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Trouble with solid state relay closing for mains voltage bed

Posted by imotion 
Trouble with solid state relay closing for mains voltage bed
October 21, 2019 12:10AM
I purchased a solid state relay to switch 240V silicone heating pad, but I get no continuity when its receiving power (it doesnt close).

I guessed it was a dud, but a replacement (different brand) also doesnt close when it receives power. I have tried WITH the load to see if maybe it required that to latch closed or something weird but no luck.

Any ideas why? Its 24V control side, correct polarity everywhere etc etc. LED lights up but no closed circuit (and therefore no heating of the bed). Eventually Marlin firmware shuts down from a temp error (due to no increase in bed temp after a set amount of time).

See this link [imgur.com] for how I have wired them up, LED on but no continuity whatsoever on the output side. Tried12V and 24V.

Did I get two duds in a row? Neither was ever put under any load, so no possibility of it "overheating" at any stage or subject to any other risk that would typically cause a failure. Brand new, both of them. Any ideas? Thanks a lot

Edited 1 time(s). Last edit at 10/21/2019 01:30AM by imotion.
Re: Trouble with solid state relay closing for mains voltage bed
October 21, 2019 02:28AM
You can't use a multimeter to measure continuity of a DC-AC SSR. Nor will it work using a DC supply and load, because most DC-AC SSRs are zero crossing types that will only switch on as the mains voltage crosses zero. To test it you must use an AC supply and load.



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Re: Trouble with solid state relay closing for mains voltage bed
October 21, 2019 03:51AM
Quote
dc42
You can't use a multimeter to measure continuity of a DC-AC SSR. Nor will it work using a DC supply and load, because most DC-AC SSRs are zero crossing types that will only switch on as the mains voltage crosses zero. To test it you must use an AC supply and load.

They are both 3-32VDC inputs (pos and neg, marked) on the control side, the outputs are 24-380VAC (FOTEH SSR-25 DA) and 24-480VAC (Meger MGR-1 D4825). Regardless, if there is no continuity with control voltage applied on the AC output side - then it hasnt switched despite being given the correct input voltage and no AC will flow because its not closed.

If I am not correct in that assumption, I have still attempted to test its operation by disregarding the continuity verification and literally wired the VDC control input to my bed output (which provides 24V) and still got no response from the heating pad which was wired directly to N (at the plug) and L (which went from the pad to the SSR, which was supposed to close and flow from L at the plug).

Testing for continuity was what I did to determine the component wasnt closing AFTER I straight up wired it to mains on the output side and 24V on the control side. It should have triggered when the mainboard lit up the LED on the SSR.

Unless you are saying I need 3-32VAC to the input side which is DC (marked 3-32VDC; positive and negative), as well as AC flowing through the output side. I have not heard of that.

Edited 2 time(s). Last edit at 10/21/2019 03:53AM by imotion.
Re: Trouble with solid state relay closing for mains voltage bed
October 21, 2019 05:06AM
"They are both 3-32VDC inputs (pos and neg, marked) on the control side, the outputs are 24-380VAC (FOTEH SSR-25 DA) and 24-480VAC (Meger MGR-1 D4825). Regardless, if there is no continuity with control voltage applied on the AC output side - then it hasnt switched despite being given the correct input voltage and no AC will flow because its not closed."

Its not a mechanical relay. It doesn't work like that

The Output will only pass a high enough AC Voltage. (not a small dc voltage as used in continuity tester)

"If I am not correct in that assumption, I have still attempted to test its operation by disregarding the continuity verification and literally wired the VDC control input to my bed output (which provides 24V) and still got no response from the heating pad which was wired directly to N (at the plug) and L (which went from the pad to the SSR, which was supposed to close and flow from L at the plug)."

This sounds like it should have worked. (did you also have the thirmistor attached, as heated bed will not turn on if It cant see a sane temperature. )


Check the continuity of the heated bed. Perhaps its broken.

Edited 1 time(s). Last edit at 10/21/2019 05:07AM by Dust.
Re: Trouble with solid state relay closing for mains voltage bed
October 21, 2019 05:18AM
Quote
Dust
Check the continuity of the heated bed. Perhaps its broken.

Oh god, Bingo. Thanks for fault finding with me and sharing the SSR knowledge while you were at it.
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