Howto power 24VAC valves from 12VDC

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How to make from input 12VDC output 24 VAC

I found commercial product but its really expensive
http://www.powerstream.com/inv-1...

I have 24VAC/400-500mA sprinkering valves
and only self powered solar garden.

Valves are not working on 24VDC they need really VAC.
Current workaround solution is 12VDC->220V->24VAC

Does somebody other and better and more effecient solution howto power 24VAC valves?

Last Edited: Wed. Apr 24, 2013 - 05:36 PM
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First Google hit:
http://www.powerstream.com/inv-1...

Only $100. ;)

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Seems like they should work on DC doesnt it?

Imagecraft compiler user

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I've tried with some that I have, and they don't. There may be some eddy current effects in the actuator as it appears to be soft iron (in mine).

I made a watering timer, many years ago, from generic CMOS logic. The output was a relay that controlled the circuit on the output of a line->24VAC transformer.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Perhaps change the valves?

JC

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@theusch:

Quote:
First Google hit:
http://www.powerstream.com/inv-1...
Only $100.
Did you see url in my initial post? I dont want buy this one but make it and a lot cheaper. btw first and last no other products in results :-( I have price limit 50euro including shipping ;) $100+shipping :?:?:?

@bobgardner:

Quote:
Seems like they should work on DC doesnt it?

No they are not working. Valve on DC drain 2-3x times more current as on AC and I burned one :( Coil get warm in few seconds and in 30sec was damaged and valve is smoking.

Quote:
@DocJCPerhaps:
change the valves?

This is not good solution its a profesional and not cheap valves.
DC valves are problem becouse electrolyse will damage wires and maximum voltage is 24VAC allowed here
( I dont want endanger small childrens or old people )

Any other idea then buy expensive product or dig out pipes change valves and fitting on pipes?

I may use also 2x12V batteries in series then I have 24VDC.
Is it possbile go this way?
Is it easier make chopper/inverter from 24VDC to another AC and use transformer.
effeciency is not verry important now. I am openning only single valve per zone.

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How many watts does the system need to provide?

JC

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24VAC*500-800mA~20W?
valve need min 380mA

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I've used 12 VDC to operate Rainbird, Orbit, and Superior valves with no problem. Expect each one to draw about 500 mA.

 

In consideration of others, please RTFM!

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Something like this:
http://www.aaroncake.net/forum/t...

You could use a 24v with a centre tap transformer. Apply the signal to the centre tap and one of the outer taps. Pick your 24 vac from the outer taps. You'll also get 240v on what is normally the primary, so insulate that well. It's crude but should do the trick.

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I think he wants to power the valvs from his 12V solar panel installation.

if you would make your own transformer. in the center of an H-bridge. then you could make a converted sinewave. Put a low pass filter behind it to remove the sharp edges. you would have made your own 12Vdc to 24V AC converter. You could also buy a 150W power transformer ( 300W costed me 20 USD over a year ago) and then a transformer that does 120V to 24V.

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You need 24VAC, but do you really need pure sine for a valve?

I would experiment with a 12-24V DC-DC converter with a H-bridge output. Switch the H-bridge at the frequency you want, and you have a 24VAC inverter. Choose a H-bridge with tri-state output. L298 is inexpensive and goes to 46V.

Peter

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jpmargis wrote:
I've used 12 VDC to operate Rainbird, Orbit, and Superior valves with no problem. Expect each one to draw about 500 mA.
Thank for hints but changing valves is last solutions I have 30 zones :( and they are new and supplier will not accept return.

@Kartman:

Quote:

Something like this:
http://www.aaroncake.net/forum/t...

@meslomp:

Quote:
I think he wants to power the valvs from his 12V solar panel installation.
Yes, you are right. I have only solar pannels and 12V batteries there.

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Here is a simple solution commonly used for solenoids. It is called peak and hold. It only takes one low side switch, and pwm. The solenoid is energized momentarily, followed by pwm action at 30 to 50 percent for holding current. Use freewheel diode on coil. I would think the pwm frequency of 400Hz will work. To get more pwm channels, use of tiny45 may be your friends.

It all starts with a mental vision.

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It might be easier for us to help if you told us more about the valves? Manufacturer? Model?

 

In consideration of others, please RTFM!

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I will try find any technical data about valves eshop is currently down where I bought it

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Inductive reactance of the coil is 2*pi*f*L. I'd say measure the ac ma then run it from whatever dc gives the same ma. 12V maybe. Try it. The valve got hot on 24V dc because there was no reactive impedance. You on 60hz or 50hz?

Imagecraft compiler user

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This was the point of my earlier post which somehow was interpreted as a suggestion to change valves. From past experience, the valve will draw about 300 mA at 24 VAC. If it is inconvenient to use the corresponding DC voltage as suggested above, the valve will draw about 500 mA at 12 VDC. Yes, it will get hotter, but it should not smoke.

And, as a alternative, it is always possible to add a series resistor to get the correct current.

 

In consideration of others, please RTFM!

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In the past, I have taken a power transformer (step down) and driven the tapped secondary with a push pull transistor circuit. Output from primary was AC square wave, which should work. YMMV

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Cool. N = 2! We have Concensus!

Imagecraft compiler user

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bobgardner wrote:
Inductive reactance of the coil is 2*pi*f*L. I'd say measure the ac ma then run it from whatever dc gives the same ma. 12V maybe. Try it. The valve got hot on 24V dc because there was no reactive impedance. You on 60hz or 50hz?

I have f=50hz
2*pi(3.14159)*f(50)*L(unknown-yet)

I will need use resistor(1%) method for measuring inductance on my simple DMM

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Coincidentally, ChaN's owner(1) has recently published an article about measuring inductors with an oscilloscope.

http://elm-chan.org/works/lchk/r...

(1) ChaN is the cat's name. The owner remains nameless.

Ross McKenzie ValuSoft Melbourne Australia

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That's a Good Method. Sweep the signal generator until the voltage drops to .707 of the input voltage.

Imagecraft compiler user

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Wow, that's great!

The illustration of saturation behavior by core material/design is outstanding...

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Keep in mind that Bob's formula gives you the inductive reactance. To this you will need to add the DC resistance of the solenoid to get the impedance. Expect a value of about 25 ohms for the DC resistance. Then you can calculate the AC current and the corresponding DC voltage to get that same current.

 

In consideration of others, please RTFM!

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The idea is to use the 24VAC solenoids on a reduced voltage DC. Do they operate on 12VDC?

Imagecraft compiler user

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I will go to garden on Sunday or Monday its far from my working location. This is a reason why I installed valves there controlled by SMSrelay.

I will measure current on 24Vac, if is openning on 12Vdc and also current. I will try measure coil electrical impedance and inductance. I hope its all what I need if I find one spare valve I will get it to home all other are fitted on pipes and this model has fixed coil its not easy remove only valve from system.

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If the valve turns on at 12V, then limit the holding current with pwm as I suggested in my post above. I do this with different styles of fuel injection solenoids. There are also analog means of doing this, resistors, caps, transistor. Use google, peak and hold.

The pwm is efficient, the analog means will dissipate power. This is more about solenoid current, not voltage, coil resistance, not inductance.

It all starts with a mental vision.

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I dissasembled one valve from system and here are some values.

Coil Inductance
55mH at 1khz
85mH at 100hz

Values from valve package (molded on package)
inrush 375mA
holding 250mA
24VAC
6VA
Vendor or Brand is unknown.

DC resistance 44ohm

Last Edited: Mon. Apr 22, 2013 - 02:12 PM
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Whats the DC resistance?

Imagecraft compiler user

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44 ohm

Photo of valve

Note: updated and added to also previous post keep all data in single post.

I tried valve on 12VDC its clicking and drain 320mA I have no pluck leave it on 12Vdc then few seconds.

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Well, my ol buddy George Ohm told me that .25 amps x 44 ohms is 11V. Maybe try it on 12V thru a diode. I cant understand the last sentence in your last message. Something about removing chicken feathers?

Imagecraft compiler user

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I calculate the AC impedance at 70.7 ohms, so the current would be 339 mA at 24 VAC. Find some pluck, 12 VDC is about right.

 

In consideration of others, please RTFM!

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I remember I made a mistake. I drive valve from 12V battery but voltage on fully charged 12V battery about 13.5-13.75V under load is little lower but higher then 12,0V.

If you calculated with 12V and 320mA result is little different as real situation.

I haven't attached 2 DMMs when I measured current and check voltage in load. I will check exact values when I come to home.

I have question.
May I use H-bridge+555 and drive valve 12AC square L293 quad H bridge or similiar are often used as step motor driver ?
What do you think about this?
Valve will have AC will be opened and probably coil less heating. This solution is cheap I have all required IC at home.

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12VAC 50% squarewave is the same as 6VDC. Does it work if you run it from a regulated 12V power supply?

Imagecraft compiler user

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I tested it on BATT=13.08-13.17V I=310mA
it's verry softly smelling. I havent access to coil now its covered with plastic this plastic is cold but I bet coil is hot under.

I may try add resistor and go down with voltage and measure current if will smell also with lower voltage.

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One thing to remember with solenoids is that their inductance changes, it increases quite a bit when they engage. That means that once it engages the current drops. But you probably can't just apply the holding current as DC, you won't have enough current to pull it in.

I ran a sprinkler valve on DC. It was a 24VAC valve (nominally). After testing it I found what worked was to pull it in on 12VDC then hold it with 5VDC.

What you can do is to run it on AC but at 1/2 or 1/4 the rated voltage, measure the current then apply the scale factor (2 or 4 respectively) to get the pull-in current. Then connect it to the full rated voltage and measure the current, this is the holding current. You can use DC as long as you use the same current at each stage (pull-in and holding) but you have to change the current by some means.

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Nice to hear also other person has AC valve on DC ;)
Could you share more information vendor and model of yours valves please?

I contacted my local supplier yesterday.
if they don't have DC coils for valves and they said they have 9VDC but only for 1" models. I need 3/4" only. :(

How are you changing voltage with MCU or with other method.
I will try this method tomorow.

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It's fine with me if you want to use this as a reason to do a microcontroller project, but a single resistor is absolutely the most you need!

 

In consideration of others, please RTFM!

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resistor cost 0.20Eur or less if I drive valve from fully charged battery there is about 400mA current.I known its only very short time but for safety i may add 0.20eur resistor and limit the current or not ;)?

it's much more cheaper solution as recommended 100$ (12V-24VAC inverter)

I spare diode in schema better say I forgot draw it into image.
I have to add also diode there. ;)

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Add a capacitor (few thousand micro) at 16V after the resistor. When the valve is off, the cap will charge at 12V. When turn on, the cap will provide the inrush current, and then the resistor will hold the valve. Ad a diode in parallel with the switch. There is only one downside, after you turn off the valve you need some one or two seconds to let the cap to charge before you turn it on again.
George.

 

Edit: the diode is in parallel with the load (the valve), not in parallel with the switch, and only needed if the switch is an active one like a BJT, MOSFET, IGBT. Not needed if a mechanical switch is used. The capacitor can be in parallel with the resistor as mentioned later in this thread and it has the advantage that the capacitor is under voltage only when the valve is ON.

Last Edited: Sat. Feb 3, 2018 - 04:03 PM
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Project finished.

Two 33Ohm/5W resistors in parrallel giving 10W(~16ohm) in series with valve.

Valve is openning and current is floating near 185mA at 12-13.5Vdc
(depends how is battery charged)

Total cost 48cents compared with 12V->24VAC invertor (100$).
Many thanks.

I found in supermarket 8euro wattering timer with stepper motor and valve.
its powered with 2/AA batteries and stepper is rotating valve plug in single direction. This solution is more energy effecient as my old-valve which need 2.4W per hour and my micro-drop wattering require 2-6h open valve.
I think I will nextime look at lathing-valves or hacking existing wattering timer :) in Winter

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dxr,
Can you please provide a final sketch showing all the components of the solution including diodes and capacitors if any.
Thanks

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Verry simple scheme. You have to test if your valve is inbrush with same resistors values and not heating or smoking.

Attachment(s): 

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From the previous posts, it was mentioned that a Adding a capacitor (few thousand micro) at 16V after the resistor and a diode will improve the performance.

Can somebody specify a bit more? i.e., in relation to the latest sketch I presume the capacitor should bridge parallel to the the valve, between the resistors and the valve, but what about the diode, where should it be?
Thanks

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I have a 24 vac standard heating and cooling system. The 24 vac also controls the solar hot water system. If the power goes out I cannot heat the house because the natural gas valve uses 24 vac and the piezoelectric igniter uses a 24 vac coil to strike the flame. Of secondary importance is the solar hot water system, and finally the AC but of little importance since power is out anyway. A 12 (13.4) volt car battery can power a Home Depot converter to produce quasi 120 vac ( actually a modified square wave) which then passes to a standard 120 to 24 volt transformer, but the modified square waves gets in the way, it produces spikes out of the transformer which cause early failure of the natural gas valve. Such a system is not too expensive, but it wastes a lot of battery energy. Putting a sizable capacitor on the 24 vac removes some of the spikes but degrades the voltage to 20 vac and also causes early failure. The power often goes out for five days right in the middle of a terrific winter storm, followed by very low temperatures. The house gets pretty cold. 12 Vdc chopped into a square wave and then filtered into a sine wave is about 4.8 volts AC RMS, so the transformer would need to pump that up to about 68 volts AC peak to peak to be 24 vac RMS and deliver at least 1.5 amps to power both furnace and hot water systems.

Chuckieboy

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It would be possible to chop the 12 Vdc at, say 90 KHz, then use a very low weight and efficient high frequency transformer to transform that to 136 volts peak to peak with a center tapped secondary, rectify the 136 volts into 68 volts, filter it to quasi DC and then chop that at 60 Hz, and filter out the remaining 90 KHz to get 24 Vac RMS with high efficiency.

Chuckieboy

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A little history on the use of AC vs. DC to control plant operation. Imagine a time before decent semiconductors. You want to control a valve or motor in your factory. You hook up a transformer to the AC line coming into your plant because want low voltage controls so you don't kill your employees if they touch the wrong wire. The low voltage AC was cheap and easy to make and safe to handle. Why 24 volts? I don't know, perhaps to reduce line losses. Don't ask how I know this.

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This looks like the most reasonable solution to all the real world people who don't understand what a resistor and all the electronics terminology in his thread.

I found one by some Taiwan co but this one is easier to get and it is same price or lower than a 150 watt samplex 120w inverter with a .5 amp no load draw. (http://samlexamerica.com/products/ProductDetail.aspx?pid=546)

I have a 30 watt panel and a charge controller from battery minder and battery and plan to remove the transformer from the sprinkler system and tie this straight in. Done! No soldering.

**The timer will not take a modified sine wave if you are using hunter anyways...iICC 800PL gets error code with another 120volt inverter that was too big anyways. Being off grid you need smallest inverter for no losses of wattage otherwise you will need to buy big expensive batteries. This is perfect solution because they are designed with pure sine wave and you should have no error codes then and there are smallest loss on the no load I have found. .2 amps...my solenoids draw .52 amps per station and the real factor is rain days and sizing the batteries which is why I am looking for this inverter and why it is so awesome . The inverter I have uses 4.25 amps !!! 400 watt . That's more than the solenoids would have used .so I figured it out and I need about 3 hours of watering time on those .52 amps per station at 120 vac = 67.2 watts x3 hours of watering time on the 24 stations . 1.7AH roughly. The no load draw is 4.8 AH per 24 hrs so I can get a really small battery compared to using the 300 or 400 w inverters using the 12dc -24ac 40watt inverter. So with off grid you see why not to oversize inverter. Bigger systems have more efficient inverters but you have to calculate those losses, I am by no means an expert in this but this the first off grid solar system I have had to do. And you need to keep it simple stupid. Don't waste your time soldering stuff in that the next guy will never figure out. Just stick with off the shelf mass produced items if you can. They are cheaper and less time consuming. Easier to maintain or replace is also a factor in some jobs.

Run off grid stuff on battery for at least 3 days to 5days for cloudy days in south California Arizona area unless you are in a really cloudy place. Discharging as little as possible 20-10% for those every day long nights. Hen figure you max worst case scenario. We dont Ned to water when it rains anyways right! ?

Battery is 1 amp hour = 1 amp p hour so get as many as you want if you had weather all figured out in your area you will have averages listed inline somewhere if cloudy days per month. But remember those are not consecutive and they are average. The most for San diego was 10-11 per month but that doesn't matter as much for sprinklers now does it . Let the battery back up take over and reset the clock every once in a lie moon isn't a big deal.

Well that's my take on it ! Thanks for tip on the cctv inverter! Worth 100$ easy.

Matt Carter

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Carterselectricsrv wrote:
Thanks for tip on the cctv inverter!

???  According to my browser, the quoted is the only "cctv" on the page.  Closed-Circuit TV?

 

Anyway, ...

Selrahcgnol wrote:
...Home Depot converter to produce quasi 120 vac ( actually a modified square wave)...

 

Perhaps a computer-backup "UPS" would have a better inverter?

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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I used your idea of a resistor and capacitor, instead that I have them connected in parallel to each other. I can now switch the valve on and off quickly with no delay from the circuit.

 

Essentially the capacitor when discharged, acts as the short circuit across the resistor - that gives me the inrush current needed to activate the valve.

Then when the capacitor charges up to a certain voltage, it no longer allows current to flow through it, so the current will flow through the resistor instead - that gives me the holding current.

When I want to deactivate the valve by opening the switch, the capacitor discharges via the resistor in a very short time - that gives me a very fast reset time.

 

The resistor and capacitor values that I've chosen were not calculated at all but using the spare parts I have accumulated. I have tested different capacitor and resistor values and this is what works for me.

 

My project was to connect the rainwater tank to the toilet, at first I powered the valve using a 24Vac (6VA) isolated adapter from a Christmas light set, but as it spent most of the time on standby, a considerable amount of heat can be felt from the adapter and I don't like to waste energy and money. So when I used the circuit as in the diagram I got these measurements:

 

Resistor = 180 ohms

Capacitor = 470 uF (micro Farads)

Valve's holding current for 24Vac = 230mA (5.5VA)

Valve's holding current for 12VDC direct connection to battery = 680mA (8.4W)

Valve's holding current for 12VDC circuit as in diagram = 50mA (0.6W)

Standby power for 12VDC circuit as in diagram = zero

 

Using the circuit in the diagram compared to a direct battery connection, I got the holding current's efficiency improvement of 92%.

 

P.S The Battery is being recharged by solar panel, and is used for another purpose. The circuit connected is piggyback-ing from it so it didn't cost me anymore money.

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