Reluctant Alternator

[Diploman]

First short-range test drives on my made-over 1980 V50 II have been exhilaratingly successful - the many upgrades are working as intended, the bike is running beautifully and handles better than ever.  One problem, however has emerged:  As confirmed by the new digital voltmeter, the alternator is not charging the (LiPo) battery.  Within 15 minutes the voltage is down to 10.5-11 volts and the motor begins to sputter on acceleration as the coils/plugs begin to misfire.

The alternator exciter/warning light (the only incandescent light remaining on the bike) comes on when the switch is turned to "on" and subsequently does not fade off when the engine is started and revved.  At first I thought I must have mis-wired it, but test rides confirm the indication that the alternator is not providing juice.  My bike has the original Bosch alternator and diode board, but a new adjustable electronic regulator.  (The early smallblocks had the identical charging system as the bigblocks of the era.)

Troubleshooting time now.  I would welcome advice and suggestions from WildGuzzi members.  This is my first experience with an alternator problem.  How to test, diagnose and correct the unwilling alternator?  I verified that the red wire coming off the diode 12v positive spade on the hot side is in fact connected and appears to run normally to the battery via the fuse box.

Guzziology contains an extensive section on alternator Fault Diagnosis which I am using as a starting point.  One possible fault listed, a new one to me, is a stator "which requires a little residual magnetism in order to work.  If never magnetized, or if left unused for long periods, the rotor can require a brief connection with a twelve-volt power source.  Simply flash two battery leads to the two slip rings."  Has anyone done this re-magnetizing trick?  This strikes me as a distinct possibility, since my bike sat in storage, then reconstruction from 2005-20017.

I'm going to the garage now to inspect connections, can of DeOxit in hand.  Thoughts, suggestions, guidance appreciated.

[Idontwantapickle]

First short-range test drives on my made-over 1980 V50 II have been exhilaratingly successful - the many upgrades are working as intended, the bike is running beautifully and handles better than ever.  One problem, however has emerged:  As confirmed by the new digital voltmeter, the alternator is not charging the (LiPo) battery.  Within 15 minutes the voltage is down to 10.5-11 volts and the motor begins to sputter on acceleration as the coils/plugs begin to misfire.

The alternator exciter/warning light (the only incandescent light remaining on the bike) comes on when the switch is turned to "on" and subsequently does not fade off when the engine is started and revved.  At first I thought I must have mis-wired it, but test rides confirm the indication that the alternator is not providing juice.  My bike has the original Bosch alternator and diode board, but a new adjustable electronic regulator.  (The early smallblocks had the identical charging system as the bigblocks of the era.)

Troubleshooting time now.  I would welcome advice and suggestions from WildGuzzi members.  This is my first experience with an alternator problem.  How to test, diagnose and correct the unwilling alternator?  I verified that the red wire coming off the diode 12v positive spade on the hot side is in fact connected and appears to run normally to the battery via the fuse box.

Guzziology contains an extensive section on alternator Fault Diagnosis which I am using as a starting point.  One possible fault listed, a new one to me, is a stator "which requires a little residual magnetism in order to work.  If never magnetized, or if left unused for long periods, the rotor can require a brief connection with a twelve-volt power source.  Simply flash two battery leads to the two slip rings."  Has anyone done this re-magnetizing trick?  This strikes me as a distinct possibility, since my bike sat in storage, then reconstruction from 2005-20017.

I'm going to the garage now to inspect connections, can of DeOxit in hand.  Thoughts, suggestions, guidance appreciated.

Check the easy basics at the alternator. Unhook all the wires, check across the slip rings, should be a low value about 3 ohms and no continuity from either ring to ground. check between each of the 3 field coils, should also be around 3 and none to ground IIRC.
If these check out the issue lies elswhere.
And yes, the magnetization trick is a real thing, can't hurt to try it since the bike seems to have been stored for ~18000 years! 

Hunter

[Triple Jim]

I've never seen a V50's alternator, but aren't the three coils the stator's 3-phase output coils, and the rotating part with slip rings the rotating field?

[Idontwantapickle]

I've never seen a V50's alternator, but aren't the three coils the stator's 3-phase output coils, and the rotating part with slip rings the rotating field?

Yes, my terminology after eating too much chili might be off. The rotor does provide the field.

[Chuck in Indiana]

Check output at the three yella wires. Should be around 40 volts or so.. doesn't matter which three you check.
Yes, flashing the alternator by a brief touch of 12V is a real thing. It can lose it's ju ju over time..

[Kiwi_Roy]

One slipring should be grounded thru the brush, flash 12V to the  DF terminal you should get  spark off it,
The tiny current from the charge light ends up at DF, it causes the 3 stator wires to produce a weak AC which is rectified by 3 small diodes to produce more field current.


Sent from my shoe phone!

[Old Jock]

Check output at the three yella wires. Should be around 40 volts or so.. doesn't matter which three you check.
Yes, flashing the alternator by a brief touch of 12V is a real thing. It can lose it's ju ju over time..

So if it's identical to the Big Block, first thing I'd do is charge the battery off the bike and check the voltage, it should be around 13.5. Before trouble shooting battery needs to be good, otherwise you are going to get bad data.

Next get the cover off, check slip rings and brushes. Slip ring should be clean, brushes should not be worn down and when lifted should spring back down onto the slip ring when released.

When either brush is lifted the warning light should go out.

Next is as per Chuck's suggestion, just adding for clarity, disconnect the plug that has the 3 yellow wires, start the bike, its now running on the battery. Measure AC voltage  from yellow wire to yellow wire. 1-2, 1-3, 2-3 all should have the same AC voltage (more or less) at a given RPM. Rev the bike to around 3k. I can't remember the figures but I think around 40V AC at 3k, again should be the same for all 3.

If that test went well then it's not the Alternator  and you are getting field voltage. If it didn't then the next step is to run a temporary supply of +12 DC from the battery to DF, pull the wire off DF and substitute the temporary +12 wire and repeat the test.

This is "Full Field" flashing, don't rev the bike much above a fast idle when doing this and don't do it for long especially with a LiFe (I hope it's not a LiPo).

I'd really be more comfortable doing this with a good old Lead Acid or AGM battery. Lithium batteries can be fragile and do not respond well to voltage abuse either under or over voltage, which can happen if Full Field flashing. The last thing I'd want is for you to cook your expensive Lithium battery.

If that's giving you AC voltage now then the Alternator is Ok but you are not getting field

If it's still dead there is the magnetization and repeat, then its time to pull off the stator and rotor and measure resistances. Stator failures are common.

After that it's a full connection check and ensure all earths are where they should be and clean, it's going to get a little  more involved but these are just my first steps into diagnosing a charge problem.

Just what I'd do...............yo u are getting some good advice of some very knowledgeable members already (and they are not me)

John

[Diploman]

Problem solved!

First, thanks to all for the astute advice on testing and diagnosing.  I was just starting to go down this path when I noticed that the diode board mounting bracket (located full forward on the frame under the headstock) had a vacant male spade connector on the lower exterior, on the side that holds the grounded side of the board.  Having just read in Guzziology that poor/no

 rectifier grounding is the second most frequent cause of alternator faults, I quickly crimped up a black wire with a female spade on one end and an eyelet on the other.  I pushed the spade end onto the (sanded and DeOxit prepared) male spade, then bolted the eyelet to a common ground on the frame.  Put on the gas tank, turned on the key to observe the alternator light, and started the motor.  Bingo, the alternator light went out immediately, and the voltmeter climbed to 13.8.  Alternator has juice!

More testing to come, but the de-bugging process is coming closer to a conclusion.  Write-up and photos soon.