80 hp mercury 79'

sramelyk

Seaman
Joined
May 26, 2003
Messages
53
This motor has never charged the battery since I've owned it. At some point I believe I tested and deemed the rectifier bad.. Just got a new one.. How can I be sure the charging system is working?
 

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: 80 hp mercury 79'

Check battery voltage at idle and then raise the fast idle lever to bring rpm up 200-300 rpm. Note don't rev the motor above 1500 rpm in neutral, it's bad for the innards.

The voltmeter should show a rise in voltage when you raise idle speed. If you leave the motor at fast idle, voltage should continue to rise ever-so-slowly as the alternator continues to charge the battery.

If the voltage stays steady as a rock (or even goes down) regardless of engine speed, the system is not charging. If you find this to be the case even with a new rectifier, likely the stator has a problem.

Disconnect the (2) yellow stator wires from the rectifier and, with a test meter on the lowest ohms scale, check stator resistance. If it's infinite (no response) the stator is open. A good stator will have a pretty low resistance reading.

If you move the flywheel a bit by hand (make sure the ign is off and plug wires pulled!), you'll see the meter reading change, this is also a good indication that the stator is generating some sort of small voltage as you move the flywheel.

You could also check voltage output in the water, at speed, if you clip your meter leads securely to the battery and can place the meter where it's readable. If battery voltage is getting up into the 13.5 volt range or better, you've got a winner.

If you don't have a VOM or other type of test voltmeter, Sears usually has a sale on them. I'd expect their annual Memorial Day sale will include some kind of deal. Even the $9.99-on-sale meter is plenty good for checking basic volts and ohms.

Note that if you do have a tachometer, the fact that the tach works is also a good indication of the charging system's health. A bad rectifier/stator won't run a tach.

HTH...........ed
 
Last edited:
Top