best way to transfer electrical current to Dremel attachment shaft?

Discussion in 'The Projects Forum' started by dredd2929, Apr 22, 2009.

  1. dredd2929

    Thread Starter New Member

    Apr 22, 2009
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    Hello,

    I'm working on a project that requires an electrically charged rotating metal disk (angular rotation). I was thinking of using a Dremel (or similar) tool. The center of the metal disk would be attached to the end of the shaft. What is the best way to supply current to the metal disk? I was thinking of using a slip ring around the shaft, but I'm not sure if this would be the simplest approach. Here are the parameters that need to be met:

    -up to 30,000 VDC (ideally; I could probably get by with 15,000 VDC)
    -up to 3 mA
    -up to 5000 rpm

    I'm open to any and all suggestions so any help would be greatly appreciated.
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I'm sure a slip ring would be the simplest. You could make a brush out of pencil lead...I used to make motor commutators this way. :)

    good luck....but you have my curiosity glands going now!

    Eric
     
  3. KL7AJ

    AAC Fanatic!

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    I might add that at 30,000 volts, you're going to have to isolate the entire Dremel. YOu might consider a battery powered inverter to run the motor. Then you could put the whole shebang on top of a styrofoam box or such. The plastic case of the motor is probably only good for a couple thousand volts.

    Eric
     
  4. dredd2929

    Thread Starter New Member

    Apr 22, 2009
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    Hi Eric, thanks for the replies.

    I was thinking that isolating the Dremel may be necessary. Thanks for the suggestions. Do you know where I could find a slip ring that would work for my project?

    What I'm trying to do is set up an electrospinning apparatus. The high voltage is being applied to a syringe needle, and the current travels through the substance ejected from the syringe to a spinning collector disk. So actually, the spinning disk will be connected to ground. Either way, I need a good electrical connection to the shaft, and I think a slip ring would work well.

    Is it the plastic case that insulates the internal shaft from the motor, or is there some kind of insulation internally?
     
  5. KL7AJ

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    The Dremel is "double insulated". If that is going to be at ground potential, you're going to have a much simpler job. I'd just configure some widget to press a piece of graphite against the steel shaft.

    Eric
     
  6. KL7AJ

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    By the way....if you haven't worked with high voltages before, you want to be SURE you have some effective current limiting, such as 100 megohm resistance in series with your syringe. High voltage aerosols floating around with no current limiting can be a bit of a hazard, as you might imagine.

    Eric
     
  7. dredd2929

    Thread Starter New Member

    Apr 22, 2009
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    I haven't worked with high voltage before, so I appreciate the advice. Just to make sure I understand what you're saying, I've attached a diagram showing a resistor in series with the syringe and graphite attached to the shaft.

    The power source we're using is a Glassman EH 30kV 3mA DC Power Supply. It has the ability to set the current as well as the voltage, so is the resistor necessary? If I set it to 1mA, will it allow a current greater than that?

    What is the best way to stick the graphite to the shaft, what type of graphite should I use, and how do I attach a wire to it? As you can tell I'm a novice at this.
     
  8. Enigmatic Entity

    Member

    Feb 16, 2009
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    Tell me if I'm wrong, but I think they mean press the graphite to the shaft like an electric motor. See picture. The graphite is in contact with a metal pipe or holder. You could just wrap a lot of un-insulated wire around it (the graphite) for contact.
     
  9. dredd2929

    Thread Starter New Member

    Apr 22, 2009
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    OK, that makes sense. Thanks Enigmatic Entity.

    Would any old stick of graphite work, like what you'd find at an art store?
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
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    Or use an insulating shaft ??? :confused:
     
  11. KL7AJ

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    Yes...Or you could try various hardnesses of graphite pencils to see what lasts the longest. At such minuscule current, the difference in conductivity shouldn't make a measureable difference.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Seems to me that Dremels spin much faster than 5,000 RPM; more like 10,000 to 25,000 RPM. If your wheel is much larger than around 3/4" diameter, it may very well fly apart at speed with great force, likely causing damage or injuries.

    For safety, you should only use Dremel products in the tool.

    The power you're considering is another consternation; 5mA at 30kv is 150 Watts. That kind of power has the potential to at least really knock you on your keister, or far worse. :eek: I once saw a fellow technician attempt to test the 18.5kv transmitter voltage on the radar system we used to work on; the high voltage probe he was using was defective (it had a longitudinal crack). He was standing on a metal platform while testing the transmitter, another really bad idea. When he touched the high voltage terminal with the probe, he got an 18.5kv jolt that caused him to perform a backwards somersault headfirst into a trash can! :eek:

    While he turned out to only have his pride injured (thus a hilarious incident that he was ribbed about for months) it could have easily been a fatal incident.

    We don't know what you're planning on accomplishing. It would help us to help you more (and likely in a much more safe manner) if you would simply explain it.
     
  13. KL7AJ

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    Sarge:

    The newer variable speed Dremels can go down to about 3000 rpm or so. Of course it's still adviseable to stay out of the "line of fire" of a spinning disk. :)

    Of course there are always hazards with high voltage, but if he uses a current limiting resistor as I suggested, you can reduce the hazard to a tingle or two.

    Personally, getting knocked on one's keister a time or two is crucial to the scientific method. :)

    Eric
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Eric,
    I hear ya. ;) Call me the "Safety Nazi" if you want. :rolleyes: I just want our n00b's to survive their experiments, learn something useful, and have fun while doing so. :)

    While you, I, and many others on the forum have been around electricity & electronics for a good while (perhaps longer than we'd like to think about), those going through early indoctrination don't really have a good grasp on the possible dangers involved. That's why I like to have the newbies keep their experiments under 50v. Not much chance of experiments turning lethal that way.
     
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