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J G voltage regulator


Well Known and Active Forum Website User
VOC Member
An unusual problem with the Vincent, too much charging current.
The bike has a chinamo, and J G unit, the charging current is steady
at around 4-5 amps at 50 mph in top, this is with the battery fully
charged. Have fitted my spare J G unit, it produces the same results.
The battery is fairly new and of good breeding, ie Varta.
Even with the head light on it still shows a 3-4 amp charge. My concern is that the dynamo will cook.
Someone tell me I am being paranoid. John.

van drenth

Well Known and Active Forum Website User
VOC Member
most probally you have corroded connections. How high is the charging voltage. with corroded connections the regulatot has the idea that the battery is empty due to resistance and sensing a lower battery voltage. Charging votage should be 12VDCx1,2 = 14,4 VDC.

Regards, van Drenth JC


Well Known and Active Forum Website User
VOC Member
Hi John,
Stop it, You're making me paranoid too! Can you try another battery and Ammeter for a comparison?
Cheers, John


Well Known and Active Forum Website User
VOC Member
Before anything else I would check the voltage of the battery after a run. It should be about 14 v. If that is ok then leave it overnight and by morning it should still be over 13v. If not, either you have something draining the battery or the battery is not very well. Another thought. Have you changed anything? Like adding an extra item which is not taking current going through the ammeter but rather being fed directly from the battery. It took nearly two weeks of phone calls and head scratching to find that the same symptoms that you have were occurring on one of our car alternator kits following the addition of a GPS unit etc taking current directly from the battery. Good luck.

Alan J

Well Known and Active Forum Website User
VOC Member
I've never had a battery retain 13 volts overnight!-they often charge at about 14 volts, but settle down to 12 and a half or so in the morning. Maybe your battery is on its last legs, I've had batteries charge up to 16 volts-but they didn't hold a charge. When the bike is "resting" in the shed, turn on your head light and see how long it lasts!


Well Known and Active Forum Website User
VOC Member
My tatty Comet (6V) was overcharging last week by about 7 amps - continuously - headlight on or off. I got a new battery (6V 8AH Cyclon) and the problem was immediately solved. I tested the old one - about 3.2 volts!! But it had lasted about 5 years of use - summer and winter. So John, the battery will almost certainly be the culprit in your case...

Peter B
Bristol, UK


Well Known and Active Forum Website User
VOC Member
Hello, Thanks for all the suggestions, checked amp meter found pretty good, for such a crude device. Checked earth on JG OK. Checked all connections OK. Tried another battery, just the same. The substitute battery was a car sized so this may mislead.
The original battery sits at 12.5v off charge and as Alan J says this is as good as it gets.
Will just get on with riding the beast, and stop worrying. Will try to monitor the dynamo temperature though.
Regards John.
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