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

[whytwo]

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!!

 

[Diver300]

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.

 

[whytwo]

I think you're rather optimistic how fast fuses blow, and I presume resettable ones are no different? - generally you need a massive overload to blow it quickly, something like 10A through a 5A fuse could well take minutes before it blows, if it even blows at all.

Hi Nigel -- yeah, agree, think I am rather optimistic here... what has confused me is the manufacturer's tool (which the circuit is listed above), includes a Resettable Fuse that 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:

https://www.newark.com/bel-fuse/0zrr0010ff1e/ptc-resettable-fuse-0-1a-60vdc/dp/67AC9834

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:

New video by true

photos.app.goo.gl

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?

****EDIT**** Pretty sure the way I tested Voltage in the video was not the right way (at the relay outputs), so I re-tested for Voltage directly across the motor during a Close request. Shortly after the mechanical limit on the actuator shaft hits the housing, it goes from 9v -> 6v in like 1-2 seconds, and from there, it drops almost immediately and stabilizes around .6v-1v while the Resettable Fuse is heating up....****EDIT****

However, I ran into another unexpected issue. Most of my previous testing was with the Open Damper command.... and for whatever reason, even though the Damper Actuator Travel Time is a configurable option, that is specific only to the "Closed to Open" Travel Time, not the reverse...

The Open to Closed Travel Time does a "static" 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!

 

[Diver300]

Diver300, as you can see in the video, the voltage doesn't really come down much at all....even when the motor is stopped.

You have the multimeter connected across the series combination of the motor and the fuse. That will always stay near 9V because the power supply is doing its job and the relays are not dropping the voltage.

What I was looking for you to do was to connect the multimeter across the motor only, where there will be a large change in voltage.

I think that all resettable fuses will get hot when tripped. That is how they work.

 

[Diver300]

****EDIT**** Pretty sure the way I tested Voltage in the video was not the right way (at the relay outputs), so I re-tested for Voltage directly across the motor during a Close request. Shortly after the mechanical limit on the actuator shaft hits the housing, it goes from 9v -> 6v in like 1-2 seconds, and from there, it drops almost immediately and stabilizes around .6v-1v while the Resettable Fuse is heating up....****EDIT****

That is the sort of behavior I would expect.

If you just reduce the voltage of the supply, the motors will run more slowly and there will be less force when they first hit the end stops. You may be able to adjust the voltage of the supply, even if it's to find the right voltage before getting a lower-voltage one.

Also, the self-resetting fuses will get hot. Reducing the voltage will only reduce the final temperature marginally.

Can you mount the self-resetting fuses remotely, so that they are easy to replace if needed?

 

[whytwo]

If you just reduce the voltage of the supply, the motors will run more slowly and there will be less force when they first hit the end stops. You may be able to adjust the voltage of the supply, even if it's to find the right voltage before getting a lower-voltage one.

Can you mount the self-resetting fuses remotely, so that they are easy to replace if needed?

I really like this line of thinking... maybe I can tune everything so the motors have very little torque and stop easily without stressing the plastic actuator stop... I would want everything to be as gentle as possible!

I ordered some more Fast Blow resettable PPC that seem like good specs for this project and are supposed to blow in 100mS.... (Bourne CMF-RL50A-10) we'll see. I wonder if we bring the Voltage down, if it would take longer to blow the fuse?...

Either way, if the motor has less torque/power, if it takes 200ms vs 100ms, don't think it would matter much.

Would you suggest bringing voltage down by adding Resistors, or looking for an adjustable power supply??

Would be really nice to find a DIN mountable DC power supply adjustable from something like 5-10vdc, but haven't been able to dig one up this morning yet...

And YES, I can put the Resettable Fuses in a visible/available spot... some of the Resettable PPC specs I came across talked about 5000-6000 cycles as the limit, etc...

So maybe I can just replace them annually, etc.. (which would be plenty)

And as always, thanks again for all your feedback!

 

[Diver300]

Would you suggest bringing voltage down by adding Resistors, or looking for an adjustable power supply??

I was suggesting an adjustable power supply or a fixed on at a lower voltage.

A resistor wouldn't do a good job as it wouldn't reduce the speed as much for the same stall torque.

You could put diodes in series with the power supply. You will loose about 0.7 V per diode, so four or five in series will take your 9 V supply down to about 6 V.

 

[whytwo]

Looks like XP Power (the company that makes the 9vdc DIN mount supply I currently have) makes a 5vdc 15W 3Amp, and a 5vdc 30W 6Amp...

They don't appear to make a 6v.

Would either of those 5vdc supplies make sense or is that too little voltage?? More Wattage or less??

EML30 Series Power Product Range | XP Power

XP Power are a leading manufacturer & provider of Power Supplies, including AC-DC Power Supplies, DC-DC Power Converters and High Voltage Power Supplies.

www.xppower.com

Thanks again!

 

[whytwo]

Just another quick update -- I ordered a couple different DIN mountable Pheonix Contact Power supplies:

https://www.mouser.com/ProductDetail/651-2904595

This unit looks to be adjustable from 5vdc to 6.2vdc (~$100 USD)​

​

https://www.mouser.com/ProductDetail/651-2866721

This unit is pretty fancy and adjustable from 5vdc to 56vdc (Very pricey @ ~$700 USD... I know I maybe should just get a countertop power supply for cheaper, but I thought this device was nice and compact if I need to be really specific with the tuning of the voltage here...)​

​

I'm hoping the up-to 6.2vdc power supply works -- I'll try that first before opening the other unit so I can still return the more expensive one if not necessary.

Will update again soon when I get more stuff.

 

[Diver300]

Would either of those 5vdc supplies make sense or is that too little voltage?? More Wattage or less??

I don't know how much voltage you would need. The maximum motor torque and the maximum speed will reduce with voltage and that would need testing.

As long as you have enough current to run however many motors you want to run at one time, there is no point in getting a larger power rating.

 

[Pommie]

If the motor is working hard (less RPM) then there will be less BEMF and the motors will take more current. The voltage just gives the maximum RPM (no RPM = no BEMF = lots of loverly current) - the AMPs give the torque. As Diver said, "If you have enough current" then everything else will fall in place.

Mike.

 

[whytwo]

Just wanting to come back for an update -- I'm still working on optimizing this solution.

I am receiving another round of PTC fusses to do more testing early this week.

I did receive a 6.2vdc DIN rail power supply to test the motors at a lower voltage, and like everybody said, they do work and simply turn slower, etc.. Current draw is almost the same at 6v vs. 9v.

I had been wondering about whether lower voltage and maybe slightly less current would cause a Resettable PTC to take longer to blow....so I went back to my 9v power supply (haven't confirmed that yet, however, I did run into an issue.)

Somehow, I made simple mistake and left the circuit connected WITHOUT a Resettable fuse and walked away...

Came back later and the stop on my new motor was broken... ugh. (the HVAC controller closed the Damper when I was away)

So that has set me back a little -- I should get 2 more DC Actuator Damper motors for more testing today...

I have continued thinking about a more resilient/reliable solution. (again, I simply cannot have the motors behind drywall break.... is not an option to leave the Dampers open/closed/partial and then stuck...)

I agree with Diver that it would likely complicate things and probably not work as well..


Any chance the "more complicated" way of a Current Limiting Circuit with an output to something like a Raspberry Pi, which could read the current and trigger a Relay that would STOP the current immediately for 3 minutes when current goes higher than 100mA? (it could also seemingly account for Inrush current in the coding)

Realize there would be some programming/scripting at the very least here, but is this possibly a more enterprise solution?

Thanks everybody.

 

[Diver300]

The programming for a Raspberry Pi is probably quite simple, although I've no personal experience.

What I do know is that you will need to measure the current and feed the signal to the Raspberry Pi. You will need either:-
A shunt resistor and a suitable amplifier
or
A Hall-effect current transducer.

You will also need 5 V relays (or transistors and higher voltage relays) to let the Raspberry Pi control the motor.

 

[whytwo]

Thanks Diver, I came across this Hall-Effect device already a number of times... and using a transistor to a higher power relay makes sense since I would be working off of signal, not Line Voltage.

If I got something like the above designed, would it make sense that when the micro controller reads current over X, it sends signal to transistor to switch a relay that would break the relaying that is Contacting my Damper Actuators??

i.e. this current detection circuit that has a relay is in-serial with the existing relay and its NC position would be to let the current flow unless triggered by this setup? (which would break the Damper current as soon as the motor stalled in either direction?)

 

[whytwo]

Diver300, any chance something like this could work?

https://www.ia.omron.com/products/family/3491/lineup.html

Looks like it's an adjustable Current Sensing relay with either Transistor OR SPDT contact output...

https://www.ia.omron.com/products/family/3491/specification.html

Maybe I could trigger a timer relay to break contact of the 24ac Open/Close supply current for 3 minutes (to make sure it goes around the long Close command)

Hmmm... thoughts?

 

[Pommie]

Came back later and the stop on my new motor was broken... ugh. (the HVAC controller closed the Damper when I was away)

Maybe the 6V supply will allow the motor to stall without breaking the stop. Or, you could add limit switches.

Mike.

 

[Diver300]

Diver300, any chance something like this could work?

https://www.ia.omron.com/products/family/3491/lineup.html

Looks like it's an adjustable Current Sensing relay with either Transistor OR SPDT contact output...

https://www.ia.omron.com/products/family/3491/specification.html

Maybe I could trigger a timer relay to break contact of the 24ac Open/Close supply current for 3 minutes (to make sure it goes around the long Close command)

Hmmm... thoughts?

The problem with those is that you need to allow for inrush current as the motor starts, and you don't want to allow that long when the motor stops. However, give it a try.

As you are interested in current profiles over time, you really need an oscilloscope to measure that (with a shunt resistor as oscilloscopes can only measure voltage)

My suggestion is:- https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview