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RE: [VanDeGraaffGenerator] resistors value

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  • DOUG
    Hi Bert; Thank you again and thanks also to all the other members who responded to my questions regarding the build of a Marx Generator. All components are
    Message 1 of 15 , May 9 6:55 AM
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      Hi Bert; Thank you again and thanks also to all the other members who
      responded to my questions regarding the build of a Marx Generator.
      All components are ordered and on their way, so I will soon be soldering
      away!
      It is great to find people such as yourselves that can find time to respond
      to a, non-technical, person with a hobby quite over his head. LOL
      Thanks again to all;
      Douglas Johnson

      -----Original Message-----
      From: VanDeGraaffGenerator@yahoogroups.com
      [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of Bert Hickman
      Sent: Tuesday, May 07, 2013 12:03 PM
      To: VanDeGraaffGenerator@yahoogroups.com
      Subject: Re: [VanDeGraaffGenerator] resistors value

      Hi Doug,

      No problem - here's a PDF of the low pass filter circuit:
      http://www.capturedlightning.com/PDF/HV_Low_Pass_Filter.pdf

      Bert

      DOUG wrote:
      >
      >
      > Hi Bert; Sorry for my ignorance, but I don't know how to do the
      > (fixed font) thing.
      >
      > Doug
      >
      > ------------------------------------------------------------------------
      >
      > *From:*VanDeGraaffGenerator@yahoogroups.com
      > [mailto:VanDeGraaffGenerator@yahoogroups.com] *On Behalf Of *Bert
      > Hickman *Sent:* Monday, May 06, 2013 12:42 PM *T**o:*
      > VanDeGraaffGenerator@yahoogroups.com *Subject:* Re:
      > [VanDeGraaffGenerator] resistors value
      >
      > Hi Doug,
      >
      > Sounds great! Marx generators are notorious for blowing up charging
      > supplies via back-fed transients through the HV lines and via ground
      > bounce :^)
      >
      > You can mitigate these problems by connecting a HV low-pass filter
      > between your HV source and the input of the Marx generator. I'd
      > recommend using the following RC circuit which will prevent both
      > types of transients from nuking your HV supply. Use a fixed font
      > (Courier) to display properly.
      >
      > R1 R1 <----/\/\/\/\----o-----/\/\/\/\------> | o--/\/\/\/\-- To | R2
      > | To HV ----- | Marx Supply ----- | input | | o------------ |
      > <----/\/\/\/\----o-----/\/\/\/\------> R1 R1
      >
      > The R1 resistor values are not critical, but they should all be
      > identical - anything above 100k will work. R2 is a bleeder, so it
      > should be in the 500 - 1000 Meg range to limit power dissipation.
      > Each resistor must be capable of handling transients at least as high
      > as your maximum supply voltage (25 kV in your case). The capacitor
      > can be a simple 30 - 40 kV ceramic doorknob cap in the 500 - 2000 pF
      > range.
      >
      > Be careful not to operate your Marx generator near any solid state
      > equipment, network wiring, computers, scopes, etc., since the EMP
      > can easily trash these devices.
      >
      > Good luck and play safely!
      >
      > Bert -- Bert Hickman Stoneridge Engineering
      > http://www.capturedlightning.com
      > ***********************************************************************
      >
      >
      World's source for "Captured Lightning" Lichtenberg Figure sculptures,
      > magnetically "shrunken" coins, and scarce/out of print technical
      > books
      > ***********************************************************************
      >
      > DOUG wrote:
      >>
      >>
      >> Thanks Bert; I do have a source for the VR68 1 watt 200K ohm
      >> resistors @.25 cents each so that sounds really good to me.
      >>
      >> Do you think I will need anything between my power supply and the
      >> first stage of the Marx?
      >>
      >> Doug
      >>
      >> ----------------------------------------------------------
      >>
      >> *From:*VanDeGraaffGenerator@yahoogroups.com
      > <mailto:%2AVanDeGraaffGenerator%40yahoogroups.com>
      >> [mailto:VanDeGraaffGenerator@yahoogroups.com
      > <mailto:VanDeGraaffGenerator%40yahoogroups.com>] *On Behalf Of *Bert
      >> Hickman *Sent:* Monday, May 06, 2013 1:21 AM *T**o:*
      >> VanDeGraaffGenerator@yahoogroups.com
      > <mailto:VanDeGraaffGenerator%40yahoogroups.com> *Subject:* Re:
      >> [VanDeGraaffGenerator] resistors value
      >>
      >> Hi Doug,
      >>
      >> A couple of alternatives would be VR68 or HVR68 1 watt HV metal
      >> film or ceramic resistors.These can handle 10 kV pulses, so you'll
      >> need to use at least two, and preferably three, resistors in series
      >> per stage. In your Marx application, the resistance value is not
      >> very critical since your stage capacitance is relatively small.To
      >> limit peak power stresses, use 100k - 200kohm resistors. You may
      >> also find something similar at a better price via eBay or through
      >> other electronic surplus vendors.
      >>
      >> Bert
      >>
      >> DOUG wrote:
      >>>
      >>>
      >>> Hi Bert;Thank you for your reply. I will be charging with a 25KV
      >>> power supply. Can you suggest something other than the 1 or 2
      >>> watt resisters?
      >>>
      >>> Douglas Johnson
      >>>
      >>> ----------------------------------------------------------
      >>>
      >>> *From:*VanDeGraaffGenerator@yahoogroups.com
      > <mailto:%2AVanDeGraaffGenerator%40yahoogroups.com>
      >> <mailto:%2AVanDeGraaffGenerator%40yahoogroups.com>
      >>> [mailto:VanDeGraaffGenerator@yahoogroups.com
      > <mailto:VanDeGraaffGenerator%40yahoogroups.com>
      >> <mailto:VanDeGraaffGenerator%40yahoogroups.com>] *On Behalf Of
      >> *Bert Hickman
      >>> *Sent:* Sunday, May 05, 2013 12:10 AM *T**o:*
      >>> VanDeGraaffGenerator@yahoogroups.com
      > <mailto:VanDeGraaffGenerator%40yahoogroups.com>
      >> <mailto:VanDeGraaffGenerator%40yahoogroups.com>
      >>> *Subject:* Re: [VanDeGraaffGenerator] resistors value
      >>>
      >>> HiDouglas,
      >>>
      >>> There is little difference in the voltage breakdown rating for
      >>> 1W and 2W carbon composite resistors. Your resistors must be able
      >>> to withstand the transient discharge voltage (i.e., the DC
      >>> charging voltage per resistor) when the Marx fires. If they flash
      >>> over, you'll dramatically decrease the output of your Marx
      >>> generator and any internal flashovers may cause the affected
      >>> resistor to explode or permanently change resistance value.
      >>>
      >>> For short (<10 uSec) pulse duty such as your Marx generator, a 1
      >>> or 2 watt carbon composition resistor can repetitively handle a
      >>> maximum of ~5-6 kV between terminals. So, if you plan to charge
      >>> your capacitors to 30 kV per stage, you'll need to use five-six
      >>> identical resistors in series (for each stage) to share the
      >>> voltage stress.
      >>>
      >>> Bert -- Bert Hickman Stoneridge Engineering
      >>> http://www.capturedlightning.com
      >>> ***********************************************************************
      >>>
      >>>
      >
      >>>
      World's source for "Captured Lightning" Lichtenberg Figure sculptures,
      >>> magnetically "shrunken" coins, and scarce/out of print
      >>> technical books
      >>> ***********************************************************************
      >>>
      >>>
      >>>
      >
      >>>
      drj11642 wrote:
      >>>> Here is my dilemma today, I need a bunch of 2 watt solid
      >>>> carbon resistors which are almost impossible to find, and when
      >>>> they can be found they are very expensive. On the other hand I
      >>>> have lots of 240ohms 1 watt solid carbon resistors. What would
      >>>> the resulting value be with 2 of these 1 watt resistors in
      >>>> series?
      >>>>
      >>>> My project that I need these for is a Marx generator using
      >>>> 30kv-1000pf ceramic disc caps.
      >>>>
      >>>> Thanks in advance to any response to my queries.
      >>>>
      >>>> Douglas Johnson
      >>>>
      >>>>
      >>>>
      >>>>
      >>>> ------------------------------------
      >>>>
      >>>> Yahoo! Groups Links
      >>>>
      >>>>
      >>>>
      >>>>
      >>>>
      >>>
      >>>
      >>>
      >>>
      >>
      >> -- Bert Hickman Stoneridge Engineering
      >> http://www.capturedlightning.com
      >> ***********************************************************************
      >>
      >>
      >
      >>
      World's source for "Captured Lightning" Lichtenberg Figure sculptures,
      >> magnetically "shrunken" coins, and scarce/out of print technical
      >> books
      >> ***********************************************************************
      >>
      >>
      >>
      >>
      >>
      >
      >>
      >
      >
      >



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