Wiring Relay for Range hood Make-up Damper??

Discussion in 'The Projects Forum' started by Mat Pond, Sep 3, 2015.

  1. Mat Pond

    Thread Starter New Member

    Sep 1, 2015
    Hey everyone,

    I have a Faber Scirocco Plus range hood installed in a house and we need to install a make-up air damper. The make up air damper is meant to open when the range hood blower is running in order to bring more air into the house to keep up with the exhausted air of the blower. Now, the Faber brand damper (and many others) activates/opens when their air pressure switch, which is installed above the range hood blower, is tripped. The issue is we do NOT have the option to splice the air switch into the hood ducting.... because reasons. Not happening. Other brands of dampers are able to be wired directly to a compatible range hood or accept a switched voltage. Our range hood does not facilitate those things.

    So the two ideas we had were:

    1. Relay - for example, the Tekmar Relay 004 - would it be possible to wire a relay on the line between the breaker panel and the range hood that would switch another circuit for the damper? Most dampers come with a 24VAC transformer.

    2. Amp Sensor - don't have any devices in mind at the moment, but an amp sensor would work very much like the standard air switch I described, but would be possible to install in this scenario.

    Am this crazy? How would you do this safely? Any other ideas? General thoughts? Experience with Faber range hoods? Aluminum or aluminium?

    p.s. bold word are links in case the formatting is confusing.
  2. #12


    Nov 30, 2010
    There was a damper on the furnace in my home in 1955 and it worked with a weight on a screw. Whenever negative pressure, open exactly the right amount. I don't know if the modern inspectors are going to allow that.

    Run a wire from the power switch on the range hood to the motorized damper? If true, and you need 24 VAC, attach the 120V to 24V transformer at the damper and run the 120 VAC power over to it with standard house wiring methods.
  3. markdem


    Jul 31, 2013
    I would be going down the relay method as this is the normal way (at least in Australia) to slave things like this. Look up a "contactor" (another word for a relay) as you will get more options for 120v on both sides.

    Or, as #12 said, just power the damper form the range hood. Just check the hood's switch and fuse (if any) to make sure it can handle the current.

    Have fun
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    It might help knowing what part of the world your in (mains power) and the climate. It will also help for suggested products.
    Knowing which side of the BIG POND your on goes a long way.

    Had a similar issue in another forum. Aux blower for an over the range microwave with no sign of tampering until the warranty expired. Said buy a replacement blower assy and make the mods there. A connectr was identified but was impossible to obtain.

    Now, you could control building pressure directly:
    http://www.bapihvac.com/content/uploads/2011/01/14358_ins_zps_out.pdf It's the most expensive option and the most energy efficient option. The link just "sort of" starts the process.

    "Dampers" sometimes aren't necessarily the easiest things. Some can have position feedback. Some are designed for a "known" fixed end to end travel time. 24 VAC is common. Some may be normally closed or normally open. Some may be spring to close, power to open and stuff in between.

    They can control static pressure on their own. The weight thing.

    "current switch" sensors do exist. Usually there is a min/max current and a detection current. Some are adjustable and more wraps of the wire mean higher sensitivity. Some have a 2-part coil so it can be inserted without removing a wire. Adding turns or even one turn means adding some wire because of the sensor itself or the place to mount. Some sensors require power, others do not.

    Obviously, the easiest place to tap is at the fan. What kind of voltage do you have to sense? 120 V?, 240 V?

    What happens if the damper doesn't work?

    So, let's say the simplest method is to detect the voltage to the fan with a relay with the same coil voltage as the fan.
    Wire a class II or energy limiting transformer Mains:24 VAC someplace and preferably on the fan circuit or one that you will notice. The 24 VAC class II wiring would not have to be in conduit (if in the US).

    ME: I like to discuss options first, then decide. Anything is up for discussion in the brainstorming phase.

    1) voltages/climate?
    2) How easy is it to tap the wires going to the blower?
    3) How easy is it to mount a sensor; say 2"x3"x2" (example) and wrap the fan wire around say a 1 cm circumference.
    4) How might we mount the power thingy.

    There's a lot of ways, but they depend a lot on the constraints. Suppose one off the constraints is a 24 VAC damper operated by a class II energy limiting transformer. See: http://www.grainger.com/category/cl...ect=40+VA+transformer&searchSortKey=bestMatch

    Voltage presence does not have to be a relay if a DC source is used or even a 24 VAC to DC source is used.
    #12 likes this.
  5. Mat Pond

    Thread Starter New Member

    Sep 1, 2015
    Thank you all for your responses. I like the simplicity of what #12 and markdem are suggesting. It just rests on what kind of access I have inside the wiring box of the range hood (and warranty I guess depending on how adventurous we get). The installation guides and the support tech I talked to were not helpful enough to know for sure if this is all possible. To me it looks like it may be possible to use the spare terminals that should be used to power a remote blower for the damper instead. I honestly just wasn't sure if people used relays for these sort of weird home solutions.

    Now somewhat ironically, KeepitSimpleStupid's response was a little more complicated to understand. But hopefully I can clarify things for you a bit because i really appreciate your input.
    1) We're in Canada. House service is 120/240VAC and this damper simply opens when powered. Comes with transformer that will take our 120V "signal" from the hood and provide 24VAC for damper motor. Climate is not really relevant, this will integrate with forced air system for temp control.
    2)Not sure, tough to say without be able to see the whole setup in person. What I know is based off of installation guides.
    3)Probably pretty easy.
    4)Power thingy? The transformer? Easy, it would be mounted near the damper in the mechanical room which is also close to the breaker panel
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    I try to look at ALL options and then whittle them down. So, yea controlling pressure in the building is the most enpensive solution, but it does come with energy efficiency. Payback is yet another issue.

    The real question, then boils down to how much power can you draw from the "120 V signal". If it's designed to drive a relay, then that's what it has to go to. if the damper is a few watts, then it can likely drive it directly.

    The simplest case is then:
    a) get the "120 V signal" to the mechanical room and feed the primary of a transformer. If the xformer is 40 VA, and the load is 3 VA, then it draws 3 VA.

    b) Treat the 120 V signal as something that drives a relay with a 120 VAC coil. Power the xformer from the same circuit. The US NEC code says, I think, that you can't have two wires on a breaker lug, but you can pigtail. You have to follow Canada's codes. You can switch the primary on a 24 VAC xformer and the secondary goes to the damper.

    Even without the relevant codes, some 'common sense' is in order. a) It can't be easy for the 24 VAC and 120 VAC to cross paths. Finger safe and physical separation can pretty much assure that.

    So, Plan A is the simplest.

    That "complex plan" won't let in much arctic air and it will only allow what it needs, so the buillding only sees a slight positive pressure. You probably don't have gas in Canada because Hydro-electric is preferred.
  7. #12


    Nov 30, 2010
    Avoid if practical.

    A relay is just one more part that might eventually go bad, but if this is a two speed fan and you don't have a terminal that is hot for all "on" speeds, a relay becomes the right tool. For instance, a, "fan control center" for certain furnace/thermostat applications is merely a relay, or a relay and a transformer, in an electrically legal box. That is the case where the relay is the right tool, and it happens often enough that the complete assembly is available for you to purchase.

    If this is a one speed job, you can avoid the relay.
    Now you know.;)
  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    Agree with #12. If you don't need one, don't use one.

    I do, however, want you to look here http://www.serelays.com/library/Launch-725/725 Spec Sheet.pdf at the panel//DIN mount version of a relay. Overkill for sure, but it has some interesting features and that's the point of this post.

    DIN rail - It's an electrical erector set. it's a mechanical tract used to mount lots of electrical things, particularly terminals.
    it's usually found in enclosures with an 1/8" thick aluminum plate in the bottom mounted on standoffs.

    Panel mount - Basically means it can be screwed to a plate.

    The fingersafe contacts.
    Which basically makes it harder for 24 VAC and 120 VAC to see each other.

    An energy limiting transformer
    It's a particular type of transformer found typically in HVAC stuff that does not need a low current fuse. Shorting the secondary, just drops the output and the transformer gets warm, but no damage occurs. 40 and 60 VA are typical powers.

    Here's http://www.functionaldevices.com/building-automation/display.php?model=CTRL-PS overkill again, but if done right, it would pass any inspection with flying colors.

    What's missing is"terminal blocks" and the "relay" if one wanted or needed to go that route. It's also a lot bigger than it needs to be.

    I'm going to use this https://www.asi-ez.com/ website to illustrate what;s available. Look at the "terminal block" link particularly. There are a wide variety of terminals available. Some just connect to the rail or ground.
    Generally, the same series snaps together with an end plate. End plates can be used to separate groups of terminals.
    There is an "end bracket" which makes the terminals between the bracket immobile. "jumpers" can connect the terminals together in busses.

    The general way to design using these blocks is to provide "connection points" for the entry cables and to internally wire with wire rated for the highest voltage in the box. Hopefully, you can design it such that the 24 VAC and 120 VAC entries and exits are "far away" from each other. e.g. The 24 VAC entry/exit point is say 6" away from the 120 V entry/exit point or whatever "the AHJ" suggests. The "AHJ" is the Authority Having Jurisdiction.

    Again, this is "an example".

    The Tekmar rely you, (the OP) picked out generally doesn't come with the base or "DIN/panel mount" base as shown and it's only part of the solution.
    Last edited: Sep 4, 2015
  9. Mat Pond

    Thread Starter New Member

    Sep 1, 2015
    Great information guys, really, thank you!