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  • Solenoid question..

    I have an unidentified solenoid I want to build into a little 'solenoid engine'.

    The solenoid is the type where the coil is in a metal frame, the armarture has a pointed end and the end of the cylinder is blocked with a matching socket. I presume this metal work is all part of the magnetic circuit.

    Although the solenoid may well have been intended for AC use it is much more powerful on rectified AC of the same voltage.

    The coil is well sealed and I cannot judge the wire gauge.

    The coil is 500 Ohms resistance and the question is, what voltage should I use? Or do I just increase voltage until the coil warms up, 260V and it is still quite cool.

  • #2
    The tapered end of the armature is a typical feature in DC solenoids that improves initial pull-in when the armature is at full extension (out) and the solenoid is weakest.

    What is the stroke? By this I mean usable stroke, not how far the armature moves before it falls out of the bore. Also, what is the diameter of the armature, coil, length of the frame, etc.

    Knowing the coil resistance and nothing else, you will have to rely on tremperature rise to know the limits of the solenoid. Most automotive and industrial solenoids must survive at least 85°C. Consumer goods, I don't know.
    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
    ~Practitioner of the Electromechanical Arts~

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    • #3
      Hi Weston. The diameter of the armature is 20mm and the length of the coil about 50mm, I am aiming to use only 5mm of the stroke (the last 5 of course).

      I think this solenoid came from an ancient computer band printer the frame of which is now my workbench.

      I made a very crude video of a very crude little engine I made to test the general idea. I put a slot in the connecting rod so that the solenoid can bottom well prior to TDC at about 300 degrees and the coil is energised for about 90 degrees prior to that point. Voltage is rectified (but not smoothed) 110.


      http://www.flickr.com/photos/[email protected]/5956704873/

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      • #4
        I think your "crude" little model is pretty well done.
        5mm sound about right for your stroke. It looks like it could go a little longer, but if you dont need it...

        I think I would choke up on the connecting rod so the solenoid armature never reaches lockup with the pole piece (that's what we call the cup on the end of the stroke). What kind of a switch? Adding a diode across the solenoid coil will prolong the life of the switch. A brass tube, if it doesn't already have one, inside the bore of the coil, for the armature to slide in, will also prolong the life of the solenoid.

        Oops, just looked at the second video. looks like you're covered with the bridge rectifier.
        Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
        ~Practitioner of the Electromechanical Arts~

        Comment


        • #5
          The problem with coils is they take FOREVER to heat up. All that insulation beween the copper turns does not help at all. What might be cool to the touch after 30 seconds, might be smoking after 10 minutes.

          When operated off DC, basicly its turning all the power into heat.

          Most solenoids are not rated for continious use at thier rated voltage. Usally more like 10% duty cycle.
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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          • #6
            Originally posted by Black_Moons
            The problem with coils is they take FOREVER to heat up. All that insulation beween the copper turns does not help at all. What might be cool to the touch after 30 seconds, might be smoking after 10 minutes.

            When operated off DC, basicly its turning all the power into heat.

            Most solenoids are not rated for continious use at thier rated voltage. Usally more like 10% duty cycle.
            So you may have to add a fan to the flywheel and some ductwork.

            Brian
            OPEN EYES, OPEN EARS, OPEN MIND

            THINK HARDER

            BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

            MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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            • #7
              Originally posted by Weston Bye
              I think your "crude" little model is pretty well done.
              5mm sound about right for your stroke. It looks like it could go a little longer, but if you dont need it...

              I think I would choke up on the connecting rod so the solenoid armature never reaches lockup with the pole piece (that's what we call the cup on the end of the stroke). What kind of a switch? Adding a diode across the solenoid coil will prolong the life of the switch. A brass tube, if it doesn't already have one, inside the bore of the coil, for the armature to slide in, will also prolong the life of the solenoid.

              Oops, just looked at the second video. looks like you're covered with the bridge rectifier.
              I am not sure why the armature should not touch the pole piece? There is some rubber like buffer in there, do you think I should add something else.

              Yes, the bore tube is brass and there is a diode, but methinks it might actually be in the wrong place! I will check on that!

              Comment


              • #8
                Originally posted by Black_Moons
                The problem with coils is they take FOREVER to heat up. All that insulation beween the copper turns does not help at all. What might be cool to the touch after 30 seconds, might be smoking after 10 minutes.
                Good point. The coil is about 30% duty cycle in that lash up but I will try to reduce that, it is pretty much a process of fiddling with the prototype before building a pukka version of the 'engine'.


                When operated off DC, basicly its turning all the power into heat.
                Sorry but I do not understand that comment.

                Most solenoids are not rated for continious use at thier rated voltage. Usally more like 10% duty cycle.
                Unfortunately I have no idea what the rated voltage of the solenoid would be.

                Comment


                • #9
                  Originally posted by Black_Moons
                  The problem with coils is they take FOREVER to heat up. All that insulation beween the copper turns does not help at all. What might be cool to the touch after 30 seconds, might be smoking after 10 minutes.

                  When operated off DC, basicly its turning all the power into heat.

                  Most solenoids are not rated for continious use at thier rated voltage. Usally more like 10% duty cycle.
                  A lot of misconception here.

                  Solenoids do take some time to heat up, but not forever. Copper is copper and a pretty good conductor of heat. When a coil starts to heat, it is conducted throughout the coil, the enamel insulation notwithstanding. Insulation failure due to heat may occur deep within the coil, but only because the heat happened faster than it could be radiated or conducted at the surface.

                  Regardless of AC or DC, heat is a by-product of current flowing through a wire. The solenoid does its work when the armature is moving, and requires the designed current to move the armature. After the armature is fully stroked and the armature is resting against the pole piece, current supplied to the solenoid can be reduced to only maintain holding force.

                  Most solenoids are designed for continuous duty - at least those designed where I work. http://pontiaccoil.com/indexhome.html
                  Indeed, very few are designed for reduced duty cycle, and even then many of those are tested for durability at continuous duty.
                  Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                  ~Practitioner of the Electromechanical Arts~

                  Comment


                  • #10
                    Originally posted by The Artful Bodger
                    I am not sure why the armature should not touch the pole piece? There is some rubber like buffer in there, do you think I should add something else.

                    Yes, the bore tube is brass and there is a diode, but methinks it might actually be in the wrong place! I will check on that!
                    The armature can touch the pole piece as it is indeed intended to in normal solenoid operation. However, your application will rapidly subject the solenoid to more cycles than it was designed for. This will probably be OK as you aren't working it very hard and if you keep the voltage down to only that needed to run the engine, it should run fairly cool.

                    Back to the armature contacting the pole piece. Why hammer the parts together if you don't need to? Even the buffer can wear out with repeated hammering. Also, the extra slop you've built into the connecting rod is another point where the parts will hammer and eventually wear out. Why not make the rod close fitting and the armature motion stop just before contacting the pole piece. You might even allow it to touch the buffer slightly. Also, open the switch contacts before the armature reaches full stroke. This will allow the magnetic field to collapse before the armature begins to withdraw, giving smoother operation.

                    Notwithstanding all my words about smooth operation and prevention of hammering, your video had a good measure of charm that reminded me of a hit-and-miss engine.
                    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                    ~Practitioner of the Electromechanical Arts~

                    Comment


                    • #11
                      Originally posted by Weston Bye
                      Regardless of AC or DC, heat is a by-product of current flowing through a wire. The solenoid does its work when the armature is moving, and requires the designed current to move the armature. After the armature is fully stroked and the armature is resting against the pole piece, current supplied to the solenoid can be reduced to only maintain holding force.
                      There are a few differences between AC & DC solenoids/relays.
                      The AC type only has the edge over DC due to fast pull in due to inrush, after that the DC has the edge, i.e. requires less force once the armature is pulled fully in.
                      AC types cannot afford a reduction in voltage.
                      DC versions draw the same current whether pulled in or not, AC require fully pulled in armature to reduce current to rated value otherwise burn out can occur.
                      The tendency of an AC sol/relay is to drop out every 120th sec on AC, so a shading ring is used in order to create a phase shift in one part of the coil to allow current flow on the zero voltage/reversal transition.
                      Placing a diode across the coil on DC types recirculates the back EMF, this will cause delayed drop out, which can be noticeable on high speed operations.
                      Max.
                      Last edited by MaxHeadRoom; 07-21-2011, 10:45 AM.

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