Using a relay to cut power to 3 DC Motors

Been trying to get this to work for a while but have not been able to size the relays correctly.

Looking for a 3pole relay, have a limit switch that I want to control the relay, 120V power going through the switch to complete the circuit and close off power to the motors.

The motors are all 90VDC 2 amps.

I have a regular lightbulb on the AC circuit that I want to be lit when the Motors are powered off.

Hi adam4,

Welcome to the Tech Forum.

So to clarify, you are looking for a 3-pole relay with a 120Vac coil voltage which will be activated by a limit switch, and when the limit switch is activated, it will open the three 90Vdc 2A motor circuits. Is that right?

Yes that’s right. I was hoping to also have a 40w bulb on the AC side to show that the power to the DC motors is cut.

Not sure about that bulb, off hand, as we tend to do more with LED’s these days. If you wanted to go that route, you might be able to find such things at the hardware store.

Back to your design, I think that you might want to reconfigure the architecture such that the default condition in the event of a failure somewhere in the circuit to the relay coil is that the motors are disengaged rather than engaged. Otherwise, a failure in the coil circuit would essentially disable the limit switch functionality and no longer prevent the motors from being disabled.

You would want to have limit switches which are normally closed when not engaged and a relay with three normally open contacts (either normally open (form A) or double throw (form C) would do). This way, in normal operation, as soon as power is applied to the system, the coil engages and provides power to the motors. When the limit switch is hit or if there is a wiring fault, the motors will be disabled.

Here’s a link to some relays with 115Vac/120Vac coils, 3 or 4 poles, either normally open or double throw contacts, can handle at least 125Vdc across contacts at 6A or more.