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Frequent Contributor

4640 electrical short

My 4640 has been sitting hooked up to the planter for a couple weeks and I went to start it two days ago and it was dead (it started just fine after sitting since December before I hooked up the planter). I put the charger on and the batteries would charge but didn't seem to get fully charged. Got it started and let it run for awhile. The next morning it was dead again. Took the batteries in to have them checked and they're good. I can get a little bit of a spark when I hook the ground terminal up so I'm assuming there's a short somewhere. I disconnected everything to the planter and power strip in the cab but still get spark. My question is, where does one start looking to find the short?

 

Thanks

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6 Replies
Frequent Contributor

Re: 4640 electrical short

It is not uncommon to see a arc when you tough the battery cables.  Some stuff (possibly memory in radio) draw for a little bit then not much.

Disconnect a battery cable and put a volt meter between the cable and the battery.  If it holds at battery voltage (12 volts?) after a minute of so, you do have a problem. 

 

One of the first things I would do would be disconnect the alternator as it isusually not to hard to do.  Sometimes a diode can start leaking and not completely short out.  By the way, if you have one diode out of your alternator, it will still charge 1/3 its amps and that is a possibility in your battery not getting completely charged. 

 

Check with a volt meter directly across the battery terminals and you should get something like 13.8 or more volts when the tractor is running.  Does that tractor have two 6 volt batteries?  You could have bad cables/connections causing it not to fully charge. With the battery partially charged,  it may not take much to run it down. 

 

Next thing to do on the power loss is start pulling fuses or possibly disconnecting a wire off of circuit breakers to see if you can isolate the problem.

 

Let us know what you find.

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Frequent Contributor

Re: 4640 electrical short

One other thing to check that has happened often to us with older batteries is one will get a dead cell, which will discharge it  (and any other batteries connected to it). To check for that is easy. Just unhook all the batteries from the system and charge them all using a battery charger. After they are charged up fully, check the voltage and then check it again in a few minutes. If it has a dead cell, a 12V battery will drop to around 9-10 volts from the 13V or so of a charged battery. Sometimes, like in a truck where you have 3 or 4 side by side, the battery that is boiling hot after running the truck for a while is a good clue, since the alternator still is trying to cram about 14V into a battery that can't take it with a dead cell. I once even had one that ballooned out like a bloated cow, but most look just like a good battery on the outside.

 

If you know your alternator is up to snuff, you can just run the tractor for 10 minutes or so, shut it off and quickly unhook the batteries and check the voltage then and again later and note if one drops too much.  You only have to remove one post from each battery for this. just do the one that is easiest to get at.Smiley Happy

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Frequent Contributor

Re: 4640 electrical short

Hooked an ammeter from the - battery post to ground and it was drawing about 3 amps. Disconnected the alternator and it dropped to about 3 milliamps. I replaced the alternator!

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Frequent Contributor

Re: 4640 electrical short

I think you found it!

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Veteran Contributor

Re: 4640 electrical short

been a heavy equiptment mech for many yrs i have only seen this once. good deal glad you foun d it

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Advisor

Re: 4640 electrical short

   I had the same thing happen last year with a Gleaner combine.   The key switch had been acting "funny" for a couple years.   I replaced it and cured the problem you describe.

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