Reversible motor control circuit for Jeep Chair

[Jason D.]

It's been many years since I built something, so I'm asking for someone to glance at the below circuit, and confirm or deny its viability. The circuit is supposed to simply move Lisa's Jeep chair tilt motor. The system is 24v DC, forgot how many amps, something like 4 ish. Basically I'm controlling 2 relays with 2 separate moment switches. The motor will always be in a state of receiving 24 volts on both lines until a button is pressed grounding one of the wires. I'm hoping this won't harm the motor with relay bounce or the 24 volts on each side, I figure there is no voltage potential so no amps will flow, this idea seems ok too me but I'm not sure? If more pictures are needed or info let me know, I'm mostly checking to make sure my idea is sound and usable. In the circuit below I just used 2 LED instead of a motor.

[Chris Savage]

In theory, it looks like it would work. If you swap the relay positions NO / NC, you can make it so the motor is connected to ground when idle, rather than 24V. This way if something shorts a wire along the way, it doesn't accidentally turn on the motor. You would definitely want a fuse coming from the power source.

May I ask, why 24V? Most vehicle electrical systems are 12V (~13.7V). I do like the simplicity of the circuit. In similar industrial circuits, you would wire the relays (multiple poles) such that you cannot engage both buttons at the same time. That really isn't needed here, since activating both relays would simply nullify the output.

[Jason D.]

Chris,

Thanks for the reply and advice, I like your idea of using ground while idle, much better idea than mine. I had to use 24v because I stole all the parts to build Lisa's Jeep chair from one of Lisa's old wheel chairs and they run on 24 volt systems to power all the motors.

Once again, appreciate you.

Thanks from us

[Chris Savage]

One other thing I would add to the design aspect of things...it helps to know the "stall current" of the motor and set the fuse and choose the relay contact ratings based on that.

For example, if your motors stalls at 7A, perhaps use a 5A fuse, and be sure to use 10A relay contacts.

You can choose a more appropriate fuse if you can get current readings under normal load, but you definitely want the fuse to blow below the stall current.

[Chris Savage]

Jason, how goes the project? Need any help with anything?

[Jason D.]

I didn't have enough room for a fuse so I used a fusible link instead. Chair been working well. I've been wanting to build an electrical driven stroller buggy for Lisa so I can take her to Bumpass Hell in Lassen volcanic national park { https://www.nps.gov/thingstodo/hikebumpasshell.htm } because It's at 8000 feet and I've lost most of my fitness from no nursing for a year and its a dirt path. I don't know anything about motor control so I was thinking about purchasing a dual driven electric bicycle and cannibalizing the parts to make the buggy but I think it would be cooler to learn how drive motors work and source the parts I need so I can develop the skills for what ever may come in the future.

[Chris Savage]

Is it safe to assume you can weld?

[Jason D.]

Tig and mig

[Chris Savage]

Tig and mig

Nice! I haven't ever tried, despite having some gear for it (helmet, gloves).

[Chris Savage]

So, how's this project coming along? I hope things are working well for you.