# Mahindra 450 electrical problem



## wbeau0408 (Mar 25, 2017)

Question related to generator output on Mahindra 450. According to the manual I should read upward of 16 volts at the generator D and F terminals. With the tractor at idle I get around 14 volts at both terminals. When I raise the RPM to operating speed the voltage on terminal F drops to around 4 volts. Can anyone tell me what the proper readings should be and why the voltage on the F terminal falls so much?


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## sixbales (May 18, 2011)

Howdy wbeau0408, welcome to the tractor forum.

A 12V battery is actually about 12.6V when fully charged. To charge the battery your generator output voltage must exceed the battery voltage to enable current flow to the battery. I think 14V should be fine for charging. As your rpm increases, the generator output voltage increases, causing the regulator to reduce the field voltage to control the armature/output voltage.


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## RC Wells (Dec 26, 2008)

When the voltage drops at operating RPM it usually means the bridge rectifiers are failing inside the alternator.

If it is generator, the field coils are breaking down.


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## wbeau0408 (Mar 25, 2017)

Thanks for the information. I have a follow up question. If I read the voltage at the battery with the tractor running should I see the 14 volts? Now it only reads 12 volts.


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## wbeau0408 (Mar 25, 2017)

Additionally I have to jump the tractor off every morning after it sets overnight. I have replaced the battery already.


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## sixbales (May 18, 2011)

With the engine running, it should read 14 volts. With the engine off, it should read 12 volts. If the battery runs down overnight, you have either a bad battery (which you say is new) or a short circuit somewhere in your system. The regulator is supposed to open the generator circuit when the engine is switched off, otherwise the generator can drain the battery. Maybe a bad regulator? You may be able to have your generator tested at an auto parts store.


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## wbeau0408 (Mar 25, 2017)

So if " The regulator is supposed to open the generator circuit when the engine is switched off" with the engine not running I should not be able to read voltage at the generator with the engine not running if the regulator is working correctly?


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## sixbales (May 18, 2011)

Correct.


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## wbeau0408 (Mar 25, 2017)

Ok thanks.


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## HarveyW (Sep 15, 2014)

You can check the generator by disconnecting the belt, and hooking up 12V power to both the field and armature terminals. It should run as a motor. If it runs as a motor, it should generate power to charge your battery.


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## wbeau0408 (Mar 25, 2017)

HarveyW said:


> You can check the generator by disconnecting the belt, and hooking up 12V power to both the field and armature terminals. It should run as a motor. If it runs as a motor, it should generate power to charge your battery.


Thanks for the info I'll give it a try.


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## wbeau0408 (Mar 25, 2017)

wbeau0408 said:


> Question related to generator output on Mahindra 450. According to the manual I should read upward of 16 volts at the generator D and F terminals. With the tractor at idle I get around 14 volts at both terminals. When I raise the RPM to operating speed the voltage on terminal F drops to around 4 volts. Can anyone tell me what the proper readings should be and why the voltage on the F terminal falls so much?


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## wbeau0408 (Mar 25, 2017)

So after extensive testing I decided to convert the tractor to a alternator. Since converting the tractor has not failed to start and keep a charge.


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