Ammeter Problem

Thanks

If you are going to replace it, be sure it's an exact replacement.

I can understand requiring a shunt with this type of metering and the shunt is merely an accurately calibrated piece of material, deliberately very large to prevent any error due to the shunt heating with higher currents. The meter then merely acts as a very low voltage volt meter, measuring the small voltage across the shunt caused by the current thru it.

There is also an iron vane, which is very rugged and could operate on it's own. I don't remember it's physical makeup, but I do remember it is very simple, uses no fine wire but is not as accurate as the former....course you don't need much accuracy in this application.

The ammeter in tractors (that I know) is too small physically to have one internally and I have never seen one external.

So I'm guessing that it's an iron vane movement and once the internal wire opened, if wired normally, all power would be lost except the high current starting circuit from the battery thru starting solenoid to starter. Course you couldn't use it as you had no current path to energize the solenoid when you hit the start button.

Mark

Having no idea what type he has (or had!) on his tractor I gave him an admittedly general answer. But his statement that when he bypassed his ammeter the engine ran better apparently due to more primary power to the coil keyed me into the fact he blew that ammeter and was very lucky. It seems as if it shorted internally and he is very fortunate he didn't experience a fire.

As you know, a properly wired tractor will have all active loads (except the starter of course) run through the ammeter which is driven by the alternator. Assuming the load never exceeds the ammeter's rating, no problem. But I did see the rusty remains of a tractor where the owner replaced the stock 40A alternator with a 100A and added some snowplow type lights. Bingo, the first time the lights got switched on, his tractor promptly burned to the ground.

Can't understand how changing a piece of metal measuring milliohms across the terminals caused his tractor to torch. Gotta be something else.

Now it could be that his wire was not sized adequately for the extra current and he melted insulation which eventually caught fire, but not the shunt. Or he fed this new power thru his ignition switch which also was not sized for the extra load.

Mark