Britbike forum Forums British Motorcycle specific Brands Norton bulletin board bad ammeter

hi everybody , still finishing off on my 1956 model 50 , with the engine running it didnt show charge so i assumed the ammeter was bad as it shows charge on the multimeter , i have bought a new ammeter and it still dont show charge , is there any way i can test my new one off the bike , ( its a Lucas lookalike) , and i might have to send it back . thanks pp

to test ... hook up the ammeter between a battery and a load ( load on minus side )
meter will deflect to minus showing the amp draw of the load .

the ammeter could simply be wired up incorrectly ?
( the full load , in and out , of the battery runs through the ammeter ) so when they go dodgy
the original wiring can get modified in creative ways that can take time to undo .

the ammeter needs to be placed in circuit
to show current that runs in-and-out of the battery .

only when "the charge current" is greater than all the loads ... will the ammeter swing to plus , showing a charge to battery .

so all loads ment to show current flow through ammeter
are wired to the minus side of the ammerer
... (an exceptions is the horn , usually wired on the battery side of the ammeter )... as it will peg the meter and isnt a consistent load needing to be measured .

hi Quinten, so if i put the pos of the battery to one side and the neg to the other side i should get some reading?

Peter,
As Quinten described above, the ammeter must be in series with the battery (the power source), and a load (such as a headlight). The headlight will create a resistance to current flow, and will determine the amount of current flow through the circuit. Wired in this way, the ammeter will respond to the current passing through it "on its way" through the load..
If you were to wire the ammeter "across" the battery the way you describe, there will be no resistance to current flow in the circuit. Thus, a high current will flow, limited only by the wires and the internal resistance of the ammeter and battery ... with the likely destruction of your ammeter.
Hope this is of help.
.. Gregg

Whatever you do, DO NOT do that.

This is the money quote!! Because the wires and ammeter will fry if you leave it connected for long. Put a known good headlight bulb in the circuit between a battery terminal and the ammeter and look for needle movement. Don't expect it to be super accurate but the needle should move one direction or the other.

If the ammeter has been bypassed in a past life, look for all the wires to be on one post,
and nothing much on the other. (Or, a wire bridging the 2 posts !)

Note also that the horn should not have power supplied through the ammeter,
but in fact is wired to bypass the ammeter - exactly as above.

thanks for that , i will try as you suggested a great help for me . pp

yes , to what Gregg and others have said . ! do not hook up the ammeter without a load in series.

the plus and minus on the ammeter are not-voltage ... they are current flow
The ammeter measures current flow , in real time ...
The ammeter is a simple GateKeeper of the amp flow ... in and out of the battery

If there is current flowing... from the battery , it is supplying the power ( needle minus )
If there is current flowing ...to the battery ... it's no longer supplying the power
... it's being charged by the charging components ( needle plus )


Referring to the above diagram , hooking up the ammeter could be as simple
As restoring two connections .
Except for the horn ,
all the loads ... and the charging power... join the ammeter on the ( negative ) side of the ammeter
... the brown /white wire

and only the horn and the positive side of the ammeter... join the minus battery terminal
... brown/blue wire

With the Lucas style ammeter ( there is no shunt )
The full amp load , in or out of the battery ,
passes through the ammeter coil (that forms a simple full current inductive Loop )

and the zero centered needle on the ammeter face
deflects and displays in real time
a magnetic reaction .... to the electromagnetic field generated by any current flow
In the nearby copper loop .

A 1956 would be pre alternator ??
A magdyno and genny, in fact.
I don't quite recall the finer details of the earlier discussions here....

Without that ridiculously complicated switch.
AND +ve earth, rather than -ve earth as on this earlier diagram
https://www.nortonownersclub.org/si...diagram%20for%20ES2%20up%20to%201952.png

P.S. Did alternator bikes even have an ammeter ?

I think you're right about the magdyno .
I know no much about Norton's
(but after 10 minutes on the Gooogle )
Here's my report .
the model 50 was gone
From the lineup during ww2
and only reintroduced in 1955 ...

...and seems to have had a mag Dyno up through 1958
and then 6 volt alternator Electrics and a distributor in the mag hole form 1959 .
... And at some point the featherbed frame

... but in either case ...the ammeter position in the circuit is the same
for alternator and Generator
... and for plus or minus ground polarity .

... depending what Peter Paul finds in the headlight shell
Hooking up the ammeter could be easy ... or a Rat's Nest of older crumbly wires

One old trick was to put a loop past the ameter , so when it fell to bits the cable was still live .

Sounds like you gotta continuity problem . the olde Bulb & cable current test trick or a multi meter at the ameter 'd sort it quick .

The Lucas ammeter has an internal shunt. There is no way that the coil could handle the potential currents.

take one apart , there is no shunt .

That heavy coil is the shunt.

The heavy coil is the coil.

I apologise to Quinten.
For some reason I thought that the ammeter was a moving coil type but in fact is a moving iron type which doesn't have a coil of fine wire.

hi, i can get a reading frpm the terminals that go to the ammeter when they are disconnected from the ammeter and the engine running with a multimeter , so perhaps it is caput , ive tried the old ammeter.

A working ammeter shows nil ohms resistance across the terminals, when tested with a multimeter.

If you shake it from side to side, the needle should wiggle.

Another simple test is to connect the terminals of a PP3 9V battery to the terminals of the ammeter. The needle should deflect. The battery has high internal resistance and won’t explode in your hand or anything. I expect it works with other small torch or radio batteries too.

Hi, Triton, yes i have nil reading resistance testing my ammeter , i have tried the small battery and it dont even flinch , if i run the engine with the battery disconnected i get a reading on the multimeter it jumps about from 2 - 7 amps on fast tickover , i have most of the lights connected up except the headlamp could that be a problem . thanks pp

I suppose it doesn’t take much to stick the needle. Some old ones had an adjuster screw on the back, for the needle bearings (which were just a point in a hole).

"If you shake it from side to side, the needle should wiggle."

Which is all they do when they are 'working'.
Totally useless instrument just there to plug the hole.

The ammeter only reads current that flows through the meter
so is placed like a fuse in the circuit , is your ammeter hooked up correctly ?
Both the ammeter and a fuse read current .
The ammeter displays the direction of current flow ( to or from the battery )
a fuse allows current to flow ... to a generally set fused limit

for ammeter bench testing
the electrical connection is from threaded pole to threaded Pole .
the resistance is minimal ( equivalent to about 12 inches or less of copper wire )
the pole to pole connection is also, or should be ... isolated/ insulated from the case .
( in essence , a few loops of wire from one post to the other ) ( insulated from the case )

the needle bits have no electrical connection .
It's a basic bit of counterbalanced clock works .
The needle pivots on a perpendicular spindle ...( a zero jeweled movement )
With some friction applied by a set screw on the bottom end .of the case

the pivoting part of the Clockworks can be repelled magnetically ( through Electro magnetic torque Force )
From the non-pivoting part of the Clockworks ... as current flows through the ammeter coil .
It's a deceptively simple instrument from the pre transistor age
that fits well with things that have pushrods
and kickstarts

If you can't read the ammeter working through the engine vibration ...
the engine mounts are probably loose or the engine needs balancing

For the coil to attract or repel the needle, must the needle not be magnetised? If the needle looses it's magnetism would it not be dead as a door nail, yet the coil would still conduct current flow?

Hi, everybody , i have the thing almost together now , i got a solid state reg , ive tested the dynamo , the bike starts easy , it still dont show charge on the ammeter ,if i turn the h/lights on without the engine running it shows a charge ,. any ideas ? thanks pp ( its a new ammeter Dave) p/s how do i test the wire from the reg to the neg side of the ammerter

It’s showing a discharge. It’s indicating on the charge side of the ammeter because the ammeter is connected backwards.