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Topic: Arduino + AC Solenoids (Read 3141 times) previous topic - next topic

daniele_dll

Hi to all,

while i know well that this argument has been discussed more and more times, i have some questions because i don't understand NOTHING about elettronic stuff (well, i love programming and i'm playing with arduino :))

For my project i initially choiced some 9v bistable electrovalves (that open when power flows in one direction and close when they got it inverse) and i'm controlling them using a TB6612FNG.
Now i want to try to control solenoid valves for many reasons, the most important is that they are faster and i can use PWM to control how much open the valve and how much faster open it.

Solenoids i want to use need 24VAC and 300mA to work, they will be powered by a 230vac to 24vac transfomer

For this reason (PWM) i can't use a normal relay, looking over the web (and arduino forum) i founded many many people talking about:
- Triac + Optoisolator;
- SSR.

As far i understand the SSR (Solid State Relay) works similarly like a Triac+Optoisolato based cicuit but i don't understand which is the difference between these two (well the SSR is self-packaged and don't need other stuff, but apart this?)

As far i understand, like the VDC solenoid controlled by a mosfet, i need a diode, which diode i should use? As far i understand, i should put a diode on the AC line, this is right or is a non sense? And, if yes, which is the direction of the diode on AC? (on DC it make a sense put the diode between vcc and gnd, but on AC?)

More, reading on the web it seems that may happen that because of a "zero crossing stuff" (really, i don't know what it means, it refers to the no power phase of AC?) the circuit (SSR or Triac+Optoisolator) may turn on on his own, i read about using a "snubber" (as far i understand a simple snubber could be composed by a resistance and a capacitor) to avoid these kind of activations, could someone give me more info?

I've founded this thread
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1230333861/all

And as far i understand, this circuit
http://lh4.ggpht.com/_liDL5ZFNsxs/SmUcmP5y9iI/AAAAAAAADw8/kXMf-cm_5aU/s800/ac_control.png

does exactly what i need, but it's for 120vac 60hz while i need for 24vac 50hz (well, i don't know which transfomer i'll use but it should maintain the frequency ... by the way i just need to fix the code if the frequency change) ... the only part i don't understand is in the lower right corner:
- there is an F1 (3A refers to 3 ampere?) that i don't know that it is, i don't recognize the symbol;
- what means ACN?

May i use 1/4 WATT resistences for that circuit? It's powered at 24v so it should be fine, right?

Side Question:
What i should change if i need to run that circuit over a 230v? I don't know yet, but there is the possibility that i need to control a water pump and to avoid pressure problem i want to be able to dimmer the power to reduce the output pressure.

Thank you!!!!
Software/Embedded/Web Developer, Linux Sys Admin

retrolefty

#1
Aug 10, 2012, 02:54 am Last Edit: Aug 10, 2012, 02:58 am by retrolefty Reason: 1
First, of all most solenoids are only full on or full off devices, much like a electro-mechanical relay. Trying to control a solenoid with a PWM signal is most likely to be very disappointing, they are not designed to act like linear actuators.

Second, even if you obtain a linear actuator designed for AC voltages (I've only come across DC models, but perhaps AC actuators exist?), trying to control most SSRs with a PWM signal just does not work. You need more special purpose AC SSR designed to be used via phase control.

Lefty

daniele_dll

Understood, ok i'm discarding PWM for AC Solenoids :)

Another question: if i send power with less frequency? If i power on the triac in a way to get a 45hz instead of 60hz, the ac solenoid will open slowly right? And if i send power with really lower frequency, it will close slowly? In this way may i be able to control how much open the internal valve?

Using the circuit posted above, if i send the power with a frequency that oscillate between 15hz and 45hz, should it open slowly and close slowly, right? Because i'm not cutting off the power to the inductive load, i'm just giving it less power.

Is this right?

Thank you!
Software/Embedded/Web Developer, Linux Sys Admin

kerimil

Quote
First, of all most solenoids are only full on or full off devices, much like a electro-mechanical relay. Trying to control a solenoid with a PWM signal is most likely to be very disappointing, they are not designed to act like linear actuators.
it's not only about solenoids - direction control valves are basicaly pneumatic equivalent of digital components - they are either ON or OFF (or in case of 3 way and 5 way valves they act pretty much like single throw switches)...

What you want is a proportional valve - you could regulate flow and openning speed with them but they are more expensive than direction control valves

To help you get the idea of what is a proportional valve imagine a ball valve with an RC servo attached to it

daniele_dll

understood :D

thanks for the info, i'll look for these kind of valves

just last question: these kind of valves are AC only or DC version exists too?
Software/Embedded/Web Developer, Linux Sys Admin

Grumpy_Mike

Quote
if i send power with less frequency? If i power on the triac in a way to get a 45hz instead of 60hz,

You can't send power with any frequency. That is what the power supply provides.

Why do you keep asking about AC solenoids? These do not have any proprieties that a DC one does not have appart from being powered by AC and AC is much harder to control proportionally.

daniele_dll

Quote

You can't send power with any frequency. That is what the power supply provides.


I asked why I do not understand almost anything electronic ^^

Quote

Why do you keep asking about AC solenoids? These do not have any proprieties that a DC one does not have appart from being powered by AC and AC is much harder to control proportionally.


i stopped asking about AC solenoids, in the last post i asked if Proportional Valve is only AC or DC based exists too
Software/Embedded/Web Developer, Linux Sys Admin

kerimil

Quote
these kind of valves are AC only or DC version exists too?
They are generally speaking DC only - mind you they are essentially servo motors/RC servos controlling a valve

you might want to write more about what you really need and what you're building - that would make things a lot easier

daniele_dll

I'm playing with garden automation trying to make a system capable to autoregulate water pressure using an electrovalve to regulate the water pressure and a water flow sensor ( this one http://www.seeedstudio.com/depot/g114-water-flow-sensor-p-1082.html?cPath=144_151 ) to check output pressure

my idea is to start a water pump and let arduino to control the single electrovalve adjusting opening for every final bistable electrovalve and let the water flow out with the right pressure without hydraulic parts to reduce pressure
Software/Embedded/Web Developer, Linux Sys Admin

kerimil

Wow sounds like a real pain in the ###... and honestly it can't be done with normal ON/OFF valves - they aren't designed to vary flow they can be set to either of their position and that's all....
ohh and they don't open fast enough to pulse width modulate them. Valves are mechanical devices - so their parts and fluid have inertia... even though some have very fast opening times (like 20-50ms) it just won't happen and work well enough

It would be a lot easier to vary the RPM of the pump - Have you considered that method ?

kerimil

#10
Aug 11, 2012, 02:01 pm Last Edit: Aug 11, 2012, 02:05 pm by kerimil Reason: 1
Quote
in the end i think will use a servo controlled valve that seems capable of doing this (btw, looking over the web i found a solenoid electrovalve capable to open and close in less than 5ms but they costs really a lot, more than 100€)
The real problem is that servo valves/proportional valves are even more expensive

If I were you I'd get a few simple flow control valves and manually adjust them so that the pressure would be the same in the entire system

The simplest flow control valve is a ball valve (but it's kind of difficult to adjust precisely) or a tap valve (pic below)


This idea has one major advantage - it's damn cheap and simple

daniele_dll

This is a great idea!!!! I can replace the knob with a cogwheel and control it through a servo!

I need to find a servo capable to apply the necessary strength to move it.

However ... this is a really great idea :DDD
Software/Embedded/Web Developer, Linux Sys Admin

Grumpy_Mike

Quote
I can replace the knob with a cogwheel and control it through a servo!

You don't get more than one rotation with a servo.
If you want to do this then look at a stepping motor. Mind you the speed will not be fast.

daniele_dll

mmm, sorry i made a mix :)

i talked about servos because i was thinking about ball valves, but with tap valves can't be controlled with servos

Thank you!
Software/Embedded/Web Developer, Linux Sys Admin

retrolefty


Quote
I can replace the knob with a cogwheel and control it through a servo!

You don't get more than one rotation with a servo.
If you want to do this then look at a stepping motor. Mind you the speed will not be fast.


Or get a quarter turn valve, lots to choose from in all sizes. Still would require a pretty high torque servo, but those are available also.


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