Electrochemistry: Liquid Power Resistor for 2000VAC
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From: VioletaPachydermata on 13 Mar 2010 22:17 On Sat, 13 Mar 2010 18:04:11 -0800, D from BC <myrealaddress(a)comic.com> wrote: >In article <eleop5lf9ee8auf5ohvn51aoj61vgiongl(a)4ax.com>, >OneBigLever(a)InfiniteSeries.Org says... >> >> On Sun, 14 Mar 2010 10:36:15 +1100, Grant <omg(a)grrr.id.au> wrote: >> >> >I dunno, 2kV + open water still sounds like Bang! to me ;) >> >> >> 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 = 99454 > >Error 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.
From: pimpom on 14 Mar 2010 00:55 D from BC wrote: > lol.. > Too laborous but 0.25W resistors are cheap. 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. > > If I were to do that, I might just glue them all to a heat sink > instead of using a fan. 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.
From: Robert Baer on 14 Mar 2010 01:58 D from BC wrote: > In article <weOdnViNweT29QbWnZ2dnUVZ_gGdnZ2d(a)posted.localnet>, > robertbaer(a)localnet.com says... > >> I thought the voltage rating of those resistors was 150V, not 200V - >> so one would need 14 resistors in series; make them 5W and be OK for >> "any" time period. > > mmm.. pile of resistors vs liquid resistor.???. > > The CuSO4+water resistor does score points for power handling, voltage > handing and flexibility(I get every value just add more CuSO4). > Well, copper sulfate DOES have the advantage that if you use copper electrodes, one does not have to worry about the chemistry going bonkers..
From: Ecnerwal on 14 Mar 2010 13:06 In article <MPG.2605e3e6e5d856be989707(a)209.197.12.12>, D from BC <myrealaddress(a)comic.com> wrote: > iic resistivity of pure water is 18.2Mohm cm^2/cm at 25C 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
From: Michael A. Terrell on 14 Mar 2010 13:48
Ecnerwal wrote: > > In article <MPG.2605e3e6e5d856be989707(a)209.197.12.12>, > D from BC <myrealaddress(a)comic.com> wrote: > > > iic resistivity of pure water is 18.2Mohm cm^2/cm at 25C > > 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. 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!' |