Ammeter reading with headlamp on

[DRC]

Hi All

I am checking the electrical system on my Matchless 250 G2 the battery is fully charged at 6.5v at rest and with engine running it is 8.5v which leads me to believe that the alternator is working ok, the ammeter is at 1 o clock with engine running so showing a positive charge going through system, but when i switch the headlamp to main beam it dips into the negative by 3-4 amps even when being revved a little, is this normal or do i have a further problem with something on the electrical circuit.

Cheers

DC

[jackstringer]

55 W ÷ 8.5 V = 6.5 A

This is assuming the 8.5 V is getting to the headlights. That isn't counting the brake like etc.

I have had the ammeter go negative before, mostly when the battery is low and the system is using a lot of current from the generator to charge the battery up.

[DRC]

55 W ÷ 8.5 V = 6.5 A

This is assuming the 8.5 V is getting to the headlights. That isn't counting the brake like etc.

I have had the ammeter go negative before, mostly when the battery is low and the system is using a lot of current from the generator to charge the battery up.

Ok cheers Jack

[Groily]

I am checking the electrical system on my Matchless 250 G2 . . . . .when i switch the headlamp to main beam it dips into the negative by 3-4 amps even when being revved a little, is this normal or do i have a further problem with something on the electrical circuit.

I don't think it should do this, no.

You say 'main beam'. Does it show the same discharge on dip? The load is not dissimilar, so if on dip it's good but main beam not good, there's a problem.
Is it therefore possible that when you go to main beam you have in fact got both filaments lit up owing to a wiring fault, which would impose a large load which the system might not be able to support? (If your globe is, say, 36/36W, then both filaments lit = 12 amps at 6v, plus ignition load and small bulbs ill add another 2+ : a total that may severely test the alternator if you've got a typical nominal 90W three wire stator.)

If everything is in order, you should see the small charge you mention with lights off and a half-decent battery, and then a similar charge with them on (with a few rpm more than with them off). At tickover, you'll see a large discharge at tickover with the headlight on, but that should disappear with a few revs, and, roughly speaking, I'd expect the ammeter to be around 0 at the equivalent of about 30mph in top gear on one of those.

[DRC]

I am checking the electrical system on my Matchless 250 G2 . . . . .when i switch the headlamp to main beam it dips into the negative by 3-4 amps even when being revved a little, is this normal or do i have a further problem with something on the electrical circuit.

I don't think it should do this, no.

You say 'main beam'. Does it show the same discharge on dip? The load is not dissimilar, so if on dip it's good but main beam not good, there's a problem.
Is it therefore possible that when you go to main beam you have in fact got both filaments lit up owing to a wiring fault, which would impose a large load which the system might not be able to support? (If your globe is, say, 36/36W, then both filaments lit = 12 amps at 6v, plus ignition load and small bulbs ill add another 2+ : a total that may severely test the alternator if you've got a typical nominal 90W three wire stator.)

If everything is in order, you should see the small charge you mention with lights off and a half-decent battery, and then a similar charge with them on (with a few rpm more than with them off). At tickover, you'll see a large discharge at tickover with the headlight on, but that should disappear with a few revs, and, roughly speaking, I'd expect the ammeter to be around 0 at the equivalent of about 30mph in top gear on one of those.

Hi Groily

Thanks for the info i will check it out and also take it for a spin to see if ammeter is zero at 30mph with lights on.

all the best

DC