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Alternator draws down battery

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bball

03-14-2004 16:17:35




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I had to put a new alternator on my 860. It had already been converted to 12 volts when I bought it. I put the new one on and hooked up the wires just like they were previously. 2 days later, I went to start it and the battery was totally dead. Any recommendations?




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RayP(MI)

03-15-2004 05:06:57




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 Re: Alternator draws down battery in reply to bball, 03-14-2004 16:17:35  
A while back, I had an alternator rebuilt for my wife's Bronco II. Then the battery kept going dead, unpredictably. Finally figured it out - if car was driven, parked, and then a voltage draw was put on battery (door opened, dome light came on,) then the voltage regulator would kick on, and drain battery through field coil, draining battery. Took a lot of instrumentation, experimentation, and just dumb luck to find that one! Rebuilder went through several new regulators with this problem before I went back, and made him find old one from junk pail, which is doing fine several years later!

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Charles (in GA)

03-14-2004 19:55:41




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 Re: Alternator draws down battery in reply to bball, 03-14-2004 16:17:35  
If the alternator you installed is exactly like the one that came off, you could have bad diode(s) in the new one. Generators use regulators w/internal cutout relay or a cutout relay by itself in a 3 brush unit, to keep the generator from running down the battery. But in an alternator, the BAT post of the alternator is connected directly to the positive side of the battery, without the benifit of a cutout relay. How? the diodes prevent the current from draining back into the alternator to ground and killing the battery. If one or more of your diodes decided to short internally (they usually go open when they fail, but ocassionally they short instead) then you have a direct path for current to go thru the alt to ground.

Yes, you do get bad new parts ocassionally.

Charles

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bball

03-15-2004 17:56:24




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 Re: Re: Alternator draws down battery in reply to Charles (in GA), 03-14-2004 19:55:41  
So basically Charles, it should not be drawing it down and I don't need a separate switch to cut off power to the alt when not in use-- I just need a working part. P.S.-I also put a new battery in when the other went dead, I let it set overnight and still had a charge this morning. Maybe the old battery just ate it's pigs?



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John IA

03-14-2004 18:10:36




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 Re: Alternator draws down battery in reply to bball, 03-14-2004 16:17:35  
Bball, first off is it an internal or external voltage regulator? The problem is you have juice to the alternator fields all the time. If it's a external regulator check the contacts to make sure there not stuck. Other wise you have to shut the juice off to the alternator either by rewiring it through the switch or disconnecting the alternator or battery every time your done using the tractor. Have you check the archives for 12v conversion wiring diagrams? A late 8n should wire close to your 860. John

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bball

03-14-2004 18:57:56




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 Re: Re: Alternator draws down battery in reply to John IA, 03-14-2004 18:10:36  
It's internal regulator. Thanks. I'll look into the archives.



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