solenoid proportional valve driver

Siri

Can I use a DC motor driver to drive a solenoid propportional valve with the prop contolling the driver.

The proportional solenoid valve is rated at 5V dc and 11 ohms. @ 500mA.
I plan in using 2 of them in my experiment.So I thought it would be nice if I can use a motor driver like "Pololu Micro Dual Serial Motor Controller driver "

If not any suggestions/advise.

Thanks.

Siri

Peter Jakacki

Siri, you only need a transistor that will handle that current and even the small TO92 packs easily handle that current. Use the PWM object and connect through a 220R resistor to the base of say a 2N2222 with the emitter to ground and the collector to the solenoid. Don't forget to use a diode across the coil. Something like a ZTX689B can handle 3A with a high gain of 500 and it's only a tiny TO92ish package.

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*Peter*

Siri

Peter,

Thanks.

siri

Martin Hodge

I'd be interested in learning more about your valves. I need something to control water flow rate through my 3 water-source heat pumps.

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Martin Hodge
"I like Pie"

DavidGreg

I"m using IRF3708 to control dc solenoid valves that pull about 8 amps at 12V. I use the PWM module to drop the voltage down once they are open so they don't pull as much current all the time.

http://www.irf.com/product-info/datasheets/data/irf3708pbf.pdf

Peter Jakacki

Most proportional valves only need to be run at a few hundred Hertz (400Hz) so using MOSFETs for higher currents and directly driven from the Prop's I/O is workable.

We on the forum normally use a series resistor from the Prop to the gate of the mosfet mainly to protect the Prop as the gate itself doesn't need current limiting, but try to keep this value very low (around 100R) when using PWM as the gate capacitance has to be charged/discharged very quickly. If the valves are simple on/off type and not proportional then this is not important.

The IRF3708 mentioned seems to be the mosfet of choice with the Prop as it has a very low Rdson even at 3V drive. For the lower currents of around 1A or so the small bipolar (ZTX689) approach makes more sense unless you don't mind having a large TO220 package on the pcb. The bipolar approach allows much higher PWM frequencies to be used as the Prop can turn the bipolar on/off very quickly.

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*Peter*

Siri

Shmoopy'

The data sheet for the proportional valves I am playing with is attached.They are used for gases as far as I know.

Siri

Siri

Peter et al

I an still trying to make the proportional valves to work.
I have used 2 circuits to test.The one with the transistors work but only when the load a LED - but when the valve is attached to the load it does not work.When I measure the
the voltage across the load - LED --> 5.1V
- Valve -->0.5 V

When I use the FET circuit - the valve opens and closes but no proportionality.

I have attached the circuits,valve data and the code I am using.

I think it is a ain adequate current issue - help me to solve it.

Thanks

Siri

Peter Jakacki

Siri, your code only changes the frequency of 12.5ns pulses which essentially this is what DUTY mode is, it is not PWM. An RC circuit can filter these pulses for analog purposes but you need digital pulses so you need the PWM object, the counters can't generate PWM directly (i.e. 20us on, 80us off).

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*Peter*

Siri

Peter.
I will try it out with PWM object.

Thanks,

Siri

Peter Jakacki

Siri,

I was in a big rush before so I didn't get time to look at your diagrams. It seems the MOSFET circuit which was hiding in a DOC file is totally unsuitable (BTW, try to post these as images). For starters the MOSFET configuration with the load in the drain source* will increase the Vgs threshold relative to ground which is already marginal for this MOSFET, it just won't work, do not use this configuration ever. Secondly the 10K gate pullup will have insufficient drive for PWM operation to charge/discharge the gate capacitance quickly enough. Thirdly operating inductive devices off low voltages like 5V means you need a lot more current than a 12V or 24V coil plus the 5V is normally used to drive the 3.3V of the Propeller in a lot of systems. Best to keep all that noise etc away from digital systems.

Your basic bipolar circuit is fine although the 10K base-emitter resistor is not really necessary but then again I see a lot of transistor circuits copied without "adjustment". These base-emitter resistors were used a lot in analog circuits and early transistor and valve circuits to control cutoff. When the base driver resistor (270R) is driven by a 0V or 3.3V signal the other resistor is completely redundant. With no drive at all the transistor is effectively off until enough base current can flow to turn on the transistor. Ok, enough of that for now.

If you do use a MOSFET then please try the IRF3708 mentioned earlier. This is suitable for direct drive from the Prop and you don't really need any other components. Of course the big device is overkill and there are other ways of driving the solenoid, some of which I have already mentioned.

*Note: You may have seen this circuit for a P channel MOSFET which would work ok but your part# indicates an N channel. Also, the symbol you have used for the MOSFET is incorrect anyway.

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*Peter*

Post Edited (Peter Jakacki) : 3/6/2010 8:00:17 AM GMT

Siri

Peter,

Thank you very much specially for explaining the inner working of these circuits.I hope more smart people like you
teach us - who are willing to really learn electronics rather than just fixing problems and not know why.

Thanks again.

Siri