How to reduce the leakage current of a solid state relay

leakage-currentpowerrelaysolid-state-relay

I have a zero-cross solid state relay (Crydom CKRD2420) that regulates the power output of a 2kW@240V heater using 10Hz PWM (e.g. here to illustrate). I need the power output of the heater to be under ~2W when OFF. However I measured the leakage current is 25mA RMS (2.5 times the 10mA garanteed in the datasheet, by the way…), which means that the power leakage is about 13W (the mains supply voltage reads 264V).

My first thought was a current divider, but the bleed resistor would reduce by a factor of 10 the available power, and reduce significantly the efficiency. I can't use a normal relay because of the lifetime required (I need at least 50-100M cycles of operation), and power MOSFETs would be tricky to implement. Are there any simple-ish fixes I have overlooked?

Best Answer

The 'leakage' is no doubt coming from the internal snubber network. Perhaps they increased the capacitor value from when the datasheet was written.

The load resistance is R = 240^2/2000 = 29\$\Omega\$, so with 25mA leakage you'll have a power in the heater of 18mW (I^2R), which is not a problem. The '13W' you calculated is actually 13VA, almost all leading in phase and does not represent power either in the relay or the load.

So, I don't think you have a real problem. Your cycle time is a bit short- you may run into beating issues with the mains, but that's another issue.

Anyway, to answer your question, the easiest way to avoid the snubber would be to make your own SSR with a opto-triac and a snubberless triac (aka alternistor). But it's not necessary.