Salt Water Dimmers | Hacker News Reader

Salt Water Dimmers

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85 pointsdcminter67 comments

As a "mad scientist" when I was perhaps eleven or so, I created a carbon arc by cutting the end off an electrical zip-cord extension cord, stripping the insulation off the two wires (lol, yeah, no ground wire) and wrapping the bare copper ends around a pair of carbon rods pulled from D-cell batteries.

I held down each carbon rods by attaching it to a brick. Move the bricks together to touch the rods together to get a spark and an orange growl, and then draw them apart into an intensely bright white-hit light.

Insane. Yes, I tripped the circuit breaker (thankfully not fuses in that place) repeatedly.

Decided to make a saltwater rheostat to control the current. This time a square glass casserole dish with salt water was the tank. One of the mains wires was cut and enough insulation stripped to wrap around two rocks placed in the brine. Move the rocks closer, more current, move the rocks apart, less current.

Holy hell, that was something. When the arc got to lighting up the basement I looked around to the rheostat to see it arcing under water as it bubbled (as another mentioned, yeah, probably chlorine gas). When the insulation on the zip cord soon started to smoke I decided the experiment was over and jerked the cord to pull it out of the outlet. This quick yank also sent the glass casserole dish crashing to the ground....

Ahhh ... if only YouTube were around then. I might have tried to do it more safely. https://youtu.be/VTzKIs19eZE

Instead I got the idea from the book "700 Science Experiments for Everyone" (p. 185): https://archive.org/details/isbn_9780385052757/page/184/mode...

Love hearing stories like this about unfiltered, unfettered (and slightly insane) childhood play. Parents today don't even let their kids walk 2 blocks to school unsupervised, lest something terrible happen.

I wouldn't let me do that now, ha ha. I could have burned the house down. (I did burn my friend's eyebrows off, but that's another story...)

The danger in that story is pretty off the charts. That could have _easily_ led to death, like maybe 1/100? That's something parents _should_ stop. It could have been redirected to safer versions, you can have a lot of fun with lower voltage DC, or at the very least safer setups.

Electrocution with mains is... actually not that common if you take care to not let the current pass through you.

I'd be more concerned about the intense UV that an arc emits ("welder's eye").

I was once playing with mains (220V) and got distracted on the phone with a friend. I literally took with each hand one cable (they were crocodile terminals) I just could not let go, the current makes impossible to let go. I reacted like 5 to 10 seconds later, by letting me fall backwards, which disconnected the leads from the plug. I was 15 or 16…

I should have gone to the hospital, but I didn’t.

So, I do bot say it is not dangerous, but it is not like it will kill you in 1ms.

I once shorted 380V with my little finger (testing industrial electric motors for overheating). It was like someone hitting the finger with a sledgehammer.

Oh I did not mention it, but the hands kept hurting one or two weeks after that. Really not funny. But 380v is another level of danger, energy goes ^2 with voltage!

Well it was really just the pinkie (and the arm a little bit), but it felt more like a kinetic hit then a electric-shock, pretty terrifying, the pain lasted for like a week (damaged bone marrow?)

The most I ever got shocked with was 560Vdc @ 10mA I know it was 10mA because it popped the safety breaker on the lab power supply. I was testing a clamp circuit for a high power solid state RF matching network. I had been so careful the whole time using only one hand, but I got complacent for one second and BOOM, hand-torso-hand circuit.

It felt like I got kicked in the chest. Was sore for a few days after.

So lucky I was using the lab supply with a good breaker.

Would have been a bad time to find out you had a heart condition. Grabbing with both hands (and being distracted) is indeed very dangerous, which is why the comment you replied to mentioned taking care. Many electricians will do small tasks without cutting off the power and it’s entirely possible to do things reasonably safely if you take some basic precautions.

I thought is needless to say that no once more in my life was distracted while working with anything above 12V... I've much more respect now.

> Parents today don't even let their kids walk 2 blocks to school unsupervised, lest something terrible happen.

Though weirdly enough, they mostly aren't even worried about the real danger, cars, but about some imagined but much less likely scenarios.

I remember getting that book from the library and reading it cover to cover. I never really tried to do any of the experiments, though, but it was definitely my favorite science book as a kid because it wasn’t full of safe and boring experiments

YouTube wasn't around back then but luckily the "mad scientist" spirit still lives on: https://m.youtube.com/watch?v=co6SUTVGqOs (en subtitles available)

I am so used to type-G plugs that I didn't initially realize why you'd be concerned about blowing a fuse.

When I was about that age I also shocked myself pretty bad a couple of times, once from replacing the fuse in a plug and pressing the plug into a socket using my palm without putting the rear cover back on. Another time touching two spoons I'd put into the live/neutral holes after using one of them in the earth hole to bypass the safety gates. (I assume I inserted the live one last) I remember finding it interesting how neither seemed to shock me individually, then touched both and leapt back across the room.

Surprised I didn't die from that second one. I still viscerally remember what 50hz sounds/feels like.

220/240V shocks hurt like all hell, and it kind of "reverberates" in your affected limb long after. The auditory experience is also quite strange. You can hear the 50hz, but it's more like an "understanding" of the sound than actually hearing it. Very weird.

If you grabbed the two spoons with both hands, you probably would have had a worse outcome. One hand touching both terminals hurts, but will likely not kill. When that current comes close to your heart you'll have trouble.

The fact that neither of them didn't shock you individually is likely because you were insulated from the ground. You had shoes or clothing on or something. If you had skin touching the ground, bad news again. I had a fridge that had broken down motor insulation or something, and it kept tripping the earth leakage. I had no money to replace it, so I cut the earth wire in the plug. Problem solved. Just made a note to not open the fridge while barefoot. Eventually I got round to getting rid of it thankfully.

The common advice when working on something dodgy is to put one hand in your pocket. That way a shock will give you ample warning to back off before killing you. Unless it's DC - that stuff scares me. My old solar installation had a 550VOC DC potential, and I stayed the fuck away from that. I have 0 problems working on domestic AC, but not solar DC!

220 scares me for exactly that reason. I've been shocked by US 110 pretty good a couple of times but the pain has never really lingered beyond a couple seconds after the initial shock. I certainly didn't hear anything.

While the plugs in the US not being shock-proof is certainly not great, I think it's a lot less of a danger than it would be in a 220 country.

> bubbled (as another mentioned, yeah, probably chlorine gas)

Suddenly I am reminded of my A-level Physics project, where I tested the relationship between salinity and conductivity with some graphite rods in a beaker of water - has to move to a chemistry lab and use their fume hoods after the first day of testing :D

That's hilariously dangerous. I will be getting my son that book.

At a previous job we manufactured fairly large trailer-mounted generators. During design engineering testing, you would want to power a load with the generator to check performance. The test load we had was a giant resistor bank, in a pallet-sized enclosure about 4 feet tall, with fans for active cooling of the oodles of resistance heat being put off by it. I talked to one of the electrical engineers about how ludicrous this device was, and he said that we used to use something even weirder. A giant tank filled with salt water (can't remember for sure if they were using NaCl or a different electrolyte) with probes just dumping all that current right into the water. Wish I had seen it.

I'm not sure what's ludicrous about this setup though? For testing you want the simplest possible setup - which a giant resistor bank really is. Power is power when you run it through simple resistance - no AC shenanigans will hide effects.

The electrolysis rig seems a bit ridiculous, since it generates a bunch of flammable gas you have to deal with. A big resistive load for testing stuff seems pretty normal though.

Not just flammable hydrogen gas — you are likely to generate chlorine gas, potentially in large amounts.

True, if it's very salty.

It's not electrolysis, it's more like electrode boiling.

It is absolutely electrolysis. You can try it yourself with a battery and dish of water.

It's absolutely not. I already tried it myself with a 3MW generator and a giant tank of saltwater.

The fun part: it does both!

I see your point, though we barely ever had to top the tank up with water or salt. The amount of gas created was minimal, at least with our setup - admittedly not as fancy as a battery and a dish of water ;)

At a previous job, we ran a nuclear reactor but didn't want much electricity, so we'd use the power to turn a giant water wheel with all the surplus steam...

Is that a euphemism for driving a sub around?

or a carrier

In which case they might have mentioned the nuclear-powered slingshots.

No, the water wheel ("water brake", they called it) was real, it was for wasting energy, and we didn't go anywhere; but also, yes, it was a submarine, in form, albeit not exactly in function.

If you can reveal, what sort of facility was this, and in what sector (e.g., business, research, government, military, NGO)?

I've worked in a rail yard where we overhauled locomotive engine & traction alternator sets, which were generating upwards of 3.3MW so we used a big saltwater resistor as a load bank. It was the only bit of equipment that scared me, because the plates and tank were fairly rusty. I was waiting for it to let go midway through a test and flood the place with boiling salty water (and who knows what chaos the suddenly unloaded generator would have caused)

Still used in 3rd world countries (quite effectively) to make dirt cheap DIY arc welders. Super dangerous but basically free, just need electrodes. Not as high-current as a modern machine, but good enough for fixing light tractors and bicycles.

???? I think you must be thinking of a different device.

They are thinking of exactly the correct machine.

A liquid rheostat is just a rheostat https://en.wikipedia.org/wiki/Liquid_rheostat

They were used in the past just like the light dimmer, but I challenge a present day photo in a developing countries workshop.

Heaps of Youtube spam and 'lets try', I'd like to see one in a real workshop in the wild. (That would be cool to see)

I think if you think it through carefully you'll understand how they are fundamentally the same.

This is essentially a big variable resistor - how does one apply that to arc welding?

What is it that you suppose a modern arc welding system does? Stick welding needs about 20-30 volts during the weld (60v to strike the arc if we have a fancy machine). In a modern machine we turn high voltage low current mains power into low voltage high current arc welding power. This rheostat would turn it into low voltage slightly lower current but it would still work fine for light gauge.

I've done a fair bit of TIG, a little bit of SMAW.

Are we talking about welding with basically reduced mains current? AC? SMAW and TIG both require current well in excess of what you can get out of a wall without tripping a breaker. I think for welding 14ga mild steel I was running at minimum 80A on the machine, but more like 130A with the foot pedal. Are you talking light gauge like as in spot welding territory?

I thought this was mildly interesting; I'd never heard of them but they popped up in a Facebook post about a retired PDP-11 system from a theatre and the term caught my eye! Presumably the "strong smell" was chlorine!?

Presumably, yes.

For more on resistance dimmers in theater, check out this video from Jonathan Bastow: https://youtu.be/lTHNYWw6yt0?si=ygt0HpSd_aPcm3tq

These things were used at fairground attractions - bumper cars, merry go-arounds etc. - until at least the 1980's. They tended to come in the shape of a wooden barrel with a hinged lid which had a number of shark fin shaped metal plates on the bottom. There was a rope attached to the lid which was used to raise and lower it. The water got quite hot in use which led to steaming barrels later in the evening.

Oh, holy hell. I thought "old sparky" was bad. It was a board cobbled together from a bunch of residential rheostats. The entire power supply of the theater flowed through that board.

But at least Old Sparky didn't produce toxic fumes. It was merely a fire hazard.

Do you know of anywhere I could learn more about this? Googling "old sparky" just yields articles about electric chairs, even when including keywords such as "rheostat" and "theatre"

That was just the theater's name for it. I imagine other theaters had similar contraptions, and because of the expression they probably came to similar names.

It was at least 40 years old. I would hope they've all been retired.

There's a period between the "beginning" of the modern age and today where we had these strange interstitial technologies. It sometimes feels like we went from living in the dark to electricity to the digital age in big jumps, but there's been a lot of evolution in between. Today will seem quite quirky to people 10, 20 and 50 years from now.

Today already feels quirky to me now.

"Salt water dimmers were gradually replaced by semiconductor dimmers, the last dimmers in London theatres being replaced in 1959."

I would have expected that they would have been replaced by adjustable transformers as soon as lights were powered using AC.

I suspect the power requirements would have required truly massive and very expensive transformers. Stage lighting requires massive amounts of power.

My guess is salt water resistors remained the cheaper and simpler alternative until semiconductors took over, completely skipping variacs.

So cool. Had no idea about this and I love theatre. Maybe someone could build a mechanical/electrical/chemical computer using these jars of salt water? Ie, Salt water dimmers are Turing complete...arxiv://doi...

Water is used because of its extremely high heat capacity and wide availability: https://en.wikipedia.org/wiki/Table_of_specific_heat_capacit...

The concentration of salt has a huge effect on the resistance --- there is an infamous YouTube video of this effect being demonstrated with an electrode boiler.

> the last dimmers in London theatres being replaced in 1959.

I'm always amazed how long some things were actually used that you'd think stopped being used 100 years ago. Another one, steam locomotives, not completely phased out in some developed countries until the 70s.

Britain used steam locomotives until the 1980s.

See https://en.wikipedia.org/wiki/Retirement_of_steam_locomotive...

Germany apparently used them from time to time until 1994, but that was a function of East Germany being behind the Iron Curtain. My grandfather also used punch cards well into the 1980s in East Germany.

Funfactlet: There's a steam locomotive in active duty shunting work trains around at the moment in western Germany. The Riedbahn between Frankfurt and Mannheim is currently being redone and they were short on Diesel engines, so one Verein for historic railroad equipment offered their steam engine and was accepted.

https://www.swr.de/swraktuell/radio/riedbahn-sanierung-dampf... (German only)

Another use for steam engines is for shunting duties in power plants - the engine has no boiler and just gets “charged” from the main plant steam generator.

A similar thing happened here in Australia (New South Wales) in the mid 80s. I was part of a rail preservation group and we were taking a stream locomotive with an empty train from West Ryde Station to Central, from were we were going to depart for an enthusiast's trip. One of the suburban trains was cancelled, so Jock, the station master, asked if we would like to run the regular suburban service, which we did. It was great fun pulling in and watching the passengers do a double take as their regular train turned out to be a steam train.

I guess it required provisioning of the infrastructure, coal and water along the line. And it couldn't be so spontaneous.

>Suburban

I imagine we're talking about a fairly short trip.

Keep in mind that in New South Wales everything is a 'suburb', even eg Sydney itself. It's weird.

It's 19km from West Ryde to Central by rail. In the 80's there was still a modicum of infrastructure available for steam locomotives. I've a memory of their still being a water standpipe at Central. These days you would have to arrange with the local fire brigade to fill the tender.

That would be something very cool to experience from the passenger side:-)

Union Pacific (IIRC) still has one in use, aptly named "Big boy". It's been converted to run on natgas as opposed to coal. Jay Leno recently put out a Youtube video about it.

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