Britbike forum Forums British motorcycles in general British motorcycles in general Useless ammeters, IMHO

Ok, so I’ll expect some flack here, aside from original restorations, why an Ammeter? What does an ammeter do for you when the voltage is the end issue to keep the bike running? I admit I am focused on the Electronic Ignition bikes here, but isn’t the same thing true with the OEM points design? Ammeters are notoriously fragile, require the highest current wire to have the ammeter inserted, and therefore put all the risk inside the congested headlight shell. I dunno, why a voltmeter wasn’t the choice in first designs at the factory. Just tradition would be my first guess. Ammeters help with trouble shooting when there is a problem, kind of like test equipment. Voltmeters on mine give me at a glance status. Just wondering, I’m not building any more……….

The only reason I can see for maintaining the ammeter is for originality which for a bike I plan to ride seems pointless. I'd much rather have a voltmeter in the headlight hole but no one seems to make one that fits. I've tried digital ones but they don't seem to hold up to the vibration. I even considered opening up the hole and using the smallest voltmeter I can find. Maybe someone can recommend an analog that fitts

My classic Britbike ammeters all seemed to read the same - a wavering fluctuation of several amps AT ALL TIMES!

Probably 3 or 4 different brands, at least as many slightly different silkscreened scales; and yet, eerily identical...

1st I will mention that this item was supplied by a fellow in the Netherlands that does not want to be in business suppling them, swore me to not give out his contact. This was several years ago, and I have since seen a few that would work OK. Mine has no numbers, just a graduated scale that DOES consistently match a voltage value. If I see it approach the - 12VDC range, I know there is a problem. If that actually happens with my Boyers, I know to take survival mode actions. (Turn off Excess loads if possible) The Ammeter would not give that warning, just show odd needle, which really isn’t very odd. Not sure why this came to mind, just saw an old saved photo and got on the soap box,…. Again.

It can be useful for quick electrical troubleshooting, assuming it works enough for the needle to move.
With key on, slowly kicking over the engine while watching the ammeter, the needle swing is a quick check for electrical faults. Needle swings? You have some battery and the points are making and breaking.

Needle doesn't move? Maybe a dead battery or something wrong with the ignition circuit like dirty points , broken or disconnected wire and so on..

So, an ammeter isn't completely useless.

Look inside a bike ammeter and look inside a voltmeter. Make a judgment about which cost more in 1930. That’s one reason why old vehicles had ammeters or just a charge warning light. A charge warning light was only convenient to fit when the vehicle had a dynamo (DC generator) and an ignition switch. Most British bikes with dynamos had no switch: the battery was isolated by the cut-out in the regulation system.

A working ammeter is useful. It shows that your charging system is operating normally. A voltmeter is probably better. That’s why voltmeters or “battery condition gauges” were a popular optional extra on cars in the 1960s.

There are neat colour changing LEDs out there that fit in the idiot light holes. i have one of Paul Goffs , its a very good thing.
Green good, charging, amber borderline, not so good , red bad discharge, higher than 14.5 volts flashes red

That's exactly what I do when starting an engine, with the ignition on, the ammeter should show a discharge as the engine is turned and coils energized, but then should swing back to nearly zero as the plugs fire.

+1 Gavin

In addition to ammeters, I have the voltage LED fitted to the headlight shell, which provides an instant indication of battery charging and voltage status.

I've never had much of a problem with ammeters although I have had one or two fry themselves. My main issue with them is that the terminals are exposed in the headlight shell so if you are doing any work inside the shell, there's a chance of shorting everything out. As a result I always fit rubber caps to the terminals.

Any mechanical meter will be subject to vibration failure. The partial fix for the Lucas ammeter was to poke a hole in the back of the case with a hot wire, then fill the meter with clear oil or glycerin and seal the hole with epoxy. The oil damped the vibrations so the meter lasted longer.
If a "digital" meter does not hold up it may have been made without surface mount components or not potted against vibration.
I suggested one like this when Don wanted an oil temperature and pressure gauge:

This has LEDs for pressure and digital readout for voltage. The voltage could be changed to LEDs so the top half LEDs show pressure and the bottom half show voltage. It may be more readable at a glance that way.

Ammeters were used with dynamos. When alternators came around they were replaced with voltmeters
in 99% of automotive applications. A series instrument device carrying heavy current is not practical.
A voltmeter is safer and much easier to fit as there is no large current cabling to be run.
The standard dynamo used on an early 60's car generated about 50% current less than the alternator
that replaced it. This situation has grown so the average car now uses an alternator with around 120 amps
capacity, that would mean 16 or 25mm cable to connect an ammeter, OR fitting shunts and voltmeters.
The method of regulation on a pm alternator will always give a shaky ammeter reading without damping.
A working ammeter will show what is being supplied to a load, a voltmeter will show the actual level of
the electrical supply including the battery. The 'cut-out' in the dynamo's regulator is/was to prevent the
battery 'motoring' the armature when the generated voltage was less than the battery voltage.

Either instrument is useful but manufacturing cost and practicality deemed the Lucas ammeter virtually useless.

The only Beesa I ever encountered with a working ammeter was a 1960 all iron low comp A10, it was smooth .

“…I suggested one like this when Don wanted an oil temperature and pressure gauge. “

DM, is that unit shown in your post an available item for purchase? It’s very unique, compact and useful! If it’s been shown before I missed it.

All analog meters are basically ammeters. An ammeter reads in series with the load, a voltmeter reads off a shunt in parallel with the load. Unless either is built stoutly with good damping they won't last any longer than a non fluid filled OP gauge.
Nothing wrong with the late Norton assimilator.

here some mo ammeter info i know it's about tractors but i think could also apply to our bikes as they are somewhat agricultural in nature

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=jd&th=336313
here one for jags (probably Lucas)

https://forum.etypeuk.com/viewtopic.php?t=955

The actual meter movement, the part with the Needle is the same. Commonly a D’Arsonval (D'Arsonval galvanometer) movement. The trick is how to control the current / AMP flow, through that meter movement and not burn it up! The Ammeter uses a HUGE shunt, looks like a bar of metal in some meters. You’d wonder why any electricity (potential difference) would bother going through the actual needle movement. Kirkchoff’s Law. The minuscule amount of current that ends up going through the needle movement is not going to burn it up. In the case of a Voltmeter, connected to the circuit in Parallel, the circuit itself is acting like the Shunt, alternate path for current. (Yes, there is still a small shunt in the movement) The voltmeter leads to the circuit can then be lighter gage wire, and do not have the entire circuit current flowing through the meter leads. That’s why a congested headlight wiring mass is a liability, and answers why you find melted ammeter plastic meter cases in the headlight shell. Interesting topic, got good responses to think over. Siging off….

Clever stuff, but it makes me think you’ve never looked inside an old bike ammeter.

What shunt?

no shunt in the Lucas type ammeter , just a few coils of wire .
the meter reads the full-current through the coil ... from one stud to the other .
( an ammeter electrical failure can only be from a broken coil )

it does not read a calibrated shunted portion of current , like some other ammeters .

the polarity of magnetism developed in this coil is what deflects the zero-centered pointer .

what about putting glycerine in gauge to dampen it? i have oil pressure gauge for my T120 that has it in it

I don’t know if the ammeter would Like it on not. But we find glycerine to be conductive and if spilt on circuit boards will short them out. I’ve just done a Google search as I didn’t want to sound completely stupid for once, pure glycerine like pure water has very low levels of conductivity however if it’s anything like pure water, being in a conduct or ionised environment will change the state of the water.

Silicone oil however has a really high resistance to conductivity and is commonly used where electronics are placed in an oil bath environment.

Any kind of oil has high enough resistance to be in a 12V ammeter!

Might leak out though.

found out new one i put in is from india research indicates stewart warner brand internally damped will try one of those

what is a shunted ammeter?

It’s when you bridge the ammeter terminals with a bit of wire. Production racers used to do it, to eliminate the breakdown/retirement hazard of the ammeter going open circuit.

hhhhhmmm i just got a new in box stewart warner deluxe internally shunted ammeter for $20 on ebay i never heard the shunted term before what is advantage of it ?

the shunt is a high load resistive element of extremely low calibrated ohmic value .

The low amount of resistance is there so the the ammeter can measure .
The extremely small voltage drop from before and then after the shunt .

a small amount of power bypasses the shunt and moves through the higher resistance ammeter
while most power still passes through the much lower resistance shunt .

this sets up 2 resistors in parallel . They higher resistive meter path
And the extremely low resistive shunt path .
the meter only needs to read a small percentage of the load to know the total amps .
because the meter reads A calibrated percentage of the total .

this can allow the ammeter and much smaller meter wiring
to be wired some distance from the load wires ( containing the shunt )
this comes in handy when the ammeter is separated some distance from the generating source

( in some cases the shunt may be inside the ammeter )
the shunt allows the meter parts to be less heavily built
the meter is only measuring a portion of total ampacity .
( a 1 , 5 or 10 amp meter can be used at 100 amp if the correct shunts are used
... and a 100amp face fitted to the smaller meter .