Intermittent charging

[John Roberts]

The battery was fully charged when I started it this morning and it started with no bother. However, it wasn't charging properly, on idle the voltage went down to 11v but when I blipped the throttle it came back up to 12v. The charge warning light was on. When I stopped the engine the voltage was still a healthy 12volts. The bike is an '82 R100RS.

I took it for a short ride (15 miles) because we were already togged up, and when we got back it was charging OK again.

It has the Motorworks 400Watt O/P alternator which has done 10/12K miles. The brushes have done rather less, 8K miles perhaps.

Now it's bound to do this again some time. Oh, hang on, for some time read when I'm far away, after dark and soaking wet. What could it be?

 

[(RIP) maverick]

The charger light on my R100T also stays lightly dimmed even on 4500 rpm. Received a new set of brushes today to fit tonight and will check all the earth connection as well. If it is still being problematic after that I hope someone has answered your question John

 

[cookie]

The charger light on my R100T also stays lightly dimmed even on 4500 rpm. Received a new set of brushes today to fit tonight and will check all the earth connection as well. If it is still being problematic after that I hope someone has answered your question John

i'd have thought that's probably a diode board fault.

 

[SJRoome]

Hi

How and where are you measuring the voltage? A voltage of 11V across the battery would indicate either a heavy drain on it or a faulty battery.


If you have a reliable multimeter can you measure the voltage directly across the battery terminals (1) when the ignition and lights are off (2) with the engine not running and full beam on (3) at idle with no lights (4) at 2000 rpm no lights, (5) at 2000 rpm with full beam.

Steve

 

[John Roberts]

Hi

How and where are you measuring the voltage?

With the dash mounted voltmeter provided on this model: one side to Earth and the other via the ignition switch to the battery +ve.

Perhaps I should have made it clear that when I was blipping the throttle the voltage rose and then dropped back to 11v when I released the throttle. Sorry. The load at the time was the ignition circuit and the sidelamps. I'm pretty sure that the battery is fine, it always starts OK.

I had another run this afternoon and all was still well. I hate intermittent faults.

 

[MickDB1]

My bike did sometimes not charge - the red light sometimes glowed just a bit-
there was a dropped diode that when the engine was hot enough -or whenever it chose to buggered me up
Thunderchilds new diode board and fixings and higher output regulator sorted it for me =
65 quid posted from san Diego cal
fit them on all me airheads as a standard now
nowt worse than a intermitant fault = maybe a moaning wife

 

[Steptoe]

With the dash mounted voltmeter provided on this model: one side to Earth and the other via the ignition switch to the battery +ve.

.

Dash mounted voltmeter - Take it off and throw it away. They're as accurate as a bmw speedo.

 

[skywalker]

Right here goes,
As Steptoe says they're not that reliable.
Here's a few suggestions on the charging system assuming the battery's not got a dead cell or two.
The charge light will always come on or flicker at tickover -thats the way they work.
You say its got a new rotor on it. Check the slip rings are clean and grease free. This is the most common fault I've come across.
If new brushes have been fitted check that the insulation washers have been fitted correctly ie the small one between the two larger ones on the right brush as you look at it from the front of the engine
Check the diode board -are the earth straps on the top of the board.Some people fit them on the bottom which is live. If its a solid mounted rather than rubber then make sure the mounting posts are bare ie no paint where they make contact with the back of the board
Disconnect the voltage regulator plug and look at the plug on the harness side. You'll see 3 letter designations D+ ,D-, DF.
With a multimeter on volts across the battery bridge D+ & DF with a split pin across the plug start the bike & it should charge up 16v.
Have a look also at the starter relay on the left side of the frame & make sure the 2 large red wires haven't corroded through.
Later voltage regulators have red tops unless you've got a police spec one which will be black.
Make sure also that the red wire to the diode board which takes its feed from the starter solenoid hasn't rubbed on the black cover that covers the starter motor

 

[John Roberts]

Thanks for that, Skywalker, I've printed your post in readiness for when it happens again. It's only happened this once so far so I'll leave it alone until it goes faulty. I spent much of my working life maintaining telephone exchanges, usually it's a lot easier to clear an intermittent fault when the fault is actually on.

Oh, and am I right in thinking that it should safely do over 50 miles or so on a fully charged battery? That should get me home most trips. (Well, unless the lights etc. are on)

 

[skywalker]

No problem John,
Thought about a couple of other things to check overnight.
With the rotor off the crankshaft measure the resistance across the slip rings -it should be about 3-6 kohms then after that put the positive probe of your meter on the front slip ring and the negative on one of the fingers of the rotor and check for short short to earth.
Rotor failure's pretty common.
If you've got the diode board off you could check out the diodes make sure they're not leaking back. If memory serves me right going across the 6 little circle points on the board between the live side & the earth you should have approx 35kohms one way and 0 the other.
If all this fails then last thing I can think of at the moment would be having a look at the charge light in the clocks as the light is reqd as part of the charging system. The bulb holders on old boxers get very corroded at the contact points with PCB in the clocks.
The blue wire in the white block connector near the starter relay - connection in that can get corroded.
There's only 2 wires in this connector - black & blue -black is for the starter.
Cheers

 

[John Roberts]

Not that I'm complaining or anything, but it seems to have sorted itself out, I had a 222mile ride today (woo-hoo! went like a dream- you know, one of those days when you don't expect much, then they turn out to be just perfick ) That's on top of some local trips during the week.

So that's sorted, then.

 

[brassmonkey001]

Not that I'm complaining or anything, but it seems to have sorted itself out, I had a 222mile ride today (woo-hoo! went like a dream- you know, one of those days when you don't expect much, then they turn out to be just perfick ) That's on top of some local trips during the week.

So that's sorted, then.