SSR issues - think I’ve killed a second one. The setup: 25A capable 24V power supply hooked up to 40A SSR DC-DC relay, powering Onyx 280mm heated bed. I have the output from the RAMBO hooked up to the input of the SSR (positive to positive, negative to negative-) and the +24V from the power supply going to the bed, with the ground from the bed going to the + of the SSR output, and the - to the power supply’s ground.
24V fan provides cooling to heatsink attached to SSR, doesn’t get to hot to touch at any point. The 20A SSR quite quickly, this SSR lasted a couple prints (120C on HB) - but appears to have given up the ghost.
I have been using a standard automotive 12v relay on my 24v heatbed with no issues thus far (knock on wood) they are like 5 bux from radio shack. I think they even have 24 v version
The only information i’ve been able to dig up on that exact SSR is one review on Amazon - which is right in line with what you’ve seen.
Dumb question: Why aren’t you using a MOSFET like everyone else? All you’re switching is (supposedly) common-ground DC, so i don’t think there’s any need for opto isolation.
And one more thing: Isn’t the Onyx rated for 12V?
make sure you aren’t switching it too fast. there should be a max switching frequency listed on the datasheet. the rambo is expecting a mosfet which can switch in the khz range (thousands of switches per second) I highly doubt that that ssr is designed for that… so, when the rambo is trying to maintain the temp by PWM based “dimming” of the output, it frys the SSR… there may be a setting in the firmware that can tell the machine to only use on and off (as opposed to PWM), and to limit the switching frequency to something reasonable for relays (a few HZ MAX)
i think as i have seen in some other components, DC spec needs to be de-rated by at least 50% in long term ops. and looking at this scenario, if i use a relay, i can do away with the heatsink/fan assy. to be safe, heck i will put 2 of those car relays, make it 3 even (100A share load, im guessing this will extend the life by at least 100%)
. btw i would suggest doing a search using “mouser” website, its a great “tool”.
I always hook mine up with mains on the SSR + side, then the SSR -, I hook up to the + of the bed, and then terminate ground at the power supply. (So basically on the other side of the bed in the circuit as you do it)…but I don’t think this should matter.
My latest kossel-alt had a bunch of problems with mosfets getting too hot and burnning up so I switched to a relay and never been happier. Repetier has a relay mode which is just fine for the bed as I don’t need exact heat, but just enough heat to stick. Why waist heat from the MOSFET when you can use the extra energy on the bed.
