreciated. 





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I don’t think the amps are an issue. As long as the isolator is “bigger” you are fine.

Your voltage regulator is not working properly.

The regulator is likely inside the alternator.

OR…you could have a sense lead problem.

I am not familiar with your coach, but if you have a sense lead, that would be a small wire from the alternator going to the start battery which is how the alternator knows to dial it back when it gets up around 13.8 or 14 volts.

It is even possible it got connected to the house batteries.

17 volts is wrecking batteries for sure.


Edited by Fonman
Clarity, add detail
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I have the same coach and had similar problems when I got it. Determined it was definitely the regulator, external by the way. The regulator was new but was a terrible replacement job. Replaced the terrible wiring job and everything functioned as normal. 
BTW the external regulator is near the alternator mounted on back wall driver side. Picture attached.




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Walt, I'm not sure what your problem(s) are, but alternators designed for the DUVAC cofiguration often engender problems from mechanics who do not understand how it works or why it is needed.  DUVAC refers to the fact that it has a remote voltage sensing wire that connects DIRECTLY to the positive battery post of the chassis battery (NO OTHER LOCATION).  When that remote sensing wire is improperly connected, the alternator will not charge correctly.  I'm not sure what happens if that sensing wire is connected to NOTHING, but possibly without the remote voltage reading, the alternator outputs its max capacity.

I think before you get too deeply into this troubleshooting, that you understand that the DUVAC configuration is employed in your coach for only ONE reason--the Solid State Isolator.  Read some of the posts here and on iRV2 about the Blue Sea ML-ACR.  It eliminates the need for SSI, the Battery Boost contactor ("Big Boy") and the auxiliary ("Lambert") charger.  The root cause of your problem has nothing to do with installing an ML-ACR, but installing the ML-ACR prevents a host of future problems and allows you to use any garden-variety alternator of sufficient capacity.

AmazonSmile : Blue Sea Systems ML-ACR 12V DC 500A Automatic Charging Relay with Manual Control, Beige : Boating Battery Switches : Sports & Outdoors

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