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Soldering High Voltage Capacitors

  1. Sep 3, 2016 #1
    Hi guys! Im fairly new to the forums so thank you for having me here :)

    I just wanted to ask some of you guys here who have a better knowledge about high voltage capacitors than me.

    I am creating a lightning impulse voltage generator as my final year project and have been provided with most of the circuit. My only job is two create two resistors and a capacitor.
    I will be creating a 1.25nF capacitor using 10nf 10kv capacitors.
    My question here is that ive heard a lot that when handling capacitors, you can get shocked especially if its a high voltage capacitor. Well ill need to solder 18 capacitors (36 in total) [ 18 capacitors in series, 2 legs in total, connecting them parallel ]and make two legs so they can handle 140kv at least.
    Now here is my question. What precautions shall i take when soldering the capacitors in order not to get shocked? As for soldering the capacitors, im going to try and make the the soldering spherical balls and then will use sandpaper to make sure there are no sharp edges. I do not want to get shocked and ive heard capacitors get charged by static electricity as well and i usually do my soldering next to a laptop playing songs and generally beside many electronics etc.

    I just dont want any accident happening since i am doing all my soldering at home and will do the rest of the work in the High Voltage lab. I dont have much access to the high voltage lab because i am not allowed to stay there unsupervised and after hours. So id like a solution which would allow me to work at home without much problems.

    If you guys need any other info, feel free to ask. Btw guys, soldering so many resistors and capacitors is so hard, i dont know how you guys do it all!
    Also id like everyone to know that i will not be conducting or charging any of the capacitors at home. That will be conducted with my supervisor inside a high voltage lab with a faraday cage. We have everything in place and i am not allowed to do any tests at home other than soldering and outer design of the project. I will be conducting the test afterwards inside the lab with my supervisor after i have finished building my 2 resistors and capacitors.





    Thank you for reading :)
     
    Last edited: Sep 3, 2016
  2. jcsd
  3. Sep 3, 2016 #2

    Bystander

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    ?
     
  4. Sep 3, 2016 #3
    Yes nF. 1.2nF or 1.2 * 10^-3 uF would you like a picture of the capacitors i will be using?
     
  5. Sep 3, 2016 #4

    davenn

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    nanoFarad a common value range

    I would assume from that, you don't do any electronics ? :wink:
     
  6. Sep 3, 2016 #5

    davenn

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    unless the caps are going to be second hand still in a working circuit, then they wont have a charge on them
    ie. NEW caps WONT have a charge on them


    spherical balls ????? makes no sense

    you heard wrong, they cannot get charged just lying around. They could be charged by static IF they come into contact with a high voltage static generator, eg a Van de Graff generator etc


    Dave
     
  7. Sep 3, 2016 #6
    Okay thanks for the clarfication dave :) Please excuse for my lack of knowledge. Not necessarily spherical balls but more like. Hmm, a picture would be better.
    Basically this is what i did. Not necessarily spherical balls but i was told not to just connect the legs but put a bit of soldering and make sure there were no sharp edges so as to make sure no corono discharge occurs. The picture is an example of resistors i soldered together. 560 ohm, 11 w (ceramic resistors )each. after i finish soldering, i make sure there are no sharp edges. Is this the correct approach to take when soldering the capacitors together?
     

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  8. Sep 3, 2016 #7

    Bystander

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    Just an odd unit --- or, I am perhaps becoming an old unit.
    0.5CV2, O(J), ... , Mythbusters search a "cropper" far as energy/ies, toss-up. Not a real hazard except under very unusual circumstances.
    pF or μF is it.
     
  9. Sep 3, 2016 #8

    davenn

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    no .... definitely not odd :smile:

    smallest to largest value ..... pF, nF, uF :smile:
    I use lots of all ranges in my manufacturing and home electronics

    Dave
     
  10. Sep 3, 2016 #9
    Thanks for all the replies guys. :) So i guess i wont be coming across any real problems when handling them. Another question, when you do look at the picture, do you think my soldering technique can be called solid, and wont cause any problems?
    Also do you think olive oil is a good insulator? I cant get my hands on transformer oil like my supervisor did when she was building her tesla coil, but i heard olive oil can be used. I plan to sold the capacitors, then put them in a PVC pipe and insulate them with olive oil.
     
  11. Sep 3, 2016 #10

    davenn

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    looks good :smile:

    yup, that's correct, less likely to have a corona with rounded surfaces, till you get to the really high voltages like from a
    Van de Graff generator etc where the voltage exceeds 100kV or so


    Dave
     
  12. Sep 3, 2016 #11

    davenn

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    encasing them in silicone sealer would be good ... there's a dozen different brands
    eg
    upload_2016-9-4_11-17-55.png


    Dave
     
  13. Sep 3, 2016 #12
    I was told to make sure the capacitors should be able to handle up to 140kv thus the need of making two legs of 18 capacitors. otherwise i wanted to use 8, 10/8=1.25 and that would only require one leg and make things easier, but that would also mean 8*10=80kv only. Thanks a lot for the replies dave, i will get to the soldering of capacitors then :)
     
  14. Sep 3, 2016 #13

    jim hardy

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    You might check this thread for pictures of a commercial high voltage capacitor based device. They stacked the stages so the full voltage was not applied across any single part.
    https://www.physicsforums.com/threa...asuring-things-etc.755959/page-5#post-5217555


    I don't have enough leftovers for your nine stages so cant help there

    but i'd suggest you include high megohm voltage dividers to assure voltage divides about equally among your caps, and that they will self discharge after the machine is powered down.

    Energy = ½CV2 , C = 1.25 X1 0--9 and V = 1.4 X105 , gives ~12 Joules , about the lowest range for defibrillators.
    doesn't sound lethal but it'd sure be a jolt.

    old jim
     
    Last edited: Sep 3, 2016
  15. Sep 4, 2016 #14
    thanks for the reply. :) Im glad to know the most ill get is a jolt xD
     
  16. Sep 4, 2016 #15

    jim hardy

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    A really substantial jolt.

    We've all felt the shock of a spark plug (i assume).

    That's on the order of 40 millijoules*. Your apparatus might deliver 12 / 0.04 = 300 X that.

    Be careful.

    old jim

    * fascinating measurements here. Should be posted to an automotive thread in ME forum.
    http://worldphaco.net/uploads/THE_SPARK_ENERGY_TEST_MACHINE.pdf [Broken]
     
    Last edited by a moderator: May 8, 2017
  17. Sep 4, 2016 #16

    Bandit127

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    "Give you a jolt" and "maybe lethal" are probably just a matter of luck apart. I am reading about smoothing caps in valve amp power supplies are they are the subject of death warnings all over the net and (if my maths is right) a 50 µF cap with 400 V in it is 4 Joules.

    Also be aware that the spark gap at 400 V is sub millimeter. I guess you already know what the spark gap is that you are dealing with but don't let bad luck come together with a slip of the wrist.
     
  18. Sep 6, 2016 #17

    NascentOxygen

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    I'm cautious about silicone sealers, don't some of them produce acetic acid (corrosive) while curing? Need to research for one that is okay for potting electronics.
     
  19. Sep 6, 2016 #18
    Trans oil is just mineral oil, available at the Hardware store. -- will be much better if you need to make changes / edits than permanent RTV Silicone -- You can use Denatured Alcohol to clean the oil off. You can get silicone oil - also used in transformers.

    As for RTV there are two general types, one cures by UV, temp - etc, the other uses acid, which could be corrosive, but for a basic experiment I doubt it would be a problem.

    If this is somthing you will handle often - you may want to "build in" a discharge resistor, to allow you an easy and convenient way to make the cap assy safe.
     
  20. Sep 6, 2016 #19

    jim hardy

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  21. Sep 6, 2016 #20
    Since someone mentioned thins you can buy at hardware stores, you can also use liberal amounts of dielectric grease. Coat your connections and solder joints with dielectric grease to prevent unintentional arcing and coronal discharge. You can buy cans of it in the electrical section of hardware stores in the US.
     
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