charging system fault finding

[pdx_r100s]

Also, re: the question about the electronic ignition that I accidentally hooked back up to the condenser above the alternator. I just checked, and it is a Dyna III ignition. I only ran it for 20-30 seconds this way.

[Rob Frankham]

Different people have different ways of doing things. I'll not junk Snowbums tests, I just don't like them and don't necessarily accept the diagnosis.

In your place, I would certainly replace the brushes in any case. They are clearly worn and replacing them will be good even if it doesn't solve the problem. I'd also look quite critically at the brush box for wear.

By all means do the 'regulator' test. This will tell you once and for all whether the fault lies with the regulator. If the fault goes away, it's the regulator, if it doesn't, it's brushes or rotor.

To clean the brushes and the commutator, use fine emery cloth. For the rubbing face of the brushes put the emery between the commutator and the brushes then pull it out a few times. Polish the commutator by running a 'ribbon' of cloth back and forth round the copper services. don't oberdo either.

Your rotor clearly isn't open circuit because if it was, you wouldn't get any charge light at all, ever. If it is short circuit, you would get a light all of the time (and no charge). A partial short would give you reduced charging and the lamp would be late going out. The only other common fault is a dynamic open circuit where the wire is broken but making contact until the rotor speeds up and the centrifugal forces force the broken ends apart.

Rob

[gspd]

Rob,
Thanks for all of this info. Your description of troubleshooting seems different from what I read on the Snowbum website--he makes it sound like testing the rotor is as simple as shorting across the two surfaces. I gathered from his all caps that this was a definitive test. Am I correct to understand from your comments that perhaps this does not mean the rotor winding is bad?

I visually inspected the brushes, and they do seem worn (perhaps even original). One is shorter than the other. What method should I use to clean the brushes, and if I clean them and then the symptom persists, have I ruled them out? I'm trying to understand how I actually achieve a diagnosis here.

It also sounds like your method is to test the regulator before returning to the rotor. Is that correct? From the snowbum website, I gathered that the order was to rule out the rortor (by shorting across the surfaces) before moving on to the regulator.

I do not have access to spare parts, so I just ordered a new rotor and brushes, which are shipping out to me. I'd rather not throw parts at the bike to trouble shoot the problem, however. It sounds like maybe I should just try testing the regulator while I wait for those parts to arrive.

Most rotor failures are open circuit but I have seen a few shorted ones (rare).
With a ohm meter probe on each rotor ring, a shorted or open circuit indicates a definite failure.
A reading indicating a resistance (but not a short) means it's most likely OK. The actual resistance varied from year to year and is strictly academic. I have never seen a failure caused by the 'wrong' resistance (partial short). (pretty sure Rob will disagree with this )
The only definitive rotor test is its replacement as rotation and heat may affect it.

If the brushes are noticeably uneven, they're shot, replace them.

Every serious airhead owner should have at his disposal (at the very minimum) a rotor, brushes, diode board and regulator. This is not "throwing parts at the bike", it's called "being prepared" or "buying in advance". The stators seem to last almost forever, extremely low failure rate.

[pdx_r100s]

thanks again for these different perspectives. So it sounds like the test of simply shorting across the rotor rings isn't as useful as I had hoped! I need to get a better meter, because the resistance readings seem kind of messed up (showing a resistance of 7 ohms when the probes are not touching anything).

My symptoms are that the light is very dim with key on, remains dim at low RPMs, and then intermittently gets brighter when the engine is revved. That's why I wasn't sure if it was in the "light doesn't come on" or "light doesn't go off" category.

I'm going test the regulator this afternoon.

The brush holder looked OK to me. I'll put the new brushes on when they arrive before playing with the rotor. Tho maybe I will have identified a problem with voltage regulator by then.

But unless I'm missing something, isn't the fact that the light doesn't come on brightly with the key on (engine off), but then turns on brightly when I short the rotor rings already evidence of a problem?

[gspd]

I have a second spare regulator bolted to my frame so I can switch the plug from one to the other and confirm or eliminate the regulator as the culprit in seconds should an issue arise.

Occasionally multiple components fail simultaneously compromising or invalidating many commonly used 'tests'. You can perform all the tests you want, or spend many hours reading stuff all over the internet, but in my (45-ish years) of experience, I have come to the solid conclusion that the only DEFINITIVE way to 'test' these components is to replace them with known good ones. It's also the EASIEST and MOST TIME EFFICIENT way to do it. By having all the known suspects in stock an accurate diagnosis of any charging issue takes less than an hour. The exception is the occasional melted or corroded wiring related issue which is usually immediately obvious.

[pdx_r100s]

So I just checked the regulator, following the method on the Snowbum site and a few other things I read.

First I grounded the solid blue wire in the female
connector, and the gen light came on. This was supposed to indicate things were ok, so I moved to the next test, jumping across the two blue wires in the connector. No light turned on. I started the bike and I do not get a charging battery—the voltage stays as 12.2 Volts regardless of rpm.

Interestingly, the dim gen light is totally gone with the bike running this way (regulator disconnected and wires connected). But no charge.

I’m guessing this means the regulator is ok, or?

Also, I got another meter with seemingly accurate resistance reading and measured across the rotor rings, which I cleaned with emory cloth. It reads an open circuit. I took this reading with the brushes lifted up and some paper insulating them, which I read to do on one of these write ups. If I read with the brushes down against the ring and no insulation, it reads 16 ohms. I also cleaned the brushes and tried running it, making sure they had good contact, but no change in symptoms.

[gspd]

The rotor is open circuit. Scrap it.
The brushes are unevenly worn. ditto.
Why don't you just order a regulator too? they're inexpensive (relatively speaking).
I recommend Bosch RE57 above all others, though most any 3 prong similar type regulator will work.

You might want to check your diodes while you're waiting (or order a spare board too)
One direction will zero the meter (continuity), reverse the probes and you'll get nothing.
Quite often the failure will be evident if you carefully examine the board visually inside and out.
I've seen a few that just needed a bit of cleaning up and re-soldering.
Back in the day I used to disassemble the boards and replace faulty diodes with ones from a donor board.
But life's too short for that now...

[Rob Frankham]

So I just checked the regulator, following the method on the Snowbum site and a few other things I read.

First I grounded the solid blue wire in the female
connector, and the gen light came on. This was supposed to indicate things were ok, so I moved to the next test, jumping across the two blue wires in the connector. No light turned on. I started the bike and I do not get a charging battery—the voltage stays as 12.2 Volts regardless of rpm.

Interestingly, the dim gen light is totally gone with the bike running this way (regulator disconnected and wires connected). But no charge.

I’m guessing this means the regulator is ok, or?

Also, I got another meter with seemingly accurate resistance reading and measured across the rotor rings, which I cleaned with emory cloth. It reads an open circuit. I took this reading with the brushes lifted up and some paper insulating them, which I read to do on one of these write ups. If I read with the brushes down against the ring and no insulation, it reads 16 ohms. I also cleaned the brushes and tried running it, making sure they had good contact, but no change in symptoms.

I agree with GSPD. The rotor is open circuit. It might be worth checking the solder joints on the commutator but otherwise it's a doorstop. I suspect it could be rewound but it would be a long and tedious process and to have it done professionally would probably not be cost effective.

The thing that is confusing me at the moment is the fact that there is a dim light (or any light at all) when the regulator is connected in circuit. With an open circuit rotor, there 'should' be no current flowing the bulb at any time. This leads me to wonder whether the regulator is also defective and is allowing a certain amount of current to leak to ground... I would suggest that a replacement regulator would also be a good idea even the existing one appears to be working. I would also want to do a function check on the diode board to rule out the possibility that the leakage is via that route. A full function check is favourite. Below is a link to the process on my website...

https://robfrankham.com/diode-board-test

In this case, I would use a test light rather than a multimeter.

Rob

[pdx_r100s]

Super helpful tips—thanks! I’ll get a regulator too, and test the diode board. The diode board was replaced a few years ago, but the regulator appears to be original.

Does anyone have experience with the enduralast regulators? That is what is a available on the site that I bought my rotor. One has an adjustable voltage output—would there be a reason to get that if I don’t have an upgraded alternator?

[Rob Frankham]

The stock regulator is quite efficient and there is no need to use an adjustable one unless you are doing a lot of short distance stop start riding.

Rob