ALTERNATOR WOES

[Atabeach]

Ok so I cleaned the slip rings with rubbing alcohol. They seem to be making good contact. I checked resistance and continuity...I have started taking apart the unit to see if the windings & or the wires have become separated. NOTE : The main nut to rotor has proven a PIA, the 3 case bolts not so much. There is a decent video explaining the whole process. I dont have a press so the bearings...however used...will probably stay put.

[Ingo]

I had a bad rectifier,  got a new rectifier board thru Amazon , replaced and all was well. Requires disassembly of alternator, soldering. If you want to go that route then you'll have to test both the exciter (the rotating part) and the 3 coils on the stator for continuity and isolation to ground.  There should be a write-up of where i did  mine.... I'll see if I can find it....new regulator was also needed due to worn brushes.
Check this: https://www.motobrick.com/index.php?topic=15675.msg139145#msg139145

[Atabeach]

Replying to Ingo…I’m not sure what part you are speaking of. The voltage regulator , the part with the brushes, was changed.  Sooo here we are. Dis assembled. Field coils show continuity 1-2, 2-3, 1-3. Doesn’t appear to go to ground. All good. ( Photo 1)  The slip rings have continuity between themselves… 5.4 resistance....no continuity between slip rings and shaft or rings to the copper coil...Should there be?  ( Photo 2) There is a video online that shows 15.5 resistance between rings...( not sure if that matters) .
What else is there to check? TIA

[Ingo]

If everything checks out you're down to most likely replacing the rectifier. In my case I put the assembled alternator in a vice, wired up as it would be in the bike, i.e. battery and excitation WITH a little bulb (3 Watt) that limits the current to the brushes, then drove with battery drill. Direction doesn't matter.  I also had meters connected.  Found that the resistance to turn the alternator increased at somewhat higher rpms. No power coming out, indicating that the induced electricity was being short circuited in the rectifier. I even checked the coils outputs with an oscilloscope... Used that same setup after installing new rectifier and it had good output and was charging the battery. Then back into the bike it went and no further issue. You could un-solder the 3 winding wires from rectifier (would have to anyways if replacing ) and test the diodes, but I did that with no reliable results,  there seems to be internal parts that are not accessible. I do not remember the ohm readings of the windings,  but yours seem in normal range. Bottom line: I believe you're looking at the rectifier...

[daveson]

The slip rings have continuity between themselves… 5.4 resistance....no continuity between slip rings and shaft or rings to the copper coil...Should there be? 

What else is there to check?

There could have been a few earlier tests, but your test results are good. I think the rectifier should have been removed before the stator lead tests. I'm not sure if the video guide was a good one. I'll guess there will be plenty of videos for testing an alternator, and that one will show a way of testing for a short in the rotor by supplying 12 Volts to the slip rings, with the result that the rotor should become magnetised.

Some auto electricians won't be interested in alternator repairs, some will. If you go on long trips, like some here do, a new alternator is probably looking like a good option, otherwise a used one is another way to go.

Below are some generic drawings of some other tests.


PANO_20250427_091639.jpg (28.13 kB . 288x576 - viewed 402 times)


PANO_20250427_091243.jpg (22.86 kB . 288x576 - viewed 389 times)



IMG_20250427_154043.jpg (29.38 kB . 432x576 - viewed 461 times)

[Atabeach]

Thanks Daveson...Very thorough. At this point I purchased a used one off of Ebay. $45 delivered. Ill play with the old one after I ascertain with certainty the problem was with the alternator.
Question: Several replies have referred to a "rectifier" ??? ..The unit has an exterior mounted " part" with brushes attached , a voltage regulator ?  The other "part" would be a base plate thingy with the field coils ( 3 wires ) soldered on. This doesn't appear to be a replaceable part or serviceable in any way...is this a rectifier?

[Ingo]

Correct,  the rectifier is the part that the field coils (3 wires) are connected to.  The sort of external part with the brushes is the regulator. The rectifier is replaceable but requires soldering.

[daveson]

What am I doing wrong, why are my photos really low quality lately?

[Atabeach]

 Question: Is the rectifier available separately? I havent seen it on eBay, Motobins or Boneyard....I could rebuild the one I have and keep as a spare. TIA

[daveson]

It might be difficult to find the rectifier separately, at least I wouldn't be much interested in removing one if I had an alternator for sale.

There is a Batt + tab on alternator. I am certain there has been no wire attached to this tab for the 6 months...
Question; what is its use?

The extra positive pin can be used for an optional extra, for example a capacitor to reduce electrical interference. This would reduce radio noise on police bikes that had CB type radios. A capacitor minimises voltage spikes which can also help to protect sensitive electronics.