GardenBanter.co.uk - View Single Post - Battery problems, troubleshooting help needed

Ken Weitzel

wrote:
Hello:

I have been trying to troubleshoot an electrical problem on my tractor
(John Deere 300 with 16 hp Kohler single cylinder) and so far I am
totally stumped. The problem is this: The battery seemed to be out of
juice so I had to jump the tractor from my car. The tractor started
right up and ran.... but as soon as I disconnected the jumper cables
from the car, the tractor stalled immediately.

I am assuming the tractor should continue to run on its own power, so I
started testing the charging system on it. The stator voltage was
fine, around 30 volts AC. However when I went to check the voltage
coming out of the rectifier, my multimeter went crazy and I could not
get any consistent reading when connecting the negative of the
multimeter to the engine block. It was as if something was interfering
with the multimeter. But when I used the frame of the tractor for the
negative, I finally got a consistent reading of around 0.3-0.7 volts
DC. The negative battery terminal runs directly to the engine block and
that connection was good. So immediately I assumed the rectifier was
bad. After connecting a new rectifier still the same problem.

So next I hooked up the jumper cables again and shut off the car,
keeping the cables attached.. and the tractor continued to run just
fine. I checked the voltage across the tractor's battery and it was
around 14.5 volts. I shut off the tractor with the key and the voltage
dropped to around 13.5 volts. When I saw this I assumed the charging
system was working and that my earlier assumption of a bad rectifier
was incorrect. Then I removed the jumper cables and the voltage then
showed 10.5 volts. Is it possible that the tractor's battery is bad or
shorted, causing these issues???

Thanks in advance for any feedback...

Hi Chris...

I suspect that you have one shorted (perhaps intermittently) cell
in the battery.

A surefire quick and dirty test would be to switch the battery
with another if one's available - but NOT with the one from your
car, unless you have a car available that's older than the current
computer ones.

Take care.

Ken