8 Replies Latest reply on Aug 28, 2017 2:26 PM by ntewinkel

    PWM for a solenoid?

    Eavesdropper

      I want to drive a solenoid rated at 12V 1A. As you can see, the power demand is quite high. Can a solenoid be driven in PWM?

       

      If so, what are some guidelines? IE: the minimum duty cycle to keep a solenoid active, etc.

       

      Thanks ahead of time.

      E

        • Re: PWM for a solenoid?
          YT2095

          In my experience with solenoids, you may well need the 1 Amp initially to pull the core inwards, after that, the further in it gets the less current you`ll need, and Holding current when in the locked position can be significantly less than 1 Amp.

          so you May be served well with a simple large value reservior capacitor for that initial hump.

          I`v had solenoids that you`de be really hard pushed to pull apart when held with a simple watch battery when in the locked position.

           

          might be worth experimenting with

          1 of 1 people found this helpful
          • Re: PWM for a solenoid?
            DonNZ

            Gidday E

             

            Can you use PWM , Yes you can.

            Often this is how it's done, usually by duty cycle rather than frequency. Alot of motorcars use this as a way to control engine idle speed, say 1500 hz and vary the duty cycle to control position to respond to load changes ( a/c, lights, heater fans , windows, engine cold , engine transmission engaged )

            This to maintain a steady idle.

             

            plunger or armature = the moving bit up the guts of your solinoid winding that does the work. Often coated to reduce friction and corrosion.

             

            Check out your local good hydraulic shop ( ask a local personal lift hire shop which one ) and you'll actually buy a black box that'll do the job if you don't wish to build it yourself. - 12v in 0- 12 v out knob to adjust duty cycle

             

            As to your second question duty cycle and frequency. This you'll need to figure out by trial and error

             

            How strong is the spring or force resisting the solinoid plugner to travel inward ?

            how much can your solinoid plunger pulse between each cycle before it's too much ?

            What frequency and harmonic of this will cause other devices around a prroblem ?

             

            where do you wish the soliniod plunger to be relative to rest and fully home ? As the more home the plunger is the more effect your magnetic force has on it therefore the less electrical energy will be required to maintain position.

            12v Car starter soliniods generally have two windings a pull in  @ approx 30 amp that gets disconnected once the contacts are made and a hold in 5-10 amp thats connected all the time solinooid is energised.

            Some LPG valves use a pulse and hold circuit ( using pwm)  to reduce power consumption while the gas is turned on.

             

            Put a diode across the winding to reduce killing your control circuit from the back emf from the collapsing magnetic field .

             

            Good Luck !!

             

            Regards Don

              • Re: PWM for a solenoid?
                bradshawlupton

                Similar solenoid question.

                 

                can I, with a pi or esp8266 board, use pwm to open/close a solenoid without water hammer.  I have caused too many of my terrible solder plumbing joints to leak, banging the water on and off.  Tnx.  A solenoid is $30 for 1/2" water, a lovely rotary gentle valve is 5x that cost.  Bradshaw at buzzards bay.

                  • Re: PWM for a solenoid?
                    michaelkellett

                    I haven't tried but I think that unless the valve you buy is designed for progressive operation it won't work well.

                     

                    We have a very long pipe run to an electric shower and after the first one failed with control valve burst due to the pressure surge when it cuts off I fitted a pressure reducer, and this tamed the flow rate in the pipe enough to control the surge problem.

                     

                    You can also buy flow restricting valves.

                     

                    Of course my suggestions are a bit of a bodge , the proper proportional valve is the good way.

                     

                    MK

                      • Re: PWM for a solenoid?
                        ntewinkel

                        Michael Kellett wrote:

                         

                        ... unless the valve you buy is designed for progressive operation it won't work well.

                        Right, Sprinkler valves are like that - the solenoid opens a small waterway, and the water pressure itself then opens the main valve. Changing the rate of opening/closing the solenoid would be very tricky and might not have much, if any, effect. But I would be very interested to see if you can make that work.

                         

                        And yes, what Peter said about using a water hammer arrestor is the easiest solution - for a sprinkler system you can even add your own by having a vertical length of pipe with a large air chamber in it to absorb the shock wave.

                        Other ways to reduce the hammer are to reduce water pressure, or in the case of a sprinkler system you can slightly overlap the zones and have the smallest zone (least water flow) last.

                         

                        Cheers,

                        -Nico

                      • Re: PWM for a solenoid?
                        peteroakes

                        You can also get specific devices to absorb the hammer in the pipes. this would be your best solution, using PWM will introduce a whole load of other complications, RFI, Severe back EMF to name a couple

                        1 of 1 people found this helpful