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Solid State Relay Question
allenb
Top  #1 Print Post
Posted on 11/22/2023 5:02 PM
Ok, here's a question for all of you seasoned process control guys/gals.

I have this SSR that I'm switching single phase 120 volts ac on and off powering a resistive heater within a typical control scenario. My question is this: When an SSR such as this is in the off state, (non- conducting state), if I apply 120 volts to the heater from another source which would obviously apply 120 volts to the SSR's output terminal, would this cause any harm to the SSR? Or, is it that when they are not in the conducting state, they will not leak anything through them as a back feed? I can obviously test the circuit to find out but would rather not melt anything down unnecessarily.


https://www.digik...l0EALw_wcB
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
btreichel
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Posted on 11/23/2023 12:27 AM
1, backfeeding like that is just generally a bad idea.
2, It says its a relay so open should mean open.
3. diode block the backfeed?
 
Yasu
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Posted on 11/23/2023 2:28 AM
In a device I built a long time ago, there was a small mistake in the circuit and voltage was applied to the secondary side from a different line, and even when the SSR signal voltage was turned off, the secondary side voltage from the SSR remained applied.
I don't know if that was the cause, but ...
 
renatoa
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Posted on 11/23/2023 2:40 AM
It's A/C, the SSR is polarized both senses 50/60 times per second.
If you mean reverse polarization by backfeed, this is the way how A/C works.
 
Piotrkurak
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Posted on 11/23/2023 8:38 AM
If you are applying the voltage to only 1 output side then it will turn off to no effect as long as current and voltages stay within the tolerances of the relay.
should be a common for return added somewhere in the heater circuit which could cause parasitic current flow unless everything is isolated/insulated from ground (earth as renatoa knows it)

Can't imagine the purpose, however as the heater would be always on unless this is like a seperate preheat option and the other voltage source is controlled also such that both sources can be off at some point

Lalso need to provide some isolation in the heater circuit such that when the second source operates it doesn't backfeed anything else that needs controll
 
allenb
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Posted on 11/23/2023 8:57 AM
Yes, it is for manually applying heat prior to start of control sequence. Voltage will only be seen on the output terminal of the SSR
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Piotrkurak
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Posted on 11/24/2023 9:26 AM
Should work just fine. You do need to add a failsafe so that both sources are not on at the same time, it would be one source or the other. A dpdt switch would suffice

If you're like me, you sometimes get so.excited........ can you say extremely dark charcoal roast?
 
allenb
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Posted on 11/24/2023 10:13 AM
Thanks Piotrkurak. We think alike! I had already included a single throw, double throw switch so that only one source could be energized at one time. I've never attempted switching it to the manual position as I wanted to be able to do lots of system tests first before potentially blowing up my SSR. At this point, I've verified that all design elements are working so I will now utilize the manual mode without worrying about it going poof.

On getting excited on a project and plunging on ahead before verifying basic operation first? Oh yeah, big time mistakes and much worse roast outcomes than even Peets or Starbucks ultra burnt flavor profile. Shock
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Piotrkurak
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Posted on 11/25/2023 9:57 AM
The other thing I will admit to being good at is forgetting to turn on the heater at all then wondering why bean temp isn't climbing.

Had to buy a starbucks coffee the other day, really needed an emergency caffiene fix for a very early flight... still gives me the shudders.
 
allenb
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Posted on 11/26/2023 8:57 AM

Quote

Had to buy a starbucks coffee the other day, really needed an emergency caffiene fix for a very early flight... still gives me the shudders.


I think most of us at one time or another had to succumb to their outdated extreme dark roasting relic of the 1970's and still refuse to join the real world of sane roasting techniques. When you need a coffee-like substance and nothing else is available it sometimes has to be endured.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Piotrkurak
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Posted on 11/27/2023 9:16 AM
Even more odd: there are people that claim to prefer over roasted and highly sugared hot beverages
 
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