Nest Learning Stat just recently started not enough power for wifi and, changing temps on its own

[walley]

Hello,

I'm very frustrated here. For years the stat has been working perfectly. In the last month or so, it has taken on a mind of its own - daily, morning and evening, changing the colling temp and, it is not changing to be more efficient, it is changing to make it cooler.

Also, at the same period, it started losing the internet connection stating the battery was low. How can this happen out of nowhere?

I don't need nor want it to "learn" anything nor do I need a schedule. How could I make it just a dumb thermostat???

Another item, it used to activate the screen from 10 or 15 feet away, now it doesn't come on at all until I push on it.

Thanks!

[CoolingWizard]

@walley , this sounds like the lithium ion battery is failing.  It appears to no longer take on a full charge. 

AC Cooling Wizard

[walley]

That was my guess, is that something that is replaceable? Because I doubt I would make the investment in another Nest. Thanks!

[CoolingWizard]

To my knowledge there is no serviceable components.  

AC Cooling Wizard

[Bobbyds1]

I am having the same problem mine keep saying no power to the c wire when i put a meter on the c wire and the rh wire i read 24 volts this just started happening and the thermostat dosen't charge on my thermostat for A/C and heat. on my second thermostat thats just heat it keeps saying no power for c Wire is there any work around for this as nest isn't to helpful.

[walley]

Howdy. Yes, as with many posts I see here, this is a very recent occurrence after many years of solid service. I just started having these issues with the last 2 months. As you may have seen in this thread, it was suggested that the battery is bad - not being able to be recharged.  My issue with this is that I'm not willing to pay for an entire new Nest when it should be possible, as with most items with rechargeable batteries, to simple replace the battery. It was also mentioned in some of the posts that defaulting the Nest could possibly correct the issues - my second issue is that the Nest keeps adjusting the temp even though I have all those items disabled - at no consistent time intervals.

I removed the Nest and connected the micro USB and it seemed to charge the battery a bit but, it is now back to where it was.

I can't help but think that an upgrade automatically happened recently that was a major change and hosed it up.

[Bobbyds1]

What I cant understand is that if the battery cant be charged by the c wire which is 24 volts and like u said when i connect to a micro usb charger which only puts out 5 volts how can that be charging the battery. that doe not make any sense to me it has to be something that came thru on an update or something.

[CoolingWizard]

@Bobbyds1 , let me see if I can help you understand how it is possible. It is called electronics. The actual charging circuitry is based on a 5VDC power source.  When the HVAC equipment sends the AC power to the Nest Thermostat, the electronic circuitry converts that AC Power to DC power and reduces it to 5 volts and about 275mA of current. This 5 volts is then sent to the voltage regulator and on to the battery. When the USB a port forwards power to the voltage regulator, them same thing happens.

If you would like to better understand the circuitry that makes this work, attend a community college and take some electronics courses.  It will amaze you how this all works. 

AC Cooling Wizard

[walley]

The battery is a 3.7 V battery. The nest overall uses 24 V but it drops down to charge the battery.

[CoolingWizard]

First of all, no HVAC transformer does not put out exactly 24.0 volts. And as the load increases the current draw increases and the voltage drops slightly.  You cannot charge a battery unless the charging current and voltage are greater than the battery base voltage state.  The typical class 2 transformer found in residential HVAC equipment is rated at 40 Volt Amps. This is sufficient current to operate the equipment and send a few hundred milliamperes to the Nest Learning Thermostat.

AC Cooling Wizard  

[walley]

Thank you but a lesson in electronics is not helpful. The question is the battery is bad or, is there something wrong with the nest after a more recent update. If there was something wrong with the c wire, the nest could not control the heating and air conditioning.  It would be helpful if the manufacturer would kindly weigh in…

[Bobbyds1 · Accepted solution]

is there a work around for this problem if i but a 24 volt trans former a put one wire to the c terminal and the other wire to either thru RH or RC as both are used in my thermostat am i going to be sending too much voltage back towards the furnace or a/c unit as mine are 2 separate units.

[walley]

There is on Amazon, a nest power adapter for that. But it makes no sense that you would need it.

[Bobbyds1]

I wondering if you factory reset the learning thermostat and do not let it update and prevent it from connecting to the internet if you would still get the c wire issue. 

[Bobbyds1]

Mister Cooling Wizard can you tell me if i use an external 24 volt power supply and connect one end to either my RH or RC will i Have a problem being that the RH goes to my heater and my RC goes to my A/C as each uses there own individual power supply.

[CoolingWizard]

@Bobbyds1 , the problem is your Nest Thermostat and the HVAC equipment must be powered by the same transformer power source,  their cannot not be “to much voltage sent back” as this is not how alternating current works.  Unless you have dehumidifier or other equipment slaved to your primary transformer there should be no need for an additional transformer.  If as you say you are measuring 24 volts of AC power, +/-4 volts, then the power source is good.  And, if your thermostat is not charging after properly measuring the voltage, then you have problem in the Nest backplate, the wire insertion into the backplate, or the Nest Display.  I have run across installations where the wire was not fully inserted into the nest backplate.  

Let me know how else I can help 

AC Cooling Wizard

[walley]

I would be cautious after blowing some stuff one day myself. This looks to be easy enough to adapt to the Nest. https://www.amazon.com/s?k=nest+power+connector+c+wire&crid=3V31IATW84GK5&sprefix=nest+power%2Caps%2...

[walley]

I have resolved the issue with the battery - not sure how resetting the schedule and away sections resolved it but doing that stopped the constant automatically changing the temperature as well. Perhaps those 2 items were using up too many cycles on the processor. I'm continuing to look for a way to stop it from "learning" anything...