Solid State Relay Problem

Hi all.

I’m having a devil of a time getting a SSR working, and I’m wondering if anyone can offer advice? I’ve wired them up before fine, but this one just isn’t working. It’s powering a kettle element (part of a heart exchanger in a homebrew system) based on current temperature. The relay is turning on, and I’m ketting a reading of 240V at the end of the kettle lead - so it does seem to be appropriately making a circuit. However the element just doesn’t come on (I’ve tested with another lead plugged directly to mains and it’s fine). I’m a bit stuck as to why that might be, ideas I’ve played with are…

  1. Not enough wattage getting through to the kettle element? Is this a possibility (I’ve a 13a fuse at the other end), and if so how do I fix it

  2. Something wrong with the arduino control. When I read resistence at the SSR outputs, I’m getting oscillation between short-circuit and no-circuit. I’m plugged in to a port with PWM, but it’s just being set to ‘HIGH’ - could this be where the problem.

Anyway I’m stumped!

Measuring the resistance of an SSR is going to tell you nothing, it is not a sensible measurement. Replace the load with a 100W light bulb, then you can see it turn on. If that works then it might be a problem with the inductance of the heating element.

You normally do not feed PWM to an SSR, unless it is the proportional type and you filter the PWM first.

Are you measuring the 240V when the heating element is connected? or just open circuit? Have you tried hooking up the SSR with just 5V and Ground to see if the element heats? Don't PWM the SSR, just use an On/Off digital output.

Thanks guys. I've now messed up the circuit completely tinkering around. I think I'll start again from scratch in a proper boxed, with some planning (and taking into account the advice above!). M.

Don't give up too soon. As Grumpy_Mike says just wire a 120 volt light bulb through the relay and put a 5 volt battery across the digital in.

If you can toggle the light bulb on and off the relay is working.

If it's working then either you are not getting a high enough voltage to the digital in or you may have wired it backwards.

I have discovered that, even with no digital input signal , the reading across the output will sometimes read 240 v. It's just that there seems to be a small leakage current, but not enough to drive any thing.