7 ms·
“You don't have a voltmeter. Do you have a potato?”
- SicSemperUranus 4y agoDon't forget to cook and eat that potato!
- etaioinshrdlu 4y agoIt might contain an unhealthy amount of copper salts if you're unlucky, I guess.
- ars 4y agoYou don't need to use an entire potato, a small 1 inch/3 cm cube will be fine.
- userbinator 4y agoThis reminds me of the old trick to detect the polarity of the ignition coil on an engine, using a pencil.
- BenFrantzDale 4y agoDo tell.
- robocat 4y agoFirst example vid I found using those keywords: https://m.youtube.com/watch?v=kXaOP8O4HpI https://m.youtube.com/watch?v=kXaOP8O4HpI
- djmips 4y agoWhich seems to show that you use the pencil graphite as an electrode and spark it to ground. The 'fatness' of the spark determines the polarity.
- userbinator 4y agoWritten description: https://navyaviation.tpub.com/14329/Figure-6-52-One-Method-Of-Checking-Coil-Polarity-287.html https://navyaviation.tpub.com/14329/Figure-6-52-One-Method-O... ...although I haven't found any explanation online why it works. This method has probably been known for over a century, so I suspect it may be in some old physics books.
- altilunium 4y agoCan anyone explain what's really happening here? Why green? Why potato?
- DeIonizedPlasma 4y agoCopper salts are green. The copper will only give up an electron and make itself available to form salts with the ions in the potato at the positive electrode. This should also work with anything else conductive, you'd probably be able to tell doing this in a glass of salt water provided that the water is still enough.
- eloff 4y agoSo does this only work with copper wires then?
- NotYourLawyer 4y agoYes.
- amluto 4y agoThere are likely other things you could observe by electrolyzing some convenient substance with just about any wire. But be careful — some electrolysis products are pretty nasty. Producing chlorine gas, for example, is straightforward. If you have a salted potato (rescued from a salad perhaps), I would not do the experiment indoors, nor would I stick my face close to it.
- CamperBob2 4y agoSheesh. You are not going to make enough of anything this way to hurt a termite, much less a human. There are ways to kill someone with potatoes, but they don't involve electrolysis.
- 4y ago
- krackers 4y agoAh I thought this would be a new take on that apocryphal bayesian story >An engineer draws a random sample of electron tubes and measures their voltage. The measurements range from 75 to 99 volts. A statistician computes the sample mean and a confidence interval for the true mean. Later the statistician discovers that the voltmeter reads only as far as 100, so the population appears to be 'censored'. This necessitates a new analysis, if the statistician is orthodox. However, the engineer says he has another meter reading to 1000 volts, which he would have used if any voltage had been over 100. This is a relief to the statistician, because it means the population was effectively uncensored after all. But, the next day the engineer informs the statistician that this second meter was not working at the time of the measuring. The statistician ascertains that the engineer would not have held up the measurements until the meter was fixed, and informs him that new measurements are required. The engineer is astounded. "Next you'll be asking about my oscilloscope".
- unlikelymordant 4y agoCan you explain the story? I understand an oscilloscope is for looking at signals, but i dont understand the significance
- fenomas 4y agoThe context can be found here: > https://en.wikipedia.org/wiki/Likelihood_principle#The_voltmeter_story https://en.wikipedia.org/wiki/Likelihood_principle#The_voltm... Specifically if you read the "Example 2" section above that blurb, and then read the "throwback" bit at the end after the voltmeter story, it makes more sense.
- quickthrower2 4y agoWhat is a good book for someone comfortable with maths (but very out of practice) to get up to speed on the topic. Not being scared of not understanding stuff and needing to learn prerequisites (so doesn’t need to be too easy). Because the wikipedia article isn’t really for learning but it does give a flavour. And it sounds fascinating, sort of like a monte hall problem to me.
- tux 4y agoSometimes low-tech works best can litterly save your life. This kind of reminds me how you can start a fire with a watter bottle [1]. Good job MTA @ diy.stackexchange.com for recommening this and jasonhansel @ HN for posting it. [1] https://www.youtube.com/watch?v=QwQJ-3pZfwc https://www.youtube.com/watch?v=QwQJ-3pZfwc
- keepquestioning 4y agoUnbelievable!
- somenameforme 4y agoThat is absolutely amazing, and I will be trying that next barbecue day. For those who don't know, on a slightly related nugget, you can also use any sort of fat as a lighter fluid as well. Cook up some bacon (for instance), collect the fat/oil from the pan, and next time you're grilling - a few napkins (or other sort of kindling) rubbed around in the bacon fat is more than enough to heat your wood/coal to burning. Now to set those napkins on fire with a water bottle!
- adrianN 4y agoLighting fire using the sun and a lens is a neat trick. You can also form a lens using ice. However, in most conditions where you need a fire to survive you don't have sufficient sunlight or sufficiently dry fuel for the method, so I'd recommend learning other methods for lighting fire, in particular the method of always carrying a lighter with you when you leave civilization.
- aequitas 4y agoYou don't even need the bottle, just make sure the water is in the correct phase: https://www.youtube.com/watch?v=thbSSuo1Z00 https://www.youtube.com/watch?v=thbSSuo1Z00
- svnpenn 4y ago> litterly > watter
- briHass 4y agoI remember this from the old 'potato clock' science kits from the 80s. They had a copper cathode and zinc anode that when inserted into a potato (most fruit/vegetables or acidic liquids also worked) generated enough power to run a small LCD clock. In a potato, the copper cathode always left a green spot.
- danielodievich 4y agoGreat potato story. Loosely related story here. My late grandfather in Belarus (the land of potatoes) loved potatoes just like everyone around. Well, he was an electrician at the concrete/brick making factory for entirety of his career, from right after the war until he retired in the late 80ies. The amount of electricity used to fire the kilns for bricks is well known to be huge. He said that they'd see the rats scutter along the power lines on the wall and every once in a while they'd touch the rails wrong and disappear in the scintillating disintegration. Oh, and he let me weld random junk together with his own cobbled together electrical welding kit when I was like 8, oh I loved that so much. I miss him.
- jve 4y agoTouch with their teeth I suppose? I was working at some other factory where rats would "cut" data cables occasionally.
- michaelt 4y agoIf they were uninsulated cables (like overhead powerlines) they might have just bridged two of them.
- fredrikholm 4y ago> he let me weld random junk together with his own cobbled together electrical welding kit when I was like 8, oh I loved that so much. I miss him. I think a lot of us have similar experiences with European (grand)parents born around the era of the two wars. Honestly think that them being born in horrible times yet living during (comparatively) great times helped form a generation of people that stood out. I miss them.
- dunno7456 4y agoThe land of potatoes is Peru.
- h0l0cube 4y agoNot sure why the downvotes. A bit pedantic and distracting from a good story, perhaps, but accurate. > The potato was originally believed to have been domesticated by Native Americans independently in multiple locations, but later genetic studies traced a single origin, in the area of present-day southern Peru and extreme northwestern Bolivia.
- WheelsAtLarge 4y agoHow dangerous is this? Just thinking about working with live wires makes me nervous.
- kuon 4y agoIt is a low voltage DC adapter, you should be safe as long you do not put it in your mouth.
- Razengan 4y agoThe potato or the wires?
- ale42 4y agoMostly the potato, I'd say... as it will probably contain potentially toxic copper salts after the operation. If the adapter generates 9-12V, it will be pretty unpleasant to have that voltage in your mouth, but probably not dangerous (like licking a 9V battery to check if it's still charged...)
- greenbit 4y agoDry skin is a reasonably effective insulator against the kinds of voltages typically produced by wall warts, i.e. less than about 24V. But wet skin, especially if there's salt involved, is considerably more conductive. As a kid I had applied a mere 12V to some slightly salty water, when some small object fell into the soup. Thinking "it's just 12V" and thinking it harmless, I went to fish the offending object out with my fingers. This was a rather unforgettably unpleasant experience, I will attest. So, cautionary tale there - even with low voltage, watch out if your hands are wet!
- slim 4y agoit's unplugged
- emmanueloga_ 4y agoAnother neat trick in the same ballpark (but not involving a potato :-p) is to create a 220v to 110v adapter with a "resistance bridge". Plugging two (hopefully pretty equal resistance) incandescent lights in series, each lamp should have a 110v potential difference... say: A ----(60W lamp)-- B --(60W lamp)----- C By plugging A and C "cables" to a 220V electrical outlet, one should be able to grab 110V from either A-B or B-C :-) (assuming both lamps have about the same resistance). Most electronic devices work with a wide range of input voltage any way, so it doesn't have to be extremely precise.
- cfn 4y agoShould work but don't plug the 110v equipment until the lights are totally on. The initial rush current will cause higher voltages for a split second that may damage it.
- unnouinceput 4y agoIf the light that is in parallel with the circuit you are trying to power up malfunctions, you going to be in for a nasty surprise. This method, ignoring the fact that you're wasting at least 120W in plus, is also quite unreliable.
- Denvercoder9 4y agoYou want to be very careful about what kind of equipment you power like this. If it has resistance that's substantial compared to the resistance of the lamps, the voltage divider won't be a neat 50:50 anymore and you'll get more than 110 V.
- kimburgess 4y agoThat's why you use two potato halves instead of light bulbs. You can calibrate the wire distances to create the exact relative resistance for the divider to function to spec with the load.
- ilyt 4y agoOh god please fucking dont
- moring 4y ago"Do not allow the bare wires to touch each other from this point on." What happens if they touch? Note that this is while the adapter is unplugged, before sticking the wires into the potato, so shorting them isn't a concern. I can't really imagine that some kind of contamination is a problem since both wires are (probably) copper, nor would I expect any kind of reaction as long as it is unplugged.
- moffkalast 4y agoWell any DC converter worth its salt ought to have short protection, so likely nothing. But power would be turned off for the duration so the experiment wouldn't work.
- Doxin 4y agoAt some point during the following steps you're turning on the power, If they were touching at that time you'd get some real nice sparks and a tripped breaker or blown fuse. To simplify instructions the poster just said don't let em touch after this step as opposed to something like "When power is applied the wires can't touch"
- unnouinceput 4y agoNah, none of that. Just your charger gets bricked so not knowing which one of the wires are positive and negative going to be the least of your worries from that point on.
- jusssi 4y agoThat's the theory. I have seen smoke coming out of a charger when the 5v DC side got short circuited due to wire damage. Quickly unplugged obviously, but I assume there was a real possibility of the AC side shorting if things melt inside the charger.
- unnouinceput 4y agoOf course, that's always a possibility.
- Eleison23 4y agoThe best touch in that story is how the poster works around the lack of a voltmeter by assuming the OP possesses a soldering iron and the skills to use it.
- wink 4y agoI've had a cheap soldering iron in the closet since I moved in and only bought a voltmeter like last year, because I've done my soldering mostly at the local hacker space for the last 10 years, so I find that part pretty relatable ;)
- 2-718-281-828 4y agoSeems to be like the answer is making fun of the question which is pretty easy to answer with very simple and cheap tools.
- greenbit 4y agoThere was a well known cheap tool retailer that had a voltmeter adequate for this kind of measurement for less than the price of a good coffee. I think they even had a coupon for it, making it practically free for a while.
- squarefoot 4y agoPotato? Who needs a potato? A glass of salt water will suffice. Just put the wires at some distance in the salt water and look. The wire emitting the blueish fog (chlorine) is the positive, and the one emitting bubbles (hydrogen) is the negative.
- joe__f 4y agoI always feel like I could have more chlorine gas in my life
- ilyt 4y agoThat's how I accidentally learned how to produce chlorine gas as a kid!
- jensgk 4y agoWell, only if chlorine is added to the water. It should also emit oxygen.
- moffkalast 4y agoSo Factorio was right, you do get chlorine from electrolyzing brine...
- BenoitP 4y ago> blueish fog (chlorine) is the positive Would that not be copper oxide? Source: did that as a teenager and did not die (trying to synthesize hydrogen as any normally constituted teenager would do), and the copper wires just ended up being entirely corroded until the immerged part disappeared. No hydrogen as I did not seal the apparatus properly. But I had a nice blueish precipitate instead. I absolutely had no idea it could have generated chlorine. I did sleep in the same room as the experiment for a full week. So I guess either my bedroom was well ventilated or it did not produce enough chlorine, or that it was just copper oxide.
- thih9 4y agoThe level of cleverness and resourcefulness is impressive. To the point that it seems magic or makes me suspicious. I guess this is how the layman feels about instructions to delete System32 to add more RAM.
- shultays 4y agoThere should be a step somewhere there that says "don't hold potato with hands while it is plugged"