Topic: 81 650 charging nightmare

[flash2042]

I've done quite a bit of reading on the awful charging system in my 81 cb650. Mine has issues as well. I had the misfortune of discovering this problem on the road near a local shop, so I limped it to them and had them fix it. A month's time and $550 later, they handed it back to me after replacing the stator and rectifier, and told me the charging system is fixed but my battery won't take a charge. Neither statement was true.

At this point, the rotor is literally the only component of the charging system that has not been replaced. The brush block was cracked and one of the brushes was soldered back together so I replaced them as well, to be safe.  I have battery voltage at both brushes, but only get 0.1v from the stator while the bike is running. After cleaning the rotor off, I get an ohm reading of 2 ohms across the rings.  I've come to understand 4-6 ohms as acceptable range, so I'm assuming this means the rotor has gone bad. I would like to get some input from the experts here before I go throwing more money at it.

[TwoTired]

The rotor windings need to be in 4-7 ohm range.  This measurement is made after noting the meter's own internal and probe lead resistance.  And subtracting that from the reading made at the rotor rings.

FYI a 2 ohm resistance, fed 12 V demands a current of 6 Amps.    Not, sure if a voltage regulator can handle that current on a consistent basis.  So, don't be surprised if your new Regulator is toast.

If your shop won't compensate for their mistake, consider avoiding that shop in the future.

Cheers,

[flash2042]

Rechecked using this method and a second multimeter. Resistance is 0.5 ohms. I'm assuming this means the rotor is bad?

[Bodi]

I would test the meter before deciding that. A typical 100W incandescent house bulb is 9-10 ohms measured cold. 8 Ohm speakers on a meter measure around 6 Ohms.
Few if any affordable meters will measure very low resistance (1 Ohm is very low) accurately.
If your meter is reading relatively accurately then yes, a 0.5 Ohm rotor is NFG.

[TwoTired]

Rechecked using this method and a second multimeter. Resistance is 0.5 ohms. I'm assuming this means the rotor is bad?

As Bodi says, if you have any trust in your meter, it is telling you your rotor is bad and the windings are shorted.

FYI; Using ohm's law, a 0.5 ohm resistance fed 12 V will draw 24 amps or 288 watts from the regulator, where the regulator normally expects to supply, at most, 2 amps or 24 watts.  Hard to imagine it could survive this rotor's high draw.  But, stranger things have happened.  Won't hurt to try it.  But, just have reasonable expectations.
Also, such current would damage wiring and connectors.  So, inspect those, and if ok, be happier the regulator failed to protect those wires/connectors.

You could check for voltage at the regulator output, I suppose.  Just to cross check before paying out money.  With a Battery below 13V-ish engine running and revved, there ought to be near battery voltage applied across the slip rings or at regulator output.

Just more info.  The shorted windings draw power, but can't make a strong magnetic field, if at all.  With a low on no magnetic field the stator can't develop voltage and current.  So, the alternator as a whole consumes way mire power than it can possibly produce.  This drains the battery of course, which you've probably noted.

Cheers,

[flash2042]

TwoTired,

I know the rotor is GETTING power because I've chased voltage all the way to it. I've got power from the battery to the starter solenoid, at the connector prong, down the harness to the regulator input, back out of the regulator, down the stator harness, and finally at both brushes. I'm sure They're leaving fresh scuff marks on clean rings. At this point, I'm assuming what happens from there is the situation that you're describing in the last paragraph. Am I likely correct in my assumption?

[TwoTired]

How much voltage was being applied to the rotor at the slip rings?

But, I think your presented assumption is correct.

Cheers,

[flash2042]

Fully charged battery and then some, maybe 13-13.2 or so. I get 12.1 across the terminals at 4k rpm.

[TwoTired]

I still question if your regulator is still good.  Won't know for sure until you get a good rotor.

The 13 volts is the battery surcharge from the charger.  Won't be maintained with a load on it.  12.1V is likely the loaded voltage, with the battery working hard.

Good that the vreg passes that, though.  Maybe there is hope for it, and you won't have to buy another.

Cheers,

[flash2042]

So, it took a month to get a rotor shipped to me. What a headache! I finally get one to me and get it installed only to find that it doesn't appear to have fixed anything.

I've noticed that a new issue has popped up. With the stator cover off, the brush connected to the black wire gets battery voltage, but the white wire does not. It gets around 1v. When I put the cover on, I can watch the voltage jump from 1.0v to battery voltage. I still get 12.xx across battery terminals while the bike is running at 4000 RPM. Checking the yellow stator wires while above 4000 RPM gives me sporadic readings that jump from 0-50v. Maybe I've just got a BS meter, who knows?

At this point I'm so frustrated that I'm half tempted to just get rid of the damn thing.

[SOHC4 Cafe Racer Fan]

Frustration is understood, but you'll need to grow some more calluses.  Old bikes are well, old.  I replaced a stator in my 750 before I discovered it wasn't the stator but an intermittent short in my wiring harness.  Keep your patience and your head. Get frustrated but come back to it.

[scottly]

With the stator cover off, the brush connected to the black wire gets battery voltage, but the white wire does not. It gets around 1v.

This is correct: the black wire provides 12v to the rotor coil, and the white wire provides a varying connection to ground, where the lower the voltage, the greater the output from the alternator.
When I put the cover on, I can watch the voltage jump from 1.0v to battery voltage.

Where are you measuring the voltage? The jumping voltage may be caused by a intermittent connection on the white wire somewhere between the cover and the regulator. 

[Killer Canary]

Good to hear.
Where did you find a good rotor.

[flash2042]

Evidently the rotor wasn't the problem. Or wasn't the ONLY problem, at least.  I'm to the point where I'm so deep in this that I question my understanding of anything related to the charging system any more.  By following the wiring diagrams I've found, it doesn't seem like the thing is wired to ever charge.  I know it will, obviously, but can't grasp the concept at the moment. Here's what I've got so far:

1. Positive battery lead connects to the solenoid and little fuse block.
2. power travels up to the ignition switch via the solid red wire
3. power goes through the ignition switch with the key turned on and back down via the black wire.
4. into and through the rectifier to the brush block via the black wire
5. through the rotor and back up to the rectifier via the white wire

From here I get confused as I don't really see anywhere else for power to reasonably go. Unless the battery power to the black harness power wire is somehow overpowered by the rectifier output, I'm at a roadblock. I've always understood as a charging system sending charging voltage (13+) to the components and their chassis ground returns power to the battery.  Please someone tell me I'm not crazy.

One other interesting item I've noticed is that the diagram shows two chassis grounds but I only have one eyelet that grounds out at the coil. Input?

[Bodi]

Man! There's a lot going on there... This is probably going to read as pedantic and condescending, it isn't meant to be... I want to be fairly precise as using electrical terms incorrectly causes a huge amount of confusion, and not a small amount of fire.

1. Positive battery lead connects to the solenoid and little fuse block.
Exactly correct. The negative pole has to connect securely to the engine case and the frame as well though!

2. power travels up to the ignition switch via the solid red wire
Well, no... power is voltage and current combined. There's no power until a load draws it. But the wiring description is right.

3. power goes through the ignition switch with the key turned on and back down via the black wire.
The battery "+" voltage is switched to the black wire with the key "ON".

4. into and through the rectifier to the brush block via the black wire
Major confusion! The rectifier does not connect to the rotor! The rectifier only connects to the stator coils, battery positive, and battery negative via ground.
The rotor has two brushes. Put voltage across them and, assuming the rotor is good and the brushes are connecting nicely to the rotor slip-rings, a magnetic field is produced from the power dissipated in the stator coil (power=volts x amps... actually the magnetic field is made only by the amps but in this situation to get the amps you need the volts).
The black wire is just switched battery "+" voltage - there is no direct black wire connection to the rectifier.
Assuming you mean regulator/rectifier, the black does connect to the regulator: it provides the battery voltage reference. (And, to add more confusion,  may indirectly provide controlled rotor power to the rotor through the regulator... but not in the wiring scheme you describe).

5. through the rotor and back up to the rectifier via the white wire
Well. I don't have a wiring diagram - the stator coil can be powered either of two ways:
The rotor gets +12 battery voltage from a black wire, and the regulator (NOT the rectifier!) varies the voltage on the white wire between +12V (no power at all from the alternator) and ground (maximum alternator output) depending on the system/battery voltage: lots of power when the voltage is low, less as it approaches battery float voltage, and none if it gets above float voltage.
The other way, used (I think?) on all the Honda fours up to the DOHC era (not counting the GL, different system altogether) grounds one field coil wire and the regulator controls the other wire between ground (no output) and +12V (max output).
People do use the DOHC regulators on SOHC engines by a simple bit of rewiring, and your bike may have come that way... no wiring diagram here, remember? But regardless, the regulator controls the rotor current on either the power or ground connection.

We get back to your 0.5 Ohm rotor... was that a mistaken measurement? What's your new one?

Measuring voltage is all well and good but it's the amps that matter to the rotor's field coil. Any failed connection on the ground side and you will get battery voltage on both wires. "When I put the cover on, I can watch the voltage jump from 1.0v to battery voltage"... that is either the regulator doing its job or a bad ground connection. I suggest you measure the current through the rotor. If you have no amp meter (it should handle 10ADC), wire a tail light bulb between one of the rotor wires and the wire it should connect to. If the wiring is good with a good regulator the lamp should light pretty bright when the key is turned on.

I don't know if this helps. Electricity isn't magic, current only flows through conductors (or lamps, motors, heaters, rotors) when there's a voltage across their ends. (please nobody get nerdy and bring up magnetic induced current)
Make sure you have a solid ground connection from battery "-". The "eyelet" is, I think, a harness ground point on a small green wire.That's important too, but the battery ground cable is the only current path from the battery to anything electrical.

PS:
I put the GL exclusion in there because without it some stooge would pipe up "The GL is a SOHC4 too, and has a shunt regulator!!" but I disagree, they have TWO CAMS (one on each side) so I say they are DOHC4s (even though a single cam operates both intake and exhaust valves).