MMC Residual charge

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

This is interesting stuff, although it seems to have drifted a long way 
from the original question and subject line ;-)  Could we please rename the 
subject line "MMC residual charge"?

D.C. - by "circulating currents", are you really suggesting that there is 
fluid-motion, some sort of convection, moving the oil about the internal 
plates, or is there some other meaning?

I don't think that this effect is due to dissimilar cap values or 
dielectric leakage resistance.  As I mentioned, I was unable to get a 
simulator to replicate a charge accumulation.  I feel an experiment coming 
on...

1) Document the residual charge on each cap of my 4-element MMC on my 4kV 
mini coil, without resistors
2) See if residual charge is dependant on capacitor orientation
3) See if there must be HF oscillations to leave residual charges, or if 
just having HV 60Hz cycling is sufficient.
4) See if the magnitude of residual charge is linear /wrt charge/discharge 
voltage, or if it only occurs above some corona threshold.

Round Tuits are hard to come by in a house with small children, so it may 
take me a couple weeks.  Stay tuned.

Gary Lau
MA, USA


Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi D.C.,

At 09:10 PM 1/13/2004, you wrote:

 >Actually, Terry, you were correct.

Oh Goody!! ;-))


 >Cooper told me they had incredible headaches with metallized type caps in
 >air.  They would discharge one section and by doing this, it would actually
 >charge up another section.  A lot of crazy things were happening in air.

Yeeeeaaaap!!!


 >In oil, the circulating currents neutralize the cap potentials.  This is one
 >reason why most all their HV caps are in oil.  Also, of course, the edge of
 >foil tracking currents are much less.

Fascinating!!  Oil can "flow around" and re-deposit charges as needed to
neutralize things...  So cool!!!!


 >He said there are 3 different reasons that can produce these strange charges
 >in air:
 >
 >(1) Unequal cap values.  They match their caps at 0.5% or better.  More
 >specifically the dielectric leakage in individual caps is important.  It's
 >not good in metalized foil caps.

MMCs always have that "self heeling thing" to fall back on...


 >(2) Dielectric polarization.  Even partial polarization produces
 >displacement currents and unequal charge distribution.

Yeap!!


 >Most important factor (3) In oil, the small circulating currents equalize
 >and discharge the caps.  This is due to the dielectric hysteresis effects in
 >energy discharge caps.
 >
 >Bob said most of their HV filter caps contain internal discharge resistors.
 >He said the high Q energy discharge caps do not because of the oil currents
 >and hysteresis effects.

So the oil acts just like discharge resistors to move the charges around
and neutralize things and make things safe...  Resistors are probably far
far faster and more predictable.   For an MMC cap, the added resistance is
expected and no problem.  "Real" cap maker's would have problems explaining
the added resistance...


 >Safety first:  In conclusion, we should continue to use bleeder resistors
 >across all metalized foils caps operated in air.  I always use pcs in
 >series, 4.7 megOhm each.  Each resistor has 1/2 watt rating.  Also, even
 >after discharging each section, Cooper warns, always handle them with rubber
 >gloves if you are not using bleeder resistors!!!

Sounds like all is coming into agreement with some exciting new info from
our "pro" buddies ;-))

We have discussed MMCs "in oil" in the past.  Oil is so messy, we all "ran
away" from the idea.  But maybe it could eliminate the resistors...  But
the effect of oil on the cap's plastics and such is scary!!  Mineral oil
may just dissolve the cap's plastics over time...  Me, I just use the
resistors and am all happy ;-))))))

Maybe the pro cap makers should just do Tesla coil caps where everything is
so much simpler :o)))))))))))  Hey!!  We probably know our application
better than most of their other customers :o)))))))))))

Many thank for you insights and the contributions from you pro pals
here!!!  To give something back...  Maybe they could add materials to their
oil to help the resistance or equalization.  We have resistance and charge
transfer going on...  Self healing must be a big deal too, but intellectual
property problems must abound too...

Cheers,

          Terry



 >Dr. Resonance
 >
 >Resonance Research Corporation
 >E11870 Shadylane Rd.
 >Baraboo   WI   53913
 >----- Original Message -----
 >From: "Tesla list" <tesla-at-pupman-dot-com>
 >To: <tesla-at-pupman-dot-com>
 >Sent: Tuesday, January 13, 2004 6:04 PM
 >Subject: Re: Magnifier Primary Capacitors - EQUIDRIVE vs. STANDARD
 >
 >
 > > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 > >
 > > Hi D.C.,
 > >
 > > It will be interesting to here what they say!  Unlike MMCs, these caps
 >will
 > > be damaged if residual or unbalanced charges happen to cause a breakdown
 >in
 > > a cell.  My guess is, the oil is so very slightly conductive.
 > >
 > > Of course, this would not be the 20th time I have been proven wrong ;-))
 > >
 > > Cheers,
 > >
 > >          Terry
 > >
 > >
 > > At 02:19 PM 1/13/2004, you wrote:
 > >
 > > >Terry has encountered this phenomonea with MMC caps which is quite
 >unusual
 > > >because Maxwell and PCI caps both use a series of small caps connected in
 > > >series inside the box --- I know Beau Meskin, when I visited the PCI
 >factory
 > > >in Chicago, showed me the interior of a 0.1 uF 30 kV cap and it has 22
 > > >separate small caps all series connected.  This construction would
 >simulate
 > > >the series connected MMC technique that we are all presently using, so
 >why
 > > >would there be any difference?  Unless, as Dave Sharpe noted, there are
 >some
 > > >different effects going on with the equi-drive system.
 > > >
 > > >I plan on calling my friends Bob Cooper and Randy Hartsock who are the
 > > >senior design engineers at Maxwell and pose this question to them.
 >Perhaps
 > > >we can get to the bottom of this mystery.
 > > >
 > > >Dr. Resonance
 > > >
 > > >Resonance Research Corporation
 > > >E11870 Shadylane Rd.
 > > >Baraboo   WI   53913
 > > > >
 > >
 > >
 > >