# Converting Motor from 115VAC to 24VDC



## splatz (May 23, 2015)

I have to replace some motor operated valve actuators this next couple months. The motors are tiny, .5A at 115VAC. The valves are in shallow vaults, about 5' deep. They are not on GFI protected circuits. There is a j-box in the vault but no disconnect. 

I was looking at the manufacturer's literature to see what to order. They actuator is currently available in 115VAC and but there are also 12V and 24V AC and DC versions. I figure I'll put in the low voltage, just a little safer for who ever is working in there, probably 24VDC since that's already available in the panel. 

Any reason not to convert to 24VDC?


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## Flyingsod (Jul 11, 2013)

You're adding another failure point to the system.

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## scotch (Oct 17, 2013)

None ....most actuators now are AC/DC with an integral 1/2 wave bridge ....so you can use 24ac as well....most common controls voltage . Europe is moving more towards 24dc even for motor starter contactors .


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## splatz (May 23, 2015)

Flyingsod said:


> You're adding another failure point to the system.


Point taken, but not really - if the 24VDC controls go off it will never move anyway.


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## Flyingsod (Jul 11, 2013)

Yep, I missed the part about it already being available. If the PS can handle the extra load my point is false.

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## John Valdes (May 17, 2007)

Sounds like a rail switching valve/motor for the railroad?
I would stick with what you got.


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## MechanicalDVR (Dec 29, 2007)

splatz said:


> I have to replace some motor operated valve actuators this next couple months. The motors are tiny, .5A at 115VAC. The valves are in shallow vaults, about 5' deep. They are not on GFI protected circuits. There is a j-box in the vault but no disconnect.
> 
> I was looking at the manufacturer's literature to see what to order. They actuator is currently available in 115VAC and but there are also 12V and 24V AC and DC versions. I figure I'll put in the low voltage, just a little safer for who ever is working in there, probably 24VDC since that's already available in the panel.
> 
> Any reason not to convert to 24VDC?


Not at all, did that many time sin the past for ease of future servicing.

Belimo and Honeywell both have a nice line of basic actuators.


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## splatz (May 23, 2015)

John Valdes said:


> Sounds like a rail switching valve/motor for the railroad?
> I would stick with what you got.


No, this is a groundwater system, it just controls a valve to control runoff.


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## sparkiez (Aug 1, 2015)

My only suggestion here is to make sure the actuators have a flyback diode installed. If they are running DC motors you don't want any 24V transients feeding back into your electronics causing issues. Usually the equipment does, but I HAVE had equipment that required you to install your own flyback diode (in this case, it was the heating elements on a small box strapping machine controlled by an OEM specific control board).


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## JRaef (Mar 23, 2009)

Be careful. .5A x 120V = 60W. 60W at 24VDC is 2.5A. That's a much bigger load on a 24VDC power supply. Small ones for instrumentation are often Class 2 power supplies, because it makes it easier to get UL listing of a device if it's going to always be fed by a Class 2 power supply. That means they are limited to 100W, so adding just one 60W valve actuator may drive your power supply into overload and it might turn off to protect itself. More than one valve actuating at the same time would definitely do it.


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## Navyguy (Mar 15, 2010)

JRaef said:


> Be careful. .5A x 120V = 60W. 60W at 24VDC is 2.5A. That's a much bigger load on a 24VDC power supply. Small ones for instrumentation are often Class 2 power supplies, because it makes it easier to get UL listing of a device if it's going to always be fed by a Class 2 power supply. That means they are limited to 100W, so adding just one 60W valve actuator may drive your power supply into overload and it might turn off to protect itself. More than one valve actuating at the same time would definitely do it.


I was also thinking voltage drop might be an issue.

Cheers
John


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## MechanicalDVR (Dec 29, 2007)

JRaef said:


> Be careful. .5A x 120V = 60W. 60W at 24VDC is 2.5A. That's a much bigger load on a 24VDC power supply. Small ones for instrumentation are often Class 2 power supplies, because it makes it easier to get UL listing of a device if it's going to always be fed by a Class 2 power supply. That means they are limited to 100W, so adding just one 60W valve actuator may drive your power supply into overload and it might turn off to protect itself. More than one valve actuating at the same time would definitely do it.


If he takes the 120v source to the current motor and powers a new 24v trans sized to the load from that he should be fine.


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## scotch (Oct 17, 2013)

Actually...depending on the actuator....many have a spring return reserve that will drive the actuator to its stop on power failure . Its surprising how much torque those small actuators...Belimo for instance...have .


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## MechanicalDVR (Dec 29, 2007)

scotch said:


> Actually...depending on the actuator....many have a spring return reserve that will drive the actuator to its stop on power failure . Its surprising how much torque those small actuators...Belimo for instance...have .


Was Belimo factory service at my last company and of the vast majority of complaints I went out on the actuator was fine, the install was corrupted in one manner or another.


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## splatz (May 23, 2015)

JRaef said:


> Be careful. .5A x 120V = 60W. 60W at 24VDC is 2.5A. That's a much bigger load on a 24VDC power supply. Small ones for instrumentation are often Class 2 power supplies, because it makes it easier to get UL listing of a device if it's going to always be fed by a Class 2 power supply. That means they are limited to 100W, so adding just one 60W valve actuator may drive your power supply into overload and it might turn off to protect itself. More than one valve actuating at the same time would definitely do it.


Good point, I was looking at that, luckily there's just one valve per control panel so it should work out OK.


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## splatz (May 23, 2015)

Navyguy said:


> I was also thinking voltage drop might be an issue.


Another good point, I am figuring on 50 feet of #12 which according to the calculator, keeps it right around 3%. I am glad to replace the existing wiring anyway - they are not marked THWN, that's been irking me for a while.


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## splatz (May 23, 2015)

I wound up ordering an actuator with 24VDC motor and two auxiliary switches to indicate whether the valve is open or closed, I can put those on dry contacts on an alarm monitor. So it looks like I'll have three #12 wires for the motor, plus a ground, and four whatever for the switches. There will be nothing else in the conduit from the control cabinet to the vault where the valve is located. 

What wire would you use? Would you worry about color coding?


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## RePhase277 (Feb 5, 2008)

For the switches? Something odd, maybe yellow or pink #16 THWN.


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## glen1971 (Oct 10, 2012)

How far? I'd use #14's then you know there is no issue, plus it is a spec on 98% of the sites I've worked at for DC control wire size..


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## splatz (May 23, 2015)

Well, I was going to use regular #12 wire for the motor and ground to keep the voltage drop under 3% at 50 feet, I am just not sure whether I am supposed to use blue / white-blue for 24VDC. 

The switches - I figured I'd use two 18/2, that's what's used other spots for the digital IOs, although not underground.


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## John Valdes (May 17, 2007)

Use any color you like. Just make sure you mark them and reference those numbers to the drawing.


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## Jlarson (Jun 28, 2009)

I'd pull a blue and white 12 since I rarely have 12 blue/white handy. And an 18/6 for the feedback since I always keep 18/6 on the truck.


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## JRaef (Mar 23, 2009)

I'd use blue and blue/white, so someone someday does not confuse the white as being an AC neutral. This is from NFPA79, which technically would not apply, but it is the generally accepted standard for conductor colors when no other specific internal standard exists.



> 14.2.3.2 The use of other colors for the following applications
> shall be as follows:
> (1) *WHITE with BLUE stripe for grounded (currentcarrying)
> dc circuit conductor.*
> ...


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