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Relays to change polarity

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WiserGuy

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Hi,

I'm working on a project where I want to control an electronic actuator from a RC controller.

The RC receiver gets power from a 7,2V battery and when connected to the actuator, the RC transmitter moves the actuator in and out as it should.

The 7,2V battery is to weak when charging the actuator with any load. I need a car battery to power the actuator, and probably need some kind of relays to isolate the current between the receiver and the actuator.

Can anyone give me some help to choose the right kind of relays, and how to wire them?

In other words, I need a setup that gives:
-zero current when no current comes from the receiver
-plus on red and minus on black wire on the actuator when getting power from the receiver.
-minus on red and plus on black wire on the actuator when opposite polarity from the receiver.

The relays will be controlled with 7,2V voltage from the RC receiver. The output voltage to the actuator should come from a car battery.

Can I use two relays which switches both plus and minus, or do I need four relays to accomplish this?


Kind Regards,
Wiser
 
Last edited:
This here actually sounds a bit like something I've done before, but not quite at the amount of current it sounds like you are using.

You could use a single DPDT relay set up in the configurations explained in the DPDT section of this page: Switches, and then would simply need something that would cut the larger power supply to turn your actuator off, such as a seperate SPST relay.

Now, don't take my word for this, but I believe there are relays out there that have a "center off" position, just like the switch in the link. If they do exist (heard about them through small talk at a component shop) this would be the closest thing to a "drop in" fix.
 
Hi WiserGuy,

this circuit might suit your needs. It uses two DPDT-relays (FINDER S30) which can be socketed using a modified DIL-16 socket.

The maximum current must not be higher than 4A at 12V.

The circuit is activated by either pulling IN1 or IN2 high. Connect battery ground of the 7.2V battery to circuit ground as well.

Pulling IN1 and IN2 high will cause no problem since both sides of the actuator will receive +12V in that case.

I added limit switches labeled LS1 and LS2. They interrupt ground connection when the maximum stroke is reached taking care of lower power consumption. When either limit switch has been activated further movement in the same direction is impossible.

If you want to omit LS1 and LS2 just solder a wire bridge from solder pad 'C' to 'NC'.

The board design is single sided and measures 54X48mm (2.1250X1.8875inches)

Regards

Boncuk
 

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