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Old 11-29-2022, 06:03 PM   #21
sam_sam_sam
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Default Re: resistor values for 2n2222a w/ SSR

Just make sure that once you have been calling for cooling or heating ( which uses the compressor for heat ) to have a 5 minute time delay before it can restart the compressor this is extremely important so you do not try to restart the compressor before the system pressure equalizes do this is very hard on a compressor

Also if your air conditioning system does use the compressor for heat you also have a reversing valve that need to be powered on in either heat or cool depending on how this was done

You might be interested in this YouTube video on different relay modules and how to use and hook them up to a micro controller

https://www.youtube.com/watch?v=FWvEEtrTGRQ
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Old 11-29-2022, 10:58 PM   #22
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Default Re: resistor values for 2n2222a w/ SSR

the relays are replacing the mercury tubes, the only job of the tubes is tell the unit if the temp is above/below the temperature it is set for, i would expect the unit to have any safeties it would need for when someone changes the temp settings at some random time, the only part of the thermostat i have modified is the temperature sensor
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Old 11-30-2022, 01:36 PM   #23
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Default Re: resistor values for 2n2222a w/ SSR

Here's some possible circuits for driving the two SSR's to make a SPDT SSR.
Using two or three transistors or a 5V IC buffer/inverter to make the inverted signal for the SSR.
One SSR is always on, so you want that to be a safe default if the RPi croaks.

I think the only sort of danger is if the SSR's switch mains to a 3-way light switch, any overlap would cause both SSR's to be on for a short time which would blow them up if one went to Line/hot, and the other to Neutral. I'm not sure if they are zero-cross or not.

For the hallway light, I would use a PIR sensor or cheap microwave sensor i.e. RCWL0516 to sense a person and turn on the light switch and stay on for a few minutes. The boards have a provision for CdS light sensor (like the PIR boards) so they won't do anything during the day. But if your RPi knows time of day, you can enable the light from say 10pm-6am.
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Old 11-30-2022, 11:07 PM   #24
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Default Re: resistor values for 2n2222a w/ SSR

the SPDT is NOT for my 120v mains bulb, that is for use in my thermostat (for the next time the relay fails), i only need SPST for the light bulb

my dad hates 3 way switches so i can't use them, the solution is to add a new light controlled via a relay, all i need to do it get my controller setup for that to be working, i got the bulb, fuse, and relay all wired, just need to program the pico, solder my transistor/resistor in place (and hook up my data inputs/sensors)

i was trying to think of a way to make it take longer for relay to switch on i was thinking of a 1uf cap, but that would also make it slower to turn off

on-on could be a problem (not 100% sure), off-off is fine, if the delay is in milliseconds i do not care until is is over ~1000 of them, maybe it is possible to use 5v going to the relay with a logic gate or something?
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Old 12-03-2022, 12:12 AM   #25
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Default Re: resistor values for 2n2222a w/ SSR

The SPDT SSR relay is for the thermostat HEAT-OFF-COOL on the 24VAC side? You'd be missing the third state OFF with only one RP2040 output pin. If this SSR is driving the air con contactor, I'm not sure it is tough enough.

Another SPST (mechanical) relay would be turning the light on? Not sure a 2A SSR would be able to switch most light bulbs due to inrush current.
You need a switch or sensor or both, somewhere.

I don't understand what hardware delay is for. If you can do it in S/W it's best. RC delay does not work well with SSR's.
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Old 01-01-2023, 12:26 PM   #26
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Default Re: resistor values for 2n2222a w/ SSR

I am using 2 relays, one is SPDT one is SPST (same model relay, but 1 pin is not used)

for the SPDT relay high is run and low is off, if you switch the slide switch the logic is inverted and the unit will change from being a heating unit to being a cooler, or vise versa

i am using the physical slide switch on the stock panel to set heat/cool/em. heat/off (also have a software off, but that will results in inf run time if the slide switch is set wrong)

the stock controller used mercury tubes, i used mechanical relays, nigher of these have the possibility of being both on and off at the same time, when the logic changes with this dual solid state relay circuit there will be a small time period (nanoseconds i think) where both relays would be in the high logic state, not sure if that could be a issue so i was trying to see how simple of a solution it would be to just assume it is a issue to work around and be on the safe side
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Old 01-01-2023, 10:30 PM   #27
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Default Re: resistor values for 2n2222a w/ SSR

I think I get what you are trying to do.
If your thermostat only had to switch a control board input, these are typically a 1kΩ resistor for a 24VAC input, the old relays would last a long time. So I'm wondering why the relays are getting chewed up. If it's not some overlap, the A/C might have contactor coil for the load?
Nest (dual mosfet) and Honeywell (smt relay) are not much for voltage/current.
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