# multiple baseboard relays, one thermostat



## mikewillnot (Apr 2, 2013)

We are trying to combine several baseboard circuits, each with older relay-type controllers, so they are controlled by a single thermostat. I.e., we are trying to connect the LV side of (5) controllers in parallel. It doesn't work, because each of the (5) units has its own 24v power supply -- 

here's a modern version, with 24v transformer


and connecting them in parallel gets weird and doesn't work. 

I see units out there that don't include the transformer -- 

here's a modern version WITHOUT the transformer


and I'm wondering: would installing 1 with the transformer, and 4 without, and connecting the thermostat in parallel across all 5, work? 



I would also be interested in any other advice/suggestions. THX


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## CoolWill (Jan 5, 2019)

Connect the C of all of them together, but only use the R of one. All the other R should be open. As long as all the transformers are in phase, it should work.


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## mikewillnot (Apr 2, 2013)

I found a wiring diagram for the relay WITHOUT the transformer, and it shows (2) stats connected in parallel with an external 24v transformer. I wonder if it would work properly with (5), connected in parallel. Can't see why not.


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## mikewillnot (Apr 2, 2013)

CoolWill said:


> Connect the C of all of them together, but only use the R of one. All the other R should be open. As long as all the transformers are in phase, it should work.



Never thought of that. Would the primaries of the controllers all have to be on the legs in the panel?


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## mikewillnot (Apr 2, 2013)




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## telsa (May 22, 2015)

Change your nic to MikeWILL.


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## CoolWill (Jan 5, 2019)

mikewillnot said:


> Never thought of that. Would the primaries of the controllers all have to be on the legs in the panel?


Maybe. You can check by connecting two Cs together and reading the voltage between the Rs. If it is zero or very close, you're good. If it is 48 V, the phasing is wrong.


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## circuitman1 (Mar 14, 2013)

is there any way of killing the other 4 transformers? then hook them together in parallel if the one transformer has the capacity for 5relays.


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## eddy current (Feb 28, 2009)

Because they are not meant to be used in parrallel I bet the transformers are not going to be wired so they end up in phase. You could polarize each one individually and then wire them so the secondaries are in phase with each other. The problem will be when one burns out (which happens often) and you need to replace it.

Probably be easier to just replace them all with relays that do not have a transformer and get an external 24 volt source like in post #5.


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## AK_sparky (Aug 13, 2013)

mikewillnot said:


> I'm wondering: would installing 1 with the transformer, and 4 without, and connecting the thermostat in parallel across all 5, work?





CoolWill said:


> Connect the C of all of them together, but only use the R of one. All the other R should be open. As long as all the transformers are in phase, it should work.





circuitman1 said:


> is there any way of killing the other 4 transformers? then hook them together in parallel if the one transformer has the capacity for 5relays.


Looking at the product pages we find 2 bits of information:
C-R can supply 1.2VA @ 24V.
W is a 40mA load.

We calulate:
1.2VA / 24V = 0.05A = 50mA


So, no, the transformer is not rated to supply enough power for more than one of these units.



eddy current said:


> Probably be easier to just replace them all with relays that do not have a transformer and get an external 24 volt source like in post #5.


This would be the way I would go. Also easier to maintain, troubleshoot, repair down the road.


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## MTW (Aug 28, 2013)

A few years back I had to do this very thing, only it was to control multiple baseboards on separate circuits from a single wifi 24V stat. No problem. I used a separate transformer and 2 non-transformer Aube relays pictured above.


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## emtnut (Mar 1, 2015)

As AKsparky said, the built in transformer won't be able to feed multiple units.

If I was doing it, I would go with installing new external Tx and use existing relays (with transformer) but just don't use the Transformer (ie, just wire the relay, C and W contacts).

No need to replace what's already there.


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