1. ## Relay Woes!

I have a problem that I hope someone can help me with. I just purchased a G540 with a 48V power supply.

I want to use a 12 volt automotive relay using the 48V power supply. What size resistor do I need to accomplish this?

Or does anyone have any recommendations on what size or type relay to use with the 48V pwr supply. I don't want to drop the voltage setting down on the power supply itself...

All I want to do is make a connection to my powermax 45 plasma cutter trigger switch and can't find a relay that will handle 48V dc input.

Never had issues with the lower voltage power supplies before (24v to 36v) since there are many relay options in this voltage range.

TIA

2. Measure the DC resistance of a 24VDC relay and then select a resistor of the same value to put in series with the coil. On a DC relay that should put 24V across both components the series circuit. Be mindful of the power being dissipated across the resistor. It will the current of the relay squared times the value of the resistor = watts.

It might be easier to use a small 12VDC DC power supply to drive the relays rather than dropping the 48VDC to some lower voltage.

It might be easier to use a small 12VDC DC power supply to drive the relays rather than dropping the 48VDC to some lower voltage.
I agree... I guess I'll have to go that route. Thanks.

• What is driving the relay?
I will make an assumption that your 48 Volt PS drives the motors/amps.
This could be a very noisey place to try using control relays/circuits.
The suggestion to use a 12 volt PS is an excellent idea.

One more thing to think of when working with high power relays is when using them on low current signals, the contacts can corrode over time and interupt the flow. Not enough current to keep them clean.

I would recommend using a low current signal relay for the trigger circuit.
Spending a few bucks on the proper relay could save lots of \$ when the other relay fails.
If you are in the middle of a job that has to ship today, you dont want to be running around trying to fix a plasma problem.

Good Luck,

• I ordered a couple of 48V relays from homanndesigns. They finally arrived yesterday.

This relay is currently driving my automotive relay thats powered by my 12V case fan power supply. I installed diodes on both relays and got everything wired up last night and all tested good.

I'll be doing some cutting today and see how it all goes.