Voltage

[SKYLER53]

I have a MF 135 with perkins gas and alternator. The battery reads 12.5 volts across when not running. When it is running it reads 12.25 volts
across the battery and from alternator. Is this enough to keep the battery charged? Is the voltage regulator bad? Thanks for any input

 

[old]

12.5 volts is a bit low on a full charged 12 volt battery. As for it being 12.25 when running that say the alternator is not charging like it should be. Time to pull it off and take it to an auto parts tore and have it checked to see what is wrong with it. Could be the VR or it could be brushes but one cannot know till it is tested

 

[rockepg]

Agreed. 12.7-12.8 is a fully charged reading. Normal charge range is 13.8 to 14.6. That is what you should see coming out of the alternator.
Is the alternator you have internally or externally regulated? If it's internally regulated is it a one or three wire unit? If it's a one wire job then it's self excited and if you are only getting 12.25 out of it then something is definitly wrong. If it's a three wire job make sure you have a 12 volt reading at the main lug and the field wire connector with the key on but engine off. If the sense wire is not getting 12v reading of some kind for whatever reason it will also not kick on the regulator and appear to be bad.

 

[ptfarmer]

rockepg is correct, it is not putting out enough voltage, you should see something in the 14 volt range when the engine is running.

 

[SKYLER53]

It has two wires connected. External voltage regulator. It is a 1965 MF 135 with Perkins gas engine. Any suggestions on how to trouble shoot it? Thanks