Rotor ohm readings

[electric_monk]

1989 R100 GS.

The charging light is not coming on at all. The bike was fitted with the 400W alternator from Motorworks a year and a half ago, but the regulator is an older high output item. I have been using Rick Jones' Classic boxer charging book as my guide, along with late night frustrated phonecalls with Dr Farkoff.
First test was the jumper wire across the terminals on the regulator plug....no change.
I then tried the charging light quick test by grounding the DF , again no change, I have already verified that the bulb is fine by swapping it around with the oil light that lives beside it in the light panel.
This pointed me towards the blue wire coming off the back of the diode board which can be a weak point. On inspection the cable was very stiff and had breaks in the insulation, so I took out the harness and very carefully replaced the damaged wire, refitted harness......no change. Cue frustrated light night call to the Dr........Farkoff.
This morning was the first I have been able to look at the bike in daylight so I lifted the brushes(Replaced with alternator and still in good condition) and took an ohms reading of 4.5 across the slip rings. The fact that there is a reading would suggest the rotor has not gone open circuit, but the reading seems very high, can anyone tell me if this reading is correct for the rotor of a 400w alternator.
Any further helpful suggestions and advice would be greatly appreciated. It is looking like the patio door may be coming off after the wife heads back to waterford and the bike coming indoors.

 

[Steptoe]

It's not high for a normal rotor, where you expect 5ish ohms.

 

[electric_monk]

The reason I suspect it to be high is because Rick Jones' book suggests the following readings for standard set up
1974-1989 3.4 ohms
1990 and later 2.8 ohms
Because my bike is a september 89 build it could reasonably be either of the above.
So I think I can rule out the rotor then

 

[DrFarkoff]

You are getting a connection on the rotor and your multimeter is likely just a home one, so may not even be near calibrated

Just check that one of the brushes is possibly hung up and not making contact

Then check if there is any volts in the blue wire?

Stop looking in Books They complicate matters

to make the warning lamp light up,

it needs volts and a source to earth

blue wire is the source to earth (well the stator to initially energise the windings)

So if you have no power in the blue wire keep jumping back up the wiring until you do and then bridge that bit out

One Rule Do NOT assume because its broken or brittle that it is not working keep going until you actually find volts

The wiring may even have a break in the clock pod area or under the lower yoke or as it passes the steering head

While you are in there photograph the back of your ignition switch and the headlamp mount for me Please, will ya ?

 

[electric_monk]

Jay

Here's a couple of shots of ignition, hopefully they are what you need. If the boss comes back and sees the scene in the 3rd picture i'm blaming you.....

 

[Ogmios]

Advance Warning:
i may be totally getting this wrong.
But, i'm going to post this anyhow, in the hope i'm getting it right.

I had a similar problem, solved by simply cleaning the bit i've pointed at.
hope it helps.

 

[electric_monk]

Cheers Marc, exactly the sort of advice required. If you're at a loose end this evening you're welcome to call over. The wife may have moved but I still have a kettle, milk, running water and digestive biscuits and more than 1 clean cup

 

[(RIP) Bin Ridin]

Is the charging light bulb ok? If open / blew, no excitement to rotor....

 

[Ogmios]

Cheers Marc, exactly the sort of advice required. If you're at a loose end this evening you're welcome to call over. The wife may have moved but I still have a kettle, milk, running water and digestive biscuits and more than 1 clean cup

Who are you and what have you done with our Electric Monk!?

Sorry but i have to stay home and replaster the dog.
Actually i am 2/3rds of the way through restoring some occasional tables and every bit of my spare time is going into them - i need them out of the house and the money in! ...Hey - you KNOW i'm crap with electrics anyhow - But feel free to phone and rant at me if it helps.

 

[(RIP) Bin Ridin]

http://www.ibmwr.org/r-tech/airheads/charging.info.shtml

 

[(RIP) Bin Ridin]

Charging System Troubleshooting links...
http://www.largiader.com/articles/charging/

http://bmwmotorcycletech.info/trbleshootALT.htm

Troubleshooting a dead GEN lamp:

Because a common problem is a GEN lamp that does not illuminate at all, this troubleshooting section is first.


The problem may not be a bad bulb. The GEN lamp SELDOM burns out. More often it is the rotor that has opened, or connection where the lamp fits, occasionally the VR, and sometimes worn brushes. You can easily test the rotor without any instruments.
As a double check: Turn on Ignition....GEN lamp should still be out.
Disconnect battery (removing all the wires to the negative post will do).
Remove front cover.
Reconnect battery.
Turn on ignition. GEN lamp should still be out.
Pull off the wire/connector going to the brush holder male spade that is marked as Df.
Df is the place the lamp and VR both apply the initializing current (and, after the alternator produces current, where the alternator self-energizes).
Stick a bent paper clip into the wire/connector, and ground the clip to the case. The lamp should light up. If you do not have a paper clip, UNplug the associated wire, which is the D- female spade connection, and plug that Df wire into the D- female. D- is ground. If the lamp lights up when grounded, and not when to the Df terminal, then the rotor is open, or the brush(s) not making contact. If the lamp does not light up when grounded, it is the lamp, or the wiring or pod connector or the VR.
To further test for the lamp circuit condition, and eliminate the VR as the problem:
Turn off the ignition.
Pull fuel tank.
UNplug the VR.
Turn on the ignition.
Ground the solid BLUE female connection wire in the voltage regulator's harness socket.
If the lamp does not light up, the wiring from the VR to the pod or its large rear plug, or internal wiring or lamp or lamp connection in the pod is at fault.

Do NOT forget to disconnect the battery before replacing the front cover.

 

[electric_monk]

Sods first law of airhead repair says that this broken part is not actually the problem but will hold up further investigation until replacement is found.

 

[DrFarkoff]

its okay it just clips back together!

Did you loose the brush spring?

MAY One Enquire did you undo this off the alternator?

You are supposed to be following blue wires and grounding them until you get a light on the dash!

YOU CAN STILL CHECK THE BLUE WIRE by grounding out on the engine without that bit in place

 

[electric_monk]

After weeks of frustration it looks like I found the problem, but not before I managed to break the brush holders and the connection on the back of the diode board.
With a fresh eye from not being near the bike for a week I decided to check the continuity at the circuit board in the dash. Lo and behold I found a break on the pcb. A temporary bridge across the gap and the charging light was back on. Hopefully my soldering skills are sufficient to ensure a permanent fix.
You can just see a little black vertical line to the lower left of the bottom right bulb