Charging system

[charlie b]

OK, so I am fairly up to date on eletrics and stuff, have read a bunch of threads and several troublshooting guides on the old charging system on the T5 (Bosch as far as I can tell).

I know the rotor is bad, having checked it with a meter and there is Zero continuity across the slip rings (Stator and brushes are removed).

My question is, what is the cause.  When it failed the charge light came on and I had no charging to the bike (I have an LED voltmeter on the bike and it only registered in the 12V range not rising above that with RPM).  The battery is a fairly new Odyssey PC545.  Then it started charging again for a bit, then quit, again with the charge light coming on.  Rode home on the battery (15miles).  When I got ready to troubleshoot the charge light did not come on at all.

I went straight to the rotor to test and it is open so did not test the voltage regulator or rectifier.  The stator windings have less than 1ohm resistance between the three lugs.  Bushes look good.

So, does the rotor just sometimes short out (which I suspect can happen easily)?  But, wouldn't the idiot light go out immediately if this happens (or stay out)?

My theory is that somehow the voltage regulator went belly up which somehow caused the rotor to go belly up?

Or, could something in the rectifier cause the failure?

Right now I only plan on replacing rotor and regulator.  If I have to replace the rectifier too then I have to evaluate upgrading the whole setup.  Funds are an issue.

[jmac851]

Remove the rotor and visually check for any broken wires.  The resistance across the slip rings should be about 3.4 ohms if all is well. I would replace it if you can't find anything that you might be able to repair. After you replace it, then do your testing to find out what else if anything is wrong. The stator windings should be at about .38 ohms between any of the three leads.   

[Chuck in Indiana]

The rotor seldom goes past 50000 miles. A wire breaks and it's done. It's the most common failure of the Bosch system.

[charlie b]

I just don't want whatever else might be broken to fry a new rotor.

[Two Checks]

Stop overthinking it. You know the rotor is bad. They are known to do so. Replace it and go from there.

[Idontwantapickle]

The rotor seldom goes past 50000 miles. A wire breaks and it's done. It's the most common failure of the Bosch system.

Amen to that. It's the weak link in that system.
There are some options to replacement:

http://www.euromotoelectrics.com/EnDuraLast-Charging-Systems-s/22.htm

Hunter

[ohiorider]

Not a Guzzi, but my R100GS is on rotor #3.  First one (Bosch OEM) failed at approx. 94,000 miles.  Replaced with inexpensive ($100+ at the time) rotor, which lasted for 40,000 miles.  Installed new brushes at that time.  Replaced with another aftermarket rotor at 134,000 miles.  In all three cases, the rotors had gone 'open', ie a broken wire in the winding, most likely. 

Rick at Motorrad Elektric provided me with a simple test to check the rotor, using the 'Gen' light on the dash.  Might not work on a Guzzi if it is wired differently.  Anyway, here's the simple rotor test for an airhead that may or may not have relevance to your Guzzi issue:
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Your BMW mechanic has got it right-no red light with key on and motor
off means no circuit thru the rotor.  It's practically NEVER just a burned out bulb, so don't waste the considerable time it takes to access the bulb on the panel.

Here's a fail-safe test to prove the condition of rotor and light : 
- Disconnect battery ground (-) wire from battery terminal. (so as not to accidentally short the diode board when removing engine cover.)
- Remove the front engine cover exposing the alternator and diode board.
- Re-connect ground wire and turn on the ignition key. 
- Disconnect the terminal marked DF on the brush holder of the alternator
  (black wire).
- Use a piece of wire or screwdriver stuck in the terminal and touch (ground) the DF terminal to the engine and note if the red light comes on.
- If the red light comes on, the entire charge light circuit (bulb,
   wiring,voltage supply) is proven good down to the end of that wire.

Re-connect the DF terminal, and then (with ignition key on) use a screwdriver or a coin to bridge across both of the copper rings on the end of the rotor. If this
turns the red light on, the problem is definitely an open (defective) rotor circuit. If the red light DOES NOT come on, the problem is with the brush circuit:  worn too short, sticking in their holders, or broken brush lead connections.

With the ignition off and brushes lifted up (they can be blocked with cardboard), there should be 2.8 ohms measured between the 2 copper rings on the rotor. A defective rotor will measure infinity (open).  In 30+ years of working on these bikes, I've seen maybe 2 or 3 times when the warning light bulb is actually blown. It's almost a non-problem.

To eliminate the possibility of a burned out bulb causing the system not to charge, there is a patch whereby a resistor is added in parallel circuit to the charge light so that exciter current will still reach the rotor in case of bulb failure.  I think it's posted on the ibmwr.org website in the tech archives.

The charge light circuit is not a weak link, as its consistent functions of light on with ignition key, and going off with engine RPM gives clear indication of system functionality. This is a feature lacking on practically every other brand of motorcycle for the last 50 years.



Responses like the above are why I continue buying from Motorrad. Old GS now starts up via NipponDenso-based starter motor, and ignition is via Alpha (bean can replacement) both from Rick.  I think he has some electrical components for MG.

[charlie b]

Yep, the rotor was isolated and checked, no complete circuit, so it is bad.

I also checked my idiot light (it was replaced with an LED a long time ago, and yes, there is an 80ohm resistor in line) and it is working fine.

The only things I have not checked are regulator and rectifier.  I am thinking it would be better just to replace the whole mess with the higher output alternator.  Bite the bullet now and not have to replace another rotor in 50k miles.  :)


PS Electromotive has a good troubleshooting chart for charging systems.