Yet another charging thread!

griffg · 08-17-2012, 03:42 PM

GEN light won't go out. First check remove the connector from the regulator and link the connectors. GEN light stayed on indicating an alternator fault. Next step was to disconnect the B+ terminal on the diode board and start the bike measure the voltage betwen the D- and B+ terminals, this was less than 2 volts. Again indicating an alternator fault. Removed the wires off the D- and DF brush connections and checked resistance, 3.4ohms and checked each of the slip rings to ground with the stator removed.and infinite resistance. Checked the stator windings and they are all good and not shorting to ground. Removed all the wiring from the alternator and diode board and check them for breaks and they are all fine.
All tests say its the alternator at fault and yet I can't find anything wrong with the rotor or stator. I'm pulling my hair out and I haven't got a lot to pull. Can someone shine a light on my problem before I start wasting money changing items that may not be faulty.

Wirespokes · 08-18-2012, 10:27 PM

Even though you've gotten the correct resistance across the slip rings, that's only a static test and probably not trust-worthy. It's possible for the windings to short to ground in motion which could cause these symptoms.

So that's a possibility.

Are the slip rings bright shiny copper color? If not, then odd things can happen.

Which two terminals of the regulator did you connect? The two, not the brown?

Stators don't normally go bad, so the best guess is the rotor, which is one of the most common failure items. Besides, it's wise to have a known good spare for this very reason. It's also wise to carry a spare when travelling.

Shango · 08-19-2012, 09:14 AM

Brushes?....

griffg · 08-20-2012, 01:24 PM

Thanks for the replies.
I've managed to get my hands on another stator and tried that with the same results. The regulator wires I linked were the blues. The brushes are good, not new but a good 10-12mm in length. I read something on another thread that ties in with one reply about the condition of the rotor slip rings. I've cleaned them with electrical cleaner, but the thread suggested cleaning them up with a bit of abrasive paper, so I'll give that a go. If that fails then as you say it must be the rotor as there is nothing else left.
Thanks again for the replies, and I'll post a mail when/if I manage to fix it.

griffg · 08-23-2012, 03:11 PM

Slip rings are now a bright shiny colour and the GEN light goes out. 13.5 - 14 volts when rev'd.
Thanks for your comments.

08-17-2012, 03:42 PM	#1
griffg ^OP n00b Joined: Oct 2011 Location: Pembrokeshire Oddometer: 7	Yet another charging thread! GEN light won't go out. First check remove the connector from the regulator and link the connectors. GEN light stayed on indicating an alternator fault. Next step was to disconnect the B+ terminal on the diode board and start the bike measure the voltage betwen the D- and B+ terminals, this was less than 2 volts. Again indicating an alternator fault. Removed the wires off the D- and DF brush connections and checked resistance, 3.4ohms and checked each of the slip rings to ground with the stator removed.and infinite resistance. Checked the stator windings and they are all good and not shorting to ground. Removed all the wiring from the alternator and diode board and check them for breaks and they are all fine. All tests say its the alternator at fault and yet I can't find anything wrong with the rotor or stator. I'm pulling my hair out and I haven't got a lot to pull. Can someone shine a light on my problem before I start wasting money changing items that may not be faulty.

08-18-2012, 10:27 PM	#2
Wirespokes Beemerholics Anonymous Joined: Jul 2002 Location: Jackson's Bottom Oregon Oddometer: 7,356	Even though you've gotten the correct resistance across the slip rings, that's only a static test and probably not trust-worthy. It's possible for the windings to short to ground in motion which could cause these symptoms. So that's a possibility. Are the slip rings bright shiny copper color? If not, then odd things can happen. Which two terminals of the regulator did you connect? The two, not the brown? Stators don't normally go bad, so the best guess is the rotor, which is one of the most common failure items. Besides, it's wise to have a known good spare for this very reason. It's also wise to carry a spare when travelling. __________________ Wanted: Dead, smashed, crashed or trashed gauges BMW GAUGE REPAIRS - TACHSPEEDOCLOCKVOLT METER PODs & LIGHT BOARD*

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08-19-2012, 09:14 AM	#3
Shango Hi Joined: Apr 2012 Location: Atlanta Oddometer: 52	Brushes?....

08-20-2012, 01:24 PM	#4
griffg ^OP n00b Joined: Oct 2011 Location: Pembrokeshire Oddometer: 7	Thanks for the replies. I've managed to get my hands on another stator and tried that with the same results. The regulator wires I linked were the blues. The brushes are good, not new but a good 10-12mm in length. I read something on another thread that ties in with one reply about the condition of the rotor slip rings. I've cleaned them with electrical cleaner, but the thread suggested cleaning them up with a bit of abrasive paper, so I'll give that a go. If that fails then as you say it must be the rotor as there is nothing else left. Thanks again for the replies, and I'll post a mail when/if I manage to fix it.

08-23-2012, 03:11 PM	#5
griffg ^OP n00b Joined: Oct 2011 Location: Pembrokeshire Oddometer: 7	Slip rings are now a bright shiny colour and the GEN light goes out. 13.5 - 14 volts when rev'd. Thanks for your comments.