WTF

[larue bones]

replaced brushes on bosch alt. charging fine till 4000rpm than charging drops off. adjustabe reg2years old same for diode

any idea where to start looking? thanks in advance. ps 80 sp1000

 

[Kiwi_Roy]

Brushes bouncing perhaps, possibly a broken wire in the rotor?

Measure the current in the brush circuit to see if it drops off at revs

 

Make sure all the connectors are tight.

[Kiwi_Roy]

The charging was dropping off on my California II. it wouldn't maintain Voltage with my heated vest on so I took some measurements. I found the front-most brush had about 1 Volt drop from slipring to the brush (new brushes recently) so the alternator was not getting fully exited, there seemed to be some sort of insulating film on the rings.

I applied some fine emery paper to the rings while idling, it fixed the problem for a hundred miles or so but I see it starting to re-occur. This is a high mileage bike 107,000, I'm wondering if the front seal is leaking slightly and coating up the rings.

 

The bike doesn't need to be running to check the Voltage drop, just turn the key On.

 

Measure the Voltage across the two brush leads then measure the Voltage between the sliprings, we can compare notes.

[gstallons]

If you are not seeing any residue of any kind , I would suspect the quality of the brush material .

 Is there a starter / alternator repair facility near you ? You might be able to replace the brushes and get things back to normal .

[Kiwi_Roy]

MG Cycle brushes - they look pretty normal but I may swap them out, I just posted it as another thing to check for

 

 

Sent from my shoe phone!

[Kiwi_Roy]

Out of curiosity I took another look at the alternator last evening (remember it was only showing the first sign of weakness) the ground brush was dropping 298mV but the positive brush was dropping 670mV, after touching up the rings with emery this dropped to 88 & 100 mV.

Now I cut my teeth on AC & DC machinery but I don't have a good explanation for the high initial Voltage drop.
Cheap Chinese brushes?
Something plating out on the positive slipring?

 

 

Update:

 I posted the problem on an electrical forum, one of the electric motor Gurus posted the following.

 

"Not so long ago, low Voltage rectifiers were built from copper with a thin oxide layer. And ordinary brushes in DC motors are known to have a slight rectifying property. That is probably what you are seeing"

 

It's interesting, I have never heard about this but the guy who responded has forgotten more than I will ever know :-).

I may try a different brush material see if it does the same.
 

[gstallons]

Were these OEM parts ? Who makes the charging systems for Moto Guzzi ? There is www.euromotoelectrics.com  in Denver , Co.

 You could buy parts and I mean parts from them .

[Kiwi_Roy]

How would I know if they are OEM or not, I doubt Bosch make their own brushes, it's a specialty business. 

http://www.mgcycle.com/index.php?main_page=product_info&cPath=37_161&products_id=598

Brushes do come in different grades depending on the application, I will try another source.

 

It may be something common to all the Bosch alternators, I am pushing it to the limits with heated vest & gloves about 60 Watts from memory

It's not a problem I am really concerned about, I only posted it in case someone else was noticing a shortage of Amps

Without running heated gear it would probably not be noticed.

 

Those look like the real deal

http://www.euromotoelectrics.com/Bosch-Alternator-Brush-Kit-BMW-R-Airhead-p/boalt-brushesx2.htm

[LowRyter]

Roy,  I am sending you a PM about the thermistor for the fuel level sensor on Wild Guzzi.  (sorry about the thread hijack) 

[larue bones]

Sorry for the late reply. I forgot about this tread.

Turns out one of the springs for the brushes , one spring had slipped a coil, uneven pressure.