Article Reference: D483D3294C8C6614
Date: Mon, 19 Feb 1996 19:47:57 -0800
Original Subject: Re: Evaluate MOV's
Harvey White wrote: > > claude@bauv.unibw-muenchen.de (Claude Frantz) wrote: > > >jlundgre@delta1.deltanet.com (John Lundgren) writes: > > >>IMHO, the only place for MOVs is in the trash can. The only place to do > >>surge protection is where there is a good ground. And this is at the > >>breaker panel, not at the outlet strip. > > The best surge protection is at the breaker panel to the house. No > questions there. However, there are other places where MOVs can help. > John is absolutely right, there is very little that can help against a > direct strike, and a tiny little MOV will certainly not do it. The > only thing that might help in that case is to put enough impedance in > the line that the lightning just wants to go somewhere else. > > However, on those near misses and things, You will get some high > voltage spikes on the line. The MOVs are meant to clamp these, and > the gas tube surge supressors are meant to help as well. These spikes > are the ones that can damage most solid state equipment by punching > through the BE and BC layers of transistors, and anything else, > either. > > Harvey > Here's a couple of factoids to add to the above: 1. Most lightning strikes occur at some distance from your equipment. 2. These are fast rise-time impulses, so inductance in power lines can have a considerable effect on the amplitude and duration as seen at a distance. 3. Most wiring devices used in homes and offices have a limiting dielectric strength of about 6KV. This means that there are effectively a number of 'spark gaps' in most feeder systems. This, too, affects the amplitude seen by equipment. 4. Power lines also have resistance. Home wiring tends to have more than commercial wiring. This limits the current. 5. Feeders from service entrances connect radially to the breaker panel. These feeders each get a share of the power from transient surges. This limits the power seen by any particular piece of equipt. 6. Surges can have differential and common mode components. Surge suppression connected to earth ground typically only helps with common mode. Differential mode suppressors need not be grounded. 7. Dielectrically isolated components, provided that they have sufficient dielectric strength, will probably be undamaged by common mode transients. 8. MOVs are inexpensive and effective for transients up to a certain magnitude, but they suffer from gradual degradation. They are easiest to apply in differential mode. 9. Tranzorbs, which are groupings of high-powered avalanche breakdown diodes, are more rugged than MOVs. They can be effectively applied in either differential or common mode, or both. Best layout, as claimed above, is to have a massive tranzorb at the service entrance, set up in both modes, with a good ground. 10. Anything is better than nothing. There are lots of small transients that can damage equipt. if not suppressed. -- Paul Mathews, consulting engineer AEngineering Co. optoeng@whidbey.com non-contact sensing and optoelectronics specialists
Article Reference: E54975EC6CB3BAA2
Date: 17 May 1996 16:24:04 GMT
Original Subject: Re: Need power supply - DC 150KV
In article <4nhp2n$p8f@dfw-ixnews1.ix.netcom.com>, mlerman@ix.netcom.co says... > >In <Jfreitag-1605961306090001@techservp2.gso.uri.edu> >Jfreitag@gsosun1.gso.uri.edu (John Freitag) writes: >> >>In article <4ne5tv$kj8@usenetp1.news.prodigy.com>, PBWD58A@prodigy.com >>(Ruth Rosenberg) wrote: >> >>> I need the above power supply. Must be variable, DC, min. 150KV, >current >>> level unimpotant. >>> Try someone who does high voltage for a living, Glassman High Voltage. Route 22, Salem Industrial Park, PO Box 551, Whitehouse Station, NJ 08889. Their phone is (908) 534-9007. E-mail:GlassmanUS@aol.com. Good luck. Bob Crable Research Instruments Electronics Shop The Pennsylvania State University
Article Reference: 36EA9397FA65926B
Date: Sat, 25 May 1996 15:10:56 GMT
Original Subject: Re: Kirlian Photography
There is a book by Delton Horn called Electronics Projects for A New Age, which describes Kirlian photography quite well, and includes a schematic and detailed instructions. The basic idea is to create a high frequency, high voltage pulse, using a coil from an automobile ignition as your HV transformer. The HV is connected to a copper clad board, which should be at least as big as your subject. The board is placed inside a plastic bag for insulation. On top of it, you place your sheet of film, then a thin sheet of plastic, then your subject (which must be grounded to the circuit ground), and then a thin sheet of plastic on top of that. Keep in mind that the exact frequency of the pulses will affect the size of the auras, so you will have to play around a little until you get a good picture. Email me if you want me to scan the schematic and send it to you. Andrew Syred (andrew@micropix.demon.co.uk) wrote: : I'm after a circuit drawing to construct a Kirlian 'Photography' gadget. : My attempts to build one so far have not been too good. Can anyone : offer any help or point me in the right direction? : Cheers, : Andrew : On-line Microscopy for Amateurs, Professionals and Big Kids alike : ***** Visit "http://www.microscopy-uk.org.uk" ***** --
Article Reference: CCF0D9DCCB6298A3
Date: 11 Feb 1996 23:24:40 GMT
Original Subject: Re: Need PCB Design Rules for Avionics
Alan Hilton (hiltona@tiw.com) wrote: : Actually the breakdown voltage of air would become greater as it thins. Isn't a vacuum a better : insulator than normal atmosphere? No, low pressure air ionizes more easily. I eventually found a 1984 spec MIL-STD-275E in our local university engineering library. It gives tables for conductor spacing both below 10000 feet and above. For example for voltages up to 100 volts, a spacing of .060" is required above 10000 feet, while only .025" is required below 10000 feet. -Bob Scott
Article Reference: CCCA178269F29DED
Date: Tue, 9 Jan 1996 16:43:29 GMT
Original Subject: Re: TV Flyback QUESTION
In article <DKwstC.90z@animal.inescn.pt> jml@bee.inescn.pt (Justino M. R. Lourenco) writes:
> Hello !
> I would like to know if i can connect directly the primary of a TV
> Flyback Transformer to 110 V a.c. to get H.V.
> The primary of the TV flyback has several primary Windings , how
> to deal with that when connecting to 110 V A.C.
No. It requires a high frequency waveform to provide any substantial
output. Furthermore, it WILL melt down if you try 110 VAC 60 Hz without
current limiting. None of the windings are suitable.
If you want to play around with a flyback to generate high voltage, try
the following or email me for a dual 555 based HV generator. Both use
low voltage DC for the primary drive power. This is safer for you
and will be less costly in the long run as you blow up fewer expensive
parts trying to get it to work!
--- sam
Simple High Voltage Generator - 12 V in, 12,000 V out inverter.
---------------------------------------------------------------
*VCC Q1 +-----------------C ||
o | C ||
| B |/ C C ||
| +------| 2N3055 C ||
| | |\ E 5T C || C-------|>|----------o +HV
| | | C || C HV Diode, usually
| | -_- C || C built in
| | C || C
+--|--------------------------C || C
| | Q2 _-_ C || C
| | | C || C Secondary (HV) winding,
| | B |/ E 5T C || C intact.
| | ----| 2N3055 C || C
| | | |\ C C || C
| | | | C || C
| | | +-----------------C || C
| | | || C
| | ------------------------C || C-------------------o -HV
| | 2T C ||
| | +----------C ||
| | | 2T C || T1 - Flyback transformer from BW
| +--------------------------C || or color TV or computer monitor.
| |
| R1 | R2
+----------/\/\/\--+--/\/\/\---+
110 27 _|_
2W 5W -
Read in Entirety!
1. Obtain flyback transformer with known good HV secondary winding. primary
may be left intact if it is known to be in good condition - non shorted.
A flyback removed due to failure may be used if it was the primary that
failed and the primary turns can be removed without damaging the HV
secondary or losing the secondary return connection! Flybacks fail
in both ways (primary and secondary).
2. Wind 10 turn center tapped drive winding and 4 turn centertapped feedback
winding using #16-20 guage insulated wire. Make sure both halves of
each coil are wound in same direction.
3. VCC should typically be in the range 12-24 volts at a couple of amps.
Circuit should start oscillating at around 5 volts VCC or so. If you do not
get any HV out, interchange the connections to the transistor bases. Heat
sinks are advised for the transistors. Be aware of the capability of
your flyback (BW monitors up to 15KV, color up to 30 KV). You risk
destroying the secondary windings and/or HV rectifier if you get carried
away. Running this on 24 volts will probably cause an internal arc-over
in a small flyback, at which point you start over with more caution
and a new flyback.
4. Actual output will depend on turns ratio of the flyback you have.
For typical monochrome computer monitors or video display terminals,
you should be able to get around 12,000 volts with 12 volts input.
I made one from a dead MacPlus flyback from which I removed the (dead)
primary windings.
5. Frequency of operation will be in the KHz to 10s of KHz range depending
on VCC, load, and specific flyback characteristics.
6. You can experiment with # turns, resistor values, etc. to optimize
operation and power output for you needs.
7. CAUTION: contact with output will be painful, though probably not
particularly dangerous due to low (a few mA) current availability.
HOWEVER, if you add a high voltage capacitor to store the charge,
don't even think about going near the HV!
Parts list:
Q1, Q2 - 2N3055 or similar NPN power transistors (reverse polarity of
VCC if using PNP transistors.) Maximum stress on transistors
are about 2-3 times VCC. Heat sinks will be needed for continuous
operation.
R1 - 110 ohms, 2W resistor. This provides base current to get circuit
started.
R2 - 27 ohms, 5W resistor. This provides return path for base feedback
during operation.
T1 - Flyback transformer from/for BW TV, color TV, or computer monitor
modified according to text above. Most modern flybacks include
built-in HV rectifier diode(s) so output without additional components
will be high voltage positive pulses. Note: this kind of flyback
transformer drives the CRT directly and uses its glass envelope
as the high voltage filter capacitor. (A foot square piece of
1/8" Plexiglas with Aluminum foil plates makes an adequate
filter capacitor.)
Wire - a couple of feet of #16-#20 hookup wire, magnet wire, or any other
insulated wire for home made primaries. Use electrical tape to
fix windings to core. Wind feedback winding on top of drive winding.
Article Reference: 2D46DA676BD96422
Date: 23 Jul 1996 12:42:35 GMT
Original Subject: Negative Ion Generator: should my homebrew one hiss and glow in the dark?
Hi
If you know anything about this topic, or the design of electron gun
accelerator electrodes, please repond. After four posting in the
electronics newsgroups only three kind souls replied. This is why I'm
cross-posting. Someone out there must know something - or are you all
busy selling negative ion generators? :-)
I've managed to build myself a negative ion generator and am currently
evaluating it to see whether it really does help to lift my gloom at
being in an office that's effectively underground - No sunlight, no
visible sky :-(
Don't bother sending lots of flak about this - even if it doesn't
work, assuming I don't produce lots of ozone, it won't do any harm!
I'm using the usual Cockcroft-Walton voltage multiplier giving (I
think) about -3.5KV and feeding this into an array of needles.
I discovered along the way NOT to build the voltage multiplier on
phenolic PC board. The voltage output was way down - fibreglass board
is better. I guess at the voltage levels involved, what is normally
considered an insulator may not be!
The generator has a chain of 15 multiplier stages (230Vac in) using
1N4007 diodes and 0.01uF 1KV ceramic capacitors feeding into four
needles via a 4.7M resistor.
When I get within about 4 - 5cm of the needles it starts to hiss -
faintly but audibly, and at night I can see tiny pin-pricks of blue
light. They're so faint that it's impossible to focus on them!
- Is the hissing normal?
- How can I tell if I'm producing any significant amounts of ozone?
Is a voltage on the end of the chain of 15 multiplier stages (230Vac
in) likely to generate ozone? or is it not just the voltage but also
the sharpness of the point? I'm using sewing needles sold as "sharps"
but I've no idea of their end diameter (although they are sharp :-).
I really would appreciate some direction - the physics texts in a
university library are not very helpful when you need practical
guidance!
Thanks
Giovanni
PS: If you have a few minutes, could you skim the following detailed
description and let me know your thoughts?
*************** More detailed description of generator ****************
and accelerator electrodes follows
To detect any ion output I'm using the usual neon and capacitor detector:
%%%%%%%%% .015uF %%%%%%%%%% <--- Square of PC board about 1" x 1"
%%%%%%%%%----||----%%%%%%%%%% 2.5cm sq
%%%%%%%%% %%%%%%%%%%
%%%%%%%%%---neon---%%%%%%%%%% <- hold or Ground this end
%%%%%%%%% %%%%%%%%%%
Pad A Pad B
place near
needles
I can't measure the voltage on the needles as the output impedance is
so high, a 100Mohm Fluke 40KV probe loads it but the neon detector
works ...
BLINK RATE:
No accelerator - at 15mm away - once every ten seconds
No Hissing at any distance
With accelerator - at 15mm - once every 3.5 seconds.
35mm - once every 10 seconds
The accelerator is a small block of aluminium with conical holes and
has about -1500V on it - it's connected 10 diodes down from the high
voltage end.
The accelerator was made by drilling conical holes with a lathe
centering bit about 1/4" (7mm) in diameter so that the side view is:
______
accellerator -> |____/
needle -------> ----------
The bottom is the same shape (eg 45 degree cone) but I can't draw it
using ascii graphics. The 4 needles are spaced about 20mm apart (0.8")
and protrude about 4mm (1/6") past the end of the 1/4" cone.
With the accelerator in place, it will start hissing at me if I get
within about 5cm of the needles - before I put it in its box. Boxing
it seems to dampen things down a bit. The black plastic box has holes
drilled in it as an approximate continuation of the flare of the
conical shape of the aluminium accelerator block which is screwed to
the back of the front panel.
It's definitely got some ion wind but how much? How I can measure the
output (ions/cc) or alternatively (and much cheaper) what's the blink
rate from a commercial unit of known output with the type of neon
detector described above?
You can probably calculate the ion output (at least within an order of
magnitude) by assuming that "if so much current is going in and
nothing's getting hot" then that current - "in ION form" - is coming
out the other end, but I've not looked at my physics texts for years
as you can probably guess by that handwaving logic!
The shape of the accelerator is also a bit of a mystery. The 4mm that
the needles now protrude is simply what "looked" reasonable. The conical
shape is simply because I had the lathe centering bits.
What's the desirable shape? - probably exponential :-(
Obviously they'll be a relationship between the flare angle, how far
the needles poke out beyond the end of the accelerator, the voltage on
the accelerator and that on the needles ...
Any info or readable references? (eg those without triple integrals :-)
Any thoughts would be very much appreciated ...
Thanks
Giovanni
__________________________________________________________________________
Giovanni Moretti "WHATEVER YOU CAN DO, OR DREAM YOU CAN, BEGIN IT.
Computer Science Dept BOLDNESS HAS GENIUS, POWER AND MAGIC IN IT" Goethe
Massey University Ph +64-6-3504184 Fax +64-6-3502259
Palmerston North, NEW ZEALAND G.Moretti@massey.ac.nz ZL2BOI
Article Reference: 9C7F9BFA89893C35
Date: Sun, 20 Oct 1996 16:09:23 GMT
Original Subject: Re: Powder Coating Gun (High Voltage Ionizing)
In article <548kcv$rob@niflheim.rutgers.edu> Phillip Debrito (debrito@niflheim.rutgers.edu) wrote: : I'm looking to build my own powder coating gun. For those not familiar : with electrostatic powder coating, let me provide some basic info... : So, do I create a series of metal loops in the gun with the (+) : lead and the pass the powder through these loops or what? How does it : work in those little air Ionizer/Purifiers? Hi Phil! I don't have direct experience with these, but I know some electrostatics. You want to generate a small area of plasma so that air passing through it becomes charged. The charged air molecules then attach themselves to the powder particles, charging them. The classic way to generate charged air is to place a sharp metal needle very close to a metal plate, then connect high voltage between the two parts and blow air between them. The voltage should be less than that needed to cause sparks. Which polarity of air comes out? If the negative supply lead goes to the needle, then the device will generate negative charged air. Another way to do the same is to suspend a very thin wire fairly close to a metal plate. (Copiers use tungsten wire, which isn't corroded as much by oxygen in the plasma.) A plasma forms around the wire, and the air passing through it will become charged. The charger assembly in your gun might take the form of a grid of needles near the inside surface of a metal plate, or maybe it's a sharp-edged cylinder held within a larger cylinder so that the sharp edge is close to the flat inner surface of the bigger one. Air blown through the slot between them will become charged. The key is to put a pointy (or sharp-edged) object near a flat object, so "st. elmo's fire" forms on the pointy object only. Two pointy objects give equal and opposite charge output, which is overall neutral. Two flat objects do the same, but only at much higher voltage. Hey, if you get it working, let me know how it turned out. Check out my electrostatics page at: "http://www.eskimo.com/~billb/emotor/statelec.html" -- ....................uuuu / oo \ uuuu........,............................. William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623 EE/Programmer/Science exhibit designer "http://www.eskimo.com/~billb/" Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page
Article Reference: E5775414C81EFD44
Date: Mon, 17 Jun 1996 01:32:50 GMT
Original Subject: Re: Van De graff Generator?
bwilson@newshost (Bob Wilson) wrote:
>HRD6959619 (hrd6959619@aol.com) wrote:
>: What is this and what does it do. HOw many volts are produced and
>: could it make cool looking lightning shots. Any info would be
>: greatly appreciated.
>It generates very high voltages of static electricity. What does it
>really do? Makes your hair stand on end when you touch it! :) Voltage
>produced? Usually in the range of 500,000 to 1,000,000 Volts as I recall
>my high school days, when we made one for a science project.
Electrostatic means for producing very high DC voltages are still used
in a few applications. The company I work for makes electrostatic
particle accelerators that operate in the range of 1MV to 25 MV.
(That's M for Mega.)
While the company that Robert Van de Graff founded has not made
particle accelerators for many years, National Electrostatics Corp
continues to dominate the field above about 4MV. In the realm below 3
MV there is actually quite a bit of competition. Most of these
accelerators are sold for physics research, but, especially lately,
more and more are going into various materials analysis applications.
I am currently working on a few that we have in the field that are to
be used for carbon dating. Running carbon atoms through an
accelerator with a 5MV terminal will allow us to produce a 25 MeV
carbon ion beam. (carbon with a charge of -1 in, carbon with a charge
of +4 out)
We spend a great deal of effort trying to avoid those "cool sparks."
Jim
---------------------------------------------------------------------
Melissa Kepner Jim Adney
mgkepner@facstaff.wisc.edu jradney@mpcug.com
Laura Kepner-Adney
Madison, Wisconsin
---------------------------------------------------------------------
Article Reference: 5181771F210201A1
Date: Thu, 07 Nov 1996 14:26:41 -0500
Original Subject: Re: ESD ZAPPPPPP ZAPPPPPPPP
Jhon wrote:
>
> I would like to know if there is anybody has had any experience in
> designing ESD/EMI compliant hardware/software, and whether you would be
> willing to share some of your experiences with meeting the
> 801-2 requirements for electromagnetic compatibility
>
> Thanks in advaced
The first rule is to ground everything that is a metal surface
accessible to the ESD gun solidly to chassis ground (metal to metal).
Masking may be necessary for painted covers. In some instances
you may need to use toothed star washers.
Second is to ground cables and shields to cables at the point
of entry to your product. In other words, as soon as you can.
You may experience two phenomena (little understood) that mean
two entirely different things:
1. Your product fails at a minimum level, say 4KV and
continues to fail at any higher value. This is
USUALLY a grounding issue.
2. Your product fails within a band of voltage, say
4KV to 6KV, but operates below AND above these limits.
This is a more complicated reaction of your system
to the different spectral content of of the pulse
within the band 4KV-6KV then outside it.
This is usually a system frequency response issue
that can be very difficult to pinpoint and usually
results in alot of grounding effort that proves
useless. For instance, there could be a slot
antenna formed between the cover and the case
that 'activates' in the KV range as a tremendous
transmitter when current circulates around it
on its way to ground.
Anyway, keep a close eye on the results of where the spark
is being applied to the product and system ground. The current
will circulate through your product to that ground point
and unfortunately through anything in between if there isn't
a good ground.
*******************************************************
Doug McKean
doug_mckean@paragon-networks.com
-------------------------------------------------------
The comments and opinions stated herein are mine alone,
and do not reflect those of my employer.
-------------------------------------------------------
*******************************************************
Article Reference: 41C0D1B0533D9680
Date: Sun, 16 Apr 2000 18:36:10 +0200
Original Subject: Re: 25uF 4Kv ?
HI! "http://www.aerovox.com". They produce C like that. I ordered one with 47uF and 4.5 KV and one with 150uF and 2.5KV both same size.(2.77x5.75x1.91) Holger omega schrieb: > > Does it exist without connecting many, many > small capacitors across together ? -- -------------------------------- Holger Cecchin ceccho@eti.etec.uni-karlsruhe.de ceccho99@gmx.de --------------------------------
Article Reference: A6D6E9503DDB67AE
Date: 25 Oct 1996 12:40:38 GMT
Original Subject: Re: How to measure a pulse?
brian whatcott, <inet@intellisys.net> said...
>
>almar@tsc1.cps.unizar.es says...
>>
>> The problem range is 12000V and only some mA. The source is a
>> piezoelectric material. I'd like to be able to see the exact form of
>> the pulse in an oscilloscope.
>
> Place a 100 Mohm and a 100 Kohm in series as a potential divider to
> ground.
The 100M-ohm would have to be a say 15kV version (i.e. Victoreen glass
resistor a few inches long, etc.). And it'll be absolutely necessary to
parallel the 1000:1 resistive divider with a capacitive divider. Say 5pF
from the pizeo and 5000pF to gnd. The 5pF must be good for 15kV - coaxial
cylinders with air dielectric. Also a shield or other element will have
to be arranged to insure that only the charge through the 5PF reaches the
divider output.
Not everyone has a 15kV resistor sitting in their parts bins! No problem!
Since the time constant of 5pF and 100M-ohms is 0.5ms, which is no doubt
longer than a pressure-induced piezo spike, just skip the 15kV resistor
entirely!
OK, how about 1M-ohm and 5000pF for the bottom end of the attenuator? Now
the high-pass time-constant is 5ms - better yet! E.g. 1M-ohm scope input,
6 feet of coax, additional 4700pF to gnd. Connect this to a homemade 5pF
with appropriate shielding.
Oops - destroy the scope input in case the homemade cap breaks down!
OK, how about 10x scope probe (includes 9M-ohms to protect the scope
inputs)? Now the bottom of the attenuator consists of the scope probe and
470pF cap to gnd. Connect this to our home-made 4.7pF cap. Time constant
still 5ms. Scope probe sees 120V, scope input 12V 1000:1 overall.
Calibration? A 10V 10kHz sig gen yields about 10mv - just measure this
and determine the actual scale-factor of your instant HV probe!
After calibration, change to 4700pF for 50ms time constant (10,000:1 attn,
1.2V scope signal) if better pulse shape range is desired.
--
Winfield Hill hill@rowland.org _/_/_/ _/_/_/_/
The Rowland Institute for Science _/ _/ _/_/ _/
Cambridge, MA USA 02142-1297 _/_/_/_/ _/ _/ _/_/_/
_/ _/ _/ _/ _/
"http://www.artofelectronics.com/" _/ _/ _/_/ _/_/_/_/
Article Reference: CE38B22FFFBD7B94
Date: Wed, 21 Aug 1996 06:34:51 GMT
Original Subject: Re: How to switch 900VDC cost effectively?
nemax@getnet.com (Doug Skabelund) wrote: >I have an upcoming project which will require me to switch 900VDC on >and off to six different channels. The current is about 40mA on each >channel. The 900VDC is full-wave rectified and does not necessarily >need to be capacitor filtered. APT (Advanced Power Technologies Bend, OR) make a line of available 1000V Power FETs... I'm using their 1000V FETs in a 3KHz circuit with peak current around 15A during the sub-microsecond transition time... jim jimk@aoainc.com
Article Reference: 1F147631D050E473
Date: 2 Oct 1996 10:33:37 GMT
Original Subject: Re: Can I build a HV probe?
John Anderson, <megavolt@io.com> said... > >Everyone keeps mentioning frequency. When you say at "high frequencies" >the probe will not be accurate, do you mean hz, khz, or mhz range? You can calculate this for yourself. The parasitic lead-to-lead capacitance of a typical small resistor is 0.05 to 0.2pF. The capacitance from the _middle_ of the resistor and from any connection node between series resistors, to ground, may range from 1pF to 5pF or more depending upon your choice of a sheilding scheme. Longer glass resistors intended for high voltages have lower lead-to-lead capacitance, but higher distributed parallel capacitance. As a worst case, imagine a 1000M-ohm probe made with a 2-inch long resistor. To start, place the capacitance to ground from the midpoint. If you assume 5pF of parallel capacitance, you'll see you're in trouble even at 60Hz! HV probes with usable high frequency response may have cleverly arranged sheilds which can be connected to ground, the attenuated signal output, and the input. Some shields may overlap and may be adjustable, to provide an adjustable capacitive divider that can swamp the remaining effects of the resistor's capacitance. These probes can be very accurate at DC and high frequencies, but the skill of the designer is tested in the transition between resistive and capacitive divider action. Poorly designed probes can suffer from mid- or high-frequency errors and from severe pickup sensitivity to nearby rapidly-changing voltages. For example, I've seen probes that provide an output even when the measuring tip is grounded! -- Winfield Hill hill@rowland.org The Rowland Institute for Science 100 Edwin Land Blvd. Cambridge, MA USA 02142-1297
Article Reference: E0B35885A28B1949
Date: Mon, 07 Oct 96 17:16:57 EST
Original Subject: Re: Can I build a HV probe?
Helmut Wabnig at wabi@mail.carinthia.co.at says...
>
>> I was thinking of taking a glass tube, and stacking lots of
>> glass-body resistors in series to drop the voltage down to
>> a managable level. Would this work? ...
>
> That is exactly right. You have the correct plan already.
> Go, make it.
> The scope input has a certain resistance, eg 10 Megohms.
> Parallel is a capacitance, several picos.
> Must be taken into the calculations, the capacitance
> will considerably reduce bandwith.
>
> Scope probe schematic:
>
>
>
> !------------------<scope input
> !
> !
> <-------------RES1-----------RES2---------!!ground
> ! ! ! !
> !--CAP1--! !--CAP2--!
>
> tau1=R1*C1 must be equal to tau2=R2*C2,
> then the frequency response is correct and you
> don't waste bandwith.
>
> where R2 and C2 are the added values of the
> scope input and the probe.
This is classic low-voltage probe architecture and it doesn't
work for HV scope probes, unless 1) you're willing to have an
overly high capacitive loading, or 2) you don't care about
mid-frequency or pulse-shape response accuracy. This is
because the RES1 value will be very high, 100M or more likely
1000M ohms, and physically long and large. So the real
circuit is like:
________ CAP1 __________
| |
<------- R -*- E -*- S -*- 1 ------ etc
| | |
Cs Cs Cs
| | |
gnd gnd gnd
Because the RES1 is so high, the probe becomes a good antenna,
and a shield is mandantory. Therefore the Cs "stray"
capacitance is higher than you might think.
I think you see the problem.
One solution is to make C1 very large, but it's just a matter
of specs - if you want 1% performance over the whole range, C1
is a severe load. There is a good overall solution, which I
think is fairly clever (after thinking of it, I discovered the
experts had beat me to it!); see my earlier posting in this
thread.
--
Winfield Hill hill@rowland.org
Rowland Institute for Science
Cambridge, MA 02142
Article Reference: B95FC74205DABE66
Date: Sun, 27 Oct 96 21:09:26 PDT
Original Subject: Re: flashtube driver needed!!!!
In article <54oqcf$ltr@ns1-1.CC.Lehigh.EDU>, <c002@Lehigh.EDU> writes:
> I need to drive a powerfull flashtube. I have neither a tube or driver btw
> (ie: if you have, i'll buy! )
> This will be exciting a Ruby rod, so its not a little camera flash i need!
We excited a Neodymium rod using two linear flash tubes and a HV power supply.
The supply was a 2000 volt transformer with an array of high-voltage
capacitors and high-voltage diodes.
We stacked up five 450 volt capacitors on either leg of the supply, with 10Meg
resistors across each capacitor to even out the voltage loading. We also put
10Meg resistors across each 1KV diode to protect it.
<bad ASCII art attempt:>
115V 2000V
----3 || E--->|-->|-->|-->|------\ [trigger circuit]
3 || E \ /
3 || E ||--||--||--||--||-------O O---------------\
3 || E---< |
3 || E ||--||--||--||--||------------[==========]--/
3 || E / Flash Tube
----3 || E---|<--|<--|<--|<------/
MAKE SURE THE CAPACITOR POLARITY IS CORRECT, or you will get big explosions of
toxic oil.
We fired this sucker by an air-gap switch. Basically you set the tube up with
two metal spheres in the circuit, seperated by about 1/4 inch. Then you use a
photo-flash trigger coil connected to a wire probe between the spheres to
ionize the air. BAM!
Warning: we blew chunks of metal out of a lead block with this device. Be
VERY careful when you set it up!
1. Capacitors can maintain a fatal charge for a long time after the power is
removed. We shorted 'em out with a copper rod on the end of a Lucite handle
before touching anything.
2. Air-gap switches can fire spontaneously. Never energize the device until
everything else is ready to go! We eventually went to an oil-quenched knife
switch for more control.
Article Reference: 0331D5DCD530A214
Date: 18 Jun 1996 19:49:58 GMT
Original Subject: Re: Building a Mains Transformer - HELP - 117VAC to 10,000VAC @ 400 MA
Steve Roberts <osteven@en.com> wrote: > You might try a catalog for neon sign supplies, they use large tranformers to cook the tube during >processing, but the cost is going to set you back say 850 dollars for a rebuilt one >plus the choke needed to regulate current in the primary is going to cost another 200 or so. A friend of mine who does this uses a pole pig and a substation transformer (both power company surplus) hooked up backwards to give him 200kV at a few amps. He demonstrated it once for me -- drew a 3-4 foot arc with a wire hooked to the end of a 4-foot long glass rod. It was most impressive. ;-) >4. disturb the space time continum No, you need a flux capacitor and a Mr.Fusion to do that ... <BGB> "http://ccwf.cc.utexas.edu/~lihan/" mailto:lihan@ccwf.cc.utexas.edu
Article Reference: DF2C89AD81C19F85
Date: 17 May 1996 21:11:32 GMT
Original Subject: Re: Need He-Ne laser pwr supply ideas
: Hello, : I would like to build the above mentioned power supply but am only : familiar with linear power supply theory. Any ideas or schematics would : be greatly appreciated. The DC to DC convertors that used to run these : tubes were rated at 1kV @ 3-4ma output but there was no information : mentioned on a striking voltage. I would like to power it with the 110VAC : line. I built a linear supply for a HeNe tube which requires 2400V @6.5mA with a striking voltage of about 5Kv. You can bet the stiking voltage for a 1kV tube is over 2KV easily. I chose a linear supply to reduce the noise in the laser light that can be a byproduct of a cheap switch mode supply - plus this was years ago and switchmode was not as prevalent. The supply was a neon light transformer feeding a normal bridge rectifier with filter caps, followed by a series pass current regulator. It is easy to burn out or greatly reduce the life of many HeNe tubes by pushing too much current through them - so the current limiting aspect of the supply was important. The striking voltage was obtained by wiring a very low current voltage tripler around the main supply. Some items which made the supply tough to design: o finding a neon xformer with an output close to 2400V o finding good quality filter caps which could be stacked to withstand 2800-3000v. o finding good quality rectifiers and caps which could withstand the full 6KV open circuit striking voltage. o designing a current regulator which would pass precisely 6.5mA with low noise, and over a voltage differential of 200-800V (the worst case difference between the highest transformer output voltage at high line voltage and the lowest HeNe tube operating voltage, and vice-versa). The supply is heavy, and the parts are hard to obtain. If I did it over now - I'd take the time to design a switch mode supply. Jim D.
Article Reference: A79FD0E0D88CC831
Date: 31 May 1996 01:58:05 GMT
Original Subject: Re: old-SF-movie device with climbing spark??
Jacob's Ladder (Climbing Arc) Construction:
------------------------------------------
This is the type of high voltage display seen on many old (and bad) sci-fi
movies. Jacob.s Ladder come in all shapes, styles, and sizes. Here is info
on a common type that is easy to construct with readily available parts.
You will need 12K-15K volts AC (50/60) Hz at say 20-30 mA. A neon sign
(luminous tube) transformer is the usual source though an oil burner ignition
transformer (e.g., 10 KV at 20 mA) will work in a pinch (some say better and
cheaper) or you could build an inverter type power supply.
Luminous tube transformers can be obtained used from sign shops or demolition
companies. Oil burner ignition transformers can be pulled from old oil
burners - probably free for the asking at your local HVAC company.
Take a pair of thick wires - the steel wire from old metal coat hangers works
pretty well - straighten them out and mount them with a gap of about 1/4
inch at the bottom and 1-3 inches at the top. Of course, all on an insulated
non-flammable material! Connect the high tension output of the transformer
to the two wires and you should be all set. Some adjustment of the spacing
at the bottom (to get the arc started) and at the top ((to determine when
the arc is extinguished and how fast it rises) may be required (but do so
only with the power off!). Depending on the voltage and power rating of
your high voltage source, these dimensions may vary considerably.
__ 1-3"
^ \ /
2-3 feet \ /
or more | \ /
v --' '--
1/4"
A Jacob's Ladder works on the principle that the ionized air in the arc
is a lower resistance than the air around it and heated air rises. The
arc strikes at the point of lowest breakdown voltage - the small gap
at the bottom. The heated plasma rises and even when it is an inch or
more in width is an easier path for the current to follow. Eventually,
the gap becomes two wide, the arc extinguishes and is reestablished
at the bottom. For best results, shield the whole thing from drafts but
don't use anything that can catch fire!
SAFETY:
------
Make sure that no one can come in contact with this - particularly curious
onlookers. Separating the potential victims from any possible contact
with the high voltage is really the only foolproof way of protecting
against fools or the unaware - and you from a lawsuit. People not
familiar with high voltage phenomena (or aware only through grade-C
sci-fi movies) can be incredibly naive.
A GFI (ground fault interrupter) is of no use in protecting against HV
contact since the secondary of a neon sign transformer is isolated from the
line but its centertap is usually connected to the case - which should be
grounded. However, a GFI would be a good idea in any case when you are
working with line connected equipment.
12,000 volts will jump approximately 1/2-3/4 inch in dry air - more under
humid conditions. Don't forget that 12,000 VAC is approximately 17,000 V
peak. Neon sign transformers have current limited outputs - 30 mA is
typical - but that is still highly dangerous - lethal under the wrong
conditions.
You can build a small Jacob's Ladder using a high voltage transformer
of lower capacity or a DC-AC inverter using a TV flyback transformer.
While these would be less dangerous, there is little room for carelessness
when working with any type of high voltage device. Even if there is no
resistive path, the stray capacitance can permit enough AC current to flow
to give you a painful experience!
* Do not work alone.
* Always keep one hand in your pocket when anywhere around a powered
line-connected or high voltage system.
* Wear rubber bottom shoes or sneakers.
* Don't wear any jewelry or other articles that could accidentally contact
circuitry and conduct current.
* Use an isolation transformer if there is any chance of contacting line
connected circuits.
* Don't make adjustments with power on.
* Finally, never assume anything without checking it out for yourself!
Don't take shortcuts!
Article Reference: 12EBB610384AF6A8
Date: Sun, 6 Sep 1998 17:39:46 +0100
Original Subject: Re: 3-D sound effect
In article <35f2eea7.45635052@netnews.worldnet.att.net>, James Meyer <notjimbob@worldnet.att.net> writes >On Fri, 4 Sep 1998 07:49:50 +0100, John Woodgate ><jmw@jmwa.demon.co.uk> wrote: > > >>No, becuase even if your hypothesis were true, you have no way of >>knowing whether the tones started simultaneously or not, so you could >>not determine the significance of any observed time-delay. > > But then.... why do you hear a high frequency "crack" before >you hear the low frequency "rumble" that happens with a lightning >strike? If you're not too close, that is. > The 'crack' is the sound arriving directly from the discharge, while the 'rumble' is reverberant sound that has been reflected from clouds and the ground, which takes time. The spectral content is weighted to low frequencies because the higher ones are absorbed and diffracted to a greater extent. -- Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. OOO - Own Opinions Only. You can fool all of the people some of the time, but you can't please some of the people any of the time.
Article Reference: 5DAA8DD306F7EFE5
Date: 17 Sep 1998 04:02:19 GMT
Original Subject: Re: Diode back conduction
>I am planning to build a high voltage power supply for a tube project, and >I need to create a reference voltage as high as possible >to compare with an output of ~ 400V. Zener diodes only seem to go up to >around 40V, and I was wondering whether it was possible to reverse bias an >ordinary diode with a breakdown voltage in the vicinity of 400V to create >a reference voltage. If I run a (small) constant current backwards >through the diode (probably in the order of micro amps), will this produce >a consistent output, and will the diode be able to withstand this >treatment for long? It will probably work, but I doubt that the stability of the voltage will be good enough. If you need real stability in a power supply I would suggest a solid state reference diode that is something like 7 V. This would be compared to the divided-down output voltage. The 7 V reference diodes are very stable with temperature. This, and a set of stable and accurate divider resistors, will get you a better overall supply. the other thing you can do is bypass the upper divider resistor with a small capacitor. This effectively provides a much higher feedback gain for ac, cutting the ripple down significantly. -- phil
Article Reference: 0B4E69A1926EB78A
Date: 28 Sep 1998 04:48:22 GMT
Original Subject: Re: A Question of Capcitance
Ken <tylereng@pacbell.net> wrote: > Yesterday in the components group I saw a request >for a 0.1 pf capcitor. Now I have been a hobbiest for quite >some time now but that value seems almost incomprehensible >to me. I've read many times that lead length alone on capacitors >can greatly impact the true value of a capacitor used in a circuit. >Especialy at lower values. > >Now for the questions: > >1.) Is there really a practicle use for a capacitor of that value ? Yup. At very high frequencies and/or voltages, such a capacitor would carry a good deal of current. >2.) Would it be possible to make your own by simply providing >two conductive plates/pins/wires with a little space between them >and use the air as a dialectric ? Yes, and this is generally how it's done. You'll often see a small capacitor made by simply placing two copper traces on a printed circuit board close together. These are sometimes adjusted by scraping away some of the copper trace. >3.) Does the dialectric value of air change with enviromental variations ? Not very much. Air is pretty close to vacuum as far as dielectric constant goes. Note that in the printed-circuit-board capacitor, the dielectric isn't air, but both air and plastic, or whatever it is that the circuit board is made out of. >4.) Does wire itself have a certain amount of capacitance in a circuit ? It sure does. And you can't get rid of it, either--at least not very easily. The capacitance values are low--like your 0.1pf--but these can be very significant at high frequencies. And if you think you're not going to be dealing with high frequencies because your circuit is meant, say, for audio frequencies, you may be in for a surprise: the capacitance of the wires may, under the proper circumstances, provide nice feedback pathways for the signal. When the output of an amplifier is thus connected back to the input, you get a high-frequency oscillator whether you wanted one or not. It's enough to drive you nuts and can be very difficult to get rid of. One method that's used is to apply other capacitors that will re-route any high-frequency signals. I suspect that this is the intended purpose of the capacitor you saw requested. The method is called "neutralization." >5.) Instead of the above use of air as a dialectric could you not use >a piece of wire extended above the circuit, looped once, give a close >approximation of a 0.1 pf capacitor ? Yup. Back before there were printed circuits, this was, as others have mentioned, called a "gimmick." You'll find them in a lot of places. If you're interested in the art of tuning a high-frequency circuit, have a look inside the tuner of an FM radio or a UHF television set. You'll see all kinds of unlikely components: one-half-turn coils (with center taps, yet,) strange ground plane designs which cut down (but don't eliminate) the capacitance between components, and other arcane tricks known only to rf guys. >6.) Does equipment exisit to accuratly measure a 0.1 pf capacitor ? Yup. You could do it yourself if you had a high-frequency oscillator and an impedance bridge circuit. We also worry a lot about small capacitances in high voltage work. The frequencies are often low, but even a very small capacitance that's charged to a million volts and then to minus one million volts every 1/120 second is pretty significant. In fact, the capacitance of electric power lines to ground and each other is always taken into account in electric power work. That +/- 1MV figure isn't an exaggeration. That's about the peak voltage you'll see on the 765kV lines that are powering your computer right now. M Kinsler still trying to figure out what the hell ThinkQuest was supposed to have been... -- ............................................................................ Interpretation and instruction of physical science and technology Athens, Ohio, USA. "http://www.frognet.net/~kinsler"
Article Reference: 8B739051078F6B66
Date: 5 Dec 1996 21:02:21 GMT
Original Subject: Re: Hints for Automotive Electronics required
Dave Hills (dhills@onramp.net) wrote: : minilinx@netaccess.co.nz wrote: : > : > Hi, : > I am experiencing problems with over voltage pikes destroying the : > power supply to a micro processor controlled circuit. : > The current conditions and ciruit are as described below. : > : > Voltage = 24V (nominal) : > : > In series with the +Ve input to the device are a 330R/2W resistor, : > 1N4007 Diode and a 1W/12V Zener Diode. Following this is a 20V/1W : > Zener diode and 100uF capacitor in shunt. This then feeds a LM7805 : > regulator. : > : > Referring to an application note by SGS-Thompson regarding protection : > for 12V automotive systems, I expect that voltages as high as 300V are : > possible for up to 300mS. I assume that the 24V system from the : > diesel engine may produce spikes well in excess of this. : Get yourself a copy of international standard "ISO 7637-2". This covers : the 24 volt vehicular requirements for immunity from electrical : transients. It provides all the waveforms and voltage levels you will : have to contend with. A good L-C filter on the input is a must to : attenuate the high voltage fast transients normally encountered. The LC filter will not necessarily help. A fast-rising tranisient will couple right on through most simple inductors due to the interwinding capacitance. This is why zeners or transzorbs are mandatory. A zener is *extremely* fast, since there is no Trr or Tfr time to contend with (it is always reverse biased, so removal of minority carriers from the PN junction is irrelivant). Most microcontroller-based electronics that I have seen in volume production (used in an automotive environment) relies on this approach, not LC filters. Bob.
Article Reference: 62916742F0FA6118
Date: Thu, 30 May 1996 23:15:02 -0600
Original Subject: Re: Huge Fucking Tesla Coil.
On Mon, 27 May 1996, Zev Berkovich wrote: > I don't know anything about Tesla coils, so I wouldn't be able to help > you. However, maybe you could help me. I want to build one, can you > tell me where to start? Ok, some parts you probably should get are: 1. neon sign transformer, 15kv 2. heavy gauge insulated wire (probably a bit thicker than double strand wire used for lamp power cords). 3. 3 foot length of 1 1/2 diameter pvc pipe 4. very fine motor wire, shellacked (sp?) this wire is like the wire used to wind electromagnets 5. 1/4 inch plate glass, 5 sheets or so, about 16" x 22" 6. plastic container for plate glass, one of those under-bed containers will do 7. motor oil, 10W-40 is ok 8. misc parts Wind the fine wire around the pvc pipe, it takes a few days usually, single layer Wind some of the thick wire around a quaker oats round box make a capacitor by putting tin foil sheets, with rounded edges, between the plates. immerse the plates in the oil, getting out bubbles hook up the transformer across a spark gap to the plates, which are in parallel with the primary winding (thick wire). put the pvc pipe with the fine wire upright and inside the quaker oats box with the primary Ground the lower wire of the secondary (fine wire from pvc, the wire on the lowest part, where you started to wind the wire) to a pipe or some suitable ground Turn on the transformer briefly; don't look at the spark gap because too much ultraviolet radiation it is loud, will interfere with radio, tv, cable, etc. > There are some equations, if I recall cost is maybe 50 to 100 dollars there are plans for a parlor-trick size device in the book _Build your own working laser, phaser, ion ray gun_ that can be readily scaled up Good luck WARNING: if you have a cat, a curious cat, make sure it stays away from the apparatus or else all that will be left will be a wisker, and your next project will have to be a crystal radio > In article <4o4486$n67@carbon.cudenver.edu> you wrote: > > : Ok, I made one that put out 2 foot sparks. > > : Now is time for the grandaddy of them all. > > : It should not be operable indoors, for obvious reasons. > > > : How? (because if I asked, "why?" that would presuppose a reason) > > > > -- >
Article Reference: 30F0DBCB583D5140
Date: Fri, 23 Jul 1999 16:58:04 GMT
Original Subject: Re: 60uF+60uF=30uF?? cap question
Carbon composition resistors exhibit lower than specified resistance at high voltages but 1/2W should be OK. Horace W Heitman wrote: > Yes. You should use a resistor in parallel with each capacitor to equalize > the voltages across the capacitors. Each resistor should have a resistance > of 1K times the voltage across it. In your case, each capacitor would have > 250V across it so each resistor would be about 250K. The tolerance of the > resistors ought to be 5% or better and the power rating should be a minimum > of 1/2W > . > sueded <kttk@netvigator.com> wrote in message > news:37988b21.3471696@news.netvigator.com... > > hi, > > > > i got a schematic that need a 30uF500V capactior in power supply part > > but i cant find that high voltage cap...only up to 450V..so i thinking > > to connect two 60u250V (or higher voltage) in series...from the > > equation i learnt...60u+60u in series should be =30u > > and by the voltage divider law...each cap should be carry 250V... > > > > is it correct and work?? > > > > sueded
Article Reference: DA5DE469BC4E6B8C
Date: Wed, 29 Nov 1995 14:04:04 GMT
Original Subject: Re: Static Generator
Hi Alan. What you have there is a Wimhurst machine. The counterrotating disks generate electricity by electrostatic induction, similar to the process in an electrophorous. The jars are Leyden jars, which are basically high voltage capacitors. If they have metal inside, they will do. Just don't shock yourself silly. A small neon light should show if electricity is being produced. Eric
Article Reference: 5399A96317294E7B
Date: Wed, 26 Aug 1998 17:38:58 -0500
Original Subject: Re: Old Album pop &scratch filter?
John Woodgate wrote: > > In article <35E27337.86C89479@io.com>, Pin 2 Hot <pinksnd@io.com> writes > >It is sitting on top of my "Kenwood Audio De-noiser" and my Pioneer > >"reverberator", the kind with springs in it. I love funky old gear. > Have you got a Keith Monks 'Dishwasher' as well? A "Keith Monks 'DisHwasher'"? I've got a DisCwasher system with the brush pad that has the little bristles all bent in one direction, the cleaning fluid, and the "Zerostat" gun that shoots HV ions from a piezo crystal, for neutralizing the static electricity on the vinyl, and a nice, block of mahogany with various odd-shaped routed holes for storing these items, along with some other doo-dads, including a little fold-out mirror, presumably for inspecting the stylus. Some people are quite anal about record care, me, I just throw 'em in a pile, unsleeved. (that's why I won't sell my pop eliminator.) :-) Wait a minute, I think I remember the item you're referring to. Do you stick a record in vertically, and the thing spins the record while brushes whirl on both sides and a vacuum runs to collect the dust? No, I don't, but NOW I want one. :-) -- Gene
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