Alternator output Briggs 16hp twin


Old 03-21-14, 03:51 PM
Thread Starter
Join Date: Dec 2008
Location: Washington PA
Posts: 178
Alternator output Briggs 16hp twin

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
Sponsored Links
Old 03-21-14, 04:56 PM
Rough Rooster's Avatar
Join Date: Feb 2014
Location: USA
Posts: 381
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.

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

Old 03-21-14, 06:31 PM
Thread Starter
Join Date: Dec 2008
Location: Washington PA
Posts: 178
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.
Old 03-21-14, 06:43 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 45,170
at 3600 rpm it should read at least 20 amps.
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.
Old 03-21-14, 08:36 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,822
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.
Old 03-31-14, 06:52 PM
Thread Starter
Join Date: Dec 2008
Location: Washington PA
Posts: 178
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!

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes