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alternator overcharging

December 20, 2010, 02:59:41 pm

On a trip 2 months ago my dash meter said chassis battery not charging. I turned on boost til I got home, and went out to start up engine and chassis battery was dead. I got it started and I noticed the monitor was showing 20 volts when I had rpms up and also drivers over head light got real bright. About that time the monitor blew a fuse, also I was smelling wires overheating I'm thinking my alternater may be over charging, Any help on this subject  Also I had to replace house battery It showed replace with tester.

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Re: alternator overcharging

Reply #1 – December 20, 2010, 04:30:51 pm

Tommy,

We need more information to be able to help.

What brand alternator?  What model if you know?

Where are you located?

Brett

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Re: alternator overcharging

Reply #2 – December 20, 2010, 10:52:25 pm

This is a 1994 U225 with probably original alternator, and since I posted this today I cranked  motor and put volt ohm meter on chassis batteries and had no voltage as for as I could tell. In other words the batteries were in a weak state, and I used boost to start and then I turned boost off and tested .  A mechanic from my brothers farm is suppose to come over and test for me but, he's been busy. I was trying to wait for him to test before I attempted to take alternator off. Tommy T.

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Reply #3 – December 20, 2010, 11:02:03 pm

Sorry Brett, I live in Donalsonville Ga. now. after 38 years in Tampa and this grandvilla has the 5.9 cummins engine.

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Reply #4 – December 21, 2010, 08:57:12 am

He will want to start by verifying that the batteries are OK-- alternators can do strange things when asked to charge dead batteries/batteries with a bad cell.

If a Powerline, give them a call-- I understand there is a good Powerline dealer in the Tampa area who can rebuild it.

No idea if yours may be the same as the one on our 1993 U240 with Caterpillar 3116, but here is the information on ours:

Powerline Alt:  Hehr Power Sys Ft Worth (800) 443-9394 190 amp model 25-15.

Brett

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Reply #5 – December 21, 2010, 10:42:22 am

I had my Powerline repaired, New bearings, Diodes, and regulator for less than $300.00 ( not much less). Any good Auto Electric can do the job.

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Reply #6 – December 21, 2010, 11:06:35 am

Tommy, We have had rallies in your area at Fort Gaines, GA. And also at Ocklocknee, and Thomasville,  Next time we are in the area we would like to invite you to join us.  The Georgia Funseekers is a FMCA Chapter with members mainly in North GA, but there are members from all over the state. .  If interested drop me a note and I'll give you some more info.

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Re: alternator overcharging

Reply #7 – December 21, 2010, 11:44:56 am

If you are handy, just pull the alternator off yourself (after disconnecting the batteries). If not, get a neighbor, etc. Should take 5 minutes if you are fast, 15 at the outside. Like another member suggested, take it to a auto electric shop and they will check it for free (or they should). I always have a local auto electric shop rebuild my starters/alternators etc. You have no idea what was done when you buy an over the counter exchange unit.  The exchange companies have a bunch of minumum wage workers sitting at benches cleaning and throwing parts together with air impacts. When you put it back on, replace the belts with new ones. Tighten belts according to accepted practices as too tight belts are responsible for almost 75% of alternator bearing failures. If you do not feel up to it, drive by your local auto electric shop and they may do the whole job on site or will inspect your handiwork. They can check batteries, cables/connections, etc. at the same time. Most members from our local EAA take their aircraft starters/generators to our little shop with excellent results.

Best for the holidays,

Pierce & Gaylie
93' U300/36

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Re: alternator overcharging

Reply #8 – December 23, 2010, 10:36:39 am

Thanks all for your comments so for, They've been helpful.
Brett ,I took coach to truck alternator shop wednesday in Bainbridge Ga, they tested with engine left running after I turned off boost, they said the alternator was putting out 18 volts til they bridged a wire to one of the lugs on the alternator with 12 volts from battery, then the alternator leveled out to 14.2 . They would not work on it any further but did not charge me. I showed him a connection point behind left duals and he said the 4 by 6 inch connection point looked as if the plastic is burned, he said probably a loose connection or burned wire causing the problem. I'm going to take those connections loose and inspect for broken wire. My problem is I'm not sure if that heat dispensing connection point is the isolator that I've heard you talk about on another post. Can you enlighten me on this. What I get from what they were saying is that a 12 volt wire is not making it to the alternator.  Also this is one other thing that might be key, and that is looking at voltage meter on dash with engine running, it shows whats in battery until I flip on boost, then I can see good voltage as I bring RPMS up. In other words it moves along with RPMS back and forth. Thanks for any knowledge you can em part. Tommy T.  

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Re: alternator overcharging

Reply #9 – December 23, 2010, 12:33:28 pm

Tommy,

Clearly the sense wire must "communicate" battery voltage (chassis battery) voltage to the alternator.

The wiring diagram for my coach (1993 U240 shows wire B59 going from the chassis battery terminal on the isolator to the alternator.  I don't know that yours is the same, but worth a look.

But, if you see a burned wire and KNOW where it attaches, that would also be a good starting point.

Yes, the "finned" device with large lugs and large gauge wires IS the diode-based battery isolator.

Brett

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Reply #10 – December 24, 2010, 10:00:18 am

Brett, took all cables loose from this battery isolator powerline 22-33 (PLI-190-3) which has 4 lugs, 1 main bat. 2 aux. and 1 alt connection. The Main bat lug has plastic burned from all around it, I can actually see a lug that was once covered in plastic. Is this a death sentence on this isolator and do I need to find another replacement. Thanks for the help, Tommy T.

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Re: alternator overcharging

Reply #11 – December 24, 2010, 10:22:18 am

Tommy,

Sorry, can't diagnose until you hook it up.  If the overheating was from a poor connection, the isolator may be OK.  If it was from a loose diode in its heat sink, it will likely shot.  If it still does not charge properly (proper voltage) after replacing the burned wire, THEN you need to decide on Plan B.

Plan B could be replacement with another diode-based isolator, simple HD switch, etc.

Brett

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Reply #12 – January 15, 2011, 03:49:56 pm

Brett, To all who helped with this, just wanted to report all is well after replacing isolator. Thanks Tommy T.

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Reply #13 – January 16, 2011, 01:02:40 am

Tommy, Your name sounds familiar to me.  What line of business were you in here in Tampa?

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