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Loop Ammeter and Tire Truing

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  • Loop Ammeter and Tire Truing

    About a week ago I finally caved and purchased a tire truing machine from Professor Motor. (Actually from eBay, but only because that was the only place I could find a tire truing machine in stock.)

    So I have been playing with it, and just yesterday I added an ammeter (amp meter) to my setup.


    Said ammeter is a bit unusual in that it is not wired into the circuit itself. Rather it uses a loop with a Hall-effect device to sense the current flowing through a wire, by the magnetic field that current creates. All you have to do is thread the wire (the red wire in the photo above) through the loop and provide a bit of power to the ammeter circuitry. My ammeter has a digital readout and can read up to 100 amps.

    I had purchased this ammeter for an automotive application that I ended up not needing. Its high current rating and non-contact design made it particularly well suited for that application. Bummer that it ended up surplus. It was consigned to a workbench drawer to await a new purpose in life.

    Which it found yesterday. I installed it on the 12-volt regulated power supply that I've been using to power my tire truing machine. Now there is no reason a conventional ammeter wouldn't work here, I just happened to have that loop ammeter in inventory, so it got pressed into service.

    Here is the point of this whole exercise. The ammeter can tell me how much current the motor of my tire truing machine pulls while it is running. And that number tells me how heavily loaded that motor is. Just free-running, without a load, it pulls just shy of an amp. If I use it to drive an axle assembly in the machine the current rises to about an amp-and-a-half. As soon as I start to true the tires the current increases by a tenth of an amp or two. So I don't have to guess when I've made contact with the tires, and I can make sure I'm not overloading the tires, and I can tell when it is safe to advance the tires.

    In other words, by watching the ammeter's readout I can monitor the tire-truing process. All I need to do is keep the ammeter readout at about 1.6 or 1.7 amps. Works great.

    One thing has become obvious. You do not need a big power supply to run your tire truing machine. The current draw is almost wall-wart spec. If you are drawing 2 amps you are probably overloading the tires.

    I custom-designed the white housing for the ammeter and printed it on my Creality Ender 3 Pro filament printer in PETG.

    If'n you want to check out my loop ammeter, here is a link:

    This ammeter has a button that resets the 'zero' reading. You press and hold it for two seconds. I needed to do that because the unit came out of the box reading a tenth of an amp high. So far the zero reading has been stable. To date I have not checked the accuracy of the amp readout. For what I am doing consistent relative readings are perfectly good.

    Ed Bianchi
    Last edited by HO RacePro; July 29, 2021, 02:14 PM.
    Ed Bianchi
    York Pennsylvania USA