Trouble with Bed Heater using SSR
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I’m working on replacing the RAMPS board in my companies 3DP Workbench with a Duet 3 Mini 5+. It uses a SSR for the bed heater. It has the negative of the SSR input tied to ground and used a Servo pin on the ramps board for the positive side. I’m having trouble where the bed is heating up as soon as the Duet powers on. Here’s the following test cases I’ve run and the results.
- Hooking up just the positive side of the SSR to the positive of Output 0 results in the bed heating and Out 0 indicator LED remaining off.
- Adding a connection to ground on the negative of Output 0 still has the bed heating but the indicator LED remains on. This is true without the SD card in as well.
- Leaving just the ground connection and removing the positive from Output 0 results in the indicator LED remaining on and 24V measured across the output.
- Removing all wires from Output 0 results in 0V being measured across the output.
The second test proves (I think) that it’s not a confit issue. With the last test, it makes me unsure if this is a hardware failure or not. I’m also unsure if the fact the negative of the SSR is tied to ground is the issue or if it is more indicative of a short or other hardware issue. Since the SSR is in a separate location, it would take some work to rewire it directly to the negative of the output so I figured I would seek advice here first.
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@bubbar0b0t most SSRs will work with between 3V and 30V on the control terminals. If your does, then you should connect the positive control terminal f the SSR to the +ve OUT0 terminal and the negative SSR control terminals to the OUT0_NEG terminal - in other words, connect the SSR control terminals to the OUT0 terminals. Do not connect either SSR terminal directly to ground.
