Charging.

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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G Dicko
Member
Posts: 8
Joined: Fri Dec 25, 2020 12:43 pm
Location: Derbyshire UK

Charging.

Post by G Dicko »

Hi all
I have a 1950 AJS Model 18. I have recently completely rewired it. Since I've had it, it has never been out in the dark until recently. That's when I found that it wasn't charging because I lost my lights.
After doing some research, I checked the Dynamo by linking the two outlets together and I got a reading of 9 volts ! So far so good.
I then found there was nothing getting to the battery and came to the conclusion that the regulator was cream crackered. I've now wired it through a new modern 6v regulator and now I'm getting 5.3 volts feeding the battery (checked from the battery leads not connected to the battery) I expected that reading to be around 7 volts, so I have 2 questions to ask.
Am I right to expect a return of 7 volts or is 5.3 ok ?
And,
I'm not certain the 2 wire's from the Dynamo are the right way around because my dynamo isn't marked E and F and I've seen conflicting drawings on which is which. Does it matter ? and what would happen if I swapped them around at the Dynamo ??

Any advice would be greatly appreciated.
Many thanks
Glen
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: Charging.

Post by Groily »

9v off a bridged D and F to earth at the dynamo is only OK if that was at low-ish rpm. Should zoom up into double figures if spun in a mains-powereddrill.

5.3 volts at the battery, or rather from the 'A' wire off the regulator, is no good. You need more than battery voltage to charge it. A fully charged 6v battery is actually 6.6v as each cell is 2.2. So you need more than that. 7.2v is the standard charging voltage for a 6v system, and should be maintained with loads on, or near enough. It should be stable from about 2000rpm odd, at which point the regulator should be in full regulating mode.

If the wires at the dynamo are the wrong way round, things won't work. In some cases you'd get excessive charging and no voltage regulation because D would be constantly connected to F (the field); in others you'd get nothing. Depends on how the regulator works inside.
The D wire off the dynamo should be connected under the cover to one brush, the F lead to one of the wires that come out of the main body of the dynamo from the field coil.
The other brush and the other inside wire from the field coil should be attached to earth with a little screw.
Swapping field coil or brush connections round reverses the direction of rotation. Swapping both brings you back to where you started on most dynamos. (Some early ones there's no choice of which brush is D and which earth because the brush mounting on one side isn't insulated on a mica plate.)

Suggest you repeat the 'bridged F and D test' and also hook a 12v 21W bulb on along with the meter when the thing is showing a charge. It should light and go up to full brightness quite easily. If it doesn't, the dynamo needs a fettle - brushes, internal connections at the cover, or more serious stuff like the armature. If it DOES light brightly with revs and the voltage rises steadily with rpm, then check the output from the regulator directly on the 'A' wire, rather than at the battery end via ammeter etc. It should rise to 7v+, but will look spikey on a digital meter. If it won't produce that sort of level, then check connections from dyn to regulator and above all the earth. Worst case the regulator isn't any good. Some of the Wassell ones don't always get to 7v in my experience, but should do 6.5 to 6.8ish. If the voltage off the 'A' wire directly IS good, then check your wiring downstream: ammeter, switch, state of any bullet connectors en route, etc.

Note that this applies if the regulator used is designed to run with the dynamo the way Lucas originally set it up. The rotation is obviously correct, and presumably the polarity (pos or neg earth) too. The only thing to upset what I've said here is if you are using a Wassell negative earth regulator, or a JG type, which require the field coil connections in the dynamo to be different - one wire to F, t'other to D (not one to F and one to E). But I don't think you have a problem there, or you'd only get about half a volt out of the thing doing the bridged F and D test, because it's the wrong test for either of those regulators.

The Matchless Clueless site gives you chapter and verse in plain English on all of this, better than is possible in a reply here:
https://www.matchlessclueless.com/elect ... as-dynamo/

PS Fit and trust your ammeter! It will tell you you have a problem long before the lights go out.
G Dicko
Member
Posts: 8
Joined: Fri Dec 25, 2020 12:43 pm
Location: Derbyshire UK

Re: Charging.

Post by G Dicko »

What a fantastic and informative reply. Thank you very much for this, you've been a great help.
Cheers
Glen
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