Linear actuator, DPDT relay, diodes

[cyberjoes]

Re: Linear actuator
I need to control a 24 v DC linear actuator, it has limit switches for both ends of travel and I will do full travel for both directions. I have a DPDT relay that I plan to control with the Duet. I do not have flyback diodes yet. - what diodes should I spec? And can someone give me an idea of how I should wire and control this thing with the Duet, or is there a better way?

[rjenkinsgb]

This is the basic circuit you need for a reversing motor with limit switches:

https://www.halloweenforum.com/attachments/relay-controlled-dc-motor-jpg.252253/

The relay flywheel diode should preferably be a schottky or fast recovery type, with a higher current rating than the relay coil and a rather higher voltage rating than the circuit operates on.

It would also be a good idea to add a kind flywheel circuit around the motor, to minimise relay contact arcing; the most effective is four diodes arranged as a bridge rectifier with the AC connections across the motor and DC out connected back to the power source (eg. the 24V supply) with bridge positive out connected to supply positive.

[cyberjoes]

@rjenkinsgb , Thanks for the help. This system was designed by someone with more circuits knowledge than I have, afraid I am more the type to follow a recipe when it comes to electronics

I have found this: the control current of the relay is 46mA, voltage is 24, motors are also DC 24V (well we are driving them at 24V - I just pulled one out and it is rated for 12V, wonder if they are going to fail?) You are suggesting 5 diodes, right. Am I giving the right specs?

I could not find the rated current draw for the linear actuators -- here are the specs, they are small:
Power: 12V DC
Stroke Length: 1.2"/30mm
Retracted Length: 3.3"/84mm
Extended Length: 4.8"/123mm
Maximum Load: 64N/14lbs
Travel Speed Without Load: (15mm/s)
Protection Class: IP54 Rated
Noise: <55 dB
Inner Tube: aluminium
Wire Length: 13 in

Thanks for your time and knowledge

Van

[dc42]

@cyberjoes have you considered using a L298N module instead of a relay?

What is the specification of the linear actuator, in particular how much current does it draw?

[cyberjoes]

@dc42 Thanks -- I ordered an L298N control board. It does seem to solve my issues. I found a good tutorial

I don't know the current draw of these motors, I will check it on my multimeter, must be very low though - the motors are no bigger than my pinkie

I did learn that the linear actuators are rated for 12V but we are driving them now with 24 V -- I just ordered a DC 24V to DC 12V 10A 120W Step Down Transformer. I think those will solve my problems. I will use the transformer for the l298n board and the motors.

Thanks for pointing me to this solution

Van