Yesterday made a beautiful trip through some of the nice areas around here. I have fitted a volt-meter recently as I had some issues before. During the trip noted that they alternator barely kept the voltage on 13 - bit later (with grip heating on) 12 Volts. Not good. Will be looking at the alternator this weekend. Any idea of some quick checks or experience? Thanks!

Hi Rene
Sub 13V is a cause for concern
I noticed my k100RS regulates at 13.8-14V or thereabouts.
I felt this was bit low compared to my old CX then realised that its
a proper alternator which can vary the field windings to give extra current
rather than the usual "Dump 14.5V in and that should keep it happy" type
usually found on bikes.
My vans the same and regulates at 13.8-14V

I did change the brushes in mine last year and it was easy enough to remove the
diode/brush pack. 2 screws and its out
I'd check that first of all
Motobins/works can provide you with new brushes, about £12 as I recall
and some easy soldering to fit new ones
checking the slip rings are clean and debris free is advised too

Hi Rene,
The other thing I would do before ripping into it is to duct tape a digital voltmeter that you know is just reasonably accurate to your tank or to the crash pad by the ignition key and go for a ride with the meter measuring across the battery, just to be sure that the bike voltmeter is accurate.

If they read the same carry on as below if not then check that the bike meter has a really good earth and then that the earths are all good. It is worth measuring with your digital meter the resistance from the bike meter earth point all the way back to the battery with everything switched off of course.

If that all checks out to get good charging you want a really low resistance connection to earth from the engine to the battery so every morsel of power from our admittedly meagre alternators gets through. Our K wire gauge (thickness) is a bit on the thin side so doubling up on the wire from the battery to the engine and from the alternator to the battery it will reduce volt drop, plus go over all the under tank earths.

I fitted one of the single LED voltage indicators and as long as I have a green I know I am OK running as I am. If it goes amber or red then I would know I have a problem.

When you were running along and had 12 volts what engine rev speed were you doing, If around 2000 you probably were not putting out enough power to run the bike load plus the grips plus possibly the lights as well.
Regards,
K-BIKE

Guys, thanks for the above. I'll have a look today. Re speed I was all over the place, so should have gotten the alternator to work properly.

Hi Rene,
Sudden thought is your battery charge warning light working correctly? If it is not then the alternator will not start charging until high revs, that can be a problem caused by converting the indication lights to LED.

Alternators work because the charge warning light passes current through the alternator and sets up the magnetic field in the alternator (excites the alternator) so that the alternator then starts generating power.

On some other makes of bike they use a permanent magnet to produce the field.

In theory if the charge warning light was not working the alternator would never put out anything but the small amount of residual magnetism that is present in the mass of the alternator will be enough at high revs to kick the generation process off. Once started it is fine.

So if the charge warning light has failed or is a poor connection or the multi pin plug on the back of the instrument cluster is making poor contact to indicator light D on Bert's diagram or H9000 as it is called on the BMW circuit diagram then the alternator will not start charging till some 2,500 rpm.

So is the charge indicator light lit when you turn the key on and start and does it go out once the bike is running?

If it is not working I suspect you have found your problem.
Regards,
K-BIKE

Hi K,

no worries, the warning light is working OK. Thanks for the follow-up!