Electrochemistry: Liquid Power Resistor for 2000VAC

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..

OR

$13.00 for a single R.

In the meantime, I'm taking my chances with a liquid cooled 2W resistor from the junkbox.

..only if you swear like a sailor...

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.

Either option seems to be OK, although in the single resistor version you're closer to the edge of over-driving it (i.e. there's more slack in the 4 resistor version voltage wise). Although you can think of the liquid as some kind of ideal heatsink the 2W resistor package is going to have a finite thermal resistance, so localised heating might damage it before the heat can flow out of the package into the liquid. Careful too with dielectric breakdown voltage.

Mark.

Another thing to watch is the type of resistor package you use. Most of the moulded types transfer their heat through the legs (unless they have an integral heatsink or provision to add one), not through the package itself which has a much higher thermal resistance, so make sure both legs are fully immersed in the liquid if it is this type.

Mark.

We used copper sulfate with copper electrodes as resistors on Marx generators. Works. May not be completely stable, but that's not going to be a drastic change in a few seconds thing, more like over weeks or months the resistance will change. If the copper sulfate solution is fully saturated, the resistance will be less likely to change. Something like 2" diameter tubing, and the whole mess drowned in transformer oil.

Voltage was DC and 10's of KV for charging. IIRC the big one erected to over a million volts, but none of the resistors would see all that.

More likely a Stalin generator - propensity to arbitrarily liquidate those around it.

try

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.

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.

Cool :)

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'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.

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.

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

D from BC Inscribed thus:

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.

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

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).

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.