Options for mutiple 12VAC relays

[jllabs]

I have multiple thermostats that share a common 12VAC power source. Each of these thermostats have a dHum output that is energized when off and de-energized when on. I would like to use the three outputs to turn one dehumidifier off/on as needed. One solution I thought of is just to use three normally closed relays with 12VAC coils and wire the output contacts in parallel so that if one or combination of the relays are de-energized the dehumidifier would turn on. However, I don't like the idea of having three relay's energized 70-80% of the time as the the dehumidifer is not required that often.

The Dehumidifer is 120VAC, apx 7 amps. Relays would be sized accordingly.

Can anyone suggest any other alternatives?

 

[ronsimpson]

In one house:
Any thermostat can turn on the furnace/ air conditioner.
Any time the (furnace/ air conditioner) is on the fan runs.
I tapped in to the wires that power the fan to also run the dehumidifier. There actually way a place to connect to. This is common.

 

[jllabs]

Thanks for the reply ronsimpson. I guess I should add that the particular thermostat I am using also has a humidistat that outputs to two terminals dHum and Hum for dehumidification and humidification accordingly. I am able to use the Hum terminal with a single normally open replay as the terminals are only energized when there is a need for humidification. Since the three thermostats share the same power source there isn't an issue if more than one is energized at the same time. The relay remains energized until all are off. The fan terminal is also energized when either the dHum or Hum thermal is energized. However, I do not want the dehumidifier to run every time the fan runs only when there is a need.

The problem I am having with dehumidification is the terminal is energized when there is NOT a need for dehumidification and de-energized when it needs to be turned on. Therefore I cannot use a single relay as it would only turn on when all three thermostats were calling for dehumidification.

I should also add the reason there are three thermostats is I have three zones that utilize one HVAC system.

 

[ChrisP58]

The problem I am having with dehumidification is the terminal is energized when there is NOT a need for dehumidification and de-energized when it needs to be turned on. Therefore I cannot use a single relay as it would only turn on when all three thermostats were calling for dehumidification.

Would it work to wire the relay contacts in series? That way the loop is open if any of the relays are open.

 

[jllabs]

Yes it would work in series. But this still would require the relays be energized the majority of the time. I personally do not like that. I have looked for some tipe of high/low logic circut that would work with 12VAC but have not been able to find anything. Still open to ideas and sugestions...

 

[ronv]

Kind of messy, but this might work.
It's and opto triac that turns on when any one of the thermostats is turned off.