Using Relays With Lego PF

[MaxBrix]

One day I was wanting to run 8 motors on one Sbrick but you can't do that. So it occurred to me that a relay would be a common solution for increasing the power capacity of an electronic signal. They are also fairly cheap. So I got a relay and as an experiment ran 14 lego motors and a power drill controled by one channel on a Lego IR reciever. Is this dumb? Is it already a common thing and I live under a rock?

 

[dr_spock]

It is common to use relays for certain applications. I used relays for my Arduino to control power to my PF motors.  You can also use MOSFETs to do the same thing.

 

 

 

[Saberwing40k]

I have not seen this often in Lego, and most other applications use a motor control system that's actually rated for the application, rather than having to kludge one together like this. It's a good idea, though.

[MaxBrix]

kludging is what I do best.

[Sadap]

Have you included a flyback diode? (https://en.wikipedia.org/wiki/Flyback_diode)

Otherwise you can destroy your receiver.

[Philo]

On 12/10/2019 at 8:02 AM, Sadap said:

Otherwise you can destroy your receiver.

Chance is pretty low: motor driver inside receiver does include flyback diodes (see datasheet). After all, LEGO motors are also inductive devices!

Edited December 11, 2019 by Philo

[Sadap]

On 12/10/2019 at 11:34 AM, Philo said:

Chance is pretty low: motor driver inside receiver does include flyback diodes (see datasheet). After all, LEGO morors are also inductive devices!

You are right, motors need flyback diodes too

[MaxBrix]

The relay separates the receiver circuit from the motor circuit. The battery does not receive a load because the relay opens the circuit between the battery and the motors. when the relay is off the motors are not connected to anything.