DIY Robot Ammeter Project

Purpose

After building the PWM Motor Tester, I realized that it would be nice to have a feature to see how much power a motor is drawing, in order to predict the motors effect on our power distribution system later. I came up with an idea for an all-in-one box, which connects inline with the motor and reads out the voltage and current measurements.

Parts

• DROK 100 Amp DC Ammeter with Display
• DROK 3-30 Volt DC Voltmeter Display
• Hammond Plastic Project Box
• Nice 10AWG Silicone Insulated Wire

Details

In order to find the voltage, I connected the Voltmeter in parallel to the load, which worked perfectly. However, when wiring an ammeter like this one, I needed to connect the current shunt in series with the load’s ground, and the display power wires in series next to the voltmeter. This made the wiring much more complex. When I tested it, the voltmeter displayed the proper voltage, but the ammeter only showed a very low number.

At first I thought the ammeter we picked doesn’t have adequate resolution to be used with a single, relatively small motor. My next step in troubleshooting this was to connect it to a much larger load, while excluding the voltmeter, to hopefully show the ammeter working properly. To accomplish this, I utilized a 12V car inverter and connected a 300 watt electric heater (a purely resistive load) to the inverter. This resulted in a >25 amp load on the 12V battery which should definitely show up on the Ammeter rated at 100 amps. To fix the ammeter that still wasn’t displaying properly, I reversed the sensing wires going to the resistor shunt and I started working.