Would like to preface this that I don't know a lot about electrical stuff but I try my best.

I am trying to control a HVAC duct damper with a raspberry pi. I have the power-open-power-close duct damper, a 2-channel relay to be controlled with 5vdc and I think can handle 24vac (I may be wrong) input. I also have a 120v to 24vac wall plug transformer.

Relay: https://www.amazon.com/gp/product/B01MUATVXX/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

I also tried this relay previously: https://www.amazon.com/gp/product/B0177WOT1E/ref=oh_aui_detailpage_o04_s01?ie=UTF8&psc=1

Powered Duct Damper: https://www.amazon.com/gp/product/B01DOB7OIC/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

24vac Transformer: https://www.amazon.com/gp/product/B0007N5LJK/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

I have been able to get the power open and power close on the vent to work no problems by just wiring it without the relay so I know the transformer and duct are working. I am also able to control the relay with the raspberry pi which is indicated by the LED lights on the relay.

INPUTS on the relay

  • IN1 - raspberry pi pin
  • IN2 - raspberry pi pin
  • VCC - 24VAC from transformer


  • Nothing is connected to the COM's
  • I have tried connecting to the NO and controlling it with the raspberry pi and just connecting either PO or PC on the vent to on of the NC outputs on the relay and neither work.

Connecting the 24VAC from transformer to either the PO or PC on the vent turns on the vent motor no problems.

The relays I have are exactly like the ones pictured in the amazon listings.

  • \$\begingroup\$ Vcc should be +5VDC. If you connected 24VAC to it you will probably be seeing smoke and be ordering another Pi (unless only one side is connected, in which case step back and make a schematic). \$\endgroup\$ – Spehro Pefhany Jan 15 '18 at 0:58
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    \$\begingroup\$ Post the schematic, please. Few [if anybody] will bother to reconstruct your wiring from a verbal description. \$\endgroup\$ – Nick Alexeev Jan 15 '18 at 1:53

One side of your AC source MUST be connected to the "COM" terminals of the relays. The "NO" terminals of the relays should be connected to the "OPEN" and "CLOSE" terminals of the damper (one relay to "OPEN", the other to "CLOSE"). The "COM" terminal of the damper connects to the remaining side of the AC source.

Edit: The relay and damper connections should be something like:


simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Holy shit.. no way. I hope I didn't fry the second relay with my fundamental misunderstanding. \$\endgroup\$ – devaju Jan 15 '18 at 1:29
  • \$\begingroup\$ Wait so if I only have one AC coming from the source do I have to find a way to split it to the two COMs \$\endgroup\$ – devaju Jan 15 '18 at 1:32
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    \$\begingroup\$ You can connect the AC supply to one relay COM, then add a jumper between the two relay COM terminals. \$\endgroup\$ – Peter Bennett Jan 15 '18 at 2:23
  • \$\begingroup\$ Got it working. Thank you Peter. That schematic is also accurate to my scenario. \$\endgroup\$ – devaju Jan 15 '18 at 20:11

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