Charging Light Troubleshooting

[DCoplin]

A month or so ago, when the weather was still resembling summer (i.e. very hot day), my charge light came full on riding home. I've been busy with work since then but have just managed spent some time looking in to it, and the charge light basically comes on full brightness when started and remains on regardless of the revs.

I've tried checking the regulator - jump wire test and the light remains on.

I've just popped the front cover off (having disconnected the negative terminal) and measured the resistance both ways across the terminals of the diode board and I'm getting c55 kOhms one way and c230 kOhms the other way across all of the terminals. There is no continuity in either direction.

Giving the charge light is full brightness regardless of the RPM, I'm assuming it's unlikely to be the alternator, but I'm not clever enough to know if the above resistance readings are good or bad...

The bike had a fabulous rebuild 4 years ago by @mikeyboy and thanks to the pandemic, I've only just started to put a few miles on (which again is why I think it's less likely to be the alternator). The (Odyssey) battery, shows as fine and is left attached to an Optimate for most of the time, but I guess it is probably 8 years old.

Can anyone confirm whether those resistance readings are OK or think of anything else I might be missing?

Thanks!

 

[DrFarkoff]

Check the Blue wire all the way down

It sometimes gets chafed and grounds out

So you get no exciter current (Power all the way to the rotor) and therefore no charge!

 

[Gelandestrasse]

Looking at Rick Jones's 'Classic Boxer Charging' guide (excellent, every airhead owner should have access to one)

Light on: Alternator or Wire problem.
Rotor Problem.
Diode Board problem (poor ground).
Loose, corroded connections or broken wires.
Stator Problem - worn brushes, weak springs.

Doesn't sound like you have a battery problem. But you have a lot to check through.

Would help to know what bike it is for further help.

 

[DCoplin]

Looking at Rick Jones's 'Classic Boxer Charging' guide (excellent, every airhead owner should have access to one)

Light on: Alternator or Wire problem.
Rotor Problem.
Diode Board problem (poor ground).
Loose, corroded connections or broken wires.
Stator Problem - worn brushes, weak springs.

Doesn't sound like you have a battery problem. But you have a lot to check through.

Would help to know what bike it is for further help.

I have that wonderful booklet and totally agree that everyone should have one. It got me as far as the resistance readings, but my brain ends at whether my readings class as "no ohm reading" or not. I know it sounds dense of me, but I have no idea as to whether 55 kOhms is a little (or no) or a lot...

And yes, how stupid of me - the bike is a 1993 R100GSPD.

 

[(RIP) Bin Ridin]

I seem to remember having tis issue on my '93 GSPD which turned out to be an open circuit in the rotor winding. New rotor fixed it.
Easy to check the resistance across the sliprings with brushes lifted.

 

[Deleted account 251024001]

What sort of meter are you using? You will need one with a diode setting to properly test it.

 

[Gelandestrasse]

The diode board would be a likely candidate (given no continuity as you state) - but are you checking with the right device? Also they are allegedly vulnerable to too much heat. However, there are other causes. That your light is not affected by revs is an indicator your alternator is not working (not as you say 'unlikely'). The rotor resistance (only a few Ohms) is easy to check. As are the stator field coils.

And you haven't stated if you have checked if the battery is receiving a charge from the bike when running. Or if any other electrical items are malfunctioning. Worth checking.

 

[DrFarkoff]

I seem to remember having tis issue on my '93 GSPD which turned out to be an open circuit in the rotor winding. New rotor fixed it.
Easy to check the resistance across the sliprings with brushes lifted.

Open circuit in the rotor is no light

there is no ground path

 

[DrFarkoff]

I just remembered an easy test!

Lift a brush on the Alternator (Carefully!) while someone watches the Alternator light once it leaves the rotor and brakes continuity it should go out
If it does not go out? its the blue wire from the lamp all the way down via the regulator grounding out some how? Chafed on casing or frame

Has the feed wire to the starter from the back of the diode board fallen off by any chance ?? That has that effect as well

 

[cookie]

Try and borrow a known good diode board and swap it out.
IME experience the 2 main problems with these Bosch systems are rotor winding broken (not your problem as Dr F noted) or failed diode board.

 

[(RIP) Bin Ridin]

Open circuit in the rotor is no light

there is no ground path

That is what is was, sorry my bad!!

 

[Gelandestrasse]

Having had another read of Rick Jones' bible and knowing that you have resistance (whatever value) both ways across the diodes, the front-runner is the diode board.

Let us know how you get on? Some us have spares if you are not in a big rush.

 

[tuftywhite]

I don't know if this applies to your bike, but it happened to mine. '81 g/s.

The circuit board that the dash lights work off, broke a connection and this stops the battery from charging. I bought a whole new board and LED lights from Kat Dash. I think you can just buy the replacement board.

 

[DCoplin]

Having had another read of Rick Jones' bible and knowing that you have resistance (whatever value) both ways across the diodes, the front-runner is the diode board.

Let us know how you get on? Some us have spares if you are not in a big rush.

I think that's exactly where I'm at too.

Thanks to the crappy weather I've had a couple of hours to fettle, I've taken out some additional wiring from accessories that have since become redundant thanks to the Beeline navigator and I've also checked through for a short on the wire.

The light is still on, but I have now noticed that it extinguishes at 3,000 RPM (starts going dim around 2,500 RPM) - I swear it wasn't doing that before and was just staying on but I can't be 100% (old age and all that).

I'm going to order a replacement diode board and see how I get on. Worst case I end up with a spare unit which probably isn't such a bad thing.

I'll report back on progress - and thanks everyone for your help!

 

[Gelandestrasse]

Worth going through all connections and break/make them, cleaning any nasty green stuff off as you go? Only on the charging circuit. But check fuse block, too.

 

[Deleted account 251024001]

If your meter reads voltage you can confirm if it is charging. With the meter on DC Volts and the engine running you should be getting 13.5 to 14.5 volts across the battery teminals. With the meter on AC Volts you should be getting near to 0. If you are getting more than 1 volts when the meter is set to AC Volts then your diodes are bad. If you are getting between 13.5 and 14.5 volts on DC Volts setting and near 0 volts on AC Volts setting then the system is charging properly and the fault is in the indication circuit.

 

[barny]

Make sure you get one of the new type diode boards https://www.euromotoelectrics.com/BMW-R-Airhead-Heavy-Duty-Diode-Board-p/boalt-rect063edl.htm
MotorBins sell them they are a good upgrade from the original and check the earth leads to the diode board.

This is worth a read - http://www.largiader.com/articles/charging

 

[DCoplin]

If your meter reads voltage you can confirm if it is charging. With the meter on DC Volts and the engine running you should be getting 13.5 to 14.5 volts across the battery teminals. With the meter on AC Volts you should be getting near to 0. If you are getting more than 1 volts when the meter is set to AC Volts then your diodes are bad. If you are getting between 13.5 and 14.5 volts on DC Volts setting and near 0 volts on AC Volts setting then the system is charging properly and the fault is in the indication circuit.

Thanks man, that's super helpful.

I'm getting 12.5v on DC regardless of revs... I haven't checked AC, but will do that now.

 

[DCoplin]

Make sure you get one of the new type diode boards https://www.euromotoelectrics.com/BMW-R-Airhead-Heavy-Duty-Diode-Board-p/boalt-rect063edl.htm
MotorBins sell them they are a good upgrade from the original and check the earth leads to the diode board.

This is worth a read - http://www.largiader.com/articles/charging

Thanks Barny,

I didn't realise Motobins had them. I ordered something similer from Motorworks which looks like the one @mikeyboy put on in the rebuild.

Fingers crossed it will do the trick!

 

[DCoplin]

Worth going through all connections and break/make them, cleaning any nasty green stuff off as you go? Only on the charging circuit. But check fuse block, too.

That's a good shout. The bike was standing for a long time during the pandemic so I suspect it could well be an issue.