LCGB Forums

I've got a strange charging problem that's manifested itself.

The 12v battery that powers horn, stop light, side/parking light and LED indicators is fully charged and without the engine running they all work perfectly.

With the engine running at 2000/2500 the voltage at the battery shows well over 15V and the indicators flash extremely fast, the inline fuse protecting them then blows in fairly short order.

I fitted a new regulator as I thought that was the problem but it seems to have had no effect.

The ignition and AC side of things appear to be functioning OK.

I've checked all the wiring and can find no issues.

Has anyone any ideas or has encountered anything similar as I am a bit flummoxes at the moment.......

Hopefully someone can give me an idea, Cheers Ian

There are only really 3 things at play here: the generator (stator and flywheel), the regulator and the wiring.

Within reason, the generator can chuck put what it wants. I've seen over 70v although not on a lambretta.

The regulator should not put put more than 15v.

The wiring fault if there is one is likely to be a ground or 0V issue.

I'd start by measuring the stator output but moving the 0V lead on my meter from stator, junction box if you have one, then regulator, then battery.

Maybe an easier way is to make sure that all 0v or earth connections are good.

My next suspect would be the regulator even though you've already replaced it.

Tell is how you get on.

Hi Ian,

Is the stator a fairly normal six-pole item as sold for many 12v electronic ignition? It’s not a VAPE, varitronic, Casatronic or something else? If it is a six pole stator, has it been modified to suit DC operation? I guess not as you mention the AC side of the lighting which would not be available to you if you had gone “full DC”.

You mention the regulator, but surely you mean a regulator/rectifier. I assume this is just an omission, but how are you rectifying the AC to DC for the battery? Is the rectifier a separate box?

Thanks for the replies,
The regulator is the good old Vespa PX 5 pin that has the regulating and rectification in the one box, I have tried both the old one and the new one back to back and both give approx the same voltage reading at the battery when the engine runs.

the stator is a 6 pole that supposedly has 120/130W output that I have been using for the last 4 or 5 years totally unmodified with electronic ignition setup.

I have been suspecting earth problems and have checked the most obvious but maybe I need to dig deeper.

I will keep on trying and report how I get on

Thanks again Ian

There is a large Zenor diode in those regulators that are set to trigger at approx 14 volts and short anything above that to earth where it's dissipated as heat (hence the fins on the regulator). If as you say you are seeing 15 volts across the battery terminals then it has be be either a faulty regulator or possibly the regulator and flywheel earths, check them all very carefully

Thanks Coaster for the reply, I hope to have a good dig in at the weekend.
Cheers. Ian

To add to what Coaster says the regulator/rectifier is designed to work best with cool air stream running over it

Well I think I may have two issues,

having taken the flywheel and stator off I found the green stator wire had a nick in it and was almost broken through, (possibly touching earth with vibration), having fixed that and reassembled everything I now have around 13.5 volts at the battery with the engine running slow or fast.

The issue with the LED indicators appears to still be there, without the engine running they work perfectly, however as soon as the engine is running they go ballistic and flash fast and randomly (almost as if they are getting AC) then blow the fuse............getting fed up now having checked every earth I can find, had the headset and horn-casting off to check the wiring going up to and from the switch.

I'm beginning to wonder if it's worth doing away with the battery charging, (just charge it up occasionally with battery charger), and running the bike on AC.
Any thoughts on that gratefully received

Cheers Ian

I'd measure the supply voltage to the indicator circuit, with engine off, then engine running. Both measurements with the indicators off.

From what you're saying, it sounds like it will be too high with the engine running.

It's quite difficult to advise without a circuit diagram; is it standard and if so, which model?

If, when you have got to the bottom of the electrical issues, you are still having a problem with the indicators flashed too fast, I can vouch for these Puretek adjustable relays. They are cheap enough to warrant a try anyway.

https://www.ebay.co.uk/itm/272345319953 ... media=COPY

I think I've found the problem, a tiny wire going through the hole alongside the dip switch and horn wiring had been rubbed a bit by the twist grip rod and was allowing a bit of earthing to happen with movement of the throttle.

I had the indicators flashing ,( I am using the relay unit that Storkfoot mentioned), for 15 minutes with engine running etc and no apparent problem, so I need to go out for a good ride tomorrow and see if it is truly fixed.

Fingers crossed.

Thanks for the help Ian

50 mile run today, all good