I've got an electric HLT with a 5500 W element being controlled by a cheap little PID (1/16 DIN dual digital) and an Amico 25W SSR. At 5500 W, the current is 25A, 100% of the SSR rating. Now, I previously had a 4000W element, so I had some current head room.
The problem I'm having is the heating element not turning off when the controller turns it off. The PID seems to work while heating up to the set point (heater doesn't appear to be running open-loop). In fact it regulates fine for a minute, then always starts to overshoot.
It seems like the relay is latching up. The controller is putting out near 0 volts to the control pins on the SSR (measured with DMM), but 220V is still powering the heater. Any hints besides getting a bigger relay?