over charging battery

18 years ago

Craftsman 42" rider 917 276601 B&S model 441777 type 0283E1

I used my mower to jump start another mower with a dead battery. A few days later, my battery was dead and I bought a new one. After starting my mower, I tested the voltage at running RPM and found that the voltage kept rising. After a few minutes, it reached 15VDC and I killed the mower, fearing it would fry my new battery. Can someone tell me why the voltage keeps rising?

The skematic shows an alternator [#696459] with a diode in the circuit but I cannot find a diode part # on parts list, unless it is inside the wiring. Also, I did not see a voltage regulator. The only other electrical part I saw was the armature-magneto [#691060]. Did I possibly blow the alternator or diode? How do I test them? Thanks.

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Comments (9)

davidandkasie
18 years ago
it is possible, but usually it would blow the fuse. when you use a mower to boost somethign else, hook it up and let it charge the other battery for a bit. then DISCONNECT IT and try to crank the other machine.
don_1_2006
18 years ago
That charging voltage is correct. Let it charge.
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tomplum
18 years ago
DC voltage is ok. The diode is near the end of the pigtail coming from the stator. If you have AC going to the battery, the diode is cooked.
danfut
Original Author
18 years ago
So if I understand correctly don and tomplum, rising voltage is normal as the engine runs. Do you have any idea how high the voltage will rise and what limits it? It probably took 2-3 minutes to reach 15VDC at normal running RPM. Thanks for your comments.
mikie_gw
18 years ago
Car here that I dont drive often enough to keep the battery charged, put a charger on it sometimes when I know I'm going to use it.... when it starts the voltage rises up around 16.5 then as it charges awhile it tapers down to fourteen something.

Fast charger I have puts 20v to it initially then switches to about the same volts mentioned above... full charge it holds it at 13.2v
tomplum
18 years ago
There isn't harm in voltage rising to 15V over a few minute time- unless it continues to rise into oblivion. You will see that to some degree over a matter of seconds at times when testing. You find commonly between 13x and 15 Dc volt at high rpms. Sometimes they creep a bit over 15. These alternators aren't normally high output. Do check for AC feeding into the battery. Batteries don't like AC. AC is a sign of a diode gone bad. If so, you can get the diode kit instead of replacing the whole stator.
bill_in_nc
18 years ago
How do you check for AC feeding into the battery?
wayneinala
18 years ago
I checked the voltage recently on a Murray rider just to see if it was charging the battery and the voltage went to about 16.2 volts before dropping off.
tomplum
18 years ago
How do you check for AC feeding into the battery?

If a the diode has failed, you will pickup ac just by touching your meters terminals to the battery terminals- same as doing an dc test except using the ac scale on your meter. It isn't abnormal to get a small initial reading that then goes away. If danfut has no ac and 15v dc, nothing more needs to be done.