AJS & Matchless Owners Club

Hi, I have recently acquired a 1957 Model 30 twin with dynamo/mag ignition. It's my first AMC machine, and am impressed with after a break from British bikes for a number of years (after many years with big Guzzis).


I was hoping someone on here with their vast knowledge could help me solve a problem with the charging side of things. The motorcycle has been recently rewired by a professional motorcycle engineer.

I have had the dynamo checked by a qualified electrical engineer, and the readings were well within tolerances.

The dynamo is pushing out 7 odd volts without load (lights on) and manages over 6 with lights on.


That side of things is fine.

The issues I am having is what the ammeter is reading.

With lights off it shows 4 amps above tickover straight away. This is normal.

With headlight on the needle is off the scale (positive).

Engine off, headlights on and it is at zero. This isn't right-no discharge showing.

It has a DVR2 regulator installed. The battery is a modern non spill MK ES13-6. I have replaced the ammeter with a genuine Lucas 6v one.


We're scratching our heads here. We've gone over the circuit several times, and it all seems correctly wired, with no dodgy connections at all.

It must be something simple, but it's beaten me and my electrical engineer mate with 40 odd years experience!

Can any of you nice people offer advice on what to look for please?

A

Something is wrong with the wiring to the ammeter. It sounds like the lights are wired to the battery side of the ammeter, rather than the dynamo side.

This would explain the zero reading with the lights on (and the engine off) and the excessive reading with the engine on (because the ammeter is showing the battery charging current + the current to the lights i.e. the sum total of the dynamo output). The ammeter should be measuring the current to/from the battery, not the dynamo!

is ammeter reading the right way , i put a replacement meter on mine and it was wired back to front compared to previous meter , just had to swap wires over on it .

the charging wont start to register until revs have reached something like 1100rpm and above .

if you put lights on without engine running it would show a discharge on an 8-0-8 ammeter of about half scale with a bpf bulb in the light , mine is around that figure .

with lights on and engine running at idle you may see discharge and then when the revs go above the point that the dynamo comes alive the ammeter will rise to positive charge .

i have a model 30 1956 , magneto ,dynamo and solid state regulator .

i did have an LED bulb in headlight but whilst it draws very low current it was a problem for me when my dynamo stopped charging and i didnt notice it due to meter readings being so low , i only noticed it when the battery went flat and lights went out one day .
it was just oil in the dynamo housing getting in from the timing side seal , cleaned all off with brake cleaner and replaced brushes and bearings etc and all fine again .

if you are using the old style voltage regulator using air gaps and contacts it might have been set wrong by someone and is cutting in too early , or its just a simple fact that the ammeter is wired back to front and showing a discharge when its actually charging .

there are only 2 terminals on the back of ammeter, its more fiddly to get in and swap the wires over than anything else .

hope you get it sorted , ive stopped taking my ajs out now as ive just seen the gritter lorry go past the house and so dont want salt deposits and corrosion setting in , will just be a run up and down the driveway until next spring boohoo .

all the bast
ian

clanger9 wrote:Something is wrong with the wiring to the ammeter. It sounds like the lights are wired to the battery side of the ammeter, rather than the dynamo side.

This would explain the zero reading with the lights on (and the engine off) and the excessive reading with the engine on (because the ammeter is showing the battery charging current + the current to the lights i.e. the sum total of the dynamo output). The ammeter should be measuring the current to/from the battery, not the dynamo!

Thanks for that-on he DVR2 regulator it says to connect the brown wire to the ammeter. Which it was. This however is incorrect as it needs to connect to the light switch. The field and dynamo cables were ok. I went through all of the loom and connections to make sure. I didn't have to check the ECU or diagnostics!!!

I scratched my head for a few days, and today sorted it out successfully this afternoon. An hour with a multimeter, soldering iron, a bit of heat shrink and it's fixed. I am happy as now have a discharge (I never thought I'd say that!!) with the headlight on! It's charging well, with or without the lights on.

A

Great news!

But for the avoidance of confusion to others, those instructions are certainly not wrong.

Wire 'A' from the regulator (whatever type it may be) goes to one side of the ammeter and then straight to the switch - or vice versa if you prefer - but it is electrically the self-same wire.
The other side of the ammeter goes to the battery live side. The horn supply may also be wired off the same battery-side ammeter terminal.

The attached 'typical' diagram shows what I mean: the A wire could physically go to switch position 3 or to the ammeter. As long as the two are linked at the same side of the ammeter, with the battery wire on the other, all will be well. The net current status at the battery is what the ammeter will then show, regardless of what is switched on. (Rather than, as Clanger9 said, the ammeter telling you what the total demand on the dynamo is at any given moment.)

By way of illustration, if you had the brake light wired straight from the battery you'd see a surge on the ammeter matching the extra demand when you put the brake on - with the engine running. But you'd see no discharge if you applied the brake with the engine stopped because the load isn't going through the ammeter.

That's right. The regulator does indeed need to be "connected to the ammeter", but to the lighting side, NOT the battery side.
From plugsnpoint's description, it sounds like it was connected to the battery side.

The only things on the battery side of the ammeter are the battery, the horn and the brake light. Everything else goes on the other side.