Suspected Voltage drop shuts down WYZE Thermostat when AC is engaged, what are my options?

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So this is a problem I was running into in October but as I wouldn’t need A/C any time soon, I pushed it off and tried to think of a solution. I have my WYZE thermostat hooked up to my A/C (with outside condenser unit) and electric heat system with a C-Wire adapter, and everything works fine until I call for A/C. When a solenoid/contractor engages with a thud ( it sounds just like a pinball machine) to turn the A/C on, the Wyze screen goes black, the solenoid disengages from a lack of relay connection through the thermostat, and the A/C stops (it was only receiving power for about 1/3 of a second). Then the Thermostat restarts, see’s the temperature being too high, and calls for A/C, connects the relay, moves the solenoid/contactor, turns the A/C on, voltage drops, shuts down, A/C goes off, rinse and repeat. I’m lead to thinking it’s due to voltage drop from the load of the condenser fan motor spinning or the compressor or maybe a combination of the two.

A few ideas I have thought of to fix this would be to work a capacitor in at some level (possibly past rectification to DC within the thermostat itself to give it a second or so more for the voltage to come back to a normal level without power disruption, but I’ve got no idea where it would go as the FCC diagrams make it really hard to follow the traces and I’m not sure what voltage the system runs at (I see a solder point for 3.3v on the board but I font know if that’s just for writing data to a chip or if it can truly power the board).

Another idea would be to power the thermostat from a 24v AC power supply from the wall which would allow me to remove the C-Wire adapter from my HVAC, but I’m not sure how to wire it up to the thermostat and isolate the 24V AC transformer from the HVAC unit and the 24V AC transformer from the wall, I cant imagine wiring them both up together would yield amazing results (like I assume I cant have the 24v from the HVAC and the 24v from the wall outlet transformer on Rc and then have the ground from the wall outlet transformer be the C connection).

I can send some photos of my setup in case it’s a fault of my wiring, but to me it seems to be an inherent problem with the HVAC setup which I would be unable to easily fix, fixing the thermostat would be my best route.

Let me know what you guys think and what I can do to help.

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mmm. what VA is your transformer?

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It’s 20va on the secondary winding

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That’s a bit low. A/C contactors can take up to 32VA inrush current, so when it kicks the A/C on, the transformer is overwhelmed and the voltage sags below what the wyze needs for power - with a battery powered thermostat, it isn’t too much of an issue, it just takes longer for the contactor coil to saturate the core and pull in all the way, but with a transformer powered thermostat, it will reset like you are experiencing.

40VA transformers are pretty standard these days, you could probably pick one up at a big box store for under $40 and install it, or have a hvac/furnace tech do it if you aren’t comfortable with it.

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