Announcement

Collapse
No announcement yet.

How to judge shield effectiveness?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by bklein View Post
    I don't know of any litz wire that is "commonly available". Could you post a link to a source/spec? I see some on ebay and could order some from a wire specialist, but I don't know of a "common" variety anywhere. Is that clear insulation the same stuff that is on non-litz speaker wire?
    In this case, commonly available means cheapest and ubiquitous thing you can find on local flee market or everywhere. Very little Cu inside and lot of plastic around. Very low quality and cheap product, not good for anything else, but just fine for PI coils, no mfg. specifications available.

    It consists of 2x 14 individual .15mm dia. uninsulated wires (something between #34 or 35 AWG) giving total cross section of some .25mm sq. (or like #23 or 24 AWG, to hell whit imperial units) per wire, but this is not important. Main reason i’m using this is larger insulation diameter (around 2mm) to keep wires separated and reduce coil self-capacitance. Also very nice to work whit mechanically. Similar conductor to insulation diameter ratio can be found only in specialized, high voltage rated, more expensive and hard to obtain cables. I never actually measured insulation specs, just tried it as is and coil worked just fine.
    Attached Files

    Comment


    • #17
      just to clarify then, it is common "speaker wire" as it doesn't look like litz from the photo...

      Comment


      • #18
        This is exactly same wire like posted in previous photos, (just may look different on pics, not exactly Hollywood production) may not be best for speakers, products of similar “quality” (this is almost junk but good for this purpose) may not be available everywhere.

        Regular “speaker” wire usually have larger cross-section conductors and less insulation around, but in this case, cheapest thing does the job.

        Comment


        • #19
          Thanks for info Tepco,

          I've made today coil with some 0.5 mm wire with insulation thickness 2mm, it took me some 18 meters of wire.

          Coil is coated with epoxy and for now unshielded, and on first test I got good detection so I'm pleased with results.
          I think is quite better than dual-field coil.
          Btw. the inside diameter is 12,5cm (DVD spindle cover) but outer diameter is 24 cm, probably because I wounded it damn tight.

          Tommorow i will play with some damping resistor value (it's bit tricky to do this without oscilloscope) and post results after.

          Regards Marko.
          Attached Files

          Comment


          • #20
            Coil out of speaker cable is not really lite due to heavy insulation.

            Better is to use some sort of UHF/CCTV cable with light (PE)foam inner insulation and remove outer shield and outer insulation of the cable. A little annoying work, but you can get lighter coil.


            Comment


            • #21
              In addition it seems focus on insulation material type is "out the window" and more distant winding spacing is of more benefit.
              So next are you going to try using two pairs instead of one?
              Or what about a double-sided pcb?

              Comment


              • #22
                We need a name for this new type of Tepco coil?
                something like twin parallel spiral.

                I have some twisted pair wire, I wonder if it would would work
                being wound like this coil.

                Correct me if I am wrong, but I think when he called it Litz wire
                I think in this case he meant multi strand wire as shown in the picture.

                Comment


                • #23
                  Originally posted by 6666 View Post
                  We need a name for this new type of Tepco coil?
                  something like twin parallel spiral.

                  I have some twisted pair wire, I wonder if it would would work
                  being wound like this coil.

                  Correct me if I am wrong, but I think when he called it Litz wire
                  I think in this case he meant multi strand wire as shown in the picture.
                  Already named. This is Tesla coil. And twisted pair would work also, read moodz serials here.

                  Comment


                  • #24
                    Curious, I visited my local Radio Shack today. They sell the common speaker wire - perhaps not enough on a spool - but also a couple other interesting varieties. One is a pair of flat wires already sold wrapped in a coil! The other is a wire that seems to have the center taken up by an insulator. This is marketed towards the audio afficianado.. but I wouldn't call the wire Litz.... Both of these are beyond my level of experimentation expense... I'll wait for one of you guys to spend the big bucks and report back...

                    Comment


                    • #25
                      Originally posted by 6666 View Post
                      Correct me if I am wrong, but I think when he called it Litz wire
                      I think in this case he meant multi strand wire as shown in the picture.
                      Multi-stranded wire is exactly what it says - many strands of wire twisted together. This makes it more flexible and less liable to break than a single solid core.

                      Litz wire is not the same as multi-stranded. In Litz wire, each separate strand is insulated from the other strands, with the main purpose of reducing eddy currents in the wires at high frequencies.

                      Comment


                      • #26
                        This has been painful.

                        Comment


                        • #27
                          Sorry, my mistake, i messed up this wire issue, not intentionally, just wrong name for it.

                          This IS multistrand wire, i call it litz wire, just because local term for it is ”licna”, and not checked what i wrote.

                          Otherwise, making this type of coil on PCB is not recommended. Aside being more expensive and more difficult for DIY, PCB version will end up with excessive resistance, even double sided and using 70um Cu. Shielding problem still remain, so back to sq.1 again.

                          Coil is very lightweight, even with shield, epoxy and all in place, not much Cu in it, mostly plastic. Encapsulated in epoxy-fiber still one of lightest.

                          Comment


                          • #28
                            Originally posted by WM6 View Post
                            Coil out of speaker cable is not really lite due to heavy insulation.

                            Better is to use some sort of UHF/CCTV cable with light (PE)foam inner insulation and remove outer shield and outer insulation of the cable. A little annoying work, but you can get lighter coil.


                            It ain't heavy WM6 (including enclosures and all epoxy in it) , but the coil with antenna cable is lighter for sure, have made couple of those and they have too big outside diameter for my needs.

                            Because of this i now making coil with litz wire (not multistranded) pushed into foam insulation from coaxial cable, which will have needed induction and not too big outside diameter.

                            Comment


                            • #29
                              Originally posted by Tepco View Post
                              Whit graphite shielding, no gap is needed, like whit foil, graphite is not conductive enough to sustain eddy currents, just spray it all over.
                              I completely agree with you Tepco, made couple coils with no gap at all and all worked pretty good (talking about graphite shielding) .

                              For this Tesla coil i first rubbed both covers with fine graphite powder and then sprayed with Graphite 33, for connection i used CU plate 0.5X0.5mm pulled out from PCB.

                              Coil it self is placed inside cover in sandwich with 2 layers of rubber insulation on both sides (because of coil to shield capacity) .

                              See pictures here: http://imageshack.us/g/513/imag0047gb.jpg/

                              Also here is the video showing possible discrimination with PI machine: http://www.youtube.com/watch?v=ue1km94NolI&feature=plcp

                              Regards Marko.

                              Comment


                              • #30
                                coil measurements

                                Hi there,

                                I tried making this coil and i seem to get some good depth on it (10" faint reading on a US quarter). I had a question pertaining to the readings of the coil while putting it together though. Wouldnt you have to take the readings of the coil while it is coupled to the full legth of whatever it is youre connecting the coil to the circuitboard (ig. coax, usb, etc.)?

                                Essentially, wouldnt the length of the connecting cable from circuit board to coil change the characteristics of the coil?

                                I have very little knowledge of electronics, so maybe the cable makes very little difference to the coil even if connected?

                                Thanks

                                Comment

                                Working...
                                X