I dunno, 2kV + open water still sounds like Bang! to me ;)
A ladder of 10 x 10k, 5W ceramic resistors in series would hold back that voltage, as Robert states. For example Welwyn - WMO5S-10KJA05 is rated at
500V breakdown.Grant.
Would not do anything with pure water.
iic resistivity of pure water is 18.2Mohm cm^2/cm at 25C
If I got this right.. Given a water wire with a 1cm^2 cross section and a length of 1cm then the resistance of the water is 18.2Mohm.
The bare resistor leads from a 100k resistor in this amount of water has an error about
100k//18.2Meg = 99454Error 100k - 99454/100k * 100% = 0.5%
Take two tablespoons and a rubber band. Coil up the rubber band and put it between the two, stacked spoons, keeping them separated the whole time (very important). Bind together with additional rubber bands being sure to continue following rule #2 above. Attach wires to it and drop in a glass of cold water and plug the wires in the wall.
It boils a cup of water pretty quickly. Likely inside of two minutes.
Add instant coffee, sugar, and creamer, and you have a nice, hot, steaming cup of contraband jailhouse coffee. Blow a fuse, and they come shake down the entire cell block.
Awww, you're too lazy. :-) You can solder 50 resistors in less time than you spent reading and replying to all the posts here. I was serious with my suggestion. It's the most straightforward and most predictable as well as one of the least expensive of all the suggestions so far.
For a one-time use for 5 secs, pointing a fan in the right direction is easier than gluing them. If it turns out you want to use them again, you can lay them out at the bottom of a plastic dish, stick them on with epoxy that will also serve as insulation, and then put in some water to act as a coolant.
Well, copper sulfate DOES have the advantage that if you use copper electrodes, one does not have to worry about the chemistry going bonkers..
Ultrapure water is a great insulator. It's also "not found in the wild" and takes constant deionization filtration to maintain in an ultrapure state. If you go putting copper in it, it won't be staying ultrapure. One of our pulse machines did use it (with stainless steel inner and outer conductors) as the insulator for a coaxial line about 5 feet in diameter (outer - inner was about 18 inches as I recall.) Transformer oil was used for most applications requiring high-voltage and access to parts - presumably the water gave a better capacitance for the transmission line in that case (I worked on them, I didn't design them).
From the practical point of view, the string of carbon (or wire-wound) power resistors (or multiple strings in parallel if need be for power handling) is simpler to implement, has no leaking fluid potential, and is often cheaper. Strings of 2-watt resistors inside a vinyl tube (no doubt not helping with power handling, but making them safer as far as inadvertent shorting) were a common way to get a high-voltage resistor without breaking out the big bucks (research budgets are not generally lavish) for all-in-one piece high voltage resistors. Better cooling can be had by wiring them into perfboard instead.
-- Cats, coffee, chocolate...vices to live by
The RCA TTU-25 series transmitters had over 7 KV across the water in the cooling system. the was a monitor to constantly test the purity. I believe the trip point was 100 MOhm per cubic centimeter where it would shut down the transmitter. It's been almost 20 years since I've seen one of them.
-- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
Since I make my own boards, I might order 50 2k 1/4W chip resistors.
0.05 cents each * 50 = $2.50 I could solder paste and solder (one shot) on a hot plate. Or... Use I could use throughhole R and perf board.
This is Sandia's Z-pinch fusion machine. All the final HV stuff is in a big swimming pool, insulated by pure water.
"When the accelerator fires, powerful electrical pulses are delivered by 36 transmission cables protected by insulation techniques developed over the last 30 years. Highly synchronized laser-triggered switches allow the stored energy to be discharged simultaneously through the 36 cables, each as big around as a horse and 30 feet long, arranged like spokes of a wheel and insulated by water. The enormous electrical pulse of 50 trillion watts strikes a complex target about the size of a spool of thread."
John
Neato... Perhaps I can call it 'wetware' :P
That was my desktop wallpaper 8 years ago, idiot.
Cool.. :) Looks like something out of a sci-fi movie..
18.2 Mohm-cm is the right value for ultrapure water at 20 C (or thereabouts). However it's a fairly steeply declining function of temperature, so with enough dissipation, it's likely to run away. Using a solution of some salt that disassociates fully would stabilize the conductivity vs temperature. (It still wouldn't be that stable, since the viscosity of water drops steeply with temperature too.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
^^^^^^^^^^ It won't stay pure when you place the resistor pack within, let=20 alone when you apply voltage.
=20
That would give you insulation breakdown problems.
True.. Two parameters in conflict, thermal coupling and electrical isolation. I probably thought of using nonconductive thermal epoxy.
Did you see my suggestion to fix the resistors with epoxy to a plastic box and then put some water in the box?
Of course it does, look up any high school text on electro-chemistry. Acid dissociation constant is a good phrase. Electrovalency etc. Wikipedia has a reasonable article.
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