Newbie-electical problem?

[RichardC]

Hey all,
I have a Mahindra 3510, 300 hours, and yesterday my tach went crazy on me ..... it only reads about 1/2 the rpm I'm
turning. Any ideas on what it might be and how to correct it? Thanks for any info you can share.

 

[Keoke]

Richard, I'm assuming the tractor has a diesel engine and the tach is either mechanical or electrical.
If it is electrical then tach is most likely run off the alternator. Most alternators are three phase units. The tach is a AC frequency meter that converts the AC sine waves coming out of the stator coils into an RPM signal. One rotor revolution equals three voltage peaks. If one, or more, of these phases goes south then the number of AC voltage peaks will drop and accordingly the RPM signal will go down.
A check of alternator for maximum current output under load should determine if this is case.
Also, the alternator will continue to charge enough to put out the charge lamp if just one of the phases goes out so it can't be used as test of alternator preformance.
The other, through rare possibilty, is that the alternator drive belt is slipping causing lower AC frequency numbers.

lots of luck,
george

 

[RichardC]

Thanks for the reply. I had suspected the alternator, but when I called the dealer he said it was probably the circuit board in the dash and wanted to sell me one of those. I'll check alt. output. And yes, it is a diesel.

Thanks,
Richard