Components for Converting AC->DC + voltage step-down + reversing of polarity

I would arrange a separate 9 V dc supply, probably 120 Vac input, but you could power it from anything you want, and you could run as many actuators from one power supply as you want, just bearing in mind that the voltage drop at 9 V needs to be considered on building-sized wire runs, and making sure that the power supply can supply enough current for all the actuators you connect to it.

Then you need two 24 Vac single pole changeover relays for each actuator. Connect the coil of one relay to the 24Vac common and open terminals of the HVAC controller output. Connect the coil of the other relay to the 24Vac common and close terminal of the HVAC controller output.

At this point you can check that one relay operates when the controller is trying to close the vent and the other operates when it is trying to open the vent.

Now connect the NC connections of both relays to -ve of the 9 V supply. Connect the NO connections of both relays to the +ve of the 9 V supply. Connect the actuator between the Common connections of the two relays. Swap these two over if the actuator runs the wrong way.

It doesn't matter if both relays operate at the same time, the actuator will just stop, as it would when neither relay operates.

You need relays with 24 V ac coils. The ones with 24 V dc coils may not work on ac, and relays with 24 V dc coils are far more common. If a 24 V relay doesn't say if it's ac or dc, it's going to be dc. Something like this:-
https://www.newark.com/omron-indust...-ac24-s/relay-dpdt-250vac-30vdc-5a/dp/08J0973 would work and you can get a socket for it that mounts on DIN rail.

There may be much cheaper relays that are just as good for you.

Here is a the only 9V, DIN rail power supply that Newark have in stock:-
https://www.newark.com/xp-power/ece40us09-sd/ac-dc-converter-din-rail-1-o-p/dp/24T5140
but it wouldn't be too difficult to bolt any power supply onto DIN rail.

My guess is that one power supply and 16 relays per floor would be a good way to go, but I don't know what the arrangement is and whether you have enclosures with DIN rail on each floor.

Two relays per actuator is almost certainly not the cheapest way of doing it, but it seems that you want to use DIN rail mount, and stuff that any competent electrician can wire up once the circuit has been drawn up, and get parts for it in future, so that is what I would do.

I don't know if you need two functions per actuator (open - close) or three functions (open - do nothing - close). Two relays gives you all three functions. If you only need open or close and can leave the actuators powered one way all the time, you only need one relay per actuator. Wire the coil between open and common on the 24 V ac output of the controller. Connect the -ve of the 9V supply to the NO of one pole and the NC of the other pole. Connect the +ve of the 9 V supply to the remaining NC and NO contacts. Connect the actuator between the two common connectors, and swap those if it goes the wrong way.

Diver300, thank you so much -- everything this all makes a lot of sense!

I really like the idea of a separate 9vdc power supply that is simply triggered by relays.

Some more information:

My DC Damper Actuators are considered "Floating" Dampers... i.e. there is a 20 second Open time and 20 second Close time... if you stop applying current at 10 seconds (in either direction), the Damper Actuator would "stop" at the halfway point... (essentially)

I cannot continue applying current continuously. My Zone Controller is programmed to deliver 250mA @ 24vac for the Open Command via 1 wire, and then 25 seconds of 250mA @ 24vac for the Close Command via another one. (25 seconds being a bit more than 20 seconds to ensure the Dampers are fully opened or fully closed). Additionally, during "start-up" or during Heating/Cooling, any Zone that doesn't require demand, the Zone Controller applies 2min 30 seconds of Close to "reset" the damper to zero, essentially... (I'm trying to get the manufacturer to make this configuration as I'd be applying current for over 2 mins longer than I want....)

Again, I cannot continuously apply current to the Dampers, only during Open/Close commands. (to ensure maximum life)

Traditionally, most Dampers are AC and have 3 wire (vs. 2) Common, Open, and Closed and are setup for "Spring Closed" or "Spring Opened" (i.e. once current stops, they mechanically "spring" to either the Open or Closed position to avoid continuous current...

I'm happy enough with the time-based Floating Schema, but I need to be able to trigger +9vdc Open (for a short period until the 24vac output stops), or -9vdc Closed (for a short period until the 24vac output stops. But when the Zone Controller is NOT either Opening or Closing a damper, I need NO current going to the Damper Actuator motor.

And, as you saw, the additional challenge of DC is polarity switching is a necessity here! A typical 24vac Damper Actuator has 3 Inputs (Open/Close/Common) just like the Zone Controller's output...

Couple questions: Above, you noted "two 24 Vac single pole changeover", but looking at the link to the OMRON it seems to maybe be a DPDT. Can you clarify??

When looking at DPDT, I kept coming across them being able to be used for polarity reversing.

I am totally fine with 16 relays per 8 dampers, but if it were possible to use a DPDT relay to reverse the DC polarity on a single relay, that would be great too!

Thank you again for everything, I am now much closer putting together a solution.

whytwo said:

Couple questions: Above, you noted "two 24 Vac single pole changeover", but looking at the link to the OMRON it seems to maybe be a DPDT. Can you clarify??

Click to expand...

The relay that I linked to was just about the first 24V ac one I found, and it happened to be a DPDT.

whytwo said:

When looking at DPDT, I kept coming across them being able to be used for polarity reversing.

I am totally fine with 16 relays per 8 dampers, but if it were possible to use a DPDT relay to reverse the DC polarity on a single relay, that would be great too!

Click to expand...

You can use a DPDT relay to reverse polarity, but a single relay can have two conditions, so forward and reverse but he actuators would be powered all the time.

whytwo said:

I'm happy enough with the time-based Floating Schema, but I need to be able to trigger +9vdc Open (for a short period until the 24vac output stops), or -9vdc Closed (for a short period until the 24vac output stops. But when the Zone Controller is NOT either Opening or Closing a damper, I need NO current going to the Damper Actuator motor.

Click to expand...

If you need some way to only power the actuators when the 24V ac is turned on, then you will need two relays per actuator.

As I understand it, the HVAC controller only puts out 24V ac when the dampers are either opening or closing, in which case the actuators will be turned off most of the time if you connect up the way that I suggested for two relays.

If the "Close" output turns on for 2 minutes 30 seconds and you don't think that the actuators will survive that, it could be quite a problem. If you have a spare zone that isn't used, but the "Close" output operates at start-up, you could use that output to turn off the 9 V supply to everything each whenever it operates.

Other solutions would involve timers and it would all get complicated quite quickly.

Diver300,

OK, I think I got it... thanks for your clarification on the Single Pole vs. Dual -- agree that it makes sense since I also need a Not Opening and/or Not Closing State.

To complete my POC (hopefully), I went ahead and ordered the following:

• 2 x https://www.newark.com/omron-indust...c-10a/dp/08J0953?CMP=e-email-sys-orderack-GLB (Single Pole 24vac coil powered Relays)
• 2 x https://www.newark.com/omron-indust...-1-b/dp/48AC2024?CMP=e-email-sys-orderack-GLB (Relay socket adapter for DIN)
• 1 x https://www.newark.com/omron-indust...n/din-mounting-rail-35mm-aluminium/dp/93B2043 (DIN Rail)
  
  
• 1 x https://www.newark.com/xp-power/ece...1-o-p/dp/24T5140?CMP=e-email-sys-orderack-GLB (DIN Rail mountable 9vDC Power Supply)

If you see anything that doesn't make sense, please let me know. Otherwise, I'll follow-up soon.

Thank you again for your guidance here!

BTW, here is the DC Motor that is installed on all of the HVAC Supply Damper Actuators:



I wouldn't anticipate anyone would know much about the device, but this was all I could dig up.

I tried reaching manufacturer and have not had a response.

Any opinion on whether this would be the type of device I should be worried about my equipment applying current when either full opened or full closed?? (for a short period of time, hopefully)...

The way the Damper Actuator works is there is a tang that "bottoms out" in both directions to "stop" it from rotating... (so assuming the motor is still under load and can't move when applying current and it's in its respective maximum position).

I'm trying to get a 25+ Year solution put together here...

Thanks again!

Just following up here... got my 24vac coil relays and 9Vdc power supply.

Good news and Bad news....... good news first!

The SPST Omron Relays with XP Power 120vac->9vdc power supply recommended by Diver300 worked PERFECTLY! (almost)




(please ignore the lack of soldering... I'm still waiting on my relay Sockets... ha)

But wired as described by Diver300 it worked exactly as expected.... putting the DC motor +and- across the COM (center terminals) provided +9vdc when the 24vac for Open was output from the thermostat as well as -9vdc when the 24vac for Close was output from the thermostat.

Stepping back for a moment, the DC motors on my Damper Actuators are supposed to be adjusted MANUALLY using the following tool from the manufacturer:

https://www.greenheck.com/shop/accessories/damper-accessories/893199

This is 9vdc battery powered....and connects via RJ11 plug into wall jack. You simply Open and Close the dampers with the tool...

There are some LED/lights on the product to indicate when full Open or full Close... I did wonder how they were indicating Full Open or Full Closed since there is only 2 wires...not a Status wire from the DC motor. I'm thinking I may now know...

So back to my issue.... These are 20 seconds Dampers, but this test actuator was in the half-way position when I had my Relay power +9vdc to "Open" my test Damper.... so about 10 seconds later, when the damper got to Full Open, (mechanical limit) I could hear the motor REALLY working (and not really slowing down)...and it basically broke the center plastic tang...ugh... (you can see a crack in the plastic where the motor wanted to keep spinning the metal shaft while the plastic stopper was pushed up against the metal frame...



The Tool does NOT seem to do this..... so maybe the Tool must be sensing current spike and then switching current off?... (was wondering how the LED lights were lighting up since there is not a "status" from the DC motor, just an Open or Close..)

So, it sounds like the tool has some more advanced sensing circuits than I thought.

When I measure the DC motor, it draws 255mA, which is essentially what is spec'd by the manufacturer...

So maybe there is a circuit in the tool that detects a spike over 255mA which shuts off current (and then illuminates an LED/Light indicator Open or Closed)...

Never Easy!

Anyone familiar with any off-the-shelf plug-in style components that would allow me to switch off/away current if/when draw exceeds 255mA?! (this could also solve the 2min 30 second Damper Close command the Zone Controller does upon Startup to "reset" the position...)

Thank you again

Just thinking out loud here a bit... but I may also be able to re-purpose the Tool's circuitry itself... hmmm



I may be able to remove the board, wire this direct to 9vdc power supply and use relays to essentially "close" the Open/Close contacts on the board....

EDIT: looks like it's insanely simple actually...could this possibly have the current shut-off circuit or am I losing it?.. Maybe when resistance gets high enough, the current goes to the LED instead of motor output??


But since there are ~8 Dampers per floor that could be Opened or Closed at the same time, I may need one of these boards for each Damper?... Crazy idea or no?

Is the 255 mA current measured with the motor running?

On the tester board, F1 is a resettable fuse. With that, and the relatively high internal resistance of the 9 V battery, there won't be much current available to the damper motors.

When the motor is running, and it is only taking a bit of current, there will not be much voltage drop across the fuse and so the LED will light up. When the motor stalls, the current will increase and the fuse will get hot. Its resistance will increase, and the voltage across it will increase, leaving only a couple of volts across the motor and the LED, so the motor won't do much and the LED will go out.

When the buttons are released, the fuse will cool down so that it's working normally when the tester is used again.

I've got to say that I'm impressed by the simplicity of the design.

You can simply add a resettable fuse in series with each damper. All you have to do is work out the rating.

I am not sure but I think that the fuse is one of these:- https://uk.farnell.com/bel-fuse-cir...ff2e/fuse-resettable-ptc-6vdc-0-5a/dp/2834926

However, different manufacturers have different trip currents for the same marking.

If you can, connect the fuse to a variable current source, slowly increase the current and measure the current which it trips at. Just about any resettable fuse with about the trip current will be do. You can buy resettable fuses in a variety of styles.