resistor values for 2n2222a w/ SSR

[redwire]

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.

[evilkitty]

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

[redwire]

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.

[evilkitty]

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?

[redwire]

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.

[evilkitty]

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

[sam_sam_sam]

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

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

What is the voltage to the blue relays I am guessing that they are 5 volts if they are you can use a 4N25 with a drop down resistor for each relay coil power and then use the 24 volts from the transformer of the air conditioner or use much better relays or a SSR on separate board in an enclosure

just 5v songle relays i got for ~0.25 each

Do not be tempted to use the power of the thermostat electronic output directly to power your up graded relays or SSRs this not good idea because these thermostat boards are very easily damaged by voltage spikes and static electricity and some of these thermostat are not cheap sometimes over $100.00 depending on the features that it has

Are you talking about the board in the HVAC unit? if you are talking about inside my thermostat, i have VERY dumb (actually quite a clever design) but it was designed to not need any electronics

• https://github.com/GM-Script-Writer-...o_DSCI0050.JPG

my dad was complained saying the tubes were 'sticking' guessing there is some metal fatigue going on and it is not as accurate as it used to be, i was looking at how i was gonna solve this and asked my self why am i trying to replace all of this, the only issue is the tubes, one is a double throw switch and the other is a single throw switch and a pair of mechanical relays would do the exact same thing, then i decided to log the temp and the tube states so i can log there behavior and se how much variance they have

One note if you go this route please make sure that the thermostat still function correctly before attempting to do this upgrade

I had a customer that had one of these electronic thermostat that had a relay issue but also had an issue with the outside temperature sensor not reporting so they want to replace the thermostat so I got them a replacement thermostat but unfortunately it would not operate the defrost function correctly because this one of those air conditioning units that has to use a special thermostat

But a few months later the compressor would not turn on now the real issue was that the thermostat wires were so full corrosion that wires were coming apart after running new thermostat wires I was able to get back the outside temperature sensor function and the heating issue and the cooling issue with there original thermostat that I thought was the issue because I know about the relay issue that these thermostat have

my dad had gotten a new thermostat and returned it cause it did not seem to properly support aux heat, our unit has 2 heat levels, low and high, with my current design i have had issues cause of the contact wearing out in the relay

That would work, I tried to do it with two transistors but it would be finicky so I did not post the idea.
The debug LED's lose too much voltage though, so the SSR does not get enough voltage. You have 5V subtract the debug LED let's say 2.2V and 0.1V for the transistor on, and that leaves 2.7V but the SSR minimum is 4V. So you would move the debug LED to be in parallel with the SSR drive (adding a resistor for the LED like 1k).
The intermediate transistor can use high resistor value say 10k on the base, and no need for the second R2 at the base. R2 to 5V still around 2.2k

wait i can put it in parallel and it work? i forgot i am not trying to use a common resistor, though in the interest of saving board space how about this? [attached]
i should not really need 2 LEDs assuming my 5v wire is working and if i cared about that i would have a power led on the board (clearly i do not have this, but if i did there is no need to make that function part of the relay circuit)

** added my single throw relay to the image (also have a input pin from the tubes, a DS18B20, and a LED)

the top double throw does heat/cool and the bottom does more heat

BTW i have those snubber caps on by board (for the mechanical relay), should i remove them? when i do this modification, would it hurt anything? would it help anything?

[sam_sam_sam]

Re: resistor values for 2n2222a w/ SSR

i want to make a SPDT out of 2 SSR relays for my thermostat that has had a few of those mechanical cheap blue relays die (so when the next one fails i can permanently fix it)

I would suggest the following

What is the voltage to the blue relays I am guessing that they are 5 volts if they are you can use a 4N25 with a drop down resistor for each relay coil power and then use the 24 volts from the transformer of the air conditioner or use much better relays or a SSR on separate board in an enclosure

Do not be tempted to use the power of the thermostat electronic output directly to power your up graded relays or SSRs this not good idea because these thermostat boards are very easily damaged by voltage spikes and static electricity and some of these thermostat are not cheap sometimes over $100.00 depending on the features that it has

One note if you go this route please make sure that the thermostat still function correctly before attempting to do this upgrade

I had a customer that had one of these electronic thermostat that had a relay issue but also had an issue with the outside temperature sensor not reporting so they want to replace the thermostat so I got them a replacement thermostat but unfortunately it would not operate the defrost function correctly because this one of those air conditioning units that has to use a special thermostat

But a few months later the compressor would not turn on now the real issue was that the thermostat wires were so full corrosion that wires were coming apart after running new thermostat wires I was able to get back the outside temperature sensor function and the heating issue and the cooling issue with there original thermostat that I thought was the issue because I know about the relay issue that these thermostat have

[sam_sam_sam]

Re: resistor values for 2n2222a w/ SSR

Bump

[redwire]

Re: resistor values for 2n2222a w/ SSR

That would work, I tried to do it with two transistors but it would be finicky so I did not post the idea.
The debug LED's lose too much voltage though, so the SSR does not get enough voltage. You have 5V subtract the debug LED let's say 2.2V and 0.1V for the transistor on, and that leaves 2.7V but the SSR minimum is 4V. So you would move the debug LED to be in parallel with the SSR drive (adding a resistor for the LED like 1k).
The intermediate transistor can use high resistor value say 10k on the base, and no need for the second R2 at the base. R2 to 5V still around 2.2k

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

This should work in theory, still not sure about about the resistor values, but there are some issues

• debug led has 1.95 fV, maybe i should just put 1 led in the 3.3v logic (or the 5v logic), with a mechanical relay i could just put it in parallel with the relay, but with a SSR i would only expect the device with a lowest forward voltage to turn on
• not sure about resistor values
• when logic goes high i think both relays will be on for a ~250ns
  • off-off is fine
  • on-on could be a issue, not sure if my HVAC cares but it could (even if it does i doubt that is long enough to be a issue, but idk)

2n2222A has a turn on time of 35ns and a turn off time of 300ns

[stj]

Re: resistor values for 2n2222a w/ SSR

https://www.youtube.com/watch?v=abJCIgRKQk0

https://www.youtube.com/watch?v=9Pw7U0XFgUM

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

why not use cordless switches??

did not know that was a thing... well i have the relay installed and wired at this point and i can make the smartest auto light you have ever seen on my pico now (photocell, door sesnors/switch input as well as buttons at each door)

I'm not sure what you are trying to make - "... can i make a double throw SSR switch..." I take to mean DPST? This is like connecting the two SSR inputs in parallel, so the one 2N2222 powers both at the same time.
If you want a SPDT switch then you need another transistor.
You want to make one end of a 3-way light switch?

i want to make a SPDT out of 2 SSR relays for my thermostat that has had a few of those mechanical cheap blue relays die (so when the next one fails i can permanently fix it)

all i needed to know for the light switch problem was the base resistor value (Thanks redwire)
the issue was my dad hates 3 ways and so he does not want them installed (i think they confuse him somehow), well since i am installing a pico in this room i figured i would make a smart light so i can have a light to use to get though the room without relying on any switches, he had to use these super old T12 8 ft fixtures (from ~1995 new in box he never got around to installing), i checked the power draw with my clamp meter... 540 watts for 2 fixtures, he plans to have four and another four 4ft fixtures and there are another 4 light bulb sockets fixtures on this circuit, good thing we replaced that piece of 14awg on the 20 amp circuit from the panel (everything else was 12awg)

[stj]

Re: resistor values for 2n2222a w/ SSR

why not use cordless switches??

[redwire]

Re: resistor values for 2n2222a w/ SSR

I'm not sure what you are trying to make - "... can i make a double throw SSR switch..." I take to mean DPST? This is like connecting the two SSR inputs in parallel, so the one 2N2222 powers both at the same time.
If you want a SPDT switch then you need another transistor.
You want to make one end of a 3-way light switch?

[harp]

Re: resistor values for 2n2222a w/ SSR

I am not shure that your problem is clear to me, but maybe you can consider a implementation of some logic gates, that if two switches in opposite side of room is in same state there is no light, else it is. In this case, wire can be a small diameter and easely 'glued' on wall with (in) wall paint.

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

just used a random npn transistor i found on google images

i already modded my ethernet cable to have 9 conductors, getting a 10th is not happening

[eccerr0r]

Re: resistor values for 2n2222a w/ SSR

BTW thought PN2222A TO92 pinout was E-B-C when looking at the flat face with pins pointing down... that picture was really bothering me beyond just the lack of details...

[eccerr0r]

Re: resistor values for 2n2222a w/ SSR

Use another npn transistor as an inverter... or use another gpio pin and do the same except write it with the opposite phase...