Why not use the Common wire?


#1

In the united states, there is a 5th wire called “common” that carries a constant 24vac, which you could convert to 5vdc 600mA very cheaply. Here’s a prebuilt converter for $2.80 (plus shipping). Obviously you can do better on the price if you buy parts in bulk and include it on the circuit board. Some more designs here.

If I ever did buy a hestia pi, I would definitely suck out the 100-240v converter and hack in that smaller converter myself. I don’t know how you do things in europe, (if you have mains voltage behind all your thermostats), but it makes no sense to include a mains voltage converter behind a US thermostat. I’d either have to hire an electrician to come out and agree to leave bare wires behind (not sure that would be legally up to code), or run unsightly wires up the wall from the socket.

Another alternative is to use the dead space in the current case design to house AA batteries, for older homes that don’t have a 5th wire.

Either way, the Common wire needs to be an option, and I don’t think the mains voltage EVER makes sense to include.


#2

Unfortunately building something for yourself one-off is so much easier, faster, cheaper and can agree with only yourself the shortcuts you are happy to make.
In the HestiaPi, the case is the opposite. With only a few tweaks we managed to offer it to the US too but the need to use the common wire is obvious. We don’t know how the people who bought it in the US (surprisingly most of our orders) use it but they manage. It would be great if they would comment here.
To answer your question… we are evaluating a few solutions already but we seek:

  • Complete modules that are certified
  • Compact in size
  • Thermally efficient - that is, not producing too much heat inside the case
  • Avoid building it ourselves on the board
  • Cheaper than 20USD :slight_smile:
  • Include all the above

Our “RnD” phase has a long round-trip time between alterations as this is not a full-time job I am afraid :slight_smile:

Your AA solution is not viable for RaspberryPi Zero unless you want to have something to do every other day :wink:


#3

I’m in the US and bought one, but I don’t use it because of the power issue. If it made use of the common wire and the 24v power supply (like pretty much all other smart thermostats on the market here) I would totally use it.

All that said, I appreciate how difficult it would be to make a change like that, and I’m sure you have other priorities. I’m rooting for you! Just wanted to speak up in case it seemed like the US orderers were all using it. Who knows - maybe all the others are :slight_smile:


#4

thank you for the feedback and sorry for the missunderstanding. We’ll try and find an alternative but from what we’ve seen so far we will sucrifice on the price and/or the size compactness. Neither are good :slight_smile:


#5

Honestly for the short term, it would be good to make it a bit more clear on your website that it doesn’t utilize 24vac. Nothing about the common wire is mentioned except that it “supports 4 wire homes”. I almost bought one but when I saw in the pictures the circuit board had no possible way to convert 24vac, that was the only indication that it definitely didn’t support the common wire.

I would really have liked to use a hestiapi, but this power issue makes it infeasible for me.

That, and the fact that the honeywell zone controller my AC company installed (model HZ311) requires some proprietary (I think) signalling to communicate with the damper controls. I heard there might be some open source library somewhere for communicating with it while researching alternatives to a honeywell thermostat, but apparently even the Nest and Ecobee don’t support communication with honeywell damper controls. I’d have to replace a lot of components beyond just the thermostat to be able to use a non-honeywell based thermostat… until such point in the indeterminable future if/when someone with the motivation and know-how decides to tackle the problem.


#6

re: sacrificing on the price/compactness:
I think the only thing you have to sacrifice is the 100-240vac converter. If people really want to plug in their thermostat to a mains outlet, they can still buy a a 120vac -> 24vac transformer, but I promise, this should not be considered a typical use case in America.


#7

There was no intention to fool anyone and I thought it was clear enough like this

Please note that separate mains voltage is still needed

I changed it and made it bold :slight_smile:

Supports most HVAC systems with 4 wires R, W, Y, G (Red, White, Yellow, Green) – Please note that separate mains voltage is still needed and common wire C is not supported

There goes your plans on modifying your system :frowning: Not the first time we hear this.

The issue is that we cannot find a viable solution yet unless we design our own PSU. Of course the 100-240vac converter will be replaced but with what? Raspberry needs 5V DC not 24V AC.


#8

Great news! 2 different solutions were found to allow the use of Common Wire so no need for mains anymore!
Have been tested for the last 20 days with great thermal and electrical performance.
The only drawback is the size because it would stick out of the PCB with today’s design.
Will offer it to the website to a few pilot users for a discount. Send me a PM if anyone wants to go in that list.

I think we did it or at least getting there :wink:
Thank you for all the feedback


#9

Is there any news on these solutions? It’s been nearly a year and I’m getting antsy. I am very interested in cloudless smart home solutions but I would rather not run mains voltage to my thermostat.


#10

C-wire is coming within the next 1-2 weeks here first:


We’ve been very busy :wink:


#11

That’s awesome! I’ll check it out. (sorry… I know this doesn’t add to the discussion much but it’s exciting)


#12

I bought this hoping to hack in c-wire support. I just purchased this product this week so it will be a pleasant surprise if such support is included (site is still reading it is not supported at the time of this post). Otherwise I hope an upgrade kit will be offered on the site for existing US customers.

I can’t imagine other US customers are using the device as their main thermostat yet unless they’ve done the same hack.


#13

c-wire supported systems run off 24V AC. The PSU right now only works with mains. You will have to “swap” the soldered PSU with a 24V AC to 5V DC 3A and connect C-wire to the L terminal.


#14

Wait… So did the Crowd Supply campaign fall through? I’ve been checking… Waiting.


#15

Absolutely not :slight_smile:
The campaign’s last word comes from the company running the platform and they are not as fast as I would want them to be hence all the delays in the (58!) subtasks trying to get all the material I provide together.
Sorry about that…


#16

That’s good. (well, the part where it’s still happening, not necessarily the other stuff)


#17

Pleased to see this is coming. That was the only thing holding me up from ordering it.

I registered for notification for the Crowd Supply.


#18

It’s official!
Launch date: 7th of May
Very limited early bird orders (I think 20)!


#19

Any timeframe as to when on the 7th? 20 units are sure to go fast…

Is the design of the early bird version expected to differ from the final product? Would it be more advisable wait for the final product?


#20

Not sure. Need to check with the company running the platform.
Early bird and final product will be identical, only cheaper and shipped faster :wink:

If by “final product” you mean after the campaign, any changes will affect only the software delivered with which will also be downloadable once it is ready, so you won’t be missing out anything unless you don’t want to update your copy ever.