Don't forget to check those thermostat batteries! - Page 1
Forum section: electronics / general

author: Smoky
author_rank: Frequent Contributor
timestamp: December 23, 2022, 06:12:51 pm
content: I checked over an HVAC system today that hadn't been serviced in a while.The batteries in the thermostat were shot!It's good practice to replace those batteries every yearMerry Christmas!

author: wraper
author_rank: Unknown
timestamp: December 23, 2022, 06:14:42 pm
content: Good practice is to not use alkalines whenever possible.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 23, 2022, 06:26:13 pm
content: I think the main design flaw is requiring batteries in the first place. A supercap can easily keep the RTC running for days without external power and the settings can easily be backed up to EEPROM.

author: IdahoMan
author_rank: Regular Contributor
timestamp: December 23, 2022, 07:55:49 pm
content: Quote from: NiHaoMike on December 23, 2022, 06:26:13 pmYes. And it's not a flaw, it's a feature.

author: Smoky
author_rank: Frequent Contributor
timestamp: December 23, 2022, 10:26:35 pm
content: These Honeywell thermostats will show a "Replace Battery" message when the batteries go low in voltage but the leaking batteries in the picture still measure 1.48v...most people wait until they're told to do something

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 23, 2022, 10:54:45 pm
content: Quote from: IdahoMan on December 23, 2022, 07:55:49 pmI can see the manufacturer doing that to boost sales of a product that would otherwise very easily last well over 10 years. But have they considered the mess they would get involved in if one of their thermostats failed (due to batteries running out or leaking) on a well below freezing day while the family is away for vacation?

author: james_s
author_rank: Super Contributor
timestamp: December 23, 2022, 11:57:47 pm
content: They don't do it on purpose, that's just silly. Yes of course they consider the risk of a thermostat failing, they're generally very reliable.My thermostat doesn't use batteries, it does require a common wire from the furnace though which is often not present. I was fortunate in that the layout of my house made it not too difficult to just run a whole new cable.

author: Bud
author_rank: Super Contributor
timestamp: December 24, 2022, 12:14:17 am
content: Quote from: NiHaoMike on December 23, 2022, 06:26:13 pmDays? And what would you do after that? Batteries are there not for backup purpose in case of power outage. There are thermostats like mine that are battery powered, not 24v powered. They switch the lines on and off using latching relays and last for years. As the other user said -it is a feature, not a flaw. Over the last 20 years i replaced batteries in my thermostat only may be 3 or 4 times.The other type of thermostat require 24v AC and particular wiring. Those are power hungry, with WiFi, LED display and the stupid Aleksa control and as such you cant run them from batteries or only from batteries.

author: MrMobodies
author_rank: Super Contributor
timestamp: December 24, 2022, 12:33:57 am
content: Isn't there a wired option for one that can be fixed to the wall that is unit or mains powered?That is one burden I wouldn't like for a thermostat unless that was an optional extra to the one cabled on the wall.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 24, 2022, 01:17:17 am
content: Quote from: Bud on December 24, 2022, 12:14:17 amWhen was the last time you have come across a home HVAC system that did not have a connection to constant mains power? Only examples I can think of are antique passive furnaces/boilers and off grid houses, but the latter could have an arrangement to provide constant power for the thermostat with a relay to switch on the inverter supplying the HVAC system.Given such a low power usage, a competent designer should be able to tap a little power from the wiring to keep a supercap charged. It could even work on a passive furnace/boiler that relies on a TEG to generate control power, given average power needed is on the order of milliwatts or less. (Albeit that's a rather uncommon edge case nowadays, maybe have a spot on the back for a plug in module to handle that?)

author: james_s
author_rank: Super Contributor
timestamp: December 24, 2022, 02:05:29 am
content: I do think it's stupid for a thermostat to need batteries. The common wire should have been standard decades ago, ever since electronic thermostats became popular. The power transformer is already present in the furnace, the only thing needed is another wire.I do love my smart thermostat, I can adjust it from my phone and it integrates into Home Assistant. I can adjust the heating/cooling from in bed or on the sofa, it has a big backlit display that I can read from across the room, I can check to make sure I shut off or turned down my heat when I go on vacation and I can turn it back on when I'm heading back home so the house is comfortable when I get there. Having had that convenience I'd never want to go back.

author: wraper
author_rank: Unknown
timestamp: December 24, 2022, 10:55:59 am
content: Quote from: james_s on December 24, 2022, 02:05:29 amIt's not stupid. Cable is the best when system is installed before interior finishing is made but after the fact it becomes very prohibitive. For example I installed 10 wireless room thermostats in my recently purchased home. Even though there were cables in the walls, some idiots installed all (floor temperature driven) thermostats 20cm away from the floor and near doors. So it was either ripping the walls to extend cables to normal location and height, or using wireless thermostats. I did not use Duraclell and Energizer alkalines which were included but instead purchased a bunch of IKEA LADDA LSD NiMH batteries. Alkalines would last at least a few years but I did not want to deal with broken thermostats if alkalines leak.

author: james_s
author_rank: Super Contributor
timestamp: December 25, 2022, 08:11:57 pm
content: But I'm talking about when the system was installed. Houses built 35 years ago when electronic thermostats were becoming common should have enough conductors to have a C wire, and yet even many recently built houses lack it. The difference in cost between 3 or 4 conductor and 6-8 conductor thermostat cable is negligible.

author: floobydust
author_rank: Super Contributor
timestamp: December 25, 2022, 11:24:10 pm
content: ItISstupid to have battery powered thermostats. Here with temperatures far below 0°C, no heat for many hours can cause plumbing/water pipes to freeze after the home cools down. People have rural properties, leave on a vacation etc. and they are not always attended.Berkshire Hathaway, instead of making a reasonably reliable Duracell product, have an armada of lawyers to defend their shit leaking batteries against the damages they cause. Duracell are the least reliable battery in the business.google Nest used to sorta work without 24VAC power, but no longer. Nest does not operate without a "C" wire, the lithium battery cannot power it for the duration the demand triac/relay is on, it seems to be only for the WiFi chirps.Because this screws consumers with 2-3 wire thermostat installations, they offer a "C wire adapter module" that uses all lines to parasite steal enough to make up a pseudo C wire.