# Is my 2 relay h-bridge safe?

I am trying to control a linear actuator using a cheap remote controlled 2 channel relay (it controls a gate for my workshop dust collector). I'm think it's as simple as connecting each relay the same way...

NO: +12v from power supply

Comm: one motor line on relay 1 and the other motor line on relay 2

NC: neutral (ground? Or -12v???) from power supply

This gives me the following voltages on the common lines...

No relays activated = NC / NC = neutral

Relay 1 activated / relay 2 off = NO / NC = +12v

Relay 1 off / relay 2 activated = NC / NO = -12v

Both relay activated = NO / NO = 0V

I feel comfortable I got everything above right except that last line. If I put 12v on each side of the motor then I should have no voltage difference and therefore no current running through.

This thing sits around in one of these states all the time in a remot barn so I just want to confirm nothing is dangerous about my setup.

Is there a better way to do this? If above is safe then I have to remember to shut off each relay once the actuators reaches its end position (closed or open). What I need is a circuit tho if I press 1 it closes (+12v) and if I press 2 if opens (-12v). The linear actuator has a switch that opens once it has rich its final position. So trying to press 1 or 2 more times won't do anything until it goes the other way.

Thanks for any feedback or suggestions.

simulate this circuit – Schematic created using CircuitLab

Figure 1. (a) One way. (b) Another way.

Your question was a very hard read. I think you are describing (b) which will work fine.

It could be a problem if you are using relays that are make before break. This would cause a momentary short circuit on your 12V supply when switching.

From forward to reverse. From reverse to forward. From off to forward or reverse. From forward or reverse to off.

This design will work, but it is likely to be rather hard on relays unless one includes a transient suppressor to absorb inductive flyback from motor. Normally when using a relay to switch an inductive load one would use a back-biased diode across that load for flyback suppression, but that won't work if the motor may run both ways. An alternative would be to use four flyback diodes: one from each side of the motor to the positive rail, and one from each side to the negative rail.