Topic: Charging Problems '81 CB650

[mplastow]

Battery lasts 35 miles or so, since it's not being charged.  Have already replaced alternator brushes and voltage regulator.
Test of OHMs on 3 yellow leads from stator read 0.7 OHM each.    Alternate Current test of all 3 leads gives no voltage reading when engine is idling, and gives readings of 0.3V when engine RPMs reach 5000.   Should I replace Stator or Rotor first?  Obviously, I'm trying to not replace and spend $ on something that is OK.  I will appreciate any advice     

[oldbiker]

I hope you were taking your voltage reading between pairs of yellow leads and NOT between each yellow lead and earth!  You should measure up to 50v ac between pairs but will get virtually nothing unless the field coil is energised. Your next step should logically be to see that your field coil is continuous. Its resistance should be  4 to 5 ohms. then see that there is voltage applied to this coil when the ignition is switched on and if possible measure the current flowing through this coil. This should be up to about 2.5 amps at low revs falling off as revs rise and the regulator takes over.

[Robert]

Yup, as oldbiker said. You should have about 5 Ohms between the two concentric copper slideways of the rotor.

Rotor is the weakest part of the CB650 charging system, most propably you'll have no continuity between the slideways -> if so replace rotor.

[mplastow]

Voltage readings were taken between pairs of yellow leads.   I will check continuity on rotor points tonight and will let you know my results.     I am assuming that when you refer to the "field coil" you mean the coil inside the rotor?  Thanks!

[Robert]

I am assuming that when you refer to the "field coil" you mean the coil inside the rotor?

Propably a refering to the older SOHC machines where the charging system works slightly different and consists of field coil, stator and rotor (and regulator rectifier).

The CB650 SOHC only has stator and rotor (and regulator rectifier)..

The CB650 rotor holds a coil in it, technically an exciter coil (sp?, sorry I'm not so firm in translating tech terms). The respective ends of this coil are connected to the respective round copper slideways of the rotor, and this coil should have a DC resistance of 5 ohms.

If you need to get the rotor off, which wouldn't surprise me too much, you may want to take a look at my humble photostory
http://www.sohc4.us/forums/index.php?topic=1973.0

[SCJIM]

hey mplastow

i replaced my rotor with a rebuild.

i found a guy in AL "Tim Parott Enterprizes" tim@tpe-usa.com

all this guy does, is rebuild rotors & stators

im sure he could help you.

good luck

[mplastow]

Jim, Robert, Oldbiker,
Thank you all for your help.   I measured 1.7Ohm on the concentric contracts of the slideways, then planned to measure current with engine running, but unfortunately didn't realize I had to hold firm an oil plug located under the rotor!  Anyone know why there's an oil exhaust plug in the alternator case?  In any case, I've ordered a rebuilt rotor from Tim Parrott.  I'll let you all know what comes of the rotor replacement.
Thanks again,

[Robert]

I measured 1.7Ohm on the concentric contracts of the slideways

Yup that's by far to little, the insulation of the rotor coil's magnet wires is broken.

That tricky oil plug got me by surprise more than once  I don't know why it is designed the way it is, maybe it has the function of an overpressure relief valve    I don't know. Or maybe the sense behind it is to prevent one from running the motor with the alternator cover/stator off  , unfortunately that hasn't worked always in my case...

[bryanj]

Thay plug is there all the way through from the first 500 four and simply it bungs up a machining hole where the main oil gallery is bored

[Robert]

>>>Thay plug is there all the way through from the first 500 four and simply it bungs up a machining hole where the main oil gallery is bored

That still doesn't explain to me why they didn't go for a threaded plug as used on all other oil galleries...

[mplastow]

Got the rotor rebuild from Tim Parott.  Looks like he does good work.  Ohms test out at 4.5 on rebuilt rotor...so far so good.  I used a rubber strap wrench and a 5 ft. bar to get enough torque to get the bolt off the rotor.   Tim Parott loaned me a puller to then get the rotor freed from the taper.   Worked well.    Unfortunately........new testing of charging system reveals no improvement. 

I now have new rotor, new regulator, all wiring checked (supposedly), new alternator brushes....but voltage reading off battery terminals with engine running is still a measly 12.0V regardless of RPM.   

2 non-yellow wires coming from alternator are testing at same Ohm (4.5) as rotor, indicating good connection from wire harness, from alternator brushes.   

I have not gone out and run the bike 30 miles again to see if charge is perhaps taking place in spite of low voltage reading, but I believe voltage should be up in the 13.5V range with good charging.

Electrex diagram indiacates faulty stator now, since I'm getting no alternate voltage reading from yellow wires.  (not even 1V).   Yet stator looks fine-

I'm starting to give up...but have ordered a rebuilt stator.   After that, if it's not charging, I'm afraid it's going to the shop. 

[Pinhead]

If the voltage doesn't go above 12v it's not charging.

I'm in the same situation as you are, only on my '79 CB650. Measured 0.3Vac between the three yellow wires, low resistance between the copper slide plates, battery not charging.

If I start the engine and then test the resistance of the two "non-yellow" (black/white) wires, the resistance goes up to around the 6 ohm level where it's supposed to be. Without the engine running, the resistance is .6 ohms.

You've already replaced everything but the stator. Might as well change that out. That's the first thing the shop will do, so might as well save yourself some money.

If you've still got your old rotor and replacing the stator fixes the problem, put the old one back in, and let us know if it charges or not. If it does, I won't spend the money on the thing, will just get a new stator. I'm curious if the engine is supposed to be running to read the resistance across the rotor...

[Pinhead]

This is what I've done so far to try to pinpoint my problem. Maybe it'll help you a bit.

I disconnected the "two other wires" in the block connector going from the RR to the stator and started the engine. I then hooked the two wires to a 12vdc PSU (separate from the bike's electrical system) and checked the battery voltage. It was charging! However, I tried hooking the two wires (they're the brush wires) to the battery and the battery voltage dropped... It could've been my battery, too, though because it was discharged from me cranking the engine over working on another problem.

Since the charging system works with voltage directly applied to the brushes, would I be correct to assume that the RR is bad? There is no voltage across the two wires (coming from the RR) otherwise.

Since you've got a new RR I would assume bad wiring somewhere.

Also, the two wires that I hooked up got really hot, hot enough to make the insulation sqishy and soft. This would probably be due to the low resistance between the rotor's copper slide plates. With the engine running, it's a little over 6 ohms... But with the engine shut off, it's less than 1 ohm. Would this mean I have to replace the rotor as well? Since you just replaced your rotor, this would be a good experiment to make sure everything down low is working correctly.

[TwoTired]

Pinhead,
 (I don't feel comfortable calling you that, BTW).

I don't have a 650 or any data at hand for one, but I do know something about things electrical.

I'll try to help.  Feel free to ignore me if you wish.

I'd like to address your changing resistance on the brush wires.
The slip rings/brushes connect power to a field coil that creates a rotating electromagnet.  I can think of two causes for your resistance measurement changes.  One is that there is possible residual magnetism in your alternator that allows it to generate a very small voltage when it is spun.  Since your ohm meter functions by inserting a very small voltage into the circuit it is testing, any additional voltage generated from within the circuit will give false reading on the instrument.
Two, the slip rings don't make perfect contact with the brushes and the brushes tend to fly away from the slip rings for very brief periods of time, this would add resistance to your measurements, but would average something higher than a true resistance reading of the Field coil.

I feel your 1 ohm measurement at rest is the correct reading and indicates a faulty Field coil.

Using ohm's law, your 1 ohm field coil is drawing 12 amps through your auxiliary wires. You'll be needing 12 or 10 gauge wire to keep them from heating.  And that amount of current probably took out the R/R, too.  If I remember correctly, your Field coil should be 5 or 6 ohms. and draw only 2 or 2.5 amps maximum.

At this point I would guess you will need to replace both your R/R and the rotor on your bike.

Hope this helps,

[Pinhead]

Pinhead,
 (I don't feel comfortable calling you that, BTW).

I don't have a 650 or any data at hand for one, but I do know something about things electrical.

I'll try to help.  Feel free to ignore me if you wish.

I'd like to address your changing resistance on the brush wires.
The slip rings/brushes connect power to a field coil that creates a rotating electromagnet.  I can think of two causes for your resistance measurement changes.  One is that there is possible residual magnetism in your alternator that allows it to generate a very small voltage when it is spun.  Since your ohm meter functions by inserting a very small voltage into the circuit it is testing, any additional voltage generated from within the circuit will give false reading on the instrument.
Two, the slip rings don't make perfect contact with the brushes and the brushes tend to fly away from the slip rings for very brief periods of time, this would add resistance to your measurements, but would average something higher than a true resistance reading of the Field coil.

I feel your 1 ohm measurement at rest is the correct reading and indicates a faulty Field coil.

Using ohm's law, your 1 ohm field coil is drawing 12 amps through your auxiliary wires. You'll be needing 12 or 10 gauge wire to keep them from heating.  And that amount of current probably took out the R/R, too.  If I remember correctly, your Field coil should be 5 or 6 ohms. and draw only 2 or 2.5 amps maximum.

At this point I would guess you will need to replace both your R/R and the rotor on your bike.

Hope this helps,

I don't want to hijack mplastow's thread, but we have such similar problems that I thought maybe we could help eachother out. I think you're right. I'll have to replace them both.

If you haven't already, look here:

http://www.electrosport.com/Images/fault_finding.pdf

It's an excellent diagram walking you through a step-by-step process of testing your motorcycle charging system.

Where can I find the "cheapest" rotor and/or RR? The best I've been able to find is almost $300 for a rotor and about $200 for a RR. I might as well sell the bike for those prices...