Nest thermostats & Taco SR-504 Switching Relay

Chris_102

Hey everyone,
I have gas boiler with 2 hydronic baseboard zones, controlled by nest Tstats. Going to add a 3rd zone with another Nest tstat. Currently the zones are being controlled by Taco zone valves, with one circulator...going to change that and install a Taco SR-504 switching relay with 3 new circulators....I just realized that the new Taco EXP models have a Common terminal on the 24v side...can I connect my 3 Nest tstats to on each of those common terminals...and will that be enough power to run the Tstats? Are all 4 common terminals putting out 24v (or close to it) under a load? I can't find that answer anywhere.

hot_rod

There seems to be another glitch turning up with the Nest. After some time the battery voltage drops and needs to be recharged. When it goes into that recharge mode it pulls a large amount of current. I'm hearing rumors that a max of two Nests per 40 VA transformer.

Any experience or data on that concern?

AlCorelliNY

2 Nests per 40 VA.
Been there, Done that.

Have six Nests at home.

Bob Bona_4

Good to know. Been dealing with a lot of Nests, interfacing with HVAC. Can't summon the dislike, as a Honeywell go to guy. My concern is the Google base and invasion of privacy thing.

Chris_102

Hey alcorelliny,
What is your setup where your using 6 nest thermostats? I understand about the bigger 24v transformer....but what I'm not understanding or can't get answers on is how to get power to those thermostats using a 3 wire system....thanks

AlCorelliNY

I have one running on an old SR-506 with resistors on the zones that only had 18-2 running to them. The other zones are powered through the Air Conditioning side of the Nest.
Absolutely no issues with drop outs. The thermostats are 99 percent available on the app.

[IMG]http://i36.photobucket.com/albums/e2/alcorelli/Mobile Uploads/20150421_211659_zpsigdcjvoe.jpg[/IMG]


On customers systems, I try to pull at least 5 wire, usually seven wire. Then I can power it any way I want. Even if the Nest is only doing heat, it can be powered through the AC side. Yes, the therm recognizes a combi system, but it is, and has been a great workaround.

I have a few Lyrics on steam out there powered likewise with an 18VA transformer mounted on a 1900 box on the boiler.

DieterReuther

Hi Alcorelliny,

Your post here really caught my attention. I have a 3 zone setup with TACO zone valves. 2 are controlled by NEST thermostats, 1 by a traditional thermostat. I have only 2 wires running to the NESTs and am getting a buzzing in the NESTs when they steal power to charge their battery. Replacing the wires is too complicated. Instead I am planning to feed power from a transformer close to each NEST into C and Rc. Any experience whether this will work?

Did your NESTs overload the heating system transformer? My HVAC tech is concerned this might happen in my setup.

"I have one running on an old SR-506 with resistors on the zones that only had 18-2 running to them." What are the resistors for? Would that help with my buzzing?

Thanks,
Dieter

hot_rod

"I have one running on an old SR-506 with resistors on the zones that only had 18-2 running to them." What are the resistors for? Would that help with my buzzing?


With only two wires the power stealing nature of that stat shows up as voltage, sometimes as high as 18V coming back to the relay when the stat is in the off position. The resistors "shed" or pull down that stray voltage. Basically they turn that energy into heat, so don't touch the resistor when it is powered
The 3rd wire gives a path to common and eliminates the stray.

It's not uncommon to see that in many of the power stealing stats, the old Erie, Wirsbo and many others include the resistor in the box.

There is a way to build a relay board where the pull down resistor is not needed even with two wire power stealing stats.

I agree with Al, ALWAYS pull additional conductors, it's cheap and easy on the front end and gives you many options.

FredoSP

hot rod: Would it be a correct assumption to say that if someone has a two wire Nest (red and white) and using a TACO, in my case a SR-501 1 zone switching relay, that it's best to add the resistor to the W, as stated above.

Versus

If using a three wire setup (red, white and Common) with the Nest and a TACO, a resistor is not needed with because the Common from the TACO going to the "C" on the Nest and will never have to "power steal" because it has the constant 24V going to it?

I'm asking because I believe I also am hearing a "buzz" and I have had the TACO SR-501 in the box and am debating which is best for me, i.e. Leave things the way they are, 2 wire going to a Honeywell RA89A 1074 OR setup the TACO and do a 2 wire with the resistor OR add a third Common wire.

hot_rod

with a volt meter in series you should be able to determine if stray voltage is coming back and causing a relay to buzz from a low voltage condition?

I know the Nest works with Caleffi relay boxes, check with Taco for compatibility.
It could be older versions of the relay do not work and they figured out the work around on newer models?

FredoSP

Thanks hot rod.

Here are some images from the documentation that came with my TACO SR-501. It doesn't give any mention to a three wire setup, just the two wire with the resistor. They actually supplied a small bag of 5 resistors.

hot_rod

Taco should have a wiring schematic for connecting a Nest to their box, did you check their wiring guide? Maybe online?

Jamie Hall

Is it just me? Seems to me that the party responsible for coming up with fixes is the geniuses who make the Nest, not the poor folks -- such as Taco -- who have to figure out how to make the durned things work...

hot_rod

Jamie Hall said:

Is it just me? Seems to me that the party responsible for coming up with fixes is the geniuses who make the Nest, not the poor folks -- such as Taco -- who have to figure out how to make the durned things work...

Nest did make some good changes to eliminate most of the wiring glitches. It just took a few years for them to realize what goes on in the field. Depends on which version you have.
Any power stealing t-stat really needs 3 wires to behave properly, it's not just a Nest issue.

"Add a wire" kits ship with some of the newer power stealers as the manufacturers realized most older homes only have two wires.

FredoSP

UPDATE: 3/13/2018

Thanks for all the above suggestions. I finally got the courage and dive right into this. Keep in mind that I'm a software developer by day, so plumbing, electrical and things like this make sense BUT I like to take my time and learn.

I removed the Honeywell RA89A (even though it's working fine) and installed the Taco SR501-4 Single Zone switching relay. I ran new 18/3 wire from the Nest to the Taco. I used the Taco supplied cross reference chart to wire it up. All is good, the Nest has a constant 3.93 volts.

I'm 99.99% sure I did everything correct because the heat comes on, the Nest works, the Taco red light goes on when a call for heat is made.

P.S. I'm still saving the RA89A just in case the Taco takes a dive!

Comments / Questions ?

OLD Honeywell RA89A







New Taco SR501

SuperTech

I would be more concerned with the Nest having a glitch than the Taco. They are pretty solid relays.

ratio

Looks about right, congrats!

FredoSP

You mean the Nest in general or the Nest with my specific setup?

FredoSP

SuperTech said:

I would be more concerned with the Nest having a glitch than the Taco. They are pretty solid relays.

You mean the Nest in general or the Nest with my specific setup?

SuperTech

Just the nest in general. I see more calls related to nest issues than any other tstat. But yours is wired 100 percent correctly, nothing wrong with anything there.