ALTERNATOR WOES

[Atabeach]

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

[The Mighty Gryphon]

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

[Atabeach]

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?
 

[Laitch]

B+ connects to the battery positive terminal.  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.

[Atabeach]

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.

[The Mighty Gryphon]

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. 

[Atabeach]

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?

[Laitch]

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.

[Atabeach]

Thanks Laitch...God I love this website!

[The Mighty Gryphon]

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.

[Atabeach]

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!

[The Mighty Gryphon]

That tab is not the B+ terminal.

[Atabeach]

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….😳😳😳

[The Mighty Gryphon]

Just leave it alone.  It isn't used.  Grounding it will just cause more problems.

[Atabeach]

I was joking…12V to ground will definitely cause a problem. 😜

[Laitch]

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?
33A front


33A rear


50A front


50A rear

[Laitch]

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. 

[Atabeach]

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?

[Laitch]

Did you check continuity of the B+ wire from the alternator to the battery positive? If you did, please explain how.

[Atabeach]

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.

[Laitch]

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.

[daveson]

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.

[Atabeach]

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 !

[Atabeach]

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 )

[daveson]

The problem could be something simple like say dirty slip rings.