THE dreaded G5 ELECTRICS -alternator output

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Trebor160
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Posts: 29
Joined: Fri Nov 03, 2017 9:36 pm
Location: Oldham UK

THE dreaded G5 ELECTRICS -alternator output

Post by Trebor160 »

Hi All, finished the rebuild on the G5 and it started third pump after a 3 year rebuild, oil pressure great and ticks over nicely, thanks goodness.

BUT I started it up with an external 6v batteryand forgot to connect the output (red) of the Areg to the frame earth.
So stopped the engine, connected the red wire to the frame and started it up, POP & a bit of somoke from the Areg area!
The inline fuse I put in is ok, all the lights and ancillary electrics still work and it starts ok with the battery in place. The fuse didnt blow so I'm assuming it could, for some reason, be the input side of the Areg.

I measured the voltage between the white (common) wire of the alternator (RM15) and each of the two other coil wires and it read up to (at just over tick over revs) 30Vac with no load. I also joined the orange and green together, as advised to make it two phases for the Areg and I got the same reading.

Any ideas anyone? Is the Alternator output too high, even with no load. Are the output readings correct do you think?
Thanks in advance,
Rob
Groily
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Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: THE dreaded G5 ELECTRICS -alternator output

Post by Groily »

Trebor160 wrote: Sun Aug 29, 2021 11:18 am forgot to connect the output (red) of the Areg to the frame earth.
We assume it's a positive earth machine and the A Reg is an A Reg 6 for 6 volt? With the alternator leads correctly wired to the ac terminals?
Not sure how many 'free' ac volts one should expect - to do more thorough testing you'll need to put a load between the leads I think. But they'll chuck out 'a lot', certainly.

A 1 ohm 100W resistor is what Lucas recommend, placed across the pairs of leads in all combinations. Certain current (amps that is) readings should show, give or take, on a meter set to the amps scale (must be able to handle 10A) at certain engine rpm (much higher than just off tickover). The data for each version of alternator is slightly different, but the testing routine is the same. Back in the day there weren't any combined regulator/rectifiers like the A Reg unit, so DC output tests were done off the simple rectifier, but it's pretty much the same idea.

For what it's worth, the Lucas book of words is here (and in the Archives somewhere more than likely): http://www.brightsparkmagnetos.com/libr ... %209AF.pdf

If the alternator seems OK, then with the A Reg hooked up do you see DC volts coming off the other wire (neg if you're pos earth) with the engine running?
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