MF 135 Discharging battery

[donmarlatt]

My MF 135 is discharging the battery with the key off. There is no voltage regulator and the alternator is one wire. The alternator is charging when running. I hooked a volt meter from the positive battery terminal to the battery lead and it shows 12 v. with the key off. When I unhook the terminal on the alternator it opens the circuit. I guess the alternator is bad even though it charges.

I searched for a short, but could not find one..

Any comments would really be appreciated.

Don

 

[Harry in Ky]

That's the downside with one wire alternators. They have a tendency to do just that, even when new/rebuilt. A simple, inexpensive solution would be to run the alternator output wire through a switch so it can be separated from battery when engine is shut off. I use a 75 amp push pull switch(available at most parts houses for about $10 or $12). You can replace the alternator, but chances are the condition will return sooner or later.

 

[Billrog]

If an alternator has a bad diode it will bleed back discharging the battery I never thought of using a switch.

 

[oosik]

An added advantage to the use of a switch - properly located, its an almost impossible to find anti-theft device.

 

[DLTTrekkers]

Overnight ? Bad battery ! Test battery !

 

[flusher]

Disconnect the fuel sending unit in the tank and see if the battery problem persists. These have been known to cause slow battery discharge after years or decades of operation.

Good luck.

 

[BADDBOYY21]

Not to hijack the post but do any of you have pictures of your alternator mounted on the tractor? I bought a 1 wire delco style and I am having trouble getting it mounted with the universal mounting kit.

My tractor is a 165. Not sure if they would be similar to a 135.

 

[Dave M7040]

It sounds like you have a GM alternator with an internal voltage regulator. The most meaningful test is to check the output voltage when the tractor is running.
If is is on the low side it is a good indication that all is not well with the alternator. They can be rebuilt if you have the skills but replacement is usually best.
The idea of putting a switch into the circuit will deal with the problem in the short term but I dont think it is wise as there can come a time when additional diodes start to fail and then one day you forget to open the switch and you have so much current going to ground through the alternator you start a fire.
Check the voltage when running and post the results. I would expect to see about 14 volts. A picture would help confirm that it is indeed a GM alternator.
Dave M7040

 

[donmarlatt]

Thank you all for the helpful comments. I think I'll replace the alternator and hope for the best.

I really appreciate your help and expertise. GREAT FORUM!

Don

 

[murphy1244]

Automotive alternators run at higher RPMs to charge also.