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Tech Thursday #033: How to power a big electric motor

To power an electric motor, determine the power consumption at maximum rate Then you can chose the correct wiring size. You can choose a cable size from this chart:

AWG

AWG

Then you have to choose overcurrent protection. An auto reset circuit breaker (perfect for our sealed Lead acid battery (SLA) based robot platforms) removes the need for disposable barrel fuses, and also serves as a convenient mounting point for 24V or 12V systems.

You will need a solenoid switch that holds the same amps or higher. Solenoids are a current-carrying coil of wire wrapped around an iron core. When energized, they create a magnetic field which produces high current and force. This makes solenoids very advantageous, because it allows for a low input while generating a larger output as in the case of a starter solenoid. This solenoid switch needs to be powered by a toggle switch. The toggle switch is the one in charge to turn on the solenoid switch.

The other thing you will need is a motor driver. A motor driver is a little current amplifier; the function of motor drivers is to take a low-current control signal and then turn it into a higher-current signal that can drive a motor.

Example: Powering a big electric motor

Suppose that the motors are going to be 24V-70A. We start by choosing the cable. We know the 12 AWG only holds 41A – but, instead of one, we use two cables. Now it can hold 82A. Another option is to use 8 AWG gauge – that one holds 73A. You can use whatever combination of cable, as long it holds more than 70A. By the way, you always want to leave the room for extra protection

For this, we are going to stick with the 12 AWG. Because of the cable combination, we need overcurrent protection that holds between 70A and 82A. If we choose overcurrent protection higher than the cable can hold, the cable will burn, and the protection will never actuate. Two Auto Reset Circuit Breakers – 24V, 40A will work.
The toggle switch can be wired with a smaller wire, like 18AWG, with a 10A breaker. For the switch, the SPST 24V 100A Solenoid Switch – Insulated Continuous would work. This switch holds 100A, which is more than enough, because t will support the 70A of the motors.
Now, the only thing we need is a motor driver that can hold 24V-70A. The Sabertooth Dual 60A motor driver holds two 60A motors totaling 120A. The illustration below depicts how everything is connected.

Schematic

Schematic: how to connect all power component

This configuration in the schematic is a perfect example of how our Snow Plow Robot is connected.

Snowplow

4WD RC Snow Plow Robot – WC DB

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