Nest Power Connector install questions

[mattkwi]

Hello.  I can't quite seem to find an answer to this question on the internet.  I have 2 Nest 3rd Gen Thermostats, both about 7 years old.  Last year or so I've been running into the devices going into low battery state and disconnecting from the wifi.  My system is Heat only, no C wire.  Just R and W. 

I followed the instructions to install two Nest Power Connectors.  System started right back up after installation, no errors.  I've read that the 3rd Gen Nests do not show any sort of confirmation of correct installation, but I am still trying to ascertain that it worked.

Either zone turn on when I tell them to, so seems to be wired correctly.  However, when I look in technical info, I get the following read outs.

Basement Zone:  Battery 3.7 volts
Upstairs Zone: battery 3.84 volts

These readings are barely or close to what they were before the install.  Everything is showing online at the moment and since the install.

What should I expect to see here to know this is working correctly?  Those numbers both still seem low.  Will they slowly climb?  Should they immediately be at a higher voltage?  Is there  a voltage they will cap at? 

Thanks

Matthew

[jb76]

Hi Matthew - I was also running into these issues of "low" voltage to my 3rd. generation Nest Learning Thermostat. The thermostat would get up to maybe 3.8 mV during the day when I would run the furnace etc. and when I had my furnace replaced recently no power was going to the thermostat at all - since without a Common wire, power to the Nest is only passively captured.

In order to have full functionality, the Nest thermostat will need at least 3.85 mV charge to communicate over Wifi (to your phone etc.) and send signals to your AC/Furnace. So in your case, check/confirm the number of wires coming to/from the thermostats. If you have 4 wires, make sure W1 and R1 are connected and going back to your furnace control board the (should be a labelled 24V bus on the board with inserts labeled ('W', 'R', 'C', 'G'). Not sure how old your furnace is but you should have at least the G(typically green color) (fan) control available and if you don't want to run the fan (no heat), you could borrow this 'G' wire/connection to run as your C wire back to the thermostat and charge it to the level it should be at  - 3.85 mV or as high as mine - a constant 3.93 mV.

The bottom line - you should get a Common wire power back to the Nest thermostat. Newly purchase Nests have enough battery power/charge to fully operate getting passive charge from the R(power control to furnace) but over time (3-5 years) will lose capacity to the point you will have to manually charge the thermostat if you don't run the furnace/AC enough (which may already be the case imposed by Nest to save energy).

My new thermostat wiring was simple (15 ft. run) but even then electricians/HVAC techs. wanted to charge me $1000 to do the job (no thanks) - so a $25 spool of 50 ft. 18aWg/5 (5 wire) thermostat wire from HD worked a lot better for me. I had my own issue of testing the 'Cool'/AC function of the Nest during winter (Nest will not run AC even to test if the outside temp. is below 65 apparently).

Hope this helps - let me know if you have other questions.

[mattkwi]

I appreciate the info, although it doesn't answer my question.  The NPC install was successful and I believe that is indicated by no errors and heat still working.  Per Nest itself, this should resolve my issue, not purchasing new thermostats.  I definitely cannot run a C wire myself and fish through the walls in this house and do not want to pay an electrician too. 

After a few hours of searching, I believe I finally found the answer I am looking for however here: https://www.reddit.com/r/Nest/comments/sai3vx/nest_3rd_gen_with_nest_power_connector/

I don't understand on Nest's own forums why so many people cannot find this answer.  I don't consider the question to be difficult to understand.  This is not a shot a you,  and I appreciate your help, but I confirmed I installed the NPCs as directed, Nest itself says the 3rd Gens do not confirm a correct installation one way or another, so I want to figure out how I can determine this.

I believe my Nests now show 40 lin when previously showing 20 is the answer,  but now only time will tell. 

[jb76]

Hi Matt - The NPCs are definitely an option though I don't have experience using them. Per that Reddit thread - those connectors prevent the cycling issue which has been reported with Nest 3rd gens. that constantly cycle the furnace/AC because they lose connection due to low power. It is not clear if those NPCs actually fix the charging problem. If they do draw power from the G wire (fan control typically) - is that what you connected your NPCs to?

With these connectors - you should see the charge of the thermostats increase over time (at least 2 hours) to a level of 3.85 mV or higher - is that not happening?

J

[mattkwi]

I do not have a fan wire.  The C is now only connected to my thermostats via the NPC and with only red and whites back to the thermostats.  It's been about 4 hours since I installed them, and the battery voltage has not moved much. 

3.87 volts showing upstairs, and 3.73 volts showing downstairs.    Both slightly higher than when I made this post.    Heat has not been running since its warm out here today.

The most obvious change is the Lin changing from 20 to 40 on both. 

Neither have gone low battery and display respond very fast to movement so seems like they have enough power right now

[jb76]

Also - for reference (C wire configuration) - my Nest 3rd. generation shows the following Lin power output:
(Tech. info. -->Power):
Battery: 3.932 V
Voc: 36.59 V
Vin: 35.77 V
lin: 200 mA (c) (common wire)

J

[mattkwi]

It sounds like without a real C wire it won't ever show a high lin, but 40 is enough for charge.  20 not so much.   Maybe I an wrong here, I am no electrician.  Just reading lots of forum and reddit posts. 

[jb76]

Matt - you are correct - 40 mA is small (approx. 5 volts) but it is better 20 mA! My lin - is about 10 times that so you do have a working solution with the NPCs - just not ideal if house is without power for a prolonged time (which won't matter anyways - no power to furnace). It sounds like you are 'slowly' getting charge to the thermostats...yes, this is annoyingly frustrating to not get full/frank disclosures on accessory equipment setup from Google but you would probably get even less help/feedback from a $250/hour electrician/HVAC tech. telling you, you need a thermostat and "Nest sucks". Keep an eye on the charge levels for each thermostat and probably in 1-2 days - they should get back up above 3.9 V.

J