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R75/5 Alternator / Voltage regulator
- cbclemmens
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R75/5 Alternator / Voltage regulator
Craig
- schrader7032
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Re: R75/5 Alternator / Voltage regulator
First initial test, is to start the bike and use a voltmeter across the battery terminals. What does it read at idle? And more importantly, what does it read at say 3000 RPM. At this high RPM, you should be seeing well north of 13.5 vdc and actually better if you saw 14 vdc.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
- srankin
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Re: R75/5 Alternator / Voltage regulator
That said, you get a voltage at the battery the way Kurt explained. At 3K RPM, you should be seeing DC voltage between 13.5 to 14.5. If you are not seeing this, you can pull the plug off of the voltage regulator and bridge the plug at the blue and I believe the black wire. At this point if your voltage goes up, it will read higher than or around perhaps 20 Volts DC. If it remains lower than that or less than 13.5 to 14.5 at 3K RPM, the problem is in the alternator. St.
- cbclemmens
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Re: R75/5 Alternator / Voltage regulator
Craig
- srankin
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Re: R75/5 Alternator / Voltage regulator
None of the troubleshooting information I have seen has ever given a voltage at the brushes. So I know nothing about if 2VAC is good or not? The only time any trouble shooting is done at the brushes has to do with the contact of the brushes to the slip ring on the rotor, Rotors are know to fail internally and open up, meaning they will show open on a continuity check with a meter. You can check this by pulling the two spade connectors at the brushes and measuring continuity from the terminals bromone brush to the other. This not only shows a closed or open circuit in the rotor but could show a bad brush connection to the slip ring. Usually this brush thing is a visual inspection for excessive wear on the brushes. You don't mention how many miles are on the bike?
Like I said, bypassing the voltage regulator should give you full output of the alternator at 3K RPM, this should be about 20VDC. If you don't have that, then look at the brushes, check the rotor for continuity, check the stator windings for continuity, and if all that looks good, then check the diode board. If you think you are getting AC current at the battery, then check the diode board.
If you have 20 or so VDC when the regulator is bypassed, then the problem is the regulator, put a new one in. Am I making sense? If you don't understand, I would suggest finding a Clymer manual or better yet Rick Jones's book on airhead charging trouble shooting. Perhaps Snowbum has a trouble shooting guide? If you are nearby Rochester NY, feel free to stop by and I will help you out. St.
- schrader7032
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Re: R75/5 Alternator / Voltage regulator
https://bmwmotorcycletech.info/trbleshootALT.htm
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
- srankin
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Re: R75/5 Alternator / Voltage regulator
This can be checked without removing the front cover, it takes just a few minutes to do. The rest of Snowbum's article is worth the read if you need to go further in testing.
If you are lucky, it will be the regulator and you won't have to mess with taking the cover off and dealing with further troubleshooting. Not that taking the cover off or doing any repairs to the charging system are all that hard to do. But personally I would rather keep things simple and not do anymore work than has to be done. I would rather be riding than working on a bike. Let me know what voltage you get when the regulator is bypassed. St.
- cbclemmens
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Re: R75/5 Alternator / Voltage regulator
To answer your questions; The bike has 40K miles on it, I have a Haynes repair manual (2 actually, but they are duplicates.), I show 190 ohms through the armature winding (brush to brush) (I think that's probably normal), and 2 ohms from the brush terminal to the slip ring. (I think good).
The alternator AC output should be about double the DC voltage because to make DC from AC, the diode block takes the negative swing of the AC, inverts it and adds it back to the positive swing, so I would expect to see about 30 VAC at the brushes.
I will check bypassing the regulator, but I will have to put the tank back on to do that.
So Thanks for your advise and comments. It really helps even when it just confirms what I was thinking.
craig
- srankin
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Re: R75/5 Alternator / Voltage regulator
I appreciate the lesson you post in regard to the double voltage, and stuff. Like I said, I have never used the voltage at the brush method. In all my years, if there is continuity throughout the brushes, slip ring and rotor, that system is OK. Same goes for continuity in the stator loops.
The biggest problems with airheads I have experienced have been open rotor, bad voltage regulator, or bad diode board. BMW had a lot of problems with a few years of diode boards but cleared it up. Some of the aftermarket boards are better than the OM. So diode board problems have taken a back seat to rotor and V reg. LOL, even the rotor situation has improved so now, the v regs are the number one problem I see or dead battery.
Thanks for letting all of us know the outcome and such. St.
- schrader7032
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Re: R75/5 Alternator / Voltage regulator
Most people don't think about AC and making measurements. It's really all about DC measurements at the battery and if that's not correct, then working backwards. As ST says, bypassing the regulator with engine running helps eliminate one side of the system.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.