Topic: 1981 CB650 Charging Problems

[ponchoboy]

Hello all,

I recently purchased a 1981 Honda CB650 Custom with 11K miles on it, and discovered that the bike has a charging problem.
I have been through the wonderful fault-finding diagram I found on this site, and came up with the following results:

• Voltage at the battery with the bike off is 12.5 volts or higher.
• Voltage at the battery with the bike running is around 11.75 volts.
• The regulator/rectifier seems to check out.  Also tried a spare NOS reg/rect.
• The resistance between the brushes seems to be OK (between 4 and 6 ohms).
• With the bike running, the rotor/stator are putting out around 45 VAC around 5K RPM, and around 50 VAC around 6K RPM.  Does this seem low?  The fault-finding diagram said it should be at 50 VAC or above at 5K RPM.
• The resistance between the slipping rings on the rotor seem to be at around 15-20 ohms.  This is definately high.  Should be between 3.6 and 6 ohms according to the fault-finding diagram.

From my judgement, I would guess the rotor is at fault here.  Are there any other things I should check before getting a new rotor?  Thanks in advance for the help!

 - Kurt

[Pinhead]

If you've got 45-50vac out of the stator, your alternator is working. You've either got a regulator/rectifier problem or a wiring problem. You may be getting a high reading on your rotor if the rings are dirty. Clean the contacts off to get a good reading. Since you've got around 6 ohms at the wiring harness, I wouldn't really worry about it. Especially since you're getting +45vac out of the stator. Since you're tried a new R/R, I'm leaning towards a wiring problem.

[Ibsen]

I can't find that the workshop manual for the 650 have anything listed about the ACV output reading, but it does list how to measure the stator windings:

LINK

[ponchoboy]

OK the bike still isn't charging, but here is the latest after running through some tests again:

• The resistance between each of the yellow wires on the stator is around 4 ohms at the wiring harness plug.  Is this too high?  The link you just gave me said it should be like 0.4 ohms.
• Despite that high resistance, the "alternator" system is still putting out 45 to 50 VAC when the brushes are jumped directly to the battery.  This leads me to believe that the rotor and stator are both good, and the wiring to and from them is good.  The windings show good connectivity with no apparent shorts or open circuits.
• With the brushes and rotor jumped directly to the battery, and the stator output connected to the R/R, the voltage at the battery only goes up to 11.75 volts or so.  It starts out at around 10.5 volts at low RPM, then increases with the engine RPMs, but does not continue to go up past 11.75 volts.
• If faulty wiring is the culprit, where do I start to look?  Are there any likely places to be bad?  I have already removed the main ground wire and cleaned that connection, anything else?  There seem to be a number of unused wires behind the headlight, but I assume that is normal?  Also, there is one disconnected ground wire located near the turn signal relay, but it looks like it has a solid ground from elsewhere, and there is no place to connect it.  The connector on the main fuse/start solenoid seems to have a little corrosion, but the actual main wire to the battery seems clean.

That's about it for now.  I really would like to get this bike on the road, but this charging system has me pulling my hair out.  I will update if I come across anything new.

Thanks again for all the help so far.
 - Kurt

[Jimmy V]

double check your rotor these have be none the go bad on these bikes i would say thay it would be the root of most(evil) of this kinda trouble and you dont loose as much hair 

[ponchoboy]

The rotor seems to be fine... powering the rotor directly from the battery (supplying 12 volts directly) gives good results on each of the three yellow wires (~50 VAC).
The stator seems fine too, from the previous test there is good power out of it.  No short to ground and good connectivity through the windings.
The regulator also seems fine after testing it.

I think the next step is going over all the connections on the bike.  All of my continuity/voltage tests have been performed with the key in the off position (except of course for those with the bike running).  I have been testing a few connections with the key on now.  Nothing weird to report yet, but I will definately go over all connections on the bike.  Everything seems to test out fine in isolation, so we will see if greasing up the connections helps.

If anyone else has any other thoughts, please let me know!

Thanks,
Kurt

[JSGAuto]

Kurt,

This sounds like a rotor problem.  The stator tests sound close enough.  And the regulator sounds good as well.  Have you tried cleaning the slip rings and getting another reading?  That reading is way to high.  I have seen working ones around 5/6 Ohms, but thats about it.  The "sweet spot" is 3.6-4.4. 

I have a lot of experiance with this electrical system, I am sure we can work through the problem. 

Let us know,
Jim

[ponchoboy]

I think I can chalk the high resistance readings up to a screwy meter, and trouble getting good contact with the slip rings.

I've tested the voltage at the brushes with the key on and the R/R in place.  They are getting around 10.7 volts with a battery that is showing around 12.25 volts (with the key off).  I've also tested this voltage through the field winding on the rotor and I get the same reading, 10.7 volts.  That is, I hook the one lead to a brush, and then connect the field winding in series with the other brush and the other test lead.  I would think if there is substantial resistance in the rotor, I wouldn't be getting the full voltage at the meter.

The rotor/stator seem to be outputting fine with external excitation hooking the battery directly to the brushes, as I mentioned before too.

My conclusion so far has been that everything seems to work fine in isolation.  When the components are combined into the wiring of the bike is when things seem to go awry.  Thanks for the help so far Jim, I definately appreciate it!

Thanks,
Kurt

[JSGAuto]

Hi Kurt,

What is the battery voltage when the bike is running at 5K rpm? 


Always happy to help! 
Jim

[JSGAuto]

Oops,
Just saw that you posted that it tops out at 11.75. 

I am willing to bet that this is a rotor problem.  Typically the rotor staticaly tests good then pulls apart at RPM.  This is the most common problem on the DOHC bikes (same charging system).  THe only way to really dynaimicaly test it is on a working system.  If you are willing to pay shipping both ways I will test the rotor on my bike for you, which has a good system. 

Jim
(fyi, my ebay name is granitzki11, I have 100% feedback, just trying to make you more comfortable if you want me to test it.)

[ponchoboy]

Hello all,

Jim, I really appreciate your willingness to help, but can you explain your reasoning for determining this is a rotor problem?  I've tested the rotor and stator in isolation from the bike, and I get ~50 VAC on all three wires.

I've started looking at the R/R and the inputs and outputs of it.  On the three block connector going to the R/R, there is one black wire, one red and white, and one green.  Green is ground and red is positive from the main fuse direct to the battery.  The black wire runs up through the ignition switch, and back to the main fuse.

So, with the ignition switch on, the black wire and red/white wires are both positive from the battery.  I tried jumping the black and red/white wires from the R/R directly together and connecting them to the main fuse.  This was to eliminate the wiring with regards to the ignition switch.  I also jumped the green wire to a solid frame ground to eliminate any goofiness there.  Then I ran the bike and the results were about the same, but maybe slightly higher... about 11.8 to 11.9 volts at 5-6K RPM.

To me, that test seems like it should have excersized the charging system in almost total isolation (not quite since I jumped back through the main fuse to the battery).  Should I try running a wire directly to the battery (with an inline fuse for safety)?

On another note, I tried something else...

I left all three wires (red/white, green, and black) disconnected from the R/R.  Then I tested the voltage across the red/white and green wires on the R/R.  This was less than 1 volt (since the rotor was not energized).  Then I connected the green wire to ground, and the black wire to positive through the main fuse.  The voltage across the red/white and green wires started at 11.5 at idle, and then kept going up as the bike revved.  At about 4K RPM it was over 25 volts.  What can be made of that?  I'm not exactly sure of the internal wiring of the R/R so I am not quite sure what the results of that should be.  Does anyone have a circuit diagram of the internals of the R/R on these bikes?

OK that's all that's new for now, sorry for the long post... I hope you read through all of it.

Thanks again!
Kurt

[Pinhead]

Check the link in my sig.

[wpmb]

Hello


 I have a 1981 cb650 and wanted to know does the black wire for the ingnition  go to the i terminal on the voltage regulator. Is the black wire on the connector that has the green and red white the one to the ignition.

[TwoTired]

The resistance between the slipping rings on the rotor seem to be at around 15-20 ohms.  This is definitely high.  Should be between 3.6 and 6 ohms according to the fault-finding diagram.

Either your rotor is bad, your slip rings are dirty or your meter or meter technique is faulty.

The resistance between each of the yellow wires on the stator is around 4 ohms at the wiring harness plug.  Is this too high? 

Either your stator is bad or your meter or meter technique is faulty.

I think I can chalk the high resistance readings up to a screwy meter, and trouble getting good contact with the slip rings.

Okay. Where does that leave you?  It leaves us with questionable data.

Maybe this will help.
Testing the alternator proper.
The alternator provides power relative to the strength of its magnetic field and the rpm it is spinning.
The strength of the magnetic field is relative to the voltage applied to it.  (Routed through the VREG.)

Knowing this:
What is the voltage being delivered to the field coil?
Is this any different than what the battery voltage is?
Are the slip rings allowing full delivery of voltage to the field coil?

Assuming you are getting full battery power to the field coil (rotor)...
Check if all phases of the stator output are being rectified.
With the rectifier removed, check rectifier resistance between each yellow wire and the red wire.  Reverse meter lead polarity and test again.
Now check each yellow wire to the Green wire, reverse meter lead polarity and test again. 
You should now have 12 test results.  Half will be very high readings and half will be very low readings.  If your meter is digital, be sure to use the scale that has the -|>- symbol.
A failed rectifier diode will not pass alternator power to the battery.

Seems to me if the above truly checks out you should be good to go.  However, if the bike wiring to the Vreg, both power and return paths, is not reflecting true battery voltage, the alternator can't do it's job.  Also, if the two paths from the rectifier to the battery has connectivity flaws, then the battery can't receive the power being made at the alternator.

Cheers,

[wpmb]

what would cause the fiield voltage to be low

[TwoTired]

what would cause the field voltage to be low

-Low battery.
-Connectivity issues (resistance/corrosion) between it and either battery terminal.
-Connectivity issues (resistance/corrosion) between the Voltage Regulator and either battery terminal.
-Faulty Voltage regulator.
-If the field coil resistance is seriously low (nearly shorted), this could drag down the voltage, particularly if there was resistance in the connections to the power source.

Other lesser known causes:
-Recent visitations by Murphy.
-Failure to pay proper homage to the tron god. 
(You have slaughtered a goat and placed the entrails on the bike at moonrise, haven't you?)

Cheers,