Drive bank of solenoids with a PWM signal?

Discussion in 'General Electronics Chat' started by web, Jun 12, 2009.

  1. web

    Thread Starter New Member

    Feb 17, 2008
    I would like to drive a bank of 20 solenoid valves (i.e. coils) with a PWM signal and I'm looking for any suggestions.

    Here's a bunch of details for those interested.
    I have some European proportional control solenoid valves that I want to put through their paces. The solenoid valves are air only and will be used at 15 bar. The solenoids run on 12 volts DC and I have 10 each of 2 different types. Type A has a 34.9 mH, 9.6 ohm coil and type B has a 21.2 mH, 6.1 ohm coil. Both of the solenoids draw a maximum average current of 1 amp when being driven with a PWM signal. The manufacturer uses an SPD25N06S2-40 N-channel MOSFET to drive each solenoid individually.

    I am going to run these units until they fail and have programmed a complex PWM signal in to an arbitrary waveform generator. The PWM signal is normally on and runs at 200 Hz with a complex algorithm to vary the duty cycle. The maximum output of the arbitrary waveform generator is + and - 5 volts peak to peak. I am using a 12 volt, 60 amp power supply to drive the solenoids. My plan is to run all 10 "type A" solenoids in parallel with a high power driver circuit and run all 10 "type B" solenoids in parallel with a second duplicate circuit.

    My initial thought was to make a little amplifier circuit to drive and bunch of FETs in parallel to switch the 12 volts with the PWM signal. I then recalled we had a 60 amp SSR (solid state relay) laying around so I hooked that straight up to the arbitrary waveform generator and it worked, but I don't like the slow response time of the SSR which is 1 millisecond. It's just far too slow for me. I am now thinking of using a 100-amp IGBT module to drive the solenoids.

    Now the questions.
    Question 1: Being quick and easy is more important than being inexpensive. So how would you suggest I drive the solenoids?

    Question 2: The sales person for the solenoid valves told me NOT to use a reverse polarity diode to suppress the back EMF across the coils. He could not tell me why and did not know electronics well enough to convert the Swedish in to English. So I am thinking of using back to back zeners (two 15 volt zeners with the anodes connected together) instead of a reverse polarity diode. What do you think?

    Thanks in advance for any help, comments or suggestions you may have.
  2. bertus


    Apr 5, 2008

    Can you post a schematic of the setup you have at the moment?
    This will make things more clear than a lot of words.

  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    The diode might slow the solenoid to much, try a .1μF cap in series with an 18Ω[ 2X coil resistance], combination in parallel with coil. Problem, if paralleling a bunch, might need to divide R by number of solenoids. I would also use a single zener V rated at around 2/3 of drivers break-down V, wattage ?, maybe 10 or better.
  4. web

    Thread Starter New Member

    Feb 17, 2008
    Thanks for the reply. The schematic is below. To simplify the first message...
    Question: How would you drive a high current inductive load?

    Thanks for the input, I haven't heard of the cap/resistor combination before. I will give it a try.

    The single zener idea confuses me. I am guessing it would be used with the anode to ground and the cathode to V+ but wouldn't this be the same as a reverse polarity diode? (see zener.gif below) Any additional information you could give me would help a great deal. Thanks.
  5. web

    Thread Starter New Member

    Feb 17, 2008
    Anybody else here have experience with high current inductive loads?
  6. VoodooMojo

    Active Member

    Nov 28, 2009
    I think you are on the correct path with the parallel mosfet driver idea.
    Attached is a photo of a board used for almost exactly the same purpose as you are describing. It was used to operate water valves for a water fountain display. Not unlike but nowhere near as grand as the Bellagio.

    This board is using 2SK2753 N channel mosfets in parallel. Datasheet attached.
    Current capability of this board w/heatsinks was well over the 160 amps the circuit was used for.

    Some of the boards we build for hydraulic control systems utilize BTS650.
    It is a highside high current power switch. We use this for it's diagnostic feedback and current load sense abilities as well as the high current abilities. Many hydraulic valve coils can be simultaneously activated while operating at 3000 psi levels. Operating load current is 70 amps with a 130 amp current limitation. Datasheet attached also.

    A possible reason that the external suppression diodes were not required is that they may be internally installed in the valve coil already. A datasheet on the valve coil will reveal this. A diode across the coil would indeed slow the valve down. The valve spring would be what is pushing the valve back not being assisted by the collapse of the magnetic field. Many proportional hydraulic valves are pulsed at 140Hz. They will not have a diode across them.

    It would be great to see a high-speed camera's view of some of this stuff.
    Last edited: Jan 8, 2010