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Discussion Starter · #1 ·
Can't find the answer 1981 CM400C alternator/stator voltage. "Normal Voltage Reading"

My Battery is dead on me.
Before I toss in the new one I wanted to verify the alternator/stator was supplying proper AC output voltage. And I also wanted to verify the Rectifier regulator was supplying proper DC volts as well. Based on the voltage checks this is what I got....

The first connector outside the motor for the alternator: all three phases read 17, 11, and 13 Volts AC at Idle.
With the battery completely removed, I set up my meter and checked DC Volts going to the terminals where the battery would be hooked up at I got 7.5 VDC at idle. And it was approx. 9.25 VDC at 3-4K RPM's.

So here is my question, is the alternator/stator not supplying proper voltage causing my rectifier to put out insufficient charging voltage?

Or is my rectifier receiving proper voltage from the alternator/stator but not providing proper charge voltage?

Or finally am I completely missing something and I should try checking something else?
 

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Welcome to the forum. You're on the right track. Output from the regulator should be about 14.5V. You need the Factory Service ManuaL. PM sent.
See section 15 for test procedure. Appears your generator output is low. Follow the procedures so we know exactly what points you are measuring.
 

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Discussion Starter · #3 ·
I did the voltage regulator/rectifier test and says I should be getting 5-40 Ohms and 2K Ohms minimum with polarities swapped with my meter.
Results show Open in one direction and 265K Ohms the other direction. I think with that I'm just going to order the $20 regulator/rectifier. I shouldn't be getting straight opens in 3 different spots. all my terminals checked out fine.
 

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Discussion Starter · #4 ·
Thanks for hooking me up with the diagrams. I actually had the exact same ones. but wasn't sure if they were any different since mine had CM400T as the title. My bike is a CM400C Custom. Probably no different electrically but you never know.... Thanks again!
 

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Note that factory spec for the charging system is 15V +/-.5V which means you could be charging at 15.5V which is really hard on the battery.
 

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Discussion Starter · #12 ·
Changed out the rectifier and same result. system is charging the battery at around 7.5-9.5 volts.
I did the step like the video linked above and it's not dropping anything that seems questionable, "0.021 volts DC"

How much voltage should be coming off the 3 phases of generator leads from the alternator "yellow wires". I Ohmed them out and everything checked. But my maintenance manual doesn't give me a value for AC Voltage from the generator.

I'm stuck bump starting my motorcycle and would really love to get this fixed.
 

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If the stator is passing the ohm test on the Yellow wires it's good. There is no published spec for AC output since it's not terribly relevant. The ohm test verifies that the circuits are good.
Are you still testing without a battery? If so then the voltage readings are going to be wonky. If the battery is shorted the reading will be wonky also. You can use a car battery to start and test with, be sure it's fully charge first.
The Black wire in the wiring harness which starts at the ignition switch and feeds power to the basic electrical unit also serves as a load sense wire to the regulator. If there's no voltage there the regulator doesn't know what to do.
 
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