Electrochemistry: Liquid Power Resistor for 2000VAC

[D from BC]

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.

If not a power limit, I'm guessing the 150V limit is to stay within R
tolerance due to voltage changing the resistance.
That or there's electrostatic damage.
I'd have to look at some data sheets.

 

[D from BC]

Cool

 

[D from BC]

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.

 

[D from BC]

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).

 

[markp]

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'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.

 

[D from BC]

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.

 

[Archimedes' Lever]

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'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.

You missed what he said. He said that the resistor's metallic compounds
that got dispersed into the water BECAME the resistor.

 

[Baron]

D from BC Inscribed thus:

I only need 5 seconds of circuit run time.


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.

Use the condensate from the fridge or a de-humidifier.

 

[Fred Abse]

Use the condensate from the fridge or a de-humidifier.

That can be full of all sorts of crap, especially if there are smokers
about, or coal or wood fires.

 

[pimpom]

[email protected]
says...

I only need 5 seconds of circuit run time.


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).

 

[D from BC]

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.

 

[Grant]

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.

 

[Archimedes' Lever]

I dunno, 2kV + open water still sounds like Bang! to me

Would not do anything with pure water.

 

[D from BC]

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%

 

[VioletaPachydermata]

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.

 

[pimpom]

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.

 

[Ecnerwal]

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.

 

[D from BC]

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.

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.

 

[D from BC]

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.

Neato... Perhaps I can call it 'wetware'

 

[Archimedes' Lever]

This is Sandia's Z-pinch

That was my desktop wallpaper 8 years ago, idiot.