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Solenoids: AC vs. DC power?

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  • Solenoids: AC vs. DC power?

    I'm working (in the planning stages) on a 2 "cylinder" solenoid beam "engine" to go on my desk at work. As usual, it'll be made entirely from stuff I have on hand.

    I plan to use a couple 110 volt washing machine water valve solenoids. I just won another KBIC-120 speed controller on the-bay but this one has an aux. board with forward/rev relays to go on my CNC lathe. That will leave me with an extra KBIC-120 so I thought why not use it to control the speed of said hypothetical solenoid engine?

    Yuse guys think that'll work? Any danger of the solenoids creating bad Ju-Ju back feed that'll kill the controller electronics? AC solenoids any different than DC solenoids? I'd like to use these solenoids to experiment with and maybe wind my own later.

    I know, it's a big assumption on my part that I can build the thing and get its timing and efficiency to a point where it would need slowing down but hey, I can dream can't I?
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    The main reason I always spec in DC solenoids is not only is a DC magnetic device more efficient, more importantly they are not as likely to fail and burn out the coil and/or blow a fuse if the armature sticks or if someone happens to push the manual operator over when it is energized.
    On a DC solenoid, the current is limited by the DC resistance which does not change whether the coil is picked up or not, as opposed to AC where the armature has to be shifted in order for the inductive reactance to be low enough.
    To eliminate back emf spikes on AC type requires a R/C snubber, the DC types use a reverse connected diode.
    A diode has the effect of slowing the release rate, but in all practicality this is not an issue.
    Max.
    Last edited by MaxHeadRoom; 07-16-2011, 01:11 PM.

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    • #3
      What Max said.
      Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
      ~Practitioner of the Electromechanical Arts~

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      • #4
        just bridge rectify your 110V and drive the solenoids with DC
        no need to cap smooth, the coils will iron out the lumps
        the slug (shorted turn) may slow things a little but won't be significant in your app
        as mentioned. a reverse diode across the coil will clamp back EMF
        Just got my head together
        now my body's falling apart

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        • #5
          Originally posted by Swarf&Sparks
          just bridge rectify your 110V and drive the solenoids with DC
          no need to cap smooth, the coils will iron out the lumps
          the slug (shorted turn) may slow things a little but won't be significant in your app
          as mentioned. a reverse diode across the coil will clamp back EMF
          The only problem I can see with that is the resistance is going to be way too low and may burn the coil out.
          Using a AC magnetic device on DC you do not have the inductive reactance to lower the current.
          Use a meter across the coil and you can use plain ohms law I=E/R to figure what the current will be.
          Max.

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          • #6
            fair nuff max, in that case just half wave rectify with a single diode
            even lumpier but at 60 hz I still ont see a prob in that sort of app, particularly as the solenoid has the slug
            Just got my head together
            now my body's falling apart

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            • #7
              Thanks all, I just checked and the resistance is 1120 ohms, or a bit less than .1 amp at 110v. Is that correct? 11 watts, not gonna be ate up with power, eh?
              Milton

              "Accuracy is the sum total of your compensating mistakes."

              "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

              Comment


              • #8
                Originally posted by Swarf&Sparks
                fair nuff max, in that case just half wave rectify with a single diode
                The current has to reverse in order to take advantage of inductive reactance, IF the solenoid has a shading ring, this will only have full effect on true AC.

                Originally posted by DICKEYBIRD
                Thanks all, I just checked and the resistance is 1120 ohms, or a bit less than .1 amp at 110v. Is that correct? 11 watts, not gonna be ate up with power, eh?
                Is this a 120VAC solenoid? I have Never come across an AC solenoid that high DC resistance, is there a model number on it?
                That value I would expect on a DC version.
                BTW, that sol on AC will draw much lower current than that when you factor in the reactance which is essentially in series with the DC resistance.
                Max.
                Last edited by MaxHeadRoom; 07-16-2011, 02:58 PM.

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                • #9
                  Ohms laws doesn't work well on ac - inductance needs to be known. When running AC solenoids on DC, I measure the AC current, then put a power resistor in series with the rectfied ac so the rms current remains the same.

                  I do this with garden irrigation valves - they are really noisy on AC - but you don't notice it until they are mounted inside the basement!

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                  • #10
                    "this will only have full effect on true AC."

                    true, but it will slow (slightly) operate and release on DC if cycle times are fast

                    cut me some slack man, its 02:35 here and I may be suffering mild ethanol fatigue

                    I was originally thinking of operating 24V AC gear on 12V DC but, as I said, the grey matter is getting even greyer at this time of day
                    Just got my head together
                    now my body's falling apart

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                    • #11
                      Originally posted by Swarf&Sparks
                      as I said, the grey matter is getting even greyer at this time of day
                      Tell me about it

                      Originally posted by lakeside53
                      Ohms laws doesn't work well on ac - inductance needs to be known.
                      If you have the coil DC resistance and wattage or current and operating voltage you can calculate the inductive reactance from the total impedance.
                      As a general rule, I have found the reactance to be around 4 to 5 time the DC resistance.
                      Just as putting a resistor in series on DC is wastefull, so is the DC resistance of the coil on AC, the ideal is 0 ohms.
                      Max.

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                      • #12
                        of course we could just increase the frequency of pulsed DC til the current is where it should be
                        Just got my head together
                        now my body's falling apart

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                        • #13
                          Unfortunately it is not AC (Alternating current), by increasing the DC ripple rate you are moving closer to pure DC, many confuse DC ripple with AC.
                          i.e. there is no current reversal (alternation) , however much you increase the frequency.
                          Remember, even on high (100%) ripple DC, the (important) coil current does not follow the voltage wave form by going to zero every 120th sec, the mean current is fairly constant, especially with a back EMF diode maintaining coil current during the voltage zero transitions. ,
                          Max.
                          Last edited by MaxHeadRoom; 07-16-2011, 04:24 PM.

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                          • #14
                            Sheesh, what a hassle.... I finally got Photobucket to cough up an old picture. Here's what they look like after I removed them from the old (leaking) valve assy.



                            Unfortunately I'm not up to speed on all the (to me) electrical esoterica you learned gentlemen are discussing. I suppose I can do a quick trial on the bench to see what happens. I better wait until I get the other controller in hand before trying anything.
                            Milton

                            "Accuracy is the sum total of your compensating mistakes."

                            "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                            Comment


                            • #15
                              It has been my experience that DC solenoids have better response. An AC solenoid may be energized at any time, but will respond to the AC sine wave and will have two zero crossings where nothing happens. A single-acting solenoid motor would experience some interaction between rpm and the 60 (or 50?) cycle AC line frequency. The max speed might even be limited with AC more than DC.
                              Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                              ~Practitioner of the Electromechanical Arts~

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