Charging Issue

[Will O The Wisp]

I have a 1988 R100GS. Well used at 120,000 miles and I have taken it many places. When started with headlight on it charges at 14 volt, after around 10 minutes use the voltage knocks down to around 12 volts for the rest of the ride.
If I turn the ignition switch to side light it is back up to 14 volts.
I have replaced; battery, rotor, stator, diode board, regulator, headlight relay, starter motor relay (I did this as there is a headlight bypass to ground when the starter is used),
all the charging system wiring.
Also I have looked over all the rest of the wiring.
Still the problem persists for about 18 months now, if I keep using it like this slowly the battery discharges.
I am out of ideas apart from a rewire or maybe replace the ignition switch which also does the lights.
Thank you for looking

 

[Stirlingmoz]

Does the charge warning light come on with ignition and go out when the engine comes off idle ?

 

[theoneandonly]

what is the wattage of the h/l lamp ?

 

[SBD]

after around 10 minutes use the voltage knocks down to around 12 volts

Is this a slow drift down, or sudden, like a relay or switch being operated?

 

[Will O The Wisp]

Thanks for the interest.
The charge light does not come on and the earth to the diode board is good.
It drifts down but fairly quickly. As the ammeter gives battery state that could mean it is sudden? But is taking a little while to register?
As it behaves normally on pilot light I have ruled out faulty ammeter.
Should not make a difference but it is twin plugged.
I have done 100,000 miles on the bike and know exactly where the ammeter needle used to sit.
I would need to check headlamp wattage but it would not have suddenly changed.
The problem is it is urging me to ride without headlight in the day.

 

[Will O The Wisp]

Just re read question and realised I did not properly answer.
The charge light is on with ignition but off on idle.

 

[timeandtide]

Thanks for the interest.
The charge light does not come on and the earth to the diode board is good.
It drifts down but fairly quickly. As the ammeter gives battery state that could mean it is sudden? But is taking a little while to register?
As it behaves normally on pilot light I have ruled out faulty ammeter.
Should not make a difference but it is twin plugged.
I have done 100,000 miles on the bike and know exactly where the ammeter needle used to sit.
I would need to check headlamp wattage but it would not have suddenly changed.
The problem is it is urging me to ride without headlight in the day.

As a work around why not swop to an LED?

 

[Steptoe]

Remove the ammeter from the system and see if that makes a difference

 

[Gelandestrasse]

Em, you have an ammeter? This is unusual. You also have a voltmeter (as you measure the 14V to 12V somehow). Assuming all the components and wiring you have changed have been with good replacements (new?), you cannot rule out one of these is faulty. The voltage regulator monitors the system voltage and changes the field voltage in the alternator rotor to suit. It seems this bit of the circuit is at issue (starts off ok (engine all cold?) but then after a period (engine warms up?) fails to charge?). Does the charge light glimmer at night (I say at night as the glimmer is very dim)? Suggestions:

- Perhaps remove/replace the charge light bulb to eliminate corrosion of the connections there (a bit fiddly but hey ho).
- Check all wiring to the and from the charge light bulb.
- Check the voltage regulator AGAIN against one we know works (off another bike).
- Look for wiring issues, corrosion on earth points, around the bike.
- There's a technique for bypassing the VR - read Rick Jones 'Classic Boxer Charging' book page 23.
- Check your rotor brushes.

 

[Will O The Wisp]

Firstly I had the dunces cap on for a moment! I only have a voltmeter.
The voltage regulator has been checked against another.
Brushes are all good.
However I have not looked at charging light so that maybe the next thing, although I do not understand why it would then be OK running on pilot light.
Thanks for your help.

 

[Stirlingmoz]

Just re read question and realised I did not properly answer.
The charge light is on with ignition but off on idle.

Are you sure the charge light is going out and not glowing dimly ?

This is a real clue as to where the problem might lie.

Stirlingmoz

 

[barny]

Are you sure the charge light is going out and not glowing dimly ?

This is a real clue as to where the problem might lie.

Stirlingmoz

Not wanting to hi-jack the thread but I have this after removing the Instrument panel on my 1995 GS I did change all the warning lights not fitted LEDs. But since then I have had a dim glow to the charge light when rev'ed over idle? All voltages and charge are fine.

 

[Gelandestrasse]

@barny and @Will O The Wisp :

Rick Jones's book mentions a steady drop in charging, worse when headlamp on, and with/without a low-glow charge light, indicates a problem with the Stator. A bad earth on the diode board or diode board issues could cause a dim glow charge light.

I would ask why Willow changed all the components - 'random black-box changing' or because all of them were proven faulty? Changing them all means you have inherited a whole new bunch of potential issues!

Get the book! (I have no connection or profit from its sale!). But we will continue to provide help and advice.

 

[Will O The Wisp]

@barny and @Will O The Wisp :

Rick Jones's book mentions a steady drop in charging, worse when headlamp on, and with/without a low-glow charge light, indicates a problem with the Stator. A bad earth on the diode board or diode board issues could cause a dim glow charge light.

I would ask why Willow changed all the components - 'random black-box changing' or because all of them were proven faulty? Changing them all means you have inherited a whole new bunch of potential issues!

Get the book! (I have no connection or profit from its sale!). But we will continue to provide help and advice.

Absoloutely "random black-box changing. It is not an easy thing to test for as it is not a constant fault only when in use.
The charge light is not glowing but I will investigate that avenue anyway.

 

[Gelandestrasse]

Absoloutely "random black-box changing. It is not an easy thing to test for as it is not a constant fault only when in use.
The charge light is not glowing but I will investigate that avenue anyway.

If checking the charge lamp, do it at night with the lights off (the ones in your garage as well as your bike's). It's surprising how dim the glow is. If it isn't there, it seems that your Stator, or cables/connections associated with it, hold a problem for you.

 

[Will O The Wisp]

If checking the charge lamp, do it at night with the lights off (the ones in your garage as well as your bike's). It's surprising how dim the glow is. If it isn't there, it seems that your Stator, or cables/connections associated with it, hold a problem for you.

Thank you for that, I had that many years ago which was bad earth on the diode board. But I will certainly explore this avenue.