Electrochemistry: Liquid Power Resistor for 2000VAC
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From: pimpom on 13 Mar 2010 17:26 D from BC wrote: > In article <80229uFvk3U1(a)mid.individual.net>, > map.nospam(a)f2s.com > says... >> >> "D from BC" <myrealaddress(a)comic.com> wrote in message >> news:MPG.260561b419a1f67989702(a)209.197.12.12... >>> If my junkbox resistor blows up in a jar of water, then I'll >>> try to >>> make a 100k CuSO4+water resistor. >>> Then I'll replace that with a power resistor from my next >>> parts >>> order. >>> >> >> I'm not sure I'd use water as the coolant. I'm dubious about >> using >> water, the resistor might act as a heating element and boil >> the >> water locally, it'll then be surrounded by gas bubbles which >> will >> increase further the thermal resistance and the resistor might >> then >> overheat. > > I only need 5 seconds of circuit run time. > >> >> I'd be tempted to use oil instead. Ecnerwal said that they >> used >> copper sulphate as the resistive part, then submerged the >> whole lot >> in transformer oil. >> >> Anyway, let us know how you get on! >> >> Mark. > > I had to insulate the resistor leads.. > Tap water was showing some conduction. Cl ions and other ions > are > present. I could use distilled water but that's another trip to > the > store. > > I've put 1240VAC on the 100K 2W in tap water for 5 seconds and > alls > well. > I might go up to 2000VAC at a later time. Have a good stock of 1/4W carbon resistors? Why not string 50 or so in series and blow on them with a table fan? (Quarter-watt carbons are about 30-50 US cents a hundred here).
From: D from BC on 13 Mar 2010 18:35 lol.. Too laborous but 0.25W resistors are cheap. If I were to do that, I might just glue them all to a heat sink instead of using a fan.
From: Grant on 13 Mar 2010 18:36 On Sat, 13 Mar 2010 08:57:27 -0800, D from BC <myrealaddress(a)comic.com> 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). 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.
From: Archimedes' Lever on 13 Mar 2010 20:24 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.
From: D from BC on 13 Mar 2010 21:04
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% |