[gdirwin]

I am using SSR relays (DC rated) for control of my interior heaters - when I first used them, one of them failed "on". This resulted in heat coming on when it was not supposed (the SSR relays are controlled by a PWM temperature controller).

While debugging this, I removed the SSR relay control input signal and then opened a fuse - since the heater was still connected (due to the shorted relay) this caused an arc to appear across the fuse holder - this started a small fire in my control box! Fortunately there was not much damage (some blackened stuff, but no real damage except for the fuse holder in question).

The SSR relay is somewhat buried (attached to a large heatsink against the firewall and behind my batteries) so I will probably live with only 1 heater for now.

I will chalk it up to infant mortality (the other one seems okay so far). Check your SSR relays before installing them!

 

[gdirwin]

Mine was also suitably rated and used a good heatsink.

I wanted an automatic temperature controller though - it switches the heater on/off/on/off very quickly (perhaps every 5 seconds), and continually adjusts how much time it is on (versus the amount of time it is off) using a PI controller - you just set the desired temperature. A contactor would be pretty noisy and would wear out quickly.

I think I will find a "better" SSR relay - perhaps Crydom... Sometimes you get what you pay for...