electrical trouble shooting

[Robfnk]

I have a little John Deere 790. Battery keeps going dead. I replace the battery a month ago with an Interstate battery thinking that was my issue but it still goes dead in a weeks time. I checked the alternator. It is putting out 3 amps at idle and 16 amps at the suggested running speed. My amp meter says there is nothing drawing off the batter when the tractor is shut down but something is draining it so it most likely is under .1 amp draw since that is what my meter goes down too. Can anyone give me any suggestions on where / how to start trouble shooting. If I disconnect the positive side of the battery to test I am just going to read through the alternator and starter with my ohm meter so not going to get an accurate reading. Any suggestions would be appreciated.
Rob

 

[Hoss710]

If it were me I'd pull the positive lead with the tractor shut off and key out. then measure the resistance between the positive cable and ground. it should be in the k if not mega ohms. if it's less. start disconnecting thinks until you loose the low ohm source. that will most likely be your issue.

 

[ROUSTABOUT]

Take a simple idiot light. Disconnect pos and put light one end on cable, one end on post. See if it lights up. If it lights up, start pulling fuses one at a time to make it go off. That finds what circuit it's on. If that don't find it, disconnect alternator, keep going until you find it. Because if the light lights up, the draw is there. You just have to find it.

 

[kenmbz]

Can you measure battery voltage not running and then battery voltage running and make sure running is higher than not running.
I like the lamp suggestion above too, make sure it is a very small 12v light, low wattage though or it won't get bright enough to see.
< .1amps means less than 1.2 watts.

 

[2manyrocks]

I would look at the positive battery cable as it passes from the battery under the tractor to see if the insulation has been rubbed bare.

 

[DonRybak]

Alternators have an internal regulating diode that goes bad causing a small drain on the battery. One terminal on the alternator is a direct connect to the positive on the battery. Try disconnecting that positive wire on the alternator and see if the battery is still charged after a could days. As Roustabpout mentioned, using a small test light would work too and be faster than waiting a couple days. If it's the diode in the alternator a repair shop should be able to fix it rather than replacing the whole unit. Good luck.

 

[MRTOES]

I can't offer you any better diagnostic advice than above BUT if all that fails be sure to check out all your ground connections to your engine block and anywhere else there is supposed to be a grounding strap. Bad grounds cause more problems and fires than people realize and they are very hard to diagnose.

 

[Robfnk]

Thanks, I will try the suggestions as soon as I can get back to it and let you know if I find anything.

 

[seville009]

All that I can offer is that I bought a new skidsteer in 2009.

Dealer told me to keep the battery detached when not in use so as to not drain down the battery. He was correct. About six years later, had to replace the alternator. I stopped disconnecting the battery just to see what would happen. The battery stopped draining.

So…in my case, the brand new alternator in the brand new skidsteer was apparently causing the drain.

Almost exactly six years after that, I had to replace the alternator again, as it ultimately went bad. I mention this second replacement just to point out that alternators can go bad.


How old is your alternator? Is your alternator belt tight and in good condition?

 

[ROUSTABOUT]

I can't offer you any better diagnostic advice than above BUT if all that fails be sure to check out all your ground connections to your engine block and anywhere else there is supposed to be a grounding strap. Bad grounds cause more problems and fires than people realize and they are very hard to diagnose.

I have fixed some heckuvamojo problems because the fuse box wasn't bolted on tight enough.

 

[workinonit]

You need a meter that will read in milliamps. I'm surprised yours won't.

 

[Robfnk]

All that I can offer is that I bought a new skidsteer in 2009.

Dealer told me to keep the battery detached when not in use so as to not drain down the battery. He was correct. About six years later, had to replace the alternator. I stopped disconnecting the battery just to see what would happen. The battery stopped draining.

So…in my case, the brand new alternator in the brand new skidsteer was apparently causing the drain.

Almost exactly six years after that, I had to replace the alternator again, as it ultimately went bad. I mention this second replacement just to point out that alternators can go bad.


How old is your alternator? Is your alternator belt tight and in good condition?

The alternator is 3 years old. The belt is tight. That was the first thing I checked. I will check out the alternator later today or tomorrow depending on how bad the smoke is from controlled burns going on in our area.

 

[SARG]

The alternator is 3 years old. The belt is tight. That was the first thing I checked. I will check out the alternator later today or tomorrow depending on how bad the smoke is from controlled burns going on in our area.

Check the news ... the smoke is coming out of Canada.

And I still keep trickle chargers on our 5 machines all year.

 

[woody]

I have an Exmark that was doing the same thing and I picked up a battery disconnect switch from harbor freight and it has not drained since.

 

[Robfnk]

Check the news ... the smoke is coming out of Canada.

And I still keep trickle chargers on our 5 machines all year.

I'm sure your smoke is coming from Canada but I am in Florida by a 10,000 acre forest and they do control burns on different parts every year. We will get a lot of smoke for a few days then it clears until they start another.

 

[hummertom]

Because these tracs bounce and rattle a lot a small "leak" can be nasty over time sitting, I have a truck that has this problem, most modern vehicles are designed to be driven frequently, and have a small draw when sitting, what I did was to install a battery disconnect switch at the battery and install a small solar panel at the battery, both are available cheap at Harbor Freight. it keeps the battery at full charge and the switch is just like a key switch

 

[Robfnk]

update. Found a couple of issues. Was having trouble getting good readings because of a corroded connection where the ground from the battery connected to the frame. Then I was using a clamp on amp meter to try and find any leakage but since that only went down to .1 amps it didn't pick anything up. Remembered I had a Fluke OEM that had an amp setting. Using that I found a leak of .03amps on a plug that was put in years ago to run a pump sprayer.