alternator output

greasemonkey62 · Post by **greasemonkey62** » Sun Oct 03, 2010 1:37 pm

I have now fitted the Boyer 108 power box and the points inductive discharge unit to my 1962 AJS model 31 650cc, I am concerned about the ammeter showing a discharge with the engine running without the lights on, does anyone know what the reading should be with a voltage tester between the now newly joined up green and yellow/green and black wires and the green and white wires now?
It starts up first kick now and ticks over perfectly, I fitted a new 12 volt/9AH battery with the kit.

Cheers Ray.

itma · Post by **itma** » Sun Oct 03, 2010 1:41 pm

does it show the opposite way with no engine running and lights on? if so try swapping the ammeter leads.

you may get around a reading of 14volts if you rev it hard enough as long as it shows 12 plus dont worry

Groily · Post by **Groily** » Sun Oct 03, 2010 2:08 pm

That's a PITA and v sorry to hear it.
The answer is 'Quite a Lot', Ray, varying up and down with revs. If there are none . . . alternator ain't alternating. Should see double figures at rpm not much above tickover (I'm guessing, but it's of that order) - AC volts scale mind, and red lead in Volts socket (I've made that boo-boo a time or two on some meters).
If you think about it, the alternator and regulator have to produce more than the battery's 12v at reasonable rpm - regardless of the electrical loads - otherwise the battery will go flat. In round numbers the DC wire from the rectifier should show about 14v volts DC between it and earth with the engine running above tickover with only ignition on. Or test for that sort of voltage across the battery terminals (same thing).
I fear your basic prob has been lack of output from the beginning, although the mods you've done are good ones and worthwhile.
The discharge you're seeing now is the ignition load.
Really does sound as if another alternator is the likely solution, unless there are damaged or broken wires under the insulating sleeve they go through.
More good luck!

Groily · Post by **Groily** » Sun Oct 03, 2010 2:16 pm

But do check itma's ammeter point just in case you're charging but showing it the wrong way round! Didn't think of that!
You should get more than 14 AC volts across the disconnected and unregulated AC wires though, not that I ever want to disagree with itma! The 12+ to 14 need to be DC volts (on the rectified side, ie from the minus terminal on your nice new box, to your positive earth).

Eric · Post by **Eric** » Sun Oct 03, 2010 2:18 pm

The Boyer system may use more current than the original coil ignition system and that was just about balanced or very slight charge at tick over, so a small discharge at tick over maybe the norm with the Boyer, you don't say how big the discharge is?

Equally what Ken suggests maybe the simple answer.

The main thing is that the original alternator system was only just good enough to maintain things when originally fitted new, mainly because there was no sophisticated method of controlling output so it had to be kept low rather than cook the battery.

So use as many LED lights as you can and don't go mad with your new headlight bulb a 36w halogen should still be a big improvement upon what you had before.

I think I did suggest changing your original system was not going to be the magic bullet you almost have to start again from scratch.

itma · Post by **itma** » Sun Oct 03, 2010 2:53 pm

Useing an LED rear light I run a 100/80 headlamp, a slight imbalance in the charge but by god it sorts out the Audi drivers ....

Eric · Post by **Eric** » Sun Oct 03, 2010 5:35 pm

No good for BMW drivers then Ken?

itma · Post by **itma** » Sun Oct 03, 2010 5:57 pm

fries them mate. fries them
But round here its Audis that are number one menace now.
BMW minis coming up the list fast though, closely followed by black VW golf gti's.

Groily · Post by **Groily** » Sun Oct 03, 2010 6:29 pm

Blimey, it it only discharges a bit at tickover but charges otherwise then it's probably OK. Even with a normal coil and points, there's likely to be a small discharge at zilch rpm and yup, worse with the Boyer unit. I read Ray's comment as meaning 'there's no charge with the engine running (although it ticks over nicely)'.

100/80! Double Blimey!

As revs mount, with the AC wires reconfigured and the all-singing reg/rect in there, all the coils on the stator will now (or should) be in operation all the time (they weren't when it was a three wire job) and there really should be plenty of juice to support basic ignition and charging at quite modest rpm. There should also be enough at mid- to higher revs to support lights too (subject not to having Ken's Personal AA Searchlight in there!). It's quite possible that charging could be a bit marginal in stop-start traffic riding for lack of continuous revs, but the ammeter should get to zero or better with a good blip of the throttle.

First thing to do though, as Eric said in the first place, is to be sure the alternator is producing. All else flows from there.
Think I said in my PM Ray that you might want to bite the bullet and consider a replacement alternator as well . . . Pieces of Silver for Peace of Mind, sort of thing.

greasemonkey62 · Post by **greasemonkey62** » Sun Oct 03, 2010 6:35 pm

I have one of Goffs LED rear stop/tail units all ready to connect up, and have 40/45W halogen headlight bulb along with a bright 23W pilot light, all from Goffs, it sounds as though the headlight bulbs may be too much now, aint life a bitch and I have bought two, one as a spare. Thanks to all, I will check the power output tomorrow, it should be fun as I have never used a circuit power checker before, oh heck !!!
If I fell through the mattress would I see you in the spring?

Chers Ray.