Low battery warning with frequently charging

[wxman0516]

I keep getting frequent low battery notifications and have to USB charge my thermostat in order to keep it from shutting down. I do not have a c-wire but I do have a Nest Power Connector wired in. Recently replaced the thermostat because I thought the battery was just old, but now my new thermostat is doing the same thing. 

I get an lin of 20 when the AC is running and 40 when it's not heating or cooling.

[wxman0516]

For reference, here's the wiring:
 

And output when the AC is cooling:

And when not cooling or heating:

[AxelD]

Hi wxman0516,

Thanks for posting in the community! Sorry to hear about this situation of your Nest Thermostat showing you the low battery message. No worries, help is here! I'd like to ask you a few question about your wiring:

1. Do you see a blinking LED light? If so, is it red or green?
2. What is the blue wire for?
3. Have you checked the voltage of your R-WIRE?
4. Have you verified if the Nest Power Connector is correctly connected?

I checked the photos you attached and I noticed something with the VIN readout, it says 6.80 V, it's below the recommended ones (when it's on). The right readouts without a C-WIRE should be: 

• Voltage Open Circuit (VOC): Between 29 to 42 volts (V)
• Voltage Input (VIN): Between 29 to 42V (HVAC is off) / 6 to 7V (HVAC is active)
• Current (Intensity) Input (IIN): Between 20 to 40 milliampere (mA)

Keep me posted.

Regards,

Axel. 

[wxman0516]

Sorry for the delay. Took a bunch of pics from the handler where the power adapter is attached. I know it's hard to see things but I tried to get enough pictures for tracing the wires. They can be found here: https://drive.google.com/drive/folders/1mtzfnPIpWnPogxw0pxKt1FnbF-SCt-KG

I think I got like 28V off the red wire, photo of that in the folder as well. 

 

Blue wire goes up and attaches to one of the grays from the power adapter. It's either AC or heat. 

[AxelD]

Hi wxman0516,

Thank you for your reply and the helpful photos you attached. They are much appreciated. If you've already verified sufficient power supply to the unit using a voltmeter, the display itself may be malfunctioning. To assist you further, please fill out this form and an agent will then contact you as soon as possible with additional troubleshooting steps.

Regards,

Axel. 

[wxman0516]

But this is the second unit to do so. I just swapped out my old one for this brand new one because it started doing this. And the brand new one did it is as well. Could the power adapter have failed?

[wxman0516]

 next to my hand, is that a transformer? If so do I need to wire based on the pro guide section about no c wire and a transformer?

[AxelD]

Hi wxman0516,

Thanks for your reply! Based on the fact that this is the second unit you get and it's facing the same situation. My recommendation would be getting a Pro Technician to check your wiring. They can determine if it's wired correctly or if there's a voltage problem.

Regards,

Axel.