# Speaking of 24VAC... Nest/Ecobee etc.



## CaptainK (Jan 5, 2015)

So I ran new thermostat wire for my soon to arrive Ecobee, needed a 24V C wire... So now I have it, all plugged in and powering my old thermostat... or so I thought... I decided to test it today to see how well it works and when I pulled out the batteries the thermostat would not work when I plugged it back to the base plate... 

Here is what I know.. 

I have a Taco SR503 See image attached.. you will see there is one area for 24v connections (upper left corner) and there are 2 connections available.  When I check voltage across the TOP 24v to the Rh (as recommended in the the Ecobee install manual) on the controller I get nothing.. when I check voltage across the Bottom 24v to the Rh on the controller I get 30v.

Now neither of these values are 24v albeit the 30v is closer... so 6v difference I would think would be ok with the Ecobee, the house power fluctuates more than that and everything else runs fine. But any ideas why the top connection is a no go? I have checked the documentation for the Taco SR503 and found little help... 

I have switched the wire from the top to the bottom and it powers the existing thermostat perfectly. So all should be good? Maybe?


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## velvetfoot (Jan 5, 2015)

I would say so, but what do I know?  You have around 24v, that should do it.


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## Clarkbug (Jan 5, 2015)

Top connections can handle 24v, but I do not think they supply it.  

Taco has a FAQ that says the common 24v can be picked up " from the terminal block near the transformer".  

Hopefully that helps!


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## ewdudley (Jan 5, 2015)

Can't really follow what you're asking.  

Ecobee needs existing R and W connections from the SR 503.  In addition it needs a C/COMMON wire from the SR 503 COM terminal.  

If only two wires run to the thermostat it looks like you can use their PEK, "power extender kit", instead of a C/COMMON wire.


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## bryankloos (Jan 5, 2015)

Call taco. They will walk you through where to pull the 24vac common from your 503. It's really easy!


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## velvetfoot (Jan 5, 2015)

ewdudley said:


> If only two wires run to the thermostat it looks like you can use their PEK, "power extender kit", instead of a C/COMMON wire.


I believe he already ran some more-conductor wire.


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## sigepsb (Jan 5, 2015)

Maybe Ecobee can tell you, but I know Nest has a range. Like everything else with the Nest they are wishy-washy about it though. One place Nest says it will accept anything from 21V-30V, but in another place Nest states it needs to be 24V +/- 15%. Maybe Ecobee has an acceptable range they can give you.

If not, I think you could just install a 24V transformer at the other end of your common wire. I did this for my zone controller.

I just checked my Nests after you posted this. They used to read around 25V, but right now they are both reading 32V! They are hooked to my Carrier furnace. Not sure what could have changed there, but they seem to be working fine still. Not sure why the voltage is so high right now.


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## STIHLY DAN (Jan 5, 2015)

That 24v connection is to supply voltage to, in case your zones are damper motors. need to get 24v from the unit.


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## sigepsb (Jan 5, 2015)

STIHLY DAN said:


> That 24v connection is to supply voltage to, in case your zones are damper motors. need to get 24v from the unit.



Sorry, I must have misunderstood the question. I thought he just needed a constant 24V source to power the thermostat, didn't know it had to be from the unit. 

I answered my own question about the Nest in the meantime: You have to take the Nest voltage reading and divide by 1.414 to get the actual reading. So, they are now reading 35V, which is actually 24.7V. Should just use a multimeter next time.


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## Bob Rohr (Jan 5, 2015)

sigepsb said:


> Sorry, I must have misunderstood the question. I thought he just needed a constant 24V source to power the thermostat, didn't know it had to be from the unit.
> 
> I answered my own question about the Nest in the meantime: You have to take the Nest voltage reading and divide by 1.414 to get the actual reading. So, they are now reading 35V, which is actually 24.7V. Should just use a multimeter next time.




Also there has been some changes from version1 to V2 with the Nest.  V1 we could get to operate our relays with two wires.  V2 must have 3 wires to operate, at least with the Caleffi relays.  We finally found a knowledgable tech at Nest with HVAC smarts that understands all the challenges making that stat work with so many different appliances and relays, not to mention the skill level of the installer.

We've assembled about 15 different t-stats to try on our relay boards, and found some crazy behavior.  Some "leak" as much as 18V back to the board when in the "no call" position.  Some behave with a 1000 ohm, 2W resistor add as a drain down for the stray voltage, others work with a 750 ohm, which Uponor now send with their stats.

The electronic T-87 seem to have a mind of their own, yet to find a simple fix for that one.

Longing for the days of the simple bi-metal snap switch stats.

I don't think an Add a Wire  http://www.venstar.com/Thermostats/ACC0410/  can turn two wires into 3,as it can 3 to 4 or 4 to 5.  It cannot "create" that missing common, from what I can tell.


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## velvetfoot (Jan 5, 2015)

It's a drag getting the wire up to the second floor.


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## CaptainK (Jan 6, 2015)

See attached, Circled in Red is the 24v Common connections, circled in Blue is where I had the wire originally connected and it did not work, circled in Green is where it is now, working but with 30V. Hope this helps clear things up a bit. Im starting to think there maybe an issue with the Taco...


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## Bob Rohr (Jan 6, 2015)

Best to check with Taco, maybe they have a work around.

We found the Caleffi pump relays don't get along with the Nest floating ground, which causes W to drift and give an artificial call for heat.  it's possible a pull down resistor make "fix' this, but you would want to get that Okay from Taco.


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## CaptainK (Jan 6, 2015)

velvetfoot said:


> It's a drag getting the wire up to the second floor.


No pun intended....


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## velvetfoot (Jan 6, 2015)

No.


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## velvetfoot (Jan 6, 2015)

I don't think I'd overthink this too much.


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## CaptainK (Jan 6, 2015)

After a quick call to Taco I found I have it wired right  and apparently the 30v at the 24v common is no big deal (per Taco) so bring on the new toys.. err.. tools...


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## velvetfoot (Jan 6, 2015)

Things I can think of:  I recall no problems with the Ecobee connecting with WIFI; it might be airports where it gets its weather data, not sure;  the staff is fairly responsive if you need help;  the only feature of Home IQ I've used is "Reports" which is really only once chart which has some handy data as well as the download of data in Excel format.


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## CaptainK (Jan 16, 2015)

Ecobee3 is installed and doing its thing... so far so good!  Ill have to peek in at the data some time after it gets some logging done. Should be interesting to say the least.


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## velvetfoot (Jan 31, 2015)

So, here are upstairs and downstairs.  Downstairs has the wood insert.  The higher than normal spike today is because I had the fan on high.


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## velvetfoot (Oct 9, 2015)

Hey, CaptainK!
I am trying to set up my Ecobee thermostat to stage the pellet and oil boiler with the oil boiler as auxiliary.  
I forget if you have a backup.  If so, have you messed around with this?  I think it'll be possible.  I started another thread:
https://www.hearth.com/talk/threads...ler-with-an-ecobee-smartsi-thermostat.147270/


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