Re: Tank cap charging

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Sundog,

	My MMC drain resistor study post is below.

-------------------------------------------
Date: Tue, 26 Sep 2000 20:56:08 -0600
From: "Tesla list" <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: MMC drain resistor study
Message-Id: <4.1.20000926202819.00a1ae00-at-pop.dnvr.uswest-dot-net>
Content-Type: text/plain; charset="us-ascii"

Original poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi All,

	I fired up the Bertan HV power supply and tested some 10Meg ohm  1/2 watt
YEGEO resistors from DigiKey at high voltage.  The results of a typical run
are:

Volts DC	Current (mA) 	Power	R(Mohms) Comments
1000		0.115		0.115	8.695
1200		0.138		0.165	8.696
1400		0.161		0.225	8.696
1600		0.184		0.294	8.696
1800		0.208		0.374	8.654
2000		0.233		0.466	8.584
2200		0.261		0.574	8.429
2400		0.290		0.696	8.276
2600		0.320		0.832	8.125
2800		0.351		0.982	7.977
3000		0.389		1.167	7.712	Drift
3200		0.428		1.370	7.477	Drift
3400		0.476		1.618	7.143	Drift
3600		0.548		1.973	6.569	Drift
3800		0.617		2.345	6.159	Drift	Hey! what's burning!
4000		0.684		2.736	5.848	Drift up, then down
4200		0.701		2.944	5.991	Drift down
4400		0.719		3.163	5.841	Drift up
4600		0.762		3.505	6.037	Drift all over
4800		0.815		3.912	5.890	Drift all over
5000		---		---		she on fire now! ;-))

So It looks like they are perfectly good to 1600 volts and probably to 2000
RMS.  That is like 2828 AC!  This is at the low end of the Bertan's range
so there is probably some significant calibration error but you get the
idea... 

I also tested two 1600 volt 0.56 uF Panasonic caps and they broke down at
4100 and 4800 volts and seemed to self heal in stride...  Numbers like
these explain why MMC's are so darn tough!!

Cheers,

	Terry
----------------------------------------------------

You can push 2000 volts DC across those resistors fairly safely...  The
above voltages are all DC.

The time it takes for a resistor to discharge a capacitor is:

t = 5 x R x C

So a 10Meg resistor will drain a 10nF cap in 1/2 second. 

I would keep the resistors in since they will dissipate little power.

Cheers,

	Terry


snip...
>      Do I have to remove the bleeder resistors for DC useage?  If I'm
>constantly pumping the caps up, won't the bleeders try to dissapate the
>energy?  While I am not bothered too much by the burning of the resistor
>itself, the smell is horrible.  I intend to measue the voltage across the
>cap and see for myself how long it takes to bleed down.  But, should I
>measure the voltage from the positive side of the cap to ground, or to the
>negative side of the cap? (using a voltage divider of 10mohm resistors)  I
>usually put them all in series, and measure the voltage across the last
>resistor closest to ground, keeping the total V measured at the resistor
>~200v.  Normally I hook the divider to the source and then to ground.  It's
>worked for the GMHEICSLR setup (4/30 nst, 25 resistors in series from the +
>side of the rectifier feeding the cap.  V goes from 0 to ~225v and then the
>NST output peeters out (fully charged cap to ~5656v, no bleeders), then
>*BANG* when I short the gap.  The ratio works out to 25:1, so I can pretty
>accurately charge my cap to whatever I like.  A string of resistors between
>the rectifier and the cap keeps the charging current down so I can just bump
>up the variac till I hit the voltage I want, then spin the variac back down.
>It's served me well, and requires nothing more than a bunch of resistors,
>and an analog (safer from kickbacks) multimeter.
>
>      I'd love to buy a surplus HV probe, and use a scope, but mine is dead,
>and money for one is hard to come by.  That, and I can work a multimeter a
>whole lot better than a scope ;)
>									Caio!
>									Sundog