Reversing polarity on Rectifiers (HV) - Mineral separation application

Discussion in 'General Electronics Chat' started by Suse, May 9, 2008.

  1. Suse

    Thread Starter New Member

    May 9, 2008
    2
    0
    Hi,
    I'm feeling a little out of my depth here, but I'm hoping someone will be able to explain it all to me ....
    I'm a metallurgist working with electrostatic separators. These are supplied with 0-40kV/ 15mA negative-polarity HV rectifiers, but I recently got all experimental and reversed the polarity to positive.
    I found with the -ve rectifer I was max-ed out on the current limit of the rectifier before I achieved arc-over (corona discharge); ie. 26 kV at 15 mA. However with the +ve rectifier I obtained 35 kV at 7 mA before I saw corona discharge (Wire diameters/ all other machine parameters constant)
    This is highly benefical to improving the separation of the conductor and non-conductor particles in the machine, but I honestly expected no change and now would like to understand the theory behind my observations.
    With thanks, Suse
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Having only read a few of the more basic metallurgy texts by Krauss, Bain, Grossman, and others, I feel a bit out of my depth.

    But... aren't standard electrostatic separators positively charged?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I suspect this has to do with "hole flow" vs "electron flow".

    With the polarity reversed, whatever your electrostatic plates/devices are, will soon be peppered by very high-velocity particles from your mineral samples. The particles will be travelling at such a high rate of speed that they will practically become fused to the plates, and be very difficult to impossible to remove without also removing surface material from the plates. This will cause a steady decrease in the efficiency of the separator due to an effectively reduced plate area, as it will become covered with non-conductive material.

    Years ago there were "plug in negative ion generators" on the market. They looked like a typical wall-wart power supply. You plugged them in, and they generated negative ion pulses, which were supposed to clear the air. Unfortunately, when the air was charged with negative ions, the particles would then be propelled at high speed to embed themselves in the wall surrounding the ion generator, over time leaving a very black smudge on the wall that was impossible to remove. Later versions of the device alternated between emitting positive and negative ions.
     
    Last edited: May 9, 2008
  4. Suse

    Thread Starter New Member

    May 9, 2008
    2
    0
    Thingmaker3,
    You're right .... they are. In fact, that's what started my experimental stage. If every other electrostatic circuit I'm aware of uses positive-polarity (and it worked), why did we end up with the complete opposite? The answer was in the lab (nice clean dust free, controlled environment) there was no metallurigcal difference found between different polarities. So.... if no difference logically most would have stuck to the tried and true (You'd have thought!) :rolleyes:

    I'll do some reading up on the hole flow vs. electron flow, sounds vaguely familiar from the school days. Thanks for the tips, SgtWookie.

    Who knows some other innocent passer-by in the chat forum, may have seen this before as well... Interesting for me, because it's a new venture into an unknown topic.

    Cheers for now, "Suse"
     
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