Relay to control power to motor driver

Using Arduino General Electronics
1

Hey everyone!

So I have a robotic boat project that runs on batteries and charges with solar panels. So power is relatively limited. I have 2 of these motor controllers (RobotShop Motor Controller Link) each hooked up to a bilge pump motor that gets the robot moving. The bilge pumps draw around 10 amps when running but I only ever need them running for 2 minutes at most. What I notice is that the motor controller draw around 80 mA each when idling which is wasted power. I would like to control the power to the motor controllers so that they have power only when the motor needs to move. Is it okay to use an automotive relay to control the power going into the motor drivers? My main reason for being concerned is that the motor drivers have 2 large 1000 uF capacitors that seem to be hooked straight up to the power input. So when the board is powered up there is a large current spike, enough to spark if power is hooked up manually. Will this break the controllers or automotive relay in this setup?

Thank you all

2

Look at the specs on the relays. They will draw a lot more than 80mA. That may not be a problem if your duty cycle (percentage time "on") is low.

Automotive relays are designed for unruly loads like large capacitors. If the relay can safely break the full motor current then it's almost certainly OK for thousands of repetitions of the surge current going into the capacitors.

The large current spike may cause problems for other components nearby. This will radiate lots of interference which might be picked up as an unintentional button-press or anything.

Or choose a motor driver with lower standby current. My favourite, the Sparkfun Monster Moto will use 4 milliamps for the main chips and not much more for the support components. It could be microamps if you change the pullup resistors.

3

It is usually not a good idea to disconnect the power to a device while other inputs are driven. Analysis may show that this can work. It would be best to analyze first.