Charging Problem: Replaced Rotor and Stator - same issue.

taylorsnider

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I have a charging issue on my 1981 Honda cb750. It is very strange because when the bike was sold to me, there was an issue with the battery charging. Then we scrubbed down some of the ground terminals and it seemed to work well. Over 6 months my friend and I rebuilt the whole bike and after the 6 months it seems there is a charging issue again. I am not getting over 13.5 volts at 3k or 5k rpms. I ended up replacing the stator and rotor thinking that had to be the issue because there was goop in that unit. After putting the new stator and rotor in it still has the exact same issue! Not getting past 13.5 volts.

A few notes on things that I found odd or could be wrong.
1. We rewired the bike so I wonder if there is an issue with one of those connections?
2. The stator fits into the metal side case VERY TIGHT. Had to pry it out and get the new one in very tight squeeze as well. Could this be the issue?

I found a great PDF on these charging systems and how to run tests. Below I copy and pasted it and going to put what each thing tested at. Hopefully someone can help! (Oddly enough, it seems as though the new rotor I bought is testing bad).

1a. Check System Voltage - measure DC voltage at battery terminals w/ motor off key on (~12.5VDC)
ANS: 13.3 = GOOD

1b. Check System Voltage - measure DC voltage at battery terminals @ idle (~12 VDC)
ANS: 13.0 = GOOD

1c. Check System Voltage - measure DC voltage at battery terminals @ 3000RPM (~14.4VDC)
ANS = 13.6 NOT GOOD = PROBLEM

1d. Check System Voltage - measure DC voltage at battery terminals @ 5000RPM (~14.4VDC)
ANS = 13.6 NOT GOOD = PROBLEM

1e. Check System Voltage - measure DC voltage at battery terminals @ 3000RPM with Regulator Bypassed *see 3d for bypassing the regulator explanation and do this measurement at that time.
ANS: When I did this I read it at 13.6 also. So either I did this right and the rotor is only pumping out 13.6 volts at 5k RPMS or I did it wrong.

2. Check for rotor magnetism by dangling a .0015" feeler gauge by the side of the alternator...(yes?)
NOT SURE WHAT THIS IS.

3a. Rotor voltage - measure DC volts between black & white wire on Alt/Stator connector (measure w/ motor off key on, should be close to battery voltage)
ANS: 11.2 (seems weird)

3b. Rotor voltage - measure DC volts between black & white wire on Alt/Stator connector varying DC voltage measure @ idle .
This voltage turns on and off as the motor runs to regulate the output of the charging system by turning on and off the
magnetism from the rotor as needed to keep the battery at 14.4 volts when everything is working right. The meter reading won’t give a
complete picture, as the on and off may happen frequently as the voltage regulation threshold may be crossed frequently.
(Could be as much as battery voltage)
ANS: 11.2 (seems weird)

3c. Rotor voltage - measure DC volts between black and white wire on Alt/Stator connector varying DC voltage* measure @ 3000RPM.
ANS: 13.4 = The same charge my battery is getting. Very weird.

3d. Rotor voltage with Regulator Bypassed - measure DC volts between black and white wire on Alt/Stator connector. @ idle
How to Bypass the Regulator - However, before bypassing the regulator, make sure the field coil (rotor) isn't shorted. (You already did that, right? )
Leave the alternator connector coupled, and insert an unwound large paper clip into the connector at the WHITE wire location. Run a jumper wire from the paper clip to the battery's NEGATIVE terminal. Now repeat the charge amps test, but this time, DO NOT EXCEED 3000 RPM, the voltage could go dangerously high. Also do not let it run long like this. - If the alternator starts charging, the regulator is likely the problem. This effectively bypasses the regulator and makes the charging system produce full unregulated output. If everything but the regulator is working the voltage could go quite high, so don’t rev too high, and don’t do it for long.
ANS: 13.4

4. Stator voltage - measure AC volts between any yellow to any yellow wires on Alt/Stator connector (~8 to 15 VAC)
ANS: 10 = GOOD

5. Check rectifier - out measure DC volts - red/wht wire to green wire on small r/r connector (≥14.4VDC same as battery)
ANS: 15 at 3k RPMS. This is what I should be getting our of the battery! This is the one charging spot that is right.

6. Check regulator - reference/rotor supply - measure DC volts at black wire to green wire on small r/r connector (14.4VDC)
ANS: 13.6 NOT A GOOD CHARGE.

7. Check r/r ground conductance quality - measure DC volts (voltage drop) - green wire on small r/r connector to battery negative terminal (~0 VDC)
ANS = .03 = good

8. Check rectifier out feed conductance quality - measure DC volts (voltage drop) - red/wht wire on small r/r connector to battery positive terminal. (~0 VDC)
ANS = .00 = good

8a. Check sense wire (black wire) feed conductance quality - measure DC volts (voltage drop) – black wire on small r/r connector to battery positive terminal. (~0 VDC)
ANS: .23 (seems high)


Thank you so much in advance for all your help!
 

Rampton

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Test rotor again between copper ring and black ring should be 4.6 ohms I had a good reading when stood but failed whilst running on the 2nd hand rotor I bought. I ended up buying a brand new! rotor off flea bay in the end £100. Hope this helps good luck
 
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