Alternator Problem on M4900

docmx · Jul 12, 2008

I have a M4900 with 300 hrs. Replaced the battery about 6 months ago and now find myself having to replace it again after 6 more months. Before the 2nd battery died, I noticed the alternator light was turning on and off. I put a new battery in and started it and the alternator light would not turn off. Before I take the alternator off to have it tested...does anyone have a suggestions for things I should check. The belt is good and tight and does not slip while the engine is running. The two connectors on the backside (the plastic plug connector and the post connector with the rubber cover over it) of the alternator are good and tight. The wires appear to be in good shape. Ideas appreciated...

jruss · Jul 12, 2008

If you have a volt meter available, you can hook the positive lead to the large wire terminal at the alternator(output) and negative to ground. Reading should be 13.5 to 14.5 volts with a fully charged battery at about 2000 RPM.

John

simonmeridew · Jul 13, 2008

Doc:
be sure connections are clean and brite on the battery cables too. a little bit of fur on the connections can cause some confusing issues.
simonmeridew

docmx · Jul 13, 2008

Thanks, I will look into these suggestions. Anyone else have suggestions?

docmx · Jul 13, 2008

I checked the alternator output voltage and it was 15.67.

docmx · Jul 13, 2008

That was at idle.

Builder · Jul 13, 2008

Had the same problem on my Deere. It was the voltage regulator.

docmx · Jul 13, 2008

Thanks for that tip!! I will look into it.

rbargeron · Jul 13, 2008

Builder said:
Had the same problem on my Deere. It was the voltage regulator.

If the voltage regulator is malfunctioning it is cheaper to replace the whole alternator than to replace the built-in regulator section of it. The link is to an equivalent to Kubota 34070-75602 used on the M4700 and M5400 - likely the same for the M4900. I recently bought an alternator from these people - it's perfect and yes it really was 70% less than list!

Builder · Jul 13, 2008

rbargeron said:
If the voltage regulator is malfunctioning it is cheaper to replace the whole alternator than to replace the built-in regulator section of it. The link is to an equivalent to Kubota 34070-75602 used on the M4700 and M5400 - likely the same for the M4900. I recently bought an alternator from these people - it's perfect and yes it really was 70% less than list!

Mine was an external voltage regulator