[Robaroni]

Originally Posted by Xringer

I didn't think the resistance of the DC SSR would ever get up very high.
I never noticed any build up of heat when it was still working..
The 3-32v DC control voltage into DC SSR was 12V which put it into full saturation.
At least as far as I could tell with the voltmeter.

The series heater load of 13 ohms isn't very inductive.
If it was, the standard AC hotwater heater controls wouldn't last very long, with their small air-gap contacts.

Anyways, I've sworn off DC SSRs.. I will never buy another one..
They cost too much and die too easy. (Static discharge from my finger?).

Didn't have much luck when I tried the cheap way out, with an AC SSR..
Not sure why they shouldn't work. Seems like they should.
Maybe the first one was a dud, something intermittent in the control side.?.

So, when the Golf kart relay dies, I'll try the 200v 30a HEXFETs..
I am thinking of stacking them.

Thanks,
Rich

Rich,
Here's a high side mosfet arrangement I've used. You want to keep the gate source voltage within specs, most are 20v max difference so if you have 200 volts on the source you want no less than 180 on the gate or it will blow. The 12v zener keeps the source/gate voltage in check.

With that said, it's much easier to run the mosfet on the ground leg. The source goes to ground and the gate never rises about 12 or so volts without zeners.

The thing that kills these guys often is the inductive spike you get from switching the mosfet on and off. That inductance has to go somewhere. You may not think it's much but engineers (including me!) with boxes of blown transistors will tell you they underestimated the inductive kick. If you have an inductance meter you might want to check your heater coil.

Rob