AJS & Matchless Owners Club

Hi this is not my area of expertise and so far has not caused me any issues BUT... I just thought I would check the charging with my multimeter whilst running the bike for 15 minutes or so whist it is not being used. the battery is an AGM type and was at 6.45 volts before I started ( it holds this charge for weeks on end and I just stick it on the trickle charge every month or so for a day to keep it topped up). On the bike whilst ticking over and revving (it seems to make no difference) it will gradually charge up to 6.80 volts and hold there indefinitely. If I put the lights on at full beam the charging rate drops to 6.25 volts and then holds there indefinitely, turn the lights off and it will gradually increase to the 6.80v. This seems strange to me because on my Yam, which had charging issues until I put a solid state reg/rect unit on it, which is obviously 12 volt the charging rate is almost 13 volts at tickover with all light blazing and almost 15 volts with 3000 rpm. The model 8 has a A reg on it and has been fine but not sure what would happen on a long run with the lights on and why doesn't the charging rate increase with revs??? is this normal

Cheers Paul

Without going into details, “voltage” isn't the same as “charging rate” (amps are). What is happening is that the charging rate is falling because the alternator is powering the headlight instead.

To be confident that it'll be fine at night, you need to check that the battery isn't discharging with the lights on. You can only check that with an ammeter in series with the battery terminal...

Oz, does your ammeter not show positive when riding with lights on? I have an A Reg too and there is always a charge showing in that instance so I assume (hopefully) that battery is still charging.

If in a lot of stop start riding, maybe not.

Thanks both of you.. a couple of extra questions though.

What is happening is that the charging rate is falling because the alternator is powering the headlight instead

Shouldn't this increase with revs though as it does with my RD Yam?

You can only check that with an ammeter in series with the battery terminal...

Can I use the ammeter off the bike and can you explain in nerd terms how I do it or is it just a case of connecting the ammeter across + and - on the battery

does your ammeter not show positive when riding with lights on?

Haven't ridden with the lights on but stationary with quite a few revs and held revving the ammeter stays on zero with the dip or main beam on. Once the lights go off then the ammeter shows a small charge (around 2 amps) for about 10 seconds or so until it goes back to zero again. There is no + charging showing on the ammeter with the bike running and the lights on, maybe it is because the battery is fully charged already and the A reg is doing exactly what it is supposed to do?

Ozmadman wrote:

What is happening is that the charging rate is falling because the alternator is powering the headlight instead

Shouldn't this increase with revs though as it does with my RD Yam?

Not necessarily. The electronic regulator is taking care of things - if the battery is charged, the terminal voltage will be constant regardless of revs. Too high and it'll boil the battery.

You can only check that with an ammeter in series with the battery terminal...

Can I use the ammeter off the bike and can you explain in nerd terms how I do it or is it just a case of connecting the ammeter across + and - on the battery

Eek, no! The ammeter goes in series, i.e. inline with one of the wires. Not across the + and -. The ammeter on the bike already does exactly this (it's wired in series with the battery line, only the horn and I think the brake light don't go through the ammeter).

does your ammeter not show positive when riding with lights on?

Haven't ridden with the lights on but stationary with quite a few revs and held revving the ammeter stays on zero with the dip or main beam on. Once the lights go off then the ammeter shows a small charge (around 2 amps) for about 10 seconds or so until it goes back to zero again. There is no + charging showing on the ammeter with the bike running and the lights on, maybe it is because the battery is fully charged already and the A reg is doing exactly what it is supposed to do?

That's fine then. Zero(-ish) charge with the lights on is fine. As long as it's not negative, the battery will stay charged.
If you are worried, fit an LED headlight. They are so much brighter and have hardly any current draw. Then it'll charge all the time (until the battery is fully charged...)

Paul. Just to confirm Clanger's reassurances...........

Ozmadman wrote:Haven't ridden with the lights on but stationary with quite a few revs and held revving the ammeter stays on zero with the dip or main beam on. Once the lights go off then the ammeter shows a small charge (around 2 amps) for about 10 seconds or so until it goes back to zero again.

That is perfect.

There is no + charging showing on the ammeter with the bike running and the lights on, maybe it is because the battery is fully charged already and the A reg is doing exactly what it is supposed to do?

Exactly. You've got it!

(If anything I'd say your Yam charge rate of 15v is slightly high for a 12v battery).

Enjoy.

Thanks Paul.... An LED headlight bulb was a consideration. I recently fitted one to my Yamaha RD when I had charging issues with that and it is mega bright (equivalent to 70 watt) and doesn't cause any issues with charging now (well that and a solid state reg/rect as well) unlike the 35 watt original one which was rubbish and the 60/55 watt one I tried which the bike didn't like at all. Like the AJS the Yam even then had a charging system barely sufficient for the job, and 43 years on time has taken its toll. You would have thought the Japs would have had that sorted wouldn't you? cheers

And thanks Neville as well, just a LED bulb then for a decent light