How do I add auxiliary power to Nest E thermostat?

[bobm]

After 3+ years with no issues one of my Nest E thermostats went dead with a low battery.  Unfortunately I was away & noticed it on the app.  (Neighbor reinstalled old Honeywell mercury tstat.) Have since returned and charged the problem Nest with USB cable and changed stranded input wiring to solid copper by soldering and adding an approx foot solid copper wire at the wall end to the Nest connection.  Everything seems to be working fine for last few days.   Nest showing 3.9v on app.  BTW, furnace not calling for heat as it is warm out. 

Seeking forum advice on how do I connect an auxiliary power  transformation, to my Nest E thermostat?   Looking at something like - https://www.amazon.com/dp/B085TLYBFX/?coliid=IB7HP06AMFS39&colid=3Q98A2H1MSTZ6&psc=1&ref_=lv_ov_lig_...

Want to prevent possible chance of Nest  low battery error when I am away other than if home losses power from local utility for few days. 

Note my furnace is vintage early 80s and has only two wires, red and white for thermostat.  There is no C terminal in the control box only red and white wires on the low voltage side and relays and 120V to motors, etc.  on high voltage side  BTW, looked into the Google Nest Power Connector -  C Wire Adapter as possible power source solution, but being its a two wire system and there is no C wire in my control box (Honeywell Triple Aquastat) don't understand how could get it to work. 

[Patrick_Caezza · Accepted solution]

The Nest Power Connector should work, you just need to add an external 24VAC transformer.

This is how you would wire it.

 

 

[Patrick_Caezza · Accepted solution]

Yup, that transformer will work

[Patrick_Caezza · Accepted solution]

The Nest Power Connector should work, you just need to add an external 24VAC transformer.

This is how you would wire it.

 

 

[aatienza]

Hey bobm,

I'd like to jump in here and check if you've seen Patrick_Caezza's response. Let us know if you need more help by replying to this thread.

Thanks,

Archie

[bobm]

When I looked further found "Google Nest GVNZ4 Nest Power Connector Installation Guided" dated  January 31, 2022 February 1, 2022 on the web which looks to be the same as diagram Patrick provided.   Interestingly when I looked earlier at the guide found on Amazon associated with the Nest Power Connector numbered G953-01654-01-C it was slightly different and did not have the external  24V transformer solution.

Plan to order one 24V transformer rated for 40VA and wire both of my Nest Es to it.   Will post on how I make out.    Transformer link - - www.amazon.com/Thermostat-Transformer-Compatible-Honeywell-Doorbells/dp/B07Q4PPKQ8?ref_=ast_sto_dp

[Patrick_Caezza · Accepted solution]

Yup, that transformer will work

[aatienza]

Hey folks,

Appreciate the help, Patrick_Caezza. Hope that sheds some light on the issue.

Thanks,

Archie

[Karatemom216]

I’m having the same problem as you had. Does the power connector also have to be connected to the air handler or can it only be connected to the furnace. I have my Nest for both hear and air conditioner 

[Ryan_G]

Hi Karatemom216,

Thanks for reaching out here in the Google Nest Community.

The Nest Power Connector can be connected to the furnace or air handler. You could check out this link to know more information before installing one.

I hope it helps.

Regards,

Ryan

[Ryan_G]

Hey Karatemom216,

I just wanted to follow up and see if you're still in need of help. Please let us know as we would be happy to answer any questions you may have. 

Best regards,

Ryan

[bobm · Accepted solution]

ACCEPTED SOLUTION

Made the recommended changes and tested, everything working fine.  Wired the 24V transformer 120V power input on the same circuit protected by the furnace thermal cutoff switch.  Put transformer and Nest Power Connector Modules in standard electrical enclosure metal box as there was no room in the furnace Aquastat Control boxes.    Thanks all for technical recommendations and follow-up!!!

[MelbaDT]

Hey there, 

That's awesome — thanks for keeping us posted. Glad to hear that you've managed to have it working as it should. 

Cheers, 

Melba

[Ryan_G]

Hey there,

Thanks for being here in the Google Nest Community. 

I'd like to bump in here and make sure that you’ve seen our response.

Please let us know if you have any other questions or concerns as I will be locking this thread in 24 hours.

Have a great day.

Best regards,

Ryan