Controlling Linear Actuator with 2 switches

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JoCoo26

New Member
Hi. On my truck I have a sports bar with an LED light bar connected to it, attached to a 2” actuator that raises or lowers the light bar depending on the position of the DPDT (on-off-on) switch.
I have no place to mount this switch and was looking for another alternative.
I have a push button control panel in my truck where I can turn on the light bar and other accessories. I wanted to use 2 of the switches on this panel to control the actuator in both directions. The panel consists of latching switches. The accessory turns on when the button is pressed and must be pressed again to turn accessory off.
I know I’m going to need relays in order to accomplish this, however my knowledge in relays is sub-par.
I do not want something that is on-on (so I don’t have to leave the switch on all the time to keep the actuator retracted) and I need a fail-safe incase both buttons are accidentally pushed which would create a short.
If this is possible, could someone please not only explain what I would need, but also provide a wiring diagram explaining which relay terminals go where.
Off the top of my head, I think I need 2 SPDT relays to achieve this but I’m not sure how to prevent the short in the event both buttons are pushed at the same time. Thanks for the help
 
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The fail-safe you need is something to make sure that the actuator does not stay energised all the time. If it is, it will probably burn out in a few minutes.

Switches that are pushed once to turn on and once to turn off have to have some mechanism inside to remember whether they are on or off. It's often a bit like the mechanism in retractable pens that holds them out. If you can open up the switches, you may be able to remove the mechanism that latches them, and leave the spring so that you get a switch that only operates as long as you hold the button down.

The relay circuit should be this:-

 
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Hi. Thanks for your response. I am familiar with switches and wiring just not completely comfortable and knowledgeable with relays.
The switch panel I’m using is a closed unit, they are not your average push button latching switches. I def do not want to tamper with it.

My actuator already has a built in limiter (shut off), so keeping the switch on will not pose any threat to the motor. However I was looking for a way to avoid having to keep the switch pushed in. My only concern was shorting it out in the event that both buttons were accidentally pushed at the same time.

In your suggested wiring, what would happen in the even both switches were pushed on at the same time?
 
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JoCoo26 said:
In your suggested wiring, what would happen in the even both switches were pushed on at the same time?
Click to expand...
Nothing.

The suggested circuit leaves both sides of the motor connected to +12 V when neither switch is operated. No current will flow because there is no connection between the motors and ground.

If both switches are operated, both sides of the motor are connected to ground. No current will flow because there is no connection between the motors and +12 V

If you are confident that the actuator would not be damaged by leaving it powered for long periods of time, and you only ever want the actuator to be fully deployed or fully retracted, you could use a single switch.
 
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I don’t want to use a single switch because:
1. I don’t want to keep button latched once extended
2. I don’t want it to retract when unlatched
3. Need the ability to have it extended without vehicle power on (which I think would work)
4. Already have 2 buttons ready to go

Sorry for the beginner question, but again, I’m terrible with relays. In your diagram, which wires are grounded? Is the (-) missing from the other side of the battery?
 
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JoCoo26 said:
Sorry for the beginner question, but again, I’m terrible with relays. In your diagram, which wires are grounded? Is the (-) missing from the other side of the battery?
Click to expand...
Yes, the lower sider of the battery would be grounded. That's the standard symbol for a battery and the smaller bars represent the negative.

I would guess that you would connect the four relay terminals that need to be connected to negative to the vehicle body as that would be easier than connecting to the battery negative terminal

A battery won't turn off when you turn off the vehicle, so I would expect that you would run the whole lot from a fused vehicle supply that turns on when the truck turns on. You could connect to the battery but it could risk flattening the battery if you left a switch turned on and didn't use the truck for some time. You should always have a fuse near where you connect to the power supply.

I'm assuming that it's a vehicle with a 12 V battery and that the negative is connected to the vehicle body, but as
the vast majority of vehicles made in the last 50 years is like that, it's probably correct.

However I have had three vehicles for which it wouldn't have been correct.
1) Motorbike - 6 V electrics
2) Reliant - fibreglass body panels which couldn't be earthed but it did have a metal chassis that was grounded
2) 1953 car - positive earth
 
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