Demise of the ammeter

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crusadersports

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Hi All,

When was the ammeter deleted?

Was it becuase:

A) They looked old hat in age of warning lights and assimilators.
B) Warning lights were cheaper
C) Pressing the starter button on a Mk 3 would probably take the needle off the scale and destroy the meter.
 
L.A.B. said:
End of '70.



Most likely.



No, as the starter current wouldn't have gone through the ammeter.
Click to expand...

Thanks LAB,

I've been thinking I'd like to fit an ammeter on my Mk 3. I wonder if I can fit a pre 70 headlamp shell? I know the Mk 3 shell has 3 large holes in the underside for the wiring, not to mention the clip for the flasher unit. Any other reasons it might/might not work?
 
crusadersports said:
I know the Mk 3 shell has 3 large holes in the underside for the wiring, not to mention the clip for the flasher unit. Any other reasons it might/might not work?
Click to expand...

It should work but I think the captive nuts on the shell are a different size/ thread (Cycle?) as it was attached with bolts and not the direction indicator stems.
It would also have unused holes for the headlamp switch and high beam warning bulb.
 
My '70 commando had the ammeter removed at some point. It also had the front forks/drum brake/wheel changed to a late model commando disc brake front end. With that came a late model headlight (not an early model one like you are asking about) I decided to rewire the entire bike probably 30 years ago back to the early ammeter wiring. (You can search and find the schematic pretty easily)

I took the "3 warning light hole" late model headlight and just drilled out the center hole for the ammeter. I think it was 1 5/8" size, but you need to check that sizing on that because I'm typing from memory. I also made an extended bezel ring to get some clearance inside the headlight shell for the connections. Everything was very tight in there and I recommend heat shrinking to protect against wires shorting against each other.

Demise of the ammeter


I like the ammeter because it shows the direction of current flow and the strength of the flow. So, you end up with very predictable instant feedback on your charging system based on flow direction and your situation,... meaning

If you sit at a light idling, you see that you aren't generating enough current at idle from the rotor/stator and the ammeter needle is dipping slightly into the negative

When the light turns green and you take off, as soon as you're doing ~1800 rpms the needle is passing zero, so you have eliminated your battery drain at idle.

Then as you accellerate into higher RPM's you'll notice that the ammeter will go to "+2" or "+3" as your alternator restores the surface charge you lost while you idled at the stop light. Usually that lasts less than a minute at speed and then your ammeter returns to it's normal position with the pointer just barely into the positive flow direction showing that your rotor/stator is working, and your zener diode is dumping excessive charge.

I went out for a ride last year and got a few miles from home before I noticed that my ammeter was in the negative slightly, showing battery discharge at reasonably high RPM's. I knew something was wrong so I turned around and headed home. I went through the bike and found that one of my feed wires from the rotor/stator had drooped into the front sprocket and was cut in 2 pieces. I repaired the wire, and the ammeter then read normally again.

Personally, I like an ammeter. I've never had a failure,.... BUT an ammeter is wired in series directly off your battery terminal, so that means if it fails, you are probably dead on the side of the road. People who wire in a voltmeter, wire it in parallel, so if the voltmeter fails it doesn't effect the rest of the bike. Those people also say they also use their voltmeter's in the same way I use my ammeter, to intuitively see that their system is working properly based on those small changes in the voltmeter's needle position and the current RPM's of their bike...
 
Last edited:
L.A.B. said:
It should work but I think the captive nuts on the shell are a different size/ thread (Cycle?) as it was attached with bolts and not the direction indicator stems.
It would also have unused holes for the headlamp switch and high beam warning bulb.
Click to expand...

Ah yes of course. I hadn't thought of that and it would be awkward to change, whereas the switch and warning light holes could be stopped up with a grommet.

I also thought it's already so crowded in the Mk 3 headlamp, that there may not be room for an ammeter in anycase. I had to get a shallower Wipac reflector from Paul Goff to fit his LED h/lamp bulb in there with its sizable heatsink.
 
o0norton0o said:
My '70 commando had the ammeter removed at some point. It also had the front forks/drum brake/wheel changed to a late model commando disc brake front end. With that came a late model headlight (not an early model one like you are asking about) I decided to rewire the entire bike probably 30 years ago back to the early ammeter wiring. (You can search and find the schematic pretty easily)

I took the "3 warning light hole" late model headlight and just drilled out the center hole for the ammeter. I think it was 1 5/8" size, but you need to check that sizing on that because I'm typing from memory. I also made an extended bezel ring to get some clearance inside the headlight shell for the connections. Everything was very tight in there and I recommend heat shrinking to protect against wires shorting against each other.

Demise of the ammeter


I like the ammeter because it shows the direction of current flow and the strength of the flow. So, you end up with very predictable instant feedback on your charging system based on flow direction and your situation,... meaning

If you sit at a light idling, you see that you aren't generating enough current at idle from the rotor/stator and the ammeter needle is dipping slightly into the negative

When the light turns green and you take off, as soon as you're doing ~1800 rpms the needle is passing zero, so you have eliminated your battery drain at idle.

Then as you accellerate into higher RPM's you'll notice that the ammeter will go to "+2" or "+3" as your alternator restores the surface charge you lost while you idled at the stop light. Usually that lasts less than a minute at speed and then your ammeter returns to it's normal position with the pointer just barely into the positive flow direction showing that your rotor/stator is working, and your zener diode is dumping excessive charge.

I went out for a ride last year and got a few miles from home before I noticed that my ammeter was in the negative slightly, showing battery discharge at reasonably high RPM's. I knew something was wrong so I turned around and headed home. I went through the bike and found that one of my feed wires from the rotor/stator had drooped into the front sprocket and was cut in 2 pieces. I repaired the wire, and the ammeter then read normally again.

Personally, I like an ammeter. I've never had a failure,.... BUT an ammeter is wired in series directly off your battery terminal, so that means if it fails, you are probably dead on the side of the road. People who wire in a voltmeter, wire it in parallel, so if the voltmeter fails it doesn't effect the rest of the bike. Those people also say they also use their voltmeter's in the same way I use my ammeter, to intuitively see that their system is working properly based on those small changes in the voltmeter's needle position and the current RPM's of their bike...
Click to expand...

Wow, that's an innovative solution to a crowded headlamp shell. Did you find the studs long enough that the clip still reached with the ammeter elevated like that?

You're making me think I could just drill the headlamp I do have...
 
Installing an ammeter in an OEM application is expensive - you have to run heavy gauge wires from the battery to the instrument panel (or headlamp shell) and back. A voltmeter is much simpler, you can tap into power and ground anywhere with small wires. It's even cheaper if you use an idiot light and no meter.

Why then did OEM systems employ an ammeter first? Because the battery is the most failure prone component in the electrical system and an ammeter tells you the health of your battery better than anything else. You can see while riding for instance if the battery has sulfited or has a shorted cell.

This of course assumes that the battery is only used for starting and once the engine is running the alternator supplies all needed current. That's obviously not the case with an old Brit bike, where the battery is required at idle. So for our case, a voltage monitor of some sort is perfectly adequate without the wiring hassle of an ammeter.

But they are sexy...
 
I couldn't do without one on my old Combat and retro fitted one. I miss it on my Mk3 and would also like to get better charging information.
 
Like I said, largely personal preference. A warning light may be cheaper and more compact, but you're right, the little gauge is sexy!
 
The charge output wire would also have to be extended and connected on the ignition switch side of the ammeter or it won't show a charge.

Edit: Also, on the pre-'71 models the horn circuit bypassess the ammeter.
 
L.A.B. said:
The charge output wire would also have to be extended and connected on the ignition switch side of the ammeter or it won't show a charge.
Click to expand...

Yes, good point too, thank you LAB.Is the 'charge output wire' from the regulator/rectifier (depending on spec-in my case Sparx)?
 
Basically, an ammeter would go in series with the fuse. One side of the fuse is attached to the ignition switch and charging circuit. Wires to the starter solenoid and relay would connect directly to the battery and not go through the fuse or ammeter.
 
L.A.B. said:
The charge output wire would also have to be extended and connected on the ignition switch side of the ammeter or it won't show a charge.

Edit: Also, on the pre-'71 models the horn circuit bypassess the ammeter.
Click to expand...

Yes, and as Maylar said, the ammeter is inline with the main fuse,... SO the connection to the horn is spliced into wire between the fuse and the ammeter which allows you to use the horn with the key in the OFF position. Because I like this, I also spliced in my dip switch headlight feed into the that same position on my harness, making it so I can flash my bright headlight bulb also whether the keyed circuit is on or off. The simple diagram above does not include the horn wire in it's wiring schematic.

Of course if the main fuse blows for any reason, then none of the 2 circuits I've wired to bypass the ammeter work regardless of the key position. The old saying that there's a million ways to skin a cat applies here. Neither the horn, nor in my case the dip switch need to be inserted into the wiring where they are to bypass the key circuit. You can be creative with your harness if you understand your components and wire them up to suit your preference.

Personally, I didn't see any need for the horn to work independently of the key position. Maybe there's a reason it was originally wired that way. The fact that it worked that way, gave me the idea to wire the dip switch that same way.

As far as the homemade bezel (delrin) goes, I either remade the clip out of some other material, or just shortened the arms of the existing clip so it would work with the projecting ammeter. Unfortunately, I don't take a lot of proceedural photos. I tend to just take finished product photos which aren't too instructive.

Don't be intimidated by circuitry. It's actually very logical once you get into it. A few components produce and manage charge. A battery stores charge to maintain voltage when production is low. Components use the current to power something. Switches turn certain circuits on or off... How much more simple could it be?
 
One potential issue is the ammeter becomes a single point of failure in the electrical system. What I mean is that you have to route all current (except the horn and maybe the starter) through the ammeter. This means a large cable running all the up the bike, then back to the main harness. The ammeter sits in the middle. If the ammeter fails, then the bike goes down.

I've had 2 of 3 of aftermarket ammeters fail - from vibration I expect. The ones I've been able source don't really seem to be made for motorcycles. I ended up making a jumper wire to basically short out the ammeter circuit that I can quickly attach to be used in case the ammeter fails. I now carry it in my tool bag for the inevitable on the side of the road failure (Don't ask).

I also thought it might be nice to have one of the those 3 color voltmeter leds - so I rigged up a way for the ammeter to be illuminated by one of those, so it's sort of a dual purpose indicator.

-- David
 
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