ammeter readings

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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ammeter readings

Postby Ian 14 G2 » Sun Mar 13, 2011 7:14 pm

Can anyone tell me what the ammeter on my ajs 14 should be reading when I have my engine running and,
A. my side lights on
B. my main beam on
C. full beam
as the main and full beam are giving a negative reading,is this correct or do i have a problem ?

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ammeter readings

Postby alfie » Sun Mar 13, 2011 9:03 pm

do you have a battery fitted ?
www.manchestertrf.com

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ammeter readings

Postby Groily » Sun Mar 13, 2011 9:09 pm

This is a revs related thing really and depends on the details of your electrical system.
You should see the ammeter just in the plus section, or 0 at worst, at mid-rpm with a decent battery on board. With ignition only it should be comfortably there, with the headlight on it takes the alternator a few more revs to get there, but it should.
Don't know if you're running at original 6v or upgraded 12v, with a modern rectifier/regulator or the original design. But in all cases there should not be a negative reading at above say 30/35mph in top gear, with everything on (provided you haven't stuck a searchlight bulb in for the headlight).
Original systems are poorly managed so charge rates vary according to state and size of battery, bulb wattage etc.
At tickover with lights on there will always be a big discharge as your alternator isn't turning fast enough, so 'engine running' isn't the real guide here. It's 'engine running at more than about 1500-2000 rpm' that will tell you whether the system is balancing properly or not.

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ammeter readings

Postby Ian 14 G2 » Mon Mar 14, 2011 9:20 am

I have a 6 volt battery fitted which I have checked and is correct for my year and model.

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ammeter readings

Postby Groily » Mon Mar 14, 2011 11:46 am

If you're still on the original system, 6v, three wire stator on the alternator, rectifier but no regulator, then the charge rate is primitively controlled by the switch, which brings in extra coils on the alternator when needed, to support lights.
If at medium revs the ammeter shows a charge with only the ignition on but a discharge with the lights on, then either the switch isn't cutting in the additional alternator coils the way it is supposed to (wiring fault or defective switch), or the alternator isn't up to snuff. Or possibly there is a fault on the rectifier, poor earth somewhere or other wiring fault. Unfortunately it's quite a long list of possible faults, if there really is one, that is.

You don't say whether it's a big or small discharge with the lights on, or at what revs. As I said before, at tickover and a bit above there will be a discharge with all loads on even if everything is fine, as that's the way these things are.
If you've got a wiring diagram it would be worth just following through the leads from alternator to rectifier and switch / ammeter / battery to make sure they are correctly connected. If that checks out OK and you have a meter, then you're into checking the AC output from the alternator and then seeing what the switch is doing when in its various positions.

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Location: TYNE AND WEAR UK

ammeter readings

Postby Ian 14 G2 » Tue Mar 15, 2011 11:12 pm

having carried out a full check of the electical system as instructed in my manual I found that there is some damage on the windings on the allternator causing an earthing problem so I am having it looked at and that should be the problem sorted, thanks for the advice and help.

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ammeter readings

Postby Groily » Wed Mar 16, 2011 7:42 am

Well done Ian. Those coils don't want to go anywhere near earth! If the fix isn't a simple one, with maybe other damage you can't get at, your easiest solution may be a replacement stator from the nice Mr Goff? Hope the rotor hasn't been hitting the stator, as that might require both parts to fix things, along with careful reassembly to ensure the correct air gap between the two.

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