PID Relay Controller Power Rating

Question

I've used this relay to switch this heat gun in a heat box application with no issues (heating the box to 55C). One day the cover fell off and the heat gun ran continuously for a few minutes and burned up the relay. I didnt pick the parts for this but now am trying to replace with a PID relay with a higher power rating. Looking at the datasheet for the relay that got burned up it states 8VA. I dont have a fundamental understanding of AC power but luckily VA rating seem pretty straight forward. Pav = Irms*Vrms. Heat gun rating is 11.6A (im assuming to be RMS) and 120V. So 1392VA. I guess not surprising for a heating element.

But for the relay to state a power rating of 8VA? So if my understanding is correct then at 120V it can only handle and rms current of 8/120=0.066A_rms?

I must be wrong because this relay should have burned up a long time ago.

Answer 1

As I read the datasheet:

The 8VA rating is the power consumed by the controller.

The relay contacts that you used to switch the power to the heater are only rated for 250 V 3 Amp - clearly inadequate to switch power to that heat gun.

You should find a relay with contacts rated for 120 V 12 A or more, with a 120 V coil, then have the PID controller control that relay rather than controlling the heat gun directly.

Answer 2

8VA is the power requirement of the entire controller.

The relay inside the controller has a 3A resistive rating and a life of only 100,000 operations at that current.

If you use the controller to switch something like a 12VDC 100mA coil relay with 30A rating both the controller and the relay should last a long time.

If you want to use a mains voltage relay, dig a little deeper to ensure the life will be adequate as the datasheet lists “resistive” rating and relay coils are inductive.