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Alternator and Battery Isolator

June 10, 2014, 03:30:59 pm

 While returning from the Grand Canyon I noticed that the volt gauge was fluctuating from 12.3 to 13.1. I was only a few miles from home so just ran it in. The next day started it up to take to it's bed and it was running over 13.  This weekend we went for a short trip and noticed the gauge was fluctuating down to 11.5.

 Yesterday I took the alternator off and ran it down to a local alternator repair shop. He looked at it and said "yep" and called it by name.  He was familiar with the alternator and said he would replace bearings, brushes and make it new again for about $150.00. The man then told me to check the battery isolator as sometimes when one goes bad it affects the other.  While disconnecting cable one of the terminals twisted off. I went ahead and took it down and he said that it had been real hot at one time and current was leaking back thru so it was toast. This made me feel somewhat better about twisting off the terminal.

 To wrap this up, the PowerLine isolator had 3 poles. The "main" battery pole had a smaller wire also attached with an inline 30amp fuse. Is this the exciter? While looking for a replacement I noticed that some have a separate smaller pole for, I'm assuming, the small wire. Is this correct? Any suggestions for a replacement? Saw them on line anywhere from $50.00 to $450.00. The alternator guy told me to not skimp on the isolator as it could create more problems. The old one is a PowerLine 22-31, 190 amp. Thanks for any and all help.

Bruce

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Re: Alternator and Battery Isolator

Reply #1 – June 10, 2014, 03:34:32 pm

Bruce,

Suspect the small wire is the SENSE wire and is usually on the chassis battery terminal of the isolator.  It goes to the sense terminal of the alternator so that the correct voltage reaches the battery-side of the isolator.

Should be able to trace the wire by number on it to verify.

Brett

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Re: Alternator and Battery Isolator

Reply #2 – June 11, 2014, 11:36:14 am

I've always heard good opinions of Cole Hersee products:

Battery-Related Products | Battery Isolators | 3-Stud Battery Isolators | Cole

Good discussion of this topic at:

Bad Isolator?

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Re: Alternator and Battery Isolator

Reply #3 – June 12, 2014, 11:27:04 pm

Brett and Chuck, thanks for responding. Chuck, I read over the old "Bad Isolator" thread and that has led me to another set of questions but first I'll have to dig up a schematic for my coach and see if it jives with the 02 schematic. The alternator was repaired but ran a little higher ($200.00) because the positive side of the rectifier was damaged and had to be replaced along with bearing and brushes.  All in all still cheaper than a new one though. Waiting for a new isolator and hopefully I'll be good to go after that.  Thanks again guys

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Re: Alternator and Battery Isolator

Reply #4 – June 13, 2014, 01:32:10 am

Four stud isolator should work fine also. One stud may just go unused depending on model of alternator. Make sure it is rated larger than the alternator. Cole-Hersee 200 amp 4 stud at: Cole Hersee 48162 4-Stud 200 Amp 12-36V DC Battery

Pierce

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Re: Alternator and Battery Isolator

Reply #5 – August 27, 2014, 04:28:53 pm

I am having same issue.  The gauge will show 13.5-14 but shut off the engine and restart and it is down to 12 until I shut it down and crank it back up then I'm good for a while.  It will be charging then drop down again until I restart the engine.  I was suspecting a bad chassis battery until reading about the isolator.  I use the trik-l-start on the chassis battery while coach battery is always on the smart charger but after sitting for quite a while, the chassis battery seemed weak when cranking up unless I employed the boost switch.  I replaced the alternator a few thousand miles ago so I'm thinking it is not the problem.  Will have to examine the isolator.  Is there any good test for functionality if it looks ok?

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Re: Alternator and Battery Isolator

Reply #6 – August 27, 2014, 04:36:32 pm

Isolator test:

Center lug from B+ terminal of the alternator should read in the range of 17.7- 15 VDC.  The outer lugs-- one to chassis battery bank and one to house battery bank should read between 14.0 and 14.2 VDC.

It is not uncommon for a diode in the isolator to fail, and work SOMETIMES.  Next time you see an abnormal reading check at the isolator.  Quite likely that the alternator is not feeding that battery bank because of a defective diode.

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