The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: a101960 on 17.08. 2008 14:34

Title: Ammeter
Post by: a101960 on 17.08. 2008 14:34
The pointer on my ammeter always swings from side to side over 2000 rpm. Under 2000 the pointer indicates the charge rate clearly and smoothly. I have been told that there is a friction damper screw between the ammeter positive and negative  terminals that can be adjusted to dampen the pointer swing. Has anyone tried this? I assume that the swing is caused by parallel twin vibration harmonics.
Title: Re: Ammeter
Post by: a10gf on 17.08. 2008 18:51
Hi, have the same symptom, but battery gets enough charge. Tried a new amp meter, same. Never really investigated it deeper, but I'd think it has to do with a shaky regulator not giving steady charging, so 'what we see is what we get'.

I imagine it should go away with an electronic reg, maybe someone here can tell if the pointer steadied with a new regulator?

The only damping I've seen in there is the spring that sets the pointer back to center.
Title: Re: Ammeter
Post by: a101960 on 17.08. 2008 20:36
I do not think that the problem is caused by the regulator because I have an electronic regulator. The battery is always well charged so I do not think that there is anything wrong with the charging system. It would be nice though to stop the pointer bouncing all over the place. Some people seem to suffer with this problem and some people do not. The ammeter is a genuine Lucas instrument.
Title: Re: Ammeter
Post by: LJ. on 17.08. 2008 20:41
Yes Indeed there is a friction screw to dampen the movement of the needle but only on the genuine Lucas ammeters. I found that an after market repro does not have one and they do swing to and fro. There is no difference to the performance regarding mechanical reg or electronic reg although I find that a good properly working meter will show even when the reg cuts in along with either charge or discharge. I have not had to use the dampening screw as the meter seems to work and read just fine... Maybe you have an after market repro.
Title: Re: Ammeter
Post by: groily on 18.08. 2008 11:34
Agree with all that's been said - not the regulator I would think, as the flicker is there with some ammeters always (and the old mechanical regulator works at a rate of knots that would confound any needle!). I've just put a 2 inch white-faced Miller one on the A10 (no prob for me as the h/lamp shell isn't the original type and so I didn't mind enlarging the 'ole). These instruments, which ain't cheap, are the best I have had. I forget quite what the operating mechanism is (moving magnets?), but not the same as the cheapo pattern things, and very well damped and accurate. I have 2 of these on 2 bikes one is 12-0-12A, t'other 15-0-15A. On 2 other bikes I have original  Lucas ones - and they are pretty OK with mechanical or electronic regulators at 6 or 12v. On another bike I have a replica thingy which flutters like a tart's eyelids and whose needle is poorly mounted/damped. Looks smart but isn't great, although you can tell whether it's charging or not most of the time. I've had that on twins and a single and it's as bad on either (currently on a single). If I'm ever in doubt as to whether things are charging or not, I just put the rear brake on and watch the ammeter needle surge in the charge zone as the dynamo (or alternator) meets the extra demand. But if I want one that works nicely, I've decided the big Millers are the best thing and also the easiest to read where 'original' isn't a big issue.