No power to thermostat with a C wire or nest connect

[Aromano]

I am unable to get enough power to my nest thermostat.  I have forced hot air and cooling with multiple zones.  I original had a 3 wire (R,W and Y).  I ran another 2 wire with it to my furnace zone control board.  I tried using one wire as the C Wire and found a terminal on the zone board (from the transformer feeding the board 24v) that that was common to the R wire completing the circuit. The nest tells me not enough power.  I tried adding the nest connect adapter with also no luck.  The zone control board has a common terminal where the main furnace control board wires are feed into the zoning system, but this common is somehow isolated from my thermostat terminals.  .  Any other suggestions?

[laurentbourg]

What’s the amperage of that 24V transformer? I assume you did not wire your C at the same location where your R was sourced, just making sure since you are saying “that that was common to the R wire completing the circuit”?

[Aromano]

Thank you for your reply.  The transformer feeding the board is 24v/40VA.  I used this for the common wire.  With a volt meter I get 24v between this and the R going up to my thermostat.  Was also think maybe trying  a plug in 24v/500ma transformer by the furnace and connect it to the common wire and R wire going up to the thermostat to this. Thoughts?

[laurentbourg · Accepted solution]

That’s about 1.A amps, should work fine in theory but I have seen cases in the past where it did not.  Yes you can add a 24V AC 300-500ma and join with existing R and use the common of that transformer as the C (do not join it with the existing C you have coming out of your transformer). 

[MoMoe]

Can I buy one C-Wire power supply and power two separate thermostats by daisy chaining together??  
Each thermostat control separate zones and are 8 feet from each other in height.  Not being cheap, just lessening wiring in wall.