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

whytwo

New Member
Hi all,

First, I really appreciate anyone taking time to read through this and provide feedback.

I’m working on a unique HVAC application where I have handful of problem statements and I’m trying to figure out what the most ideal components are. Additionally, I’d like to be as minimal as possible! For example, if there were a single device/PLC/relay that could do it all (even if pricey), that’s OK.

My preference would be to take off-the-shelf component(s), if possible.

Here is what I’m working with:

-My HVAC Zone Controller outputs 24vac designed to Open/Close Dampers (a typical HVAC actuator is 24vac).

-My Damper Actuator motors are 9vdc (mine are NOT typical).

-My HVAC Zone Controller has three 24vac outputs to Open/Close Dampers: 1) Common 2) Open, and 3) Close. (so common is always used, but the Open/Close terminals are used for their respective actions)

-My Damper Actuators have two wire inputs to Open/Close these Dampers. Since this is a DC motor Actuator, you simply reverse the polarity to Open/Close the Dampers.

So, when my HVAC Controller wants to Open a damper, it outputs 24vac to Common/Open terminals, and when it wants to Close a damper, it outputs 24vac to Common/Closed terminals.

I have a multimeter watching those outputs and it’s working as expected.

I am looking to Convert from AC -> DC, as well as step-down from 24v to 9v, as well as reverse the polarity of 3 wires to 2.

I believe I’ve identified components that could do everything… i.e. a Voltage Rectifier (to go from AC->DC), a transformer to go from 24vdc->9vdc, and then a Dual Pole Dual Throw Relay (DPDT) to reverse polarity of the DC motor…

Question is: Can any recommend the “cleanest” way to do this?

Another note, I have about 8 DC actuator Damper Motos per floor (3 floors total), so if there were some sort of DIN-mounted PLC/Relay/Rectifier module(s) that could take a number of inputs and outputs, that would be brilliant!

Some additional details:
-DC Damper Actuator motors draw 250mA.
-Zone Controller's AC Output is 2.5Amp max
-There is a use-case where multiple DC Damper Actuator motors may be connected to a single Zone Controller Output. (i.e. Zone Controller Open/Closed circuits could control up-to 3 Dampers)

Please let me know if you have any questions and thank you again!!
 
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Can you run a similar test while measuring the voltage across the motor? You can check that the voltage is reading correctly as it should read close to 9 V when connected directly to the power supply.
 
Hi Nigel -- yeah, agree, think I am rather optimistic here... what has confused me confused is the manufacturer's tool (which the circuit is listed above), the Resettable Fuse seems to trip very quickly and essentially stops the motor right away in both directions and doesn't seem to get too hot.

I just discovered an obvious/simple issue that was causing me to scratch my head a bit last week.... I blew a fuse in my multimeter.... ugh. That slowed me down a bit and I'm still waiting for a low current replacement fuse.

However, since that time, I did receive some more components and put the following resettable fuse in serial to my DC Actuator:


This is a 100mA hold and 200mA Trip and it actually seems to trip fairly quickly.

I also finally got my Relay Sockets and have stuff wired up a lot cleaner.

Please see the following video:


BTW, apologies for the long "wait time" in the middle of the video, you can fast forward from: ~60 seconds to: ~1min 50 seconds to avoid the wait time before the Actuator Close begins... (BTW, sometimes better to Download the video vs. trying to stream as Google Photos tends to limit stream bandwidth)

Can you run a similar test while measuring the voltage across the motor? You can check that the voltage is reading correctly as it should read close to 9 V when connected directly to the power supply.

Diver300, as you can see in the video, the voltage doesn't really come down much at all....even when the motor is stopped. I don't assume the 6v max Fuse in the Hand Tool would have any effect on things, right?

However, I ran into another unexpected issue with my HVAC product. For whatever reason, even though the Damper Actuator Travel Time is configurable, that is ONLY the Closed to Open Travel Time, not the reverse.

The Open to Close Travel Time does a "harsh" 2min 30second CLOSE as you saw in the video...

So, during the Close function, the Resettable Fuse is heating up for a good 2min30 seconds... and the one I have installed above gets up to 216 degrees F.... so quite a lot hotter than the factory tool (~136 degrees)... Hmmmm

So, I'm wondering how unacceptable that is. I'm trying to get the manufacturer to allow the Open to Close Actuator Travel time be configurable so I can make Close 20 seconds too, but not overly confident they would be willing to make that change.

I have a handful more Fast Blow Resettable Fuses arriving on Tuesday to see if I can find one that reacts quicker (you can hear the motor get buried for a coupe seconds before it stops) and doesn't get as hot...

The question I have now:

Does it seem like I'm going down a decent path still... or is there another idea/option to better manage load/heat for this application? Again, I'm willing to spend some money to ensure it's as reliable and industrial strength as I need it to work for 30+ years...

Thank you guys!
 
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