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Topic: 24VAC 3 way mixing valve actuator (Read 2360 times) previous topic - next topic

zeroprog

Hi all,
    I am new to electronics still so bare with me this might be a simple question or I might be just having a bad search day but here goes....I have arduino mega 2560 and a 3 way mixing valve actuator that runs off a 24vac line. This valve requires a 2-10vdc control value which I wish to supply with my arduino. I do not wish to power the arduino and valve off the 24vac line. This is more of a control project so on/off won't do (well i guess it would but i chose 2-10). My question is, how would I go about wiring the arduino output to the actuator control input? I understand somewhat how to get the analog 2-10 or use pwm but will simply tying the arduino output into the actuator input work?
Thanks in advance

Hi zeroprog, welcome to the forum,

Quote
zeroprog wrote in part:
I do not wish to power the arduino and valve off the 24vac line. This is more of a control project so on/off won't do (well i guess it would but i chose 2-10). My question is, how would I go about wiring the arduino output to the actuator control input? I understand somewhat how to get the analog 2-10 or use pwm but will simply tying the arduino output into the actuator input work?


Firstly, the actuator, if it is designed to be powered from 24VAC, then you don't have much option. It will need this power supply to work.
Unless you can get inside and work out if it can be adapted to work off 24vdc if that is of any help.

For the input signal of 2-10 volts, which is an industrial standard (albeit old), you will need some electronics between your Arduino and the valve.
Check to see that the valve can be configured to operate from other standard signals, such as 1 - 5 vdc or even 4 - 20mA as this might make your interfacing easier.

But if you are stuck with using 2 - 10 vdc then you may simply use a op-amp circuit with the correct amount of gain, X2 if you have 0 - 5 vdc from the Arduino. You will need the right amount of filtering on the op-amp input to smooth out the PWM if use use that.

Alternatively, you could build a simply R2R resistive ladder network driven from Arduino digital output pins that will give you a crude DAC which you then feed into the op-amp buffer driver circuit.

First, check your options for valve supply power.

Paul

zeroprog

Ok, so the actuator can apparently be run off 24vdc also, so if I convert the ac to dc, does this mean I can just step down the voltage after the actuator to arduino input specifications (i think it's 9-12v)? And thank you for the signal points, looking more into the op amp option now, i think i am stuck with the 2-10 for this particular valve.

Yes, you can then use a suitable regulator to take the 24vdc down to what the Arduino needs.
Look at using a small switch mode regulator, rather than a linear type if you can.
ebay is a good place to look and they are very cheap to buy.
You can get small switch mode regs that will handle an input up around 35vdc which will be better.

For your op-amp, just google and you will find many cicruits, or search on the Arduino forum or other electronic forums.

Paul

zeroprog

Perfect, thank you sir, you are a gentleman and a scholar.

retrolefty

I've had good luck with these switching regulator modules, nice price.

http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Lefty

Quote
Lefty wrote:
I've had good luck with these switching regulator modules, nice price.


Yes, they are the style I was thinking of, thanks Lefty for the link.

Paul

draythomp

The problem I had with a buck converter was that it was rated like the one Lefty pointed out with a max input of 35VDC.  When you rectify and lightly filter a 24VAC supply, it comes out around 37VDC which is just over the max for the buck converter.  In my case I tried two of them, neither one was the one Lefty indicated, and they both got hot and failed in a couple of days.

Lefty may have tried the one he shows at that level and had a good experience, but I had both of mine release small amounts of magic blue smoke.  They didn't work too well after that.  You might have better luck looking around for one that can handle 40VDC or better input to give you a fighting chance of a reasonable lifetime.
Trying to keep my house under control http://www.desert-home.com/

Good point Dave,

I am gathering that from what zeroprog is saying is that he is wanting to use a 24vdc supply for the valve and to feed that 24vdc into such a regulator.
He has confirmed the valve will operate on 24vdc.

Yes, you are correct Dave, rectified 24vac will bring it past the maximum input for these regulators, but 24vdc should be fine don't you agree?
GreyNomad, (Rob) uses very nice switch mode power supply modules in his designs, that I do believe will handle the 40vdc on the input ok.

Dave, what a shame you did not have your zero-point blue smoke capture canister handy at the time of release?

Paul

draythomp

Nope, the smoke got clean away.  And Yes, it will work great with a 24VDC supply.  Those little buck supplies are great.
Trying to keep my house under control http://www.desert-home.com/

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