C wires, Nests, and Gremlins

Jamie Hall

A sort of plaintive comment here. And yes, I've tried to get helpful information from Nest. Good luck with that.

Does anyone have access to how a Nest is actually wired up? Inside? I've been following the "Help C Wire" thread pretty carefully, and folks have come up with answers -- the relay, particularly -- which really ought to have worked. There are other problems with that install.

But. What does actually happen to the helpfully designated terminals inside that contraption? Is C actually a common ground to everything? What powers the nitwits computer and battery? Rc? Rh? Either? Both? What happens on a call for heat? No relays, I suppose... is Rc isolated from Rh unless there is an external jumper? What about the other terminals?

And so on.

I regard the thing as a first class, if very clever, kludge. But they seem to sell a lot of them, and it would be helpful to us who feel impelled to help the victims to know what really happens inside...

pecmsg

R and back feed from Y or W not sure.

The problem developed with computer boards. Enough current to HOLD a triac closed in turn keeping the relay, contactor closed!

hot_rod

Jamie Hall said:

A sort of plaintive comment here. And yes, I've tried to get helpful information from Nest. Good luck with that.

Does anyone have access to how a Nest is actually wired up? Inside? I've been following the "Help C Wire" thread pretty carefully, and folks have come up with answers -- the relay, particularly -- which really ought to have worked. There are other problems with that install.

But. What does actually happen to the helpfully designated terminals inside that contraption? Is C actually a common ground to everything? What powers the nitwits computer and battery? Rc? Rh? Either? Both? What happens on a call for heat? No relays, I suppose... is Rc isolated from Rh unless there is an external jumper? What about the other terminals?

And so on.

I regard the thing as a first class, if very clever, kludge. But they seem to sell a lot of them, and it would be helpful to us who feel impelled to help the victims to know what really happens inside...

Jamie, we are analog men living in a digital world

STEVEusaPA

hot_rod said:

Jamie, we are analog men living in a digital world

Sounds like you need to make a new t-shirt...

hot_rod

STEVEusaPA said:

hot_rod said:

Jamie, we are analog men living in a digital world

Sounds like you need to make a new t-shirt...

https://www.youtube.com/watch?v=il1Byvn_vMA

Jamie Hall

Yeah... !

JUGHNE

Exactly where I'm at.....but all the helpful kids aren't home anymore.
Do you think there was any vacuum tube equipment on stage?
Anyone hear any "fuzzy distortion"?

I liked to watch tubes as you could see the audio fluctuate within the glass. Sight and sound show.

ratio

The most subtle gotcha with triacs/SCRs/etc. is that they aren't open/closed like a switch or contactor, they are really-high-resistance/really-low-resistance. The implications aren't intuitive to someone who isn't familiar with electronics, but thinking of a silicon device as on/off will bite you in the hiney, sooner or later.

A bigger, but less common, gotcha is that they are occasionally switching the low side (looking at you, Trane). I don't know enough to know if this is a requirement of the particular device or merely a design choice, but couple that with the first gotcha and confusion reigns!

Jamie Hall

I have picked up enough of the modern digital age to know that switching the low side at least for automotive work is actually the normal way to do it, but there since it is DC they are working with power transistors. This can really mess with your head since it can be remarkably difficult to figure out whether the fact that your ride doesn't run is due to a bad ground -- or a bad ECM or what have you.

Does make it harder to hot-wire the beast, though... there is that.

mattmia2

Most microcontrollers can sink far more current than they can source.

EdTheHeaterMan

I want to order the T shirt

hot_rod

ratio said:

The most subtle gotcha with triacs/SCRs/etc. is that they aren't open/closed like a switch or contactor, they are really-high-resistance/really-low-resistance. The implications aren't intuitive to someone who isn't familiar with electronics, but thinking of a silicon device as on/off will bite you in the hiney, sooner or later.

A bigger, but less common, gotcha is that they are occasionally switching the low side (looking at you, Trane). I don't know enough to know if this is a requirement of the particular device or merely a design choice, but couple that with the first gotcha and confusion reigns!

Also a true RMS meter is important to own for troubleshooting these days, reading those weird sawtooth and triangular wave forms.

EBEBRATT-Ed

I wanna go back to a T87 and a relay

Jamie Hall

EBEBRATT-Ed said:

I wanna go back to a T87 and a relay

Mine seem to be working just fine...

ChrisJ

We can start> @EBEBRATT-Ed said:
> I wanna go back to a T87 and a relay

I kind of get it, but at the same time this is similar to saying you want to go back to the Ford model T.

Yes, it was cheaper to build and far easier to troubleshoot but it doesn't even have heat.......

If you look at most of the Nest threads on here including this one you'll notice the computer it self isn't the issue. The lack of a common wire is and the Nest is the only one I know of that tries to cheat at this.

Honeywell got it right with the EIM. It uses only two wires and only powers the thermostat with them. Everything else is done back at the equipment by the EIM and the thermostat communicates with the EIM wirelessly. It works and it always works.

It also won't die if the system needs to run continuously.

ratio

ChrisJ said:

Honeywell got it right with the EIM. It uses only two wires and only powers the thermostat with them. Everything else is done back at the equipment by the EIM and the thermostat communicates with the EIM wirelessly. It works and it always works.

I'd say nearly right. It actually is a wireless connection from the stat to the EIM (you can power the stat from an independent power supply, there's even a 5000 [IIRC] series that will run on batteries), but it suffers from the usual wireless issues of interference, etc.; and I have experienced those kind of issues, albeit infrequently.

Carrier has their 'Edge Pro' thermostats that can be mounted in a two-piece configuration, with only two wires connecting the face of the stat to the base. They get that part right—the two wires are power and communication—but they are hard to program if you're not familiar with them, and it's quite difficult to find a manual on-line for them. It's to the point that I just email our vendor if I need a manual.

Jamie Hall

The thing about the Nest -- and some other wi-fi enabled thermostats -- is that they really do work well, if used in their intended application (forced air heat) in a reasonably modern house, which will have the C wire at least present, if not connected. And, perhaps, it is not really a fault of the unit, so much as the chances are very good it never even occurred to the designers, secure in their Silicon Valley bubble, that there could be anything else.

ChrisJ

ratio said:

ChrisJ said:

Honeywell got it right with the EIM. It uses only two wires and only powers the thermostat with them. Everything else is done back at the equipment by the EIM and the thermostat communicates with the EIM wirelessly. It works and it always works.

I'd say nearly right. It actually is a wireless connection from the stat to the EIM (you can power the stat from an independent power supply, there's even a 5000 [IIRC] series that will run on batteries), but it suffers from the usual wireless issues of interference, etc.; and I have experienced those kind of issues, albeit infrequently.

Carrier has their 'Edge Pro' thermostats that can be mounted in a two-piece configuration, with only two wires connecting the face of the stat to the base. They get that part right—the two wires are power and communication—but they are hard to program if you're not familiar with them, and it's quite difficult to find a manual on-line for them. It's to the point that I just email our vendor if I need a manual.

Ratio,
I'm confused how you can say they suffer from the usual wireless issues but then also say it's infrequent. I just don't want someone reading this thread and then assuming they will have headaches if they try to use a Redlink setup.

I'd have to say the chances of someone having issues with a Redlink setup seem to be much slimmer than issues with a power stealing Nest. No?

ratio

ChrisJ said:

Ratio,
I'm confused how you can say they suffer from the usual wireless issues but then also say it's infrequent. I just don't want someone reading this thread and then assuming they will have headaches if they try to use a Redlink setup.

I'd have to say the chances of someone having issues with a Redlink setup seem to be much slimmer than issues with a power stealing Nest. No?

Wireless is subject to more disturbances than wired, that's all. The RedLINK connection is quite robust, but not as reliable as a wired connection. In some cases, it won't be enough for successful operation. I would like to see the EIM able to communicate with the thermostat over the power wires, that would make them just about perfect.

That said, I've recommended Honeywell over Nest every time, & will continue to do so.

EdTheHeaterMan

ChrisJ said:

We can start> @EBEBRATT-Ed said:

> I wanna go back to a T87 and a relay



I kind of get it, but at the same time this is similar to saying you want to go back to the Ford model T.



Yes, it was cheaper to build and far easier to troubleshoot but it doesn't even have heat.......





Correct... No heat at the last Christmas Parade
it was very cold!

PS, I have 2 Nest Thermostats and 2 Nest cameras

ChrisJ

EdTheHeaterMan said:

ChrisJ said:

We can start> @EBEBRATT-Ed said:

> I wanna go back to a T87 and a relay



I kind of get it, but at the same time this is similar to saying you want to go back to the Ford model T.



Yes, it was cheaper to build and far easier to troubleshoot but it doesn't even have heat.......





Correct... No heat at the last Christmas Parade
it was very cold!

PS, I have 2 Nest Thermostats and 2 Nest cameras

You only forget to retard the timing before cranking once.......

EdTheHeaterMan

Don't I know it!











not really me

HVACNUT

And if I'm elected president, I will make it mandatory that every American will have to physically stand in front of the thermostat to operate it.
Convictions punishable up to 10 years loss of cell phone. And a do not serve order at every Starbucks. We're too spoiled.

I get a lot of service call with these things so I guess it's good for me, but...

ChrisJ

> @HVACNUT said:
> And if I'm elected president, I will make it mandatory that every American will have to physically stand in front of the thermostat to operate it.
> Convictions punishable up to 10 years loss of cell phone. And a do not serve order at every Starbucks. We're too spoiled.
>
> I get a lot of service call with these things so I guess it's good for me, but...

You lost my vote.

ratio

But you gained two or three of mine.

Jamie Hall

and mine

Erin Holohan Haskell

STEVEusaPA said:

hot_rod said:

Jamie, we are analog men living in a digital world

Sounds like you need to make a new t-shirt...

We made this for all the analog guys feeling nostalgic:



Available here: https://teespring.com/analog-guy-in-a-digital-world

STEVEusaPA

What is that one set at? LOL

ratio

Maybe it comes with a sharpie to set it yourself.

EdTheHeaterMan

It depends on whether you are standing on level ground.

I just ordered mine. I hope I don't get mercury poisoning