Hi forum,
Im new to arduino, and have a project i'd like to get started with, but could do with a few pointers.
i'd like to control a proportional solenoid valve, the valve is 12vdc and is controlled by varying the current from 0mA to 330mA.
I'd like to use a pot to vary the current. Connecting the pot is not a problem as there are loads of examples of reading a signal from a pot suppiled with 5v.
The part I could do with some pointers with is supplying 24v and a current of upto 330mA controlled by the signal from the arduino.
Or you can use a "Logic Level Power FET" that Arduino can drive directly. (Remember to put a reverse-direction diode across the solenoid coil to catch reverse voltage spikes..)
Thanks for your comprehensove reply!! that gives me a great place to start.
The valves are made by a company called SMC, they have a website with all their specs on, great little valves, they are magnetic, so i'm hoping PWM will work.
I was a e. tech at a snow plow hydraulic controls company a year back.
They used mosfets drivin via PWM to do proportional. One thing that comes to mind is every solenoid valve manufacturer has a different pulse frequency spec'ed so you'll need to check with SMC to see what Hertz they call for.
I'm seeing specs on SMCs website saying their one line of valves are current controlled devices that need a range of milliamps to control them.
Yes,the current controlled valves are what I want to use. Can these be done with PWM? Or is there an easier way of varying the current?
The spec for the one I've got is 24vdc 0-330mA. I've only got rather sketchy knowledge of electronics, it seems to me that this should be very easy to do, and I'm just missing something silly.
Any pointers on how to vary the current using the output from the arduino between 0 and 330mA (but not more than 330mA so the valve is protected) at 24vdc would be great.
In terms of my requirements, speed is good. They make larger versions of this valve, which i would also like to use (if i every figure out how to wire the things up!) so whatever circitry i use will need to be adaptable to allow me to fit different spec'd valves at a later date. (perhaps by changing the spec of resistors etc)
I don't really want to power this straight off of the arduino board (i believe thats not possible anyway) and have a 24vdc supply avaiable. it feels like there should be a simple arrangement of componants that will make this work. Problem is i can't find any other examples of anything similar out there.
mikebadley:
i'd like to control a proportional solenoid valve, the valve is 12vdc and is controlled by varying the current from 0mA to 330mA.
I'd like to use a pot to vary the current. Connecting the pot is not a problem as there are loads of examples of reading a signal from a pot suppiled with 5v.
The part I could do with some pointers with is supplying 24v and a current of upto 330mA controlled by the signal from the arduino.
Well, one thing is to get a few things in order re. voltage/current. You start out by saying the valve is 12VDC, but then want to supply 24VDC. In reading the spec sheet, I see the valves can be ordered in either (nominally) a 12V or 24V configuration. But current is proportional to voltage, and current is the controlling item here. The voltage needed to drive the coil with current N will be determined by Ohm's law, V=IR. If we assume that the nominal voltage is somewhat close to what will be needed at maximum current, then we can calculate the coil resistance by V/I=R:
12/.330=36
24/.165=145
But what I suspect is that the voltage rating of valves is there as a guide for what sort of power supply you'll need, and maybe as a ceiling value to avoid burning out the coil. I didn't examine that datasheet in detail, but I suspect there are wattage ratings on those things, which are likely close to what you'll get if you calculate the wattage from the above. The further point is that as the current decreases, so will the voltage.
If I were trying to do this, I might look at current regulators, with the control pin driven from the Arduino's analog out. But I admit I haven't thought through all the details of that.
OK, it seems clear that you need to control the CURRENT:
---------------------( COPY from http://content.smcetech.com/pdf/PVQ_EU.pdf )--------------------------
Caution
Power Source Selection
This product makes proportional control possible with constant current. If controlled with voltage, the output flow rate cannot be kept constant due to current fluctuation. Use a stable DC power source with sufficient capacity without much ripple.
-----------------( END COPY )----------------------
So, I think you CAN start with the 24V, and use a Current Regulator (Can be implemented with most typical Linear Voltage Regulators like LM317T. )
---------------------( COPY from http://www.national.com/mpf/LM/LM317.html )--------------------------
it makes an especially simple adjustable switching regulator, a programmable output regulator, or by connecting a fixed resistor between the adjustment pin and output, the LM117 can be used as a precision current regulator.
-----------------( END COPY )----------------------
Google "programmable current regulator" and you'll find a LOT. I'm sure this can be done with Arduino...