Electrochemistry: Liquid Power Resistor for 2000VAC
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From: Tim Williams on 12 Mar 2010 21:52 "D from BC" <myrealaddress(a)comic.com> wrote in message news:MPG.26047cd7780c7eeb9896f9(a)209.197.12.12... > I do have CuSO4. > > http://en.wikipedia.org/wiki/Electrolysis_of_water > 'The following cations have lower electrode potential than H+ and are > therefore suitable for use as electrolyte cations: Li+, Rb+, K+, Cs+, > Ba2+, Sr2+, Ca2+, Na+, and Mg2+. Sodium and lithium are frequently used, > as they form inexpensive, soluble salts.' > > Those are all group 1 and 2 elements.. > So I suppose I should use CuSO4 to prevent H2 and O2 bubbles creating > resistance error on the electrodes. If you use Cu electrodes in CuSO4, you'll get straight electroplating. A few seconds run time won't make a difference. Tim
From: markp on 13 Mar 2010 03:52 "D from BC" <myrealaddress(a)comic.com> wrote in message news:MPG.26047ecfa9832fe9896fa(a)209.197.12.12... > In article <8004pkFd3U1(a)mid.individual.net>, map.nospam(a)f2s.com says... >> >> "D from BC" <myrealaddress(a)comic.com> wrote in message >> news:MPG.26041fc5df0edf429896f1(a)209.197.12.12... >> > I'm setting up a test circuit and I need a 100k resistor that can >> > handle >> > 2000VAC for a few seconds. >> > >> > I was going to run off to the local surplus shop but got the idea of >> > making a liquid resistor. Saves a trip. >> > >> > I added some salt to water and got 100kohm. Copper electrodes (all I >> > got >> > at the moment). >> > >> > Question is... Will this stay 100kohm +/- 10kohm up to 2000VAC? >> > My circuit only needs to run for 5 seconds. >> > >> > iows...Does salty water resistance vary with voltage? >> > >> >> EBG do a nice range. You could for example put 5 560k SSP52 in parallel: >> http://www.ppmpower.co.uk/downloads/products/PPM295.pdf >> >> Mark. > > I might track down where I can get one. > It seems from the spec that they can also be over-rated for 5 seconds at 5 times the power rating, which means you may well get away with just one 100k SSP52, or possibly two put 220k's in parallel for belt and braces. Mark.
From: D from BC on 13 Mar 2010 04:23 In article <8011svF34dU1(a)mid.individual.net>, map.nospam(a)f2s.com says... > > "D from BC" <myrealaddress(a)comic.com> wrote in message > news:MPG.26047ecfa9832fe9896fa(a)209.197.12.12... > > In article <8004pkFd3U1(a)mid.individual.net>, map.nospam(a)f2s.com says... > >> > >> "D from BC" <myrealaddress(a)comic.com> wrote in message > >> news:MPG.26041fc5df0edf429896f1(a)209.197.12.12... > >> > I'm setting up a test circuit and I need a 100k resistor that can > >> > handle > >> > 2000VAC for a few seconds. > >> > > >> > I was going to run off to the local surplus shop but got the idea of > >> > making a liquid resistor. Saves a trip. > >> > > >> > I added some salt to water and got 100kohm. Copper electrodes (all I > >> > got > >> > at the moment). > >> > > >> > Question is... Will this stay 100kohm +/- 10kohm up to 2000VAC? > >> > My circuit only needs to run for 5 seconds. > >> > > >> > iows...Does salty water resistance vary with voltage? > >> > > >> > >> EBG do a nice range. You could for example put 5 560k SSP52 in parallel: > >> http://www.ppmpower.co.uk/downloads/products/PPM295.pdf > >> > >> Mark. > > > > I might track down where I can get one. > > > > It seems from the spec that they can also be over-rated for 5 seconds at 5 > times the power rating, which means you may well get away with just one 100k > SSP52, or possibly two put 220k's in parallel for belt and braces. > > Mark. I checked Mouser using keyword SSP52. No results. I'll get resistors when I've build up a parts list worthy of making a Digikey order. I might order these .. 4 X $2.00ea.. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RSD- 25KRCT-ND OR $13.00 for a single R. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name= 850F100KE-ND In the meantime, I'm taking my chances with a liquid cooled 2W resistor from the junkbox.
From: Robert Baer on 13 Mar 2010 05:23 D from BC wrote: > I'm setting up a test circuit and I need a 100k resistor that can handle > 2000VAC for a few seconds. > > I was going to run off to the local surplus shop but got the idea of > making a liquid resistor. Saves a trip. > > I added some salt to water and got 100kohm. Copper electrodes (all I got > at the moment). > > Question is... Will this stay 100kohm +/- 10kohm up to 2000VAC? > My circuit only needs to run for 5 seconds. > > iows...Does salty water resistance vary with voltage? > ...only if you swear like a sailor...
From: Robert Baer on 13 Mar 2010 05:28
John Larkin wrote: > On Fri, 12 Mar 2010 12:02:46 -0600, "Jon Slaughter" > <Jon_Slaughter(a)Hotmail.com> wrote: > >> D from BC wrote: >>> I'm setting up a test circuit and I need a 100k resistor that can >>> handle 2000VAC for a few seconds. >>> >>> I was going to run off to the local surplus shop but got the idea of >>> making a liquid resistor. Saves a trip. >>> >>> I added some salt to water and got 100kohm. Copper electrodes (all I >>> got at the moment). >>> >>> Question is... Will this stay 100kohm +/- 10kohm up to 2000VAC? >>> My circuit only needs to run for 5 seconds. >>> >>> iows...Does salty water resistance vary with voltage? >> Why not experiment with it since you already have the setup? Try putting a >> 100k res in series and measure the voltage. Sweep up to 200VAC and see if >> the volage devates from 100VAC at the divider. >> >> I imagine if the liquid gets hot the resistance will change so you might try >> an ice bath. You could then try with and without the ice bath and find the >> deviation to get some temperature dependence relation. >> >> > > Copper will be electrolyzed into solution and the resistance will > drop. And bubbles will form on the electrodes and resistance will > increase! > > Neither happens fast at low currents. > > But the dissipation is only 40 watts for 5 seconds. A string of, say, > ten or so 2-watt carbon film resistors would work fine. > > John > 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. |