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Guzzi Alternator problem

Bill Bruno

Just got it firing!
Joined
May 3, 2019
Messages
5
Location
19087
Hello everyone.

I have been having an alternator problem for some time now and would like to possiably find a solution. The problem is as follows.
When the Alternator get warm, up to operating temp, the volts drops off and causes the battery to discharge. This only happens with the headlight on . Without the headlight being on daylight riding the charge rate is about 13.5 volts. When I put the system under load i.e. Headlight a discharge condition occurs. I replaced the following items over the years . Battery 2yrs old tests ok. Rotor new, diode board new,
Battery 2yrs old. Load tested ok.
New brushes stator cleaned, voltage regulator replaced with solid state adjustable.

Thanks in advance for any help.
Would like to be able to ride again at night :)

Cheers

Bill
In Wayne Pa.
 
Nothing to clean on stator (stator doesn't move, rotor does). Did you clean the contacts on the rotor? Have you tested the resistance of the rotor and stator once warmed up? You have to lift the brushes off the rotor to test, then each of the three phases of the stator. Read the resistance between each pair (there are 3 wires) of the stator, resistance should be 0.62 ohms. The resistance at the slip rings should be 6.9 ohms, +10%
 
Thanks so much will check with meter when hot. Have done it cold and all appears normal as far as ohm's reading go on rotor and stator.

Cheers

Bill
 
Hopefully you will get it sorted. If you have an 850T, the charging system output is less than T3 and newer Bosch systems. The newer Bosch systems should handle stock lighting just fine, but still there isn't much left over. One thing that may help is to go to an LED headlight. Amperage draw is much less and may even give you better light. What have you adjusted the voltage regulator to output? Without lights on set for about 14.2 volts.
 
Have you checked your rec/reg. Relatively rare for an alternator to fail, but quite common for a rec/reg to fail. If it does turn out to be your rec/reg, replace it with a MOSFET model - much more robust, stable and you'll get a little more usable output.
 
The alternator does not completely fail. Just when it gets warm ie operating temperature it goes below 12 volts. I have a regulator on there adjustable from mg cycle. rectifier check ok

Bill
 
The alternator does not completely fail. Just when it gets warm ie operating temperature it goes below 12 volts. I have a regulator on there adjustable from mg cycle. rectifier check ok

Bill

What Dinsdale is referring to is the diode board that rectifies the AC from the alternator to DC. When a diode gets hot it may be failing. So checking cold may not give you the answer. His comment is a good catch for the possible culprit to your charging issue. I don't think there is an after market replacement for the Bosch diode board. Good thing is it is identical to the one BMW uses on bikes with the Bosch charging system. See http://www.mgcycle.com/index.php?main_page=product_info&cPath=37_161&products_id=757 I personally haven't seen a Guzzi failure on the diode board, but because of where and how BMW mounts the diode board on their air head bikes I've seen plenty of those fail due to heat and vibration.
 
How many yrs of service? I'd get another one. Stator that is, you already did the rest.
That's what I thought also. However I am in the process of restoring a sp-1000 and I removed that stator that worked and put it the convert and it does the same thing. I charged the battery and did a load test and all looks good on battery. Passed the test and is only 2 yrs old. Without the headlight it keeps the battery charged with the headlight after about 10 miles or so it is discharged. I am investigating further when I have the time. The alternator has about 60K on it. It also has a solid metal cover which may have helped cook the stator. I did put a spacer on it which should get the heat out a bit better but. I am going to replace the cover with the plastic one with vent on the bottom to help get rid of most heat. I am also a tube radio tech and I am familiar with diodes and such and what they do. I find the system fascinating. I need a good alternator because I travel sometimes at night approx. 100 miles or so from the eastern seaboard to Philadelphia. Thanks so much guys. I want to check resistances in the harness also before changing parts out.

Cheers.

Bill
 
Have you checked the earthing of the rectifier? That's so often the cause of poor charging.
With the headlight off you should still be seeing more than 13.5v.

Those sold metal covers do cause more heat to build up. I believe you can still fit the plastic spacer behind them which helps.
 
Have you checked the earthing of the rectifier? That's so often the cause of poor charging.
With the headlight off you should still be seeing more than 13.5v.

Those sold metal covers do cause more heat to build up. I believe you can still fit the plastic spacer behind them which helps.
Thanks Brian I will take a peak
Cheers

Bill
 
I was looking at charging systems last week cause I need one for LM3, front wheel wrapped around it in the wreck in 07. I thought I saw a regulator/rectifier(like later Duc one) for the Bosch set-up.
+1 on the dodgey wiring and ground wire.
 
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