I have a twin opposed cylinder Briggs engine 402437-0666-01. It has a dual lead from the alternator that goes to a regulator/rectifier that outputs dc voltage.

I have been having trouble keeping the battery charged. Measured voltage at the battery is only 12.75 volts.

My testing problem is that when I put the multimeter leads on the output leads of the the alternator measuring ac volts, it jumps from 15 or so volts to 4 or 5 volts, as if it was making the correct current one minute then much less the next.

Is this a sign of a bad alternator, a short or ?

any help appreciated

 

Check this parts schematic and look for #877 or #877A or #877B on page 7. Corresponding wire harness connectors are pictured also.
If you have 877 or 877B there is a possibility of open diode. This will prevent it from charging.
If you were checking with a digital meter you may need to set it for DC if you have a type that uses diodes.

http://bsintek.basco.com/BriggsDocum...quIVJ1DajI.pdf

Happy hunting. There will be others along with their suggestions shortly.

RR

 

RRooster, thanks for the info. My system does not use a diode between the alternator and the regulator/rectifier. Two black leads produce AC voltage that feeds to the regulator. The Briggs test procedure says to turn the multimeter to V (AC) and connect the red lead to one of the alt. black wires and the com mult. meter lead to the other alt. lead. at 3600 rpm it should read at least 20 amps. mine reads less, so that would diagnose a bad wire/short or bad alternator. my concern was that the output seemed to vary so much......and the test procedure didn't mention that.

probably I will just pull the engine from the tractor and inspect the alternator itself for bad wire and if nothing found, I will replace it.

 

Did you mean 20vac. ? Current can only be measured in series with a load.
It sounds like you have a wire opening up in the circuit. It could be where the wire connects to the alternator winding or in the windings itself.

 

Check from each wire to ground, not from one wire to the other. You should get over 20 volts ac with the engine at full throttle on both wires.

 

thanks for the feed back fellas: Cheese, I tried the test the way you suggested, but got nothing. further investigation found a bad wire-to-connector situation. I had to pull the engine from my tractor to access the flywheel. rather than trying to re-use the old alternator, with wires that appear pretty fried in general, I am just going to replace it.

Pjax, yes, I meant volts.

thanks again for the help!