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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Atabeach on April 21, 2025, 01:25:43 PM

Title: ALTERNATOR WOES
Post by: Atabeach on April 21, 2025, 01:25:43 PM: Ok so the light on my 1990 k75S 40K was sporadically if not faintly on recently during driving..it is now fully illuminated. It turns out the voltage is 12.2 and does not rise with RPM...The Alternator appears to be suspect. I have a question! Is this an easy internal fix? Brushes/voltage regulator....or am I looking at buying a used Alt on Flea bay? TIA
Title: Re: ALTERNATOR WOES
Post by: The Mighty Gryphon on April 21, 2025, 02:11:31 PM: First, with the engine running at least 2000rpm check the voltage at the battery terminals. It should be around 13.8 volts.

Pull the battery out and charge it fully. Then take it to Auto Zone to have it load tested to make sure it hasn't passed on to it final reward.

If the battery is okay and you aren't getting enough voltage from the alternator the brushes or regulator may be bad. You can get a brush/regulator unit on eBay.

https://www.ebay.com/itm/372744802792 (https://www.ebay.com/itm/372744802792)
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 21, 2025, 02:53:06 PM: So last couple of days...Battery checked, all good..I have dash mounted Voltmeter ( Thanks Duck!) So initially the light came on and ....with good RPM we went to 13.5-13.8. That slowly ended...Now I dont get above 12.2. Ill buy and install the part in the link you provided....God I love this website!

ON A SIDE NOTE: There is a BATT+, tab next to the D+ ( Large red, small blue ) connector. I did not disconnect a wire from this terminal...nor do I see a loose one. WTF?
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 21, 2025, 04:40:30 PM: B+ connects to the battery positive terminal. :thisplacewhack That's the connection that charges the battery and helps run the Brick. Without it, the battery does all the work without being recharged and will discharge enough to stall the engine, sooner than later.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 21, 2025, 05:09:55 PM: Seriously? I’ve been driving this puppy for about six months without it. I’m out now. Let me get a closer look maybe the thing got yanked off somehow. From the stupid question department… Without that wire would the alternator light remain on? I can’t imagine that I would’ve been able to drive the motorcycle for any length of time on just battery power.

So I have looked very carefully at the area. Something is wrong. There is no wire attached to the Batt + terminal on Alternator. The tab looks like no connector has been attached for some time.
Title: Re: ALTERNATOR WOES
Post by: The Mighty Gryphon on April 21, 2025, 09:19:04 PM: You say there is a connector with a large red and a small blue wire on it. Is that correct? If so, that large red wire is the B+.

The blue wire is the excitation for the alternator. That wire runs to the alternator light in the cluster. If it is broken, it will be difficult for the alternator to start generating current. It will need the engine to be rev'd to 3000 rpm or higher to get any current out of it.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 22, 2025, 11:47:24 AM: Griff, Laitch… thanks for the replies. So I am not getting any increase in voltage across battery or at any electrical contact with RPM increase. I will assume the voltage regulator is bad & will be changed.
There is a Batt + tab on alternator. I am certain there has been no wire attached to this tab for the 6 months of trouble free ownership…Further..No where in my Clymers manual ( see photos) does it mention an electrical connector to this tab. Or a test point.
Question; what is its use?
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 22, 2025, 01:30:20 PM: No wire has been attached to that terminal because it isn't being used by the Brick's electrical system. This type of alternator was used in multiple vehicles with requirements that differed from your Brick's.

You should check for continuity of the B+ wire to the battery positive. You need to remove those D+ and B+ connectors from the alternator and thoroughly clean off the heavy oxidation that covers both their terminals and likely within the connector spade sockets themselves. Spray the cleaned connectors with DeOxit D5 after cleaning; otherwise, use a high quality electronics cleaner.

Don't assume the regulator is faulty; it could be the brushes are too worn. 10mm of brush extends from the holder of a new regulator; the wear limit is at 5mm. If they are that worn, you can replace the regulator or replace just the brushes. You'll de-solder the old brush wires and solder the new brush wires onto their connections. You have it easy because you can remove and replace your regulator without opening the case.

This could get more complicated necessitating opening the case and cleaning the commutator and the environment in there in general. There could be diode problems. Ultimately, you could just punt and install a 50A alternator if the problem gets more elusive.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 22, 2025, 01:32:49 PM: Thanks Laitch...God I love this website!
Title: Re: ALTERNATOR WOES
Post by: The Mighty Gryphon on April 22, 2025, 05:12:13 PM: The B+ you see refers to the terminal where the big red wire is connected. If you look at the other side of the connector you will see the marking D+ which is the blue excitation wire. I'm not sure what the + terminal you referred to does. It's possible it might be for a volt meter, but don't count on it.

Yes, you can replace just the brushes, but for a few bucks more you get a new regulator and save the trouble of soldering the new brushes.

If I'm not mistaken, the alternator doesn't have a commutator, rather is has slip rings that don't gave segements with gaps between them that have to be cleaned like the starter motor.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 22, 2025, 05:24:49 PM: Thanks Griff, I did everything recommended by Laitch…the brushes look fine, however, I will take your advice and swap out the entire regulator. As a side note…the regulator link you provided in a previous reply is universal for 50 & 30 amp alternators. My 1994 with 50 amp unit does not have the B + tab. It may have been used as a test point or for an accessory. No clue…Thanks again!
Title: Re: ALTERNATOR WOES
Post by: The Mighty Gryphon on April 22, 2025, 05:27:23 PM: That tab is not the B+ terminal.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 22, 2025, 05:33:48 PM: Ok I see! The D is the blue wire, the B + is the large red wire…the tab has a smaller +….Ill connect it directly to ground….😳😳😳
Title: Re: ALTERNATOR WOES
Post by: The Mighty Gryphon on April 22, 2025, 05:38:46 PM: Just leave it alone. It isn't used. Grounding it will just cause more problems.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 22, 2025, 05:41:05 PM: I was joking…12V to ground will definitely cause a problem. 😜
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 22, 2025, 07:34:00 PM: Quote from: Atabeach on April 22, 2025, 05:24:49 PM
My 1994 with 50 amp unit does not have the B + tab.
It seems to me you don't have a 50A alternator; you have a 33A alternator. Photos below from Euro Motoelectrics. Have you run the last seven digits of your Brick's id. number through a VIN checker like this one (https://www.realoem.com/bmw/enUS/select?product=M&archive=1&series=K569)?
33A front
(https://www.motobrick.com/gallery/4/1601-220425191818.png)

33A rear
(https://www.motobrick.com/gallery/4/1601-220425191857.png)

50A front
(https://www.motobrick.com/gallery/4/1601-220425191939.png)

50A rear
(https://www.motobrick.com/gallery/4/1601-220425192011.png)
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 22, 2025, 07:49:39 PM: Quote from: The Mighty Gryphon on April 22, 2025, 05:12:13 PM
If I'm not mistaken, the alternator doesn't have a commutator, rather is has slip rings that don't gave segements with gaps between them that have to be cleaned like the starter motor.
You aren't mistaken; I was in a semi-lucid dream when I wrote that. 177381
Title: ALTERNATOR WOES
Post by: Atabeach on April 23, 2025, 05:43:37 PM: OK Summarizing here. 1990 k75s 30 amp alternator. So the idiot light came on ( alternator) and I have done the following with no results.
1) battery is good. 2) all contacts are clean. 3) cleaned the armature where brushes rotate. 4) went through MOST if not all accessories looking for loose wire or wire to ground...lastly, CHANGED VOLTAGE REGULATOR!. Still no rise in voltage with RPM. In theory it could be a bad ( new regulator ) Any other things to check?
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 23, 2025, 07:50:34 PM: Did you check continuity of the B+ wire from the alternator to the battery positive? If you did, please explain how.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 23, 2025, 07:56:56 PM: Continuity was tested with my multi meter. Set to continuity...I tested from the back of clip..so I know there is good contact from alternator to wire.. I’m starting to feel as if I got a bad rectifier. The unit spins nicely...My next step… unless told otherwise is to take her out to have her bench tested professionally.
Title: Re: ALTERNATOR WOES
Post by: Laitch on April 23, 2025, 07:59:03 PM: Quote from: Atabeach on April 23, 2025, 07:56:56 PM
My next step… unless told otherwise is to take her out to have her bench tested professionally.
Probably the best course of action for you. Please update us with the results.
Title: Re: ALTERNATOR WOES
Post by: daveson on April 24, 2025, 08:08:49 AM: I'm thinking about the possibility of a short on the blue wire.

With key on, engine off, the battery warning light in the instrument cluster comes on, goodo. If you then unplug the blue wire from the alternator (therefore also unplugging the red wire) does the battery light turn off? It should. If it doesn't, you might have a short somewhere along the blue wire.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 24, 2025, 08:50:31 AM: Ok so I just performed that test. Light went out after removing clip from alternator. I’m going to pull the unit and test the Batt terminal to case ( Diode). Then pull the new voltage regulator and test continuity of brushes. Everything is now pointing to bad rectifier ( wire thingy at base ) Thanks !
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 24, 2025, 07:47:29 PM: So the bench test proved what I already knew. The alternator is not producing current..They don’t rebuild this type of alternator ( whatever that means) .
Gentlemen, what are my options?…assuming the new voltage regulator is good.
1) has anyone opened these up and Viola! …found a loose wire or obvious issue…Or actually rebuilt one?
2) Fleabay $40-$70 used
3) New on fleabay or another website ( $200ish )
Title: Re: ALTERNATOR WOES
Post by: daveson on April 25, 2025, 04:33:03 AM: The problem could be something simple like say dirty slip rings.
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 25, 2025, 08:03:34 AM: 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.
Title: Re: ALTERNATOR WOES
Post by: Ingo on April 25, 2025, 10:50:33 AM: 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
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 25, 2025, 12:48:14 PM: 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
Title: Re: ALTERNATOR WOES
Post by: Ingo on April 25, 2025, 09:32:47 PM: 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...
Title: Re: ALTERNATOR WOES
Post by: daveson on April 26, 2025, 06:27:33 PM: Quote from: Atabeach on April 25, 2025, 12:48:14 PM
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 403 times)

PANO_20250427_091243.jpg (22.86 kB . 288x576 - viewed 390 times)

IMG_20250427_154043.jpg (29.38 kB . 432x576 - viewed 462 times)
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 27, 2025, 09:45:34 AM: 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?
Title: Re: ALTERNATOR WOES
Post by: Ingo on April 27, 2025, 09:56:52 AM: 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.
Title: Re: ALTERNATOR WOES
Post by: daveson on April 27, 2025, 06:03:13 PM: What am I doing wrong, why are my photos really low quality lately?
Title: Re: ALTERNATOR WOES
Post by: Atabeach on April 28, 2025, 06:42:13 AM: 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
Title: Re: ALTERNATOR WOES
Post by: daveson on May 03, 2025, 07:19:24 AM: 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.

Quote from: Atabeach on April 22, 2025, 11:47:24 AM
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.