Electrochemical Spuds Of Death

24 April 2012 — dan

A reader writes:

Hello there Mr. Dan. I stumbled across your site whilst googling "can you get hurt making a potato battery". Yep, I googled that.

I (clearly) know little about the electronics/cathode/anode world... but could answer lots of questions about other things non electrical. :)

In planning my son's birthday party, I am considering a potato battery station (sounds odd for a party, but trust me, it fits with the theme).

I have seen several Youtube videos with instructions and examples, some done by children. My main question before I go buy a bag o potatoes and seek out the copper wiring aisle of Walmart is: Can children be hurt doing this? Yes, us grown-up types will be there too, but is there anything I should be concerned about?

Partying Mom

It is theoretically possible to kill yourself with potato batteries, but the chance of a kid managing to achieve this is much, much lower than the chance that one of them will fall over and crack his/her skull in your bathroom, and you probably won't lie awake at night worrying about that.

I could just leave it at that, but of course I won't. This is because I think an understanding of the basics of electrochemistry, which is what potato batteries are all about, is something that all modern humans should have, even if they never put it to use.

You should know why it's warmer in the summer (it's surprising how many people incorrectly say "because then we're closer to the sun", which, even if it were true, would make summer happen at the same time for both the northern and southern hemispheres...), you should know how tax brackets work, and you should also know the basics of the technology that envelops modern humans so completely that we hardly notice it at all.

Sorry, didn't mean to lecture you. This is just something I'm rather passionate about.

Getting back to potato batteries: The power output of an individual potato, or lemon, or what-have-you, "battery" is extremely low, which is why there are few-to-no things you can power from one spud with two pieces of dissimilar metal in it.

"Battery" is in quotes up there because one tuber and two bits of metal are a single electrochemical "cell"; technically, it's not a "battery" unless it has more than one cell in it. (So, of the things sold in the supermarket as "batteries", AAs and Cs and Ds are cells, but 9V or 6V batteries, composed of six and four 1.5-volt internal cells respectively, really are batteries.)

The open-circuit voltage of any electrochemical cell is determined by the electrode potential of the materials you use for the electrodes. If you build the usual kind of potato battery with copper and zinc electrodes (like, a copper or copper-plated coin, and a zinc-plated galvanised nail), each cell will have an open-circuit voltage of 1.1V, but a current capacity into a short circuit of less than a milliamp.

The larger the surface area of the electrodes, the higher the current capacity will be. But even with really big electrodes you'll probably only get half a milliamp into a short circuit - and the more of the cell's current capacity you use, the lower its output voltage will be.

(For comparison, I just grabbed a rather old but unused off-brand "super heavy duty" - meaning, carbon-zinc, not even alkaline - AA cell out of my Drawer Of Many Batteries, and it still reads more than 1.6 volts open circuit, with a short-circuit current capacity of more than 1.5 amps. Here's a PDF datasheet for an Energizer carbon-zinc AA; they've got a sub-site devoted to these things.)

If you make multiple potato batteries and put them in series and/or parallel, you can increase the voltage and/or current capacity of the whole battery, respectively. Two cells in series (both of which can be stabbed into the same potato; just connect the copper of one cell to the zinc of the next) and you get 2.2 volts open circuit and the same miserably tiny current capacity. Two cells in parallel, and you get 1.1 volts but double the current capacity. Six cells, wired up as series strings of three with the two strings in parallel with each other, and you get 3.3 volts and double current capacity. And so on.

(Many people seem to find the concept of series and parallel circuits tricky to grasp. It's another of those bedrock pieces of information about the world that I urge everyone to learn, though, because it explains a great deal of everyday electrical things. Why does one bulb dying in a string of old Christmas lights kill the whole string? Because they're ten or twenty 12V bulbs {depending on your local mains voltage} wired in series to connect directly to the mains. Why, in contrast, can you have a couple of things turned on and a couple of things turned off all plugged into the same powerboard and have everything work? Because the powerboard's outputs are in parallel!)

Getting back to your actual question, this is how you could, if you tried very hard, kill yourself with a potato battery. 30 milliamps across the heart has a pretty good chance of stopping it, and even lower currents have upon occasion been fatal. Kids might be more susceptible, too; I don't know.

Even sweaty skin is a good enough insulator that sundry low-voltage current sources aren't dangerous - grab the terminals of a 12V car battery with bare wet hands and you probably won't even feel a tingle, though a tiny current really will be flowing through your arms and across your chest. But if you stab probes into yourself, into your hands or preferably into your chest right on either side of the heart, then an array of potato batteries big enough to deliver tens of milliamps really could, if connected to the electrodes, kill you.

(One reason why high voltage can be especially dangerous is that it can spark a hole right through the skin, giving it access to your wet salty conductive innards.)

Given, of course, that this particular means of death starts out with stabbing yourself, you could simplify the process by just stabbing your heart directly.

Hence: Not worth worrying about.

(There's also an outside chance that you could poison yourself by eating a potato or lemon or whatever that's been used as a battery for a while, because it'll now be contaminated with various metallic salts. It probably wouldn't do more than make even a small child slightly ill, though, presuming he or she somehow managed to choke the vile-tasting thing down. This situation is even less likely to happen than chest-stabbing, unless you use some particularly delicious fruit instead of a potato or lemon.)

The great problem with potato-battery demonstrations in the past was not, of course, kids somehow killing themselves, but that it was very difficult to do anything with the extremely feeble output of such a battery. Turning even a tiny motor, or lighting even a grain-of-wheat incandescent bulb, was impossible without a ridiculous number of cells. Getting a feeble glow from a grain-of-wheat bulb rated for 12 volts and 80 milliamps could perhaps be done with as few as 50 potato cells, though I suspect you'd need a hundred or more.

So potato batteries usually ended up doing something lame like powering a pocket transistor radio with a piezoelectric earpiece, which is a feat that you can more impressively achieve with no battery at all.

Today, you could similarly fail to impress the youngsters by potato-powering one of those little LCD clocks and kitchen timers that're meant to run from a couple of button cells. Two or three potato cells in series might, at a stretch, be able to run one of those. A far better target, though, is lighting a light-emitting diode (LED).

A modern high-intensity red or amber LED will only want about two volts and a couple of milliamps to light dimly, and will be quite impressively bright at only 10mA. Ten parallel strings each containing two potato cells ought to be enough to give a pretty bright light, and each two-cell "string" could be only one potato.

Here's a red LED...

LED and lemon battery
(image source Flickr user trvance)

...just barely glowing from only three copper/zinc lemon cells in series...

Multi-cell lemon battery
(image source Flickr user s8)

...and here's an excellent example of multiple cells in one lemon...

Joule Thief lemon battery lighting LED
(image source Flickr user s8)

...which works extremely well because it's cheating, and using a simple four-component circuit (counting the LED) called a "Joule Thief", which I learned about years ago on the excellent Web site of the inimitable Big Clive.

I recommend you provide sufficient spuds and/or lemons, electrodes and alligator-clip leads to make lots of cells, and also provide a grab-bag of water-clear high-intensity LEDs so the kids don't know what colour they've got until they get it to light up.

A lot of LEDs will not cost you a lot of money. I find it mind-blowing that the going price on eBay for a pack of a hundred mixed waterclear high-intensity LEDs has, for some time now, been under five US bucks, delivered. I suggest you get 5mm LEDs, not the 3mm ones that're the absolute cheapest, because the smaller ones are a bit fiddly even for kids' hands.

(I don't actually need any more LEDs, but I just felt morally obliged to buy this hundred-5mm-LED pack, from this seller, for $US2.99 delivered. At this price you could use these things, which were a miracle of the age in the 1970s and have for years now been revolutionising a significant portion of the lighting industry, as notice-board pins. They are literally cheaper than thumbtacks. Even the ones with three different-coloured dies and an invisibly minuscule controller chip built in cost damn close to nothing.)

You should play with this stuff yourself before the party, so you can introduce the kids to the series/parallel idea, and help them if they don't know to chain the cells nose-to-tail (copper to zinc or zinc to copper, not copper to copper or zinc to zinc), and also see which way round you have to connect the LEDs to make them work. (They're light-emitting diodes; they only work one way around. Long leg positive.)

It would also be a really good idea to get the finest, cheapest digital multimeter eBay has to offer, so you don't have to rely on licking the ends of wires to estimate how many volts your potatoes have managed to make. Every home should have a crappy ten-buck yellow plastic multimeter; you may not use it often, but it can be very handy at times. (Put it in the kitchen drawer with the screwdriver, the hammer, the random screws and washers and the polycaprolactone.)

Depending on age and disposition, the kids may figure this all out for themselves, of course. LEDs only work one way round, a battery setup that'll light a 1.8V red LED probably won't light a 3.6V blue or white one, a setup that'll light a blue LED may very satisfyingly turn a red one into...

Dead LED

...a friode, you can series- and parallel-wire LEDs as well as batteries...

While you're shopping for quantum-physics miracles on eBay for three cents each, you could add a couple more things that used to be super-tech and are now super-cheap: Lithium coin cells, and rare-earth magnets.

2016 (20mm diameter, 1.6mm thickness) and 2032 (3.2mm thick) coin cells aren't as cheap as LEDs; if you buy them in a supermarket or pharmacy you can pay dollars for one. Again, though, just hit eBay and you can find fifty for less than 15 US cents each.

Rare-earth magnets can be even cheaper. If you restrict this search to Buy It Now items more suited to the impatient, you can get twenty 8mm-diameter 1mm-thickness neodymium-iron-boron disks for less than ten cents each; hundred-packs drop it to about seven cents apiece.

Why am I suggesting you buy these items?

Because you can light an LED by just pressing its legs to either side of a coin cell...

LEDs on a coin cell
(image source Flickr user spike55151)

...and if you put LEDs (preferably diffused 10mm ones, but any with legs will work), coin cells and magnets together, you get...

LED throwie production line
(image source Flickr user c3o)

..."LED throwies".

LED throwies
(image source Flickr user chopsueyphoto)

Which are easy to make, and awesome.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Electricity, Electronics, Psycho Science. 13 Comments »

An exciting new thing to worry about

5 March 2012 — dan

Australia, or at least Victoria, is getting "smart" electricity meters.

Unlike the old spinning-disc or slightly newer digital meters, smart meters can report power usage in real time, to the customer via a display inside the house and to the power company as well, without any requirement for legions of meter-readers. Smart meters can do various other tricks, too, like for instance changing the cost of electricity by time of day, to make it more expensive when there's high demand and deter some people from turning on the air conditioner and adding their own little electrical vote for a new coal-fired power station.

Heck, the smart meters may even be able to measure power factor, and theoretically create a need for those zillions of "power saver" gadgets. Which the power saver gadgets will not actually fill, of course, on account of how they usually don't do anything at all, but you can't have everything.

The Australian meters seem to report every thirty minutes, via radio.

So, naturally, people think they cause cancer.

But I'm getting ahead of myself.

I was delighted beyond human comprehension to discover a one-stop shop for Aussie smart-meter opposition, stopsmartmeters.com.au. Actually, I was first pointed to this page on "Holistic Help", but I only made it to the oddly popular claim that smart meters somehow kill nearby plants before I went somewhere else, lest I burst an important blood vessel.

Herewith, a response to Smart Meters in Victoria: Information and Concerns.

There are some valid complaints on that page. Apparently some smart meters have overcharged customers, for instance. And there've been some typical government-program deployment boondoggles - cost blowouts, the possible need to spend more money to change the radio frequency band the meters communicate on because of interference, and so on.

There are also privacy concerns about the every-30-minutes communication of household electricity use, and whose hands this information could get into. I'm having a hard time figuring out a way in which selling of this data to marketing firms could be a major problem, beyond just contributing its own particle to the mountain of privacy-damaging things in the modern world. But if the data isn't encrypted well enough, and meter IDs can be converted into addresses relatively easily (possibly even if you need a directional antenna to do it), then it might become possible for one burglar in a van to quickly figure out who, nearby, seems to have gone on holiday.

There are also concerns about coupling of the radio-frequency output of the smart-meter antennas to household wiring, possibly damaging appliances, though I don't think anybody's done a proper study to see whether the rate of appliance failure is actually any higher after the new meter's installed.

And then there are some real, but not necessarily valid, complaints. People object, for instance, to power being made more expensive at certain times of day, which they say is unfair, though I'm not sure exactly how. If it's unfair to charge more for peak-period electricity, then it's also unfair if you're only allowed to park your car in some particular location for half an hour during the day, but can legally occupy the same space all night.

There's a claim that consumers don't benefit from the new meters. OK, that's a reason to object, I suppose, but consumers don't benefit when, say, petrol becomes more expensive, either. This is an argument against silly PR from the electricity companies that tries to make you think the new meters will make your life better, especially since the stingy buggers don't even seem to be providing any indoor display units. But that's all this complaint is. Just because you want to keep paying low prices for something doesn't give you a right to do so, especially when that "something" is electricity which previously sold at an artificially low price because the cost of warming the damn planet wasn't factored in.

And then there are feeble complaints, like the possibility that the meters will not be installed safely.

And then, there's the bulk of the lengthy page, which is proudly devoted to ridiculous complaints.

To start with an easy one, the notion that coupling radio energy to household wiring could cause fires betrays a serious misunderstanding of the amount of energy the meter emits, and how well it could be received by household wiring. You could pump that one whole watt of high-frequency RF directly into your wall wiring, and I swear to you upon my beloved Necronomicon that no wires would get hot and start fires. If the only way in is the fraction of one per cent of the energy that the household wiring will manage to receive... well, it's good of Stop Smart Meters to so quickly make clear their opinion of mere "knowledge" and "logic".

And, of course, now we're off and racing with good old mobile-phones-cause-brain-cancer claptrap. The smart meters broadcast in the same 900MHz band as our GSM mobile phones here in Australia, so clearly they pose a similar risk, right?

The World Health Organisation say it's "possible" that mobile phones cause cancer. People who relay this information are generally less eager to make clear that the WHO has categorised this possible risk, from "long-term, heavy use" of mobile phones, as being in the same "Group 2B" class as traditional Asian pickled vegetables, and coffee.

The Stop Smart Meters page is at least aware of this, and points out that there are plenty of straight-up poisons on the Group 2B list too, like for instance lead. But then the author erroneously tries to claim that since lead is poisonous and phone radiation is now on the same possible-carcinogen list as lead, phone radiation should be treated as something similar in danger to lead.

This is, to be frank, stupid. Yes, lead is poisonous, but there's only feeble evidence that it's a carcinogen, which is why it's on the 2B list, and not for instance the 2A "probably carcinogenic" list, or the Group 1 "definitely carcinogenic" list. Phone radiation is self-evidently not a poison like lead. None of the IARC carcinogen lists are lists of poisons. Phone radiation is on the same list as lead because there's only feeble evidence that it's a carcinogen.

Stop Smart Meters go on to claim that "a significant proportion of Victorians refuse to use devices such as mobile phones or baby monitors because of sensitivities or concerns about future health implications". This not only uses a rather stretched definition of the word "significant", but also pretends that science is a democracy. Which it isn't. It doesn't matter how many people think baby monitors cause cancer, if they don't. Likewise, it doesn't matter how many Koreans think having an electric fan in your bedroom is very dangerous, if it isn't.

Trundling down the extra-big Stop Smart Meters page, there's a fine example of the kit-and-kaboodle routine of collecting supporting quotes from as many people as possible, without paying any attention to the reliability of the sources.

The American Academy of Environmental Medicine, for instance, claim that smart meters are dangerous, and that claim is mentioned on the Stop Smart Meters page. The AAEM also oppose fluoridation of drinking water (PDF), on the grounds that "fluoride is a known neurotoxin and carcinogen even at the levels added to the public water supplies". This is news to the World Health Organisation that Stop Smart Meters were so enthusiastic about a moment ago.

The AAEM also believe that "mercury in vaccinations constitutes a significant exposure" (PDF), even though the mercury-containing preservative thiomersal is no longer in almost any vaccines that anti-thiomersal campaigners insisted were causing terrible harm to children, and this change has caused no epidemiological effect at all. I refer you once again to the World Health Organisation.

Oh, and the AAEM are really keen (PDF) on that whole multiple chemical sensitivity thing. Which is one of those illnesses that doesn't seem to manifest when a sufferer is exposed to the alleged causative agent but doesn't know it, and does manifest when a sufferer thinks they're being exposed, but they aren't.

The World Health Organisation has little to say about MCS, except to point out that people who believe they have it seem rather like the people who think they're "electrosensitive".

Funny they should mention that. Because Stop Smart Meters believe, of course, that "electrosensitivity" is real. Which it is, in a sense; people who suffer from it really do suffer. There's just no good reason to suppose that this suffering actually has anything to do with "radiation", and numerous studies that show it does not.

Anything a smart meter broadcasts is, apparently, bad. Stop Smart Meters complain that mesh-networked meters broadcast more frequently than meters with long-range radios, because mesh networks need relays to get the feeble signal from each meter to the actual power-company receiver for the area, and the relays are built into the meters. But since this is all because the radios are more feeble, I fail to understand why Stop Smart Meters automatically assume that this is yet another thing to worry about.

People hold mobile phones to their heads, often for extended periods. So if a watt or two of nine hundred and something megahertz radio waves actually can hurt you, it's sensible to presume that heavy mobile phone users would develop these diseases, presumably in their head, and presumably preferentially on the side they habitually press their phone to.

People are not in the habit of leaning their head on their electricity meter all day. And even the mesh meters do not normally broadcast all day. I think the non-mesh meters broadcast for a total of about five minutes a day, but I don't have a strong enough source for that to bet anything on it.

Even if you're sitting in a chair on the other side of the wall from the meter, with its antenna a mere metre from your head, then you'll be exposed to way, way less RF energy per second than you would with an iPhone pressed to your head in a dodgy reception area, and the exposure may be for only minutes, or even seconds, per hour. Arguing that this is a major risk, even if heavy cellphone use is dangerous, is like saying that hypothermia is lethal, so you'd better never eat ice cream.

Stop Smart Meters also appear to think that RF from the meter getting into the home wiring will cause those terrible microwaves to radiate from all of your house wiring. Once again, this completely ignores the concept of "power", how much of it there is in the first place, how much of it can manage to get into the house wiring via a miserably inefficient "antenna", and how much it attenuates with distance from the wires.

I could go on with this, but life's too damn short. Yes, there are reasons to object to the new meters; the new system seems very likely to come with more electricity price hikes, for instance, and you may even be overcharged on top of that.

But the bulk of Stop Smart Meters' argument isn't about that.

Stop Smart Meters appear to be, like many other people, under the impression that anything called "radiation" must be bad. I would not be surprised if they also don't want any "chemicals" in their food. People like this should logically therefore be frozen into a zero-Kelvin lump and stored in a an earthed lead box containing a hard vacuum, but for some reason they seem to be fine with light bulbs and moonlight and the drinking of dihydrogen monoxide.

If you don't know what radiation is, and you don't know what chemicals are, and the inverse-square law might as well be the Collected Proceedings of the Vorlon Linguistic Society for all the sense you can make of it, then I implore you to seek education, and remind you that activist organisations of any kind are much more likely to be in the bullshit business than the education one.

If you don't fancy the idea of education, I suggest you live a life of happy-go-lucky ignorance, taking cues from a housecat, or a domestic dog, depending on your preferences.

Just please don't spend your time worrying about the terrible threat someone says is posed by technologies, cultural changes or particular types of other human whom you do not understand. Every minute you spend worrying about Islamists conquering the world, or commercial airliners spreading mysterious poisons, or electricity meters giving you cancer, does nothing but move you one minute closer to your actual death, and gains you nothing at all.

Posted in Electricity. 19 Comments »

Fire from, or at least near, ice

20 February 2012 — dan

A reader writes:

Got a science question of sorts.

WTF is actually going on here?

Chris

The ice cube is not glowing. The induction coil is.

Induction heaters are interesting things. You make a coil out of a sturdy conductor - usually copper bar stock - and you put a whole lot of current through it at, usually, a pretty high AC frequency. The alternating current then induces current in any conductive object you put inside the coil, and the resistance of the object turns the current into heat, which heats the object. It's the same principle that heats up a wire, or an actual heating element, when you put current through it. The source of the current in an induction heater is just less obvious, and the electricity in the heated object isn't going round and round in a circuit; it's just jiggling eddy currents.

(Magnetic braking relies on induced eddy currents as well, and also heats up the object the eddy currents are being induced in.)

The induction coil was actually the first, and worst, kind of transformer. It was the worst because the purpose of a transformer is to turn one voltage of AC into another (or keep the same voltage but isolate two circuits). The more energy a transformer wastes as heat, the less useful it is. Modern transformers have laminated cores made from "electrical steel", specifically to minimise unproductive transformer-heating eddy currents.

A powerful enough induction heater can do all sorts of neat tricks, like heat-treating part of a piece of metal - all the way to glowing hot - so fast that the heat won't have managed to conduct through the metal to other parts of the object before the bit you're heating gets to the right temperature and can be quenched. You can also use an induction heater to melt metal in a crucible without a flame.

Or even to levitate a light enough metal, while it melts!

Induction cooktops work this way too. That's why they'll heat a metal pot, but not glass cookware. If it's conductive, they heat it; if it isn't, they don't.

[UPDATE: As commenters have pointed out, only ferromagnetic cookware actually works on an induction cooktop. I'll fix this properly when I have a moment.]

Ice is very slightly conductive (as I have proved to my own satisfaction), but can generally be considered an insulator, and won't be significantly warmed by an induction heater. So the induction coil in the ice-cube video is essentially being run "empty", and just rapidly heating itself up, and in due course glowing, in a simple resistive way. That ice cube will actually melt pretty quickly, because of radiant heat and air convection from the coil. But it'll last as long as you'd expect it to if it were sitting next to a similarly glowing plain resistive heating element.

(The glow probably isn't really as impressive as it looks, either, because digital cameras of all sorts are sensitive to infrared light. Most digital image sensors have an IR-blocking filter on them to minimise this effect, but the filters aren't completely effective, and so very hot things like this coil or the aftermath of certain pyrotechnic entertainments look hotter than they are. The human eye may see some glowing metal as orange, but most digital cameras will think it's white.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Electricity, Psycho Science, Science. 8 Comments »

Short-stopping

19 January 2012 — dan

A reader writes:

When I release the trigger on my old AEG power drill (so old that it's from when a power tool was an INVESTMENT), the motor takes at least a second to spin down to stationary.

When I release the trigger on my Black and Decker cordless drill, though, the chuck stops spinning instantly.

Why the difference? Is there a mechanical brake in there? Is this some sort of regenerative braking to keep the battery charged for longer? Is there just a lot of friction in the drill because they don't make them like they used to?

Timothy

Old-style power drills have a simple design, in which the trigger connects mains power to the drill motor, releasing the trigger disconnects the power, and if you want more than one speed you can maybe move a clunky slider to change between two gear ratios and count yourself lucky because in my day laddie we used to have a bit and brace made frae whalebone wi' a sandstone chuck, et cetera.

Most modern corded power drills have a proportional speed-control system, where the further you pull the trigger, the faster the motor spins. When you release the trigger with the drill spinning, though, the motor will still take its time spinning down, unless of course there's a source of outside friction like a bit in the chuck that's still sticking through a piece of wood.

This spin-down behaviour is natural for almost all rotary electric motors. If you don't count certain odd birds like stepper motors, any spinning electric motor will, when you disconnect the power, coast down to a halt.

Except, as you say, cordless drills always stop at pretty much the exact moment you release the trigger, as long as you're not spinning some large object with the drill, like a hole-saw or sanding drum. And even then, they stop pretty quickly.

The reason for this is that cordless drills use simple, inexpensive brushed DC motors. (Actually, brushless motors are starting to show up in fancy cordless tools, but I'll shamelessly handwave that awkward fact for the purposes of the current conversation.)

Brush motors are really easy to stop dead: You just short out the input terminals.

If you've got a bare DC motor sitting around somewhere - I'll wait, while you dig up your box of old radio-controlled car parts or smash open that useless bloody $5 electric screwdriver that the batteries never even properly fit into - you can demonstrate this for yourself. Spin the motor's spindle by hand, and then short the terminals on the back of the motor with a paper clip or something and spin the spindle again. In the second situation, the faster the spindle spins, the greater the braking power on it.

The reason for this is "back EMF", a special case of the counter-electromotive force which, in brief, causes the currents induced in a piece of metal by a magnetic field to create another magnetic field opposing the first one. You can make an "eddy current brake" that employs this force to convert motive power directly into heat in the brake assembly, without any friction; this is useful in everything from heavy industrial applications to the delicate aluminium-paddle magnetic brake that sticks out of the side of a laboratory balance, whose purpose is to stop the darn scales from swinging back and forth around the correct reading until the research project runs out of funding.

In brushed DC motors, back-EMF braking works really well, which is why it is, for instance, the normal braking system for the abovementioned electric radio-controlled cars. A fast-stopping drill is a desirable thing to have, too, so releasing the trigger disconnects the power from the motor, and shorts the terminals to each other. There's no simple way to do the same thing in an AC motor, so you don't get this feature in corded drills.

Back-EMF braking won't instantly stop a motor if it's turning fast enough. I've got a Dremel Stylus, for instance, which is a brilliant little tool for all of those jobs for which my old mains-powered Dremel is a bit too powerful and clumsy, but for which a cheap AA-powered Dremel or similar suspiciously inexpensive rotary tool would be too feeble. I think the Stylus has a simple brush motor in there (as you change its speed, it sings the distinctive song of a brush motor vibrating because of audio-frequency pulse-width modulated speed adjustment), but its top speed, as with all rotary multi-tools, is much higher than the top speed of a cordless drill. So when you turn the Stylus off, it stops pretty darn quickly, and quite a bit quicker than the mains-powered Dremel, but it still takes about a second to run down.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Electricity, Psycho Science, Science. 3 Comments »

The amazing power-saving box of nothing!

23 November 2011 — dan

I wrote, in 2010, about the miraculous Keseco Current Improvement System. It's a power-saving device that's claimed to work because of, in brief, technologies unknown to science.

I like this kind of power-saving box. Most power-savers are claimed to be some sort of power-factor corrector. Ones like the Keseco devices that're supposed to work by "rotating electromagnetic waves" or "non-Hertzian frequencies" are more fun. They still don't work, but at least they're more original.

When I saw a new comment on the Keseco post today, I presumed it'd be one of the spammers who occasionally get through the net and spray ads for handbags or wristwatches all over my old posts.

I was wrong, though. It was this:

We are representing Ultra device, made by Keseco in EU market.
We do agree that claims to achieve superconductivity in wires seem to be unrealistic. And we partly agree with that. However we confirm that we have tested Ultra in various cases: domestic and industrial. We have used Chauvin Arnoux ca 8335 power analyzer to measure w,kva,kvar,Amps, U, harmonics, cos fi, etc. We confirm that Ultra device really works in reducing active power, reactive power, slightly improving cos fi.It reduces total consumption by 5-12%. The saving % depends on a number of factors.It does not turn wires into superconductors, but reduces energy loses in them.Detailed reports can be send upon request. Currently Keseco obtained SGS, TGM reports on saving. The patent they have for energy saving device is real.It is not for design, it is for energy saving.See: http://www.wipo.int/patentscope/search/en/detail.jsf?docId=WO2003061097&recNum=1&docAn=KR2003000104&queryString=AN:PCT/KR03/00104&maxRec=1 . Ultra device really saves energy For more information on research works we have done with ultra,please, send request to :info@energita.lt.

Energita

If it's all the same to you, unnamed Energita representative, I'll just wait for this miraculous device to make you the billions of dollars you so richly deserve. Then I'll be able to learn about it from, say, the paperwork for the Nobel Prize the Keseco designers have won, or the sticker on the side of the Keseco box that I, like everyone else in the world, will have purchased.

Just look at that patent. It's for a box...

Keseco power-saving device

...with some busbars in it, the busbars only being connected to power at one end, and the inside of the box provided with some mysterious ceramic coating and "conductive plates" that aren't electrically connected to anything.

And that's it.

Conventional electrophysics says that this box, plugged in parallel with household mains power, will do nothing. It's not even part of a circuit.

You allege that you have real evidence that it's a power saver.

So now all you have to do is send these patented boxes to universities, technical colleges and appropriate governmental bodies until someone takes notice, and then here comes all that money and that definite Nobel Prize, for the staggering discovery of how "rotating electromagnetic waves" make the magic happen.

(Or the people who invented it could, after patenting their discovery, have written it up as a scientific paper. Get it published and the results replicated, then sell licenses, and you could become billionaires without having to actually manufacture anything at all.)

You'd think that in the several years the Keseco device has been around, they'd have managed to do this. But instead, just like every other magic power saver or magic gasoline pill, the devices are sold piecemeal to whatever end-users can be persuaded to buy one.

Electrical components that aren't connected to anything are strangely popular in scientifically... novel... devices and talismans.

Inside the "EMPower Modulator", for instance...

EMPower Modulator interior

...are three aluminium plates that aren't connected to anything.

The "Q-Link Pendant"...

Q-Link pendant

...is similarly electrically innovative. And now we've got this Keseco box-of-nothing, too.

Energita sell a few other odd devices (machine-translated English version).

This power-monitoring system (translated) seems kosher, as do these light bulbs (translated), and I think this gadget (translated) may be OK too; it seems to be some sort of improved thermostat for freezers.

But then there's something called a "Fuel Activator" (translated), magnetic fuel improvers (translated) and, of course, the Keseco doodad (translated).

I'm never sure what to think when someone who sells these sorts of products remonstrates with me. I presume they quite often, especially when they're a reseller instead of the originator of the product, actually believe what they're saying. They're seldom abusive or clearly mentally peculiar.

There but for the grace of critical thinking, I suppose.

Posted in Electricity, Scams. 12 Comments »

From SLA to car

4 November 2011 — dan

A reader writes:

Having read this...

What could possibly go wrong?

...I became inspired to upgrade my UPS as it's time to replace the 5.5AH gel cell, so why not kill two birds with one stone.

Unfortunately, I don't know a heck of a lot about the ratings and other tech jargon behind what will make this all work, so I am sending this email in the hope that perhaps you could take a moment to take a look at what I have and let me know if it seems likely that it will work for a start and then what I should go out to buy to make it happen. I should at this point mention that I live in Thailand, the land where no matter what you want to buy, you can't find it. But still, given that I have a UPS unit and access to a place that sells cheap car batteries, I figured there may be hope.

Firstly, this is what I have. (The specs are in English at the bottom of the page.) The gel cell inside is a "Model AC-1255" rated at 12V 5.5AH/20Hz in case that means anything to you.

Does it seem likely that if I connect a car battery (or two) to this device I will be able to achieve similar results to what you did in your article? () Or is this UPS just not up for the task of keep a car battery or two charged and ready for the task at hand.

Out where I live power is OFTEN interrupted, but rarely more than 5-10 minutes at a time (90% of the time it's just a few seconds), but of course those few seconds are the ones immediately preceding my clicking "submit" on a 2 hour email type-up marathon. I NEED to have some form of UPS going but am not looking for hours of use after power-out. Just enough time for me to shut down the system gracefully.

I would appreciate any insight you could offer to my options and if you need any further information on the bits I have here, just let me know.

Many thanks

David

Fortunately, this is a pretty easy job. If you screw up, though, it can be quite dangerous.

Here are the ways in which you can get it wrong when hooking up new batteries, especially bigger new batteries, to a UPS:

1. A given UPS runs from 24 volts, so it wants two 12V batteries in series; you give it one, or two in parallel.

Danger: Possibly high, if you thus barbecue the batteries with too much charge voltage. You'll probably just get loud complaints from the UPS, though, and if you're not completely daft you'll disconnect the batteries before anything can go pop.

2. The opposite of the above; it wants one battery (as your particular UPS, like most small UPSes, does), but you give it two in series. (Two in parallel would be fine.)

Danger: Will probably kill the UPS. Probably will not set it on fire.

(Home/small-office UPSes are almost always 12V or 24V on the battery side, meaning one or two 12V batteries. Big serious UPSes may run more batteries in series - possibly built out of individual two-volt cells that are each bigger than the whole 12V battery in your UPS - because the higher the voltage the lower the current for a given power output, and big serious UPSes can usually deliver a lot of watts. Lower current is desirable because it means thinner wires and cheaper power transistors and other components. This is also, essentially, why big long-distance power lines run at such high voltages.)

3. You connect the battery or batteries backwards.

Danger: May or may not blow up the UPS. It's quite easy for the designers to guard against this mistake, but I've no idea how many do.

If your new battery is the same type as the old one, you have to be pretty seriously dedicated to screwing up in order to connect it backwards. It'll probably be connected with two spade lugs of different sizes; getting them the wrong way around can only be achieved if you're the sort of person who hammers a USB plug into a VGA socket.

If you're connecting a UPS to a bigger battery that has different connectors, though, it's usually quite easy to connect it backwards.

Whatever happens, this particular mistake probably won't set anything on fire.

4. You accidentally short out one or more of the batteries. Even little sealed-lead-acid "gel cells" can deliver a lot of current into a dead short, and very high current delivery is the major design goal of car batteries. The worst possible way to do this is to have a couple of batteries you're trying to connect in parallel, and to accidentally connect one of them backwards. (This is also what happens if you get the leads mixed up when jump-starting a car. In that situation one of the batteries is usually pretty flat, but a quite stimulating physics demonstration may still ensue.)

Result: From alarming to spectacular. Red-hot wires. Smoke and possibly flame. If you break the short-circuit quickly, though, the batteries themselves should be OK.

If you're building a battery pack for a cordless drill or R/C car or something, you can do it with discharged cells, which makes accidental short-circuits harmless. You generally can't do that with lead-acid batteries, because running them flat damages them. On the plus side, if you're upgrading a UPS battery you're probably not soldering any cells or batteries together; on the minus side, while you're running longer wires to connect a bigger battery outside the UPS, there are many opportunities to short the battery out.

(If you've got a liquid-electrolyte lead-acid battery, you can drain it of electrolyte while you work, which makes it harmless, just like building a battery pack from flat cells. The best solution if you're going to be fooling around with wires connected to a high-current-capacity battery is to buy a brand new battery that comes "dry", and buy your electrolyte separately. Note that lead-acid battery electrolyte is roughly 30% sulfuric acid, and should be treated with respect; battery acid won't melt the flesh from your bones, but it is still not your friend. This is all overkill for what we're talking about here, but I want to be as exhaustive as possible in writing about this stuff for the benefit of readers whose situation is not the same as yours.)

By now you are probably just about ready to throw up your hands and trade your computer for a manual typewriter, but I really did mean it when I said this job is pretty easy. You'll very probably be fine. Take your time, do not mitigate any uncertainty you feel with alcohol, and keep track of which wire's meant to be positive. If you do not own a cheap plastic multimeter, buy a cheap plastic multimeter. Some basic soldering ability will also be handy for extending power wires, but you'd get away with using wire nuts or something. (You'd probably also get away with twisting wires together and then mummifying them in leccy tape, but doing so makes the ghost of Nikola Tesla cry.)

And now, finally, specific answers to your actual questions.

I don't know whether your UPS will actually be happy running from a car battery, but it very probably will. I used to be less confident about this, but I've done it more times myself now and corresponded with plenty of other people about it, and it really does seem that most, if not all, consumer-market UPSes will work fine from much bigger batteries. They don't charge a big battery very quickly, but unless your local electricity is a ten-minutes-on, two-hours-off sort of deal, that's not a problem.

Car batteries are not an ideal choice for running UPSes, because they've got less capacity per kilo than batteries made to run, for instance, golf carts or fishing-dinghy trolling motors. Car batteries also don't like being run flat. But the price/performance ratio for low-end car batteries is much better than that of fancy deep-cycle batteries, and car batteries' shortcomings are largely irrelevant to someone like you who mainly just wants to ride out short power interruptions, and doesn't anticipate running from battery power for any great length of time.

(It also seems pretty definite now that lead-acid batteries that've "sulfated" because they were run flat and left that way can be rescued, with "desulfator" gadgets. I haven't done enough research of my own to be able to speak authoritatively about this, though.)

The specs on the side of your battery only matter if you're trying to buy a new one that'll fit inside the UPS, without having to know the exact dimensions of your old battery or the one you're buying. There is unfortunately no standardised naming for SLA batteries, so the "Model AC-1255" on the sticker is not helpful.

The most common battery in small consumer UPSes is a brick-shaped 12V unit with about a seven amp-hour capacity; the battery you've got is I think probably this size, but it doesn't matter since you're not after another weedy little gel cell.

(I've no idea what the "20Hz" on the sticker means, by the way. Batteries are not alternating-current devices, so whatever that is, I don't think it's meant to mean 20 cycles per second.)

One cheap car battery will probably do the job for you just fine. If you needed longer run time then you could add one or more extra car batteries in parallel (preferably identical batteries, by the way, though in relatively low-drain applications like this you can get away with all sorts of unsightly alternatives), but that doesn't seem to be the case.

Get a set of cheap jumper leads along with your cheap battery as I did, cut 'em up and splice them onto the UPS's existing battery leads, hook it up, and enjoy some relatively reliable computing.

Posted in Electricity, Hacks. 13 Comments »

Hurrah! Another power-saving doodad!

2 February 2011 — dan

Thanks, once again, to all you readers and your ceaseless campaign to make me sad and irritable, I now know that a couple of days ago that jewel in Australia's investigative-reporting crown, A Current Affair, ran a story about yet another bloody "power saver".

You can see the five-minute ACA segment here.

(Pleasingly, as I write this, the comments on that page are overwhelmingly negative. I've only clicked the "10 more comments" button a couple of times, but thus far it's the sanest comment thread I've ever seen on a mainstream-media site.)

This latest magic electricity talisman is the "Oz Power Saver", the Web site for which is immensely proud of the ACA story, but oddly bereft of further information. You can't even buy one. All you can do is "register your interest".

The basic claims on the site are par for the energy-saver course, though. "Save up to 25% off your electricity bills", "reduces energy usage", and the inevitable "guarantee".

That ACA video fills in the rest of the blanks, with the same stuff we've seen over and over from other magic-box salesmen.

Like the guarantee, for instance, which this time says that they'll refund the purchase price if you don't save at least the Oz Power Saver's purchase price in three years.

It would be churlish and tendentious of me to point out that scam-gadgets, definitely including "power savers", almost always have alleged money-back guarantees, and that power-saver hucksters have a tendency to spawn new businesses rather more frequently than once every three years.

So I shall, of course, not point that out.

On goes the video, dum de dum, it's "already a huge hit in the US and Europe", here's a testimonial from the "one lucky family" in all of Australia who've had the chance to try the thing out, here's no testimonial from anybody equipped to test it properly, "big energy users like factories and hotels have been using this technology for years"... all right, I reckon we're ready for an atrociously mangled explanation of power factor, and power-factor correction, now.

Ah, there it is.

Peculiar power-factor explanation

The ACA explanation actually starts out well, with a double-sine-wave depiction of the voltage/current phase relationship, but then spears off into the bushes with some gibberish about the phase relationship getting messed up as the electricity "travels to your home". (Later on, they tell us that the further you are from a distribution transformer, the worse your power will be.)

It's actually reactive loads that mess up power factor, not the length of wire between your house and a pole-pig transformer. But, more importantly, the people who worry about power factor are the suppliers of the electricity, not its consumers.

To try to get my umpteenth repetition of this lecture out of the way as quickly as possible:

1: There are many, many "power saver" products on the market. Most are little plug-in things, but there are also versions like the Oz Power Saver that are hard-wired in the breaker box. Actually, there are some that're very, very like the Oz Power Saver, to the point of looking exactly the same, as we'll see in a moment.

2: There is no known way for devices like this to work. Power-factor correction is a real thing, but it is completely impossible for it to save a domestic power consumer any money at all, even if their house has a lousy aggregate power factor, which it almost certainly doesn't.

3: The reason why it can't save you any money is that domestic (and most commercial) power consumers aren't billed for a bad power factor. Domestic (and most commercial) power meters can't even detect a bad power factor. Promoters of these gadgets always come up with some sort of tortured pseudoscientific word-salad that suggests that your electricity meter actually measures the "bad electricity" or "dirty power" or whatever that the magic box cures, but this is not actually the case unless you're running a factory full of motors, and it's not always the case even then.

Back to the Oz Power Saver.

I applied the terrifying black-hat hacker firepower of the TinEye image search to...

Oz Power Saver picture

...this picture of the product, on the Oz Power Saver site. Whaddayaknow, there was the same image...

Power-Save 1200 picture

...being used on numerous sites selling the good old Power-Save 1200!

Now, the Oz Power Saver can't be the exact same thing as the Power-Save 1200, because the Power-Save 1200 is a US product, and Australia's mains voltage is twice that of the USA.

(Well, OK, it could be the exact same product, if it contains auto-sensing multi-voltage circuitry, or no circuitry at all, which latter situation turns out to be not far from the truth for certain products in this market sector. I don't think either is likely in this case, though.)

One quite marked difference between the Oz Power Saver and the Power-Save 1200 is price. The Power-Save 1200 is about a $US300 product, while the Oz Power Saver, according to the cheerful distributor in the ACA story, revels in a price of eight hundred and ninety-five Australian dollars, which is about the same number of US dollars, as I write this.

But it's guaranteed to save you at least that much in three years, et cetera et cetera.

In the ACA-story demonstration of the Oz Power Saver's incredible qualities, we get to see the traditional Wooden Partition with Wires and Motors On It, and the similarly traditional Cheap 'N' Dodgy Power Meter (sometimes replaced by one or more $10 multimeters) giving its imaginative impression of the power factor of a load.

The demo load manages to achieve a truly miserable power factor of 0.39 according to said meter, which leaps to 0.87 when the Oz Power Saver's activated.

These power-factor numbers may actually be accurate, since the test load appears to be a free-spinning unloaded AC motor, which can be counted on to have a crappy power factor. AC motors that're matched passably well to their load, like most AC motors in the world, can be expected to have a much better power factor. Power tools - electric drills, angle grinders - may have a lousy PF when they're spinning free, but you'll have to spend rather a lot of time standing there grinning at a free-spinning drill bit for that load to make any significant difference to your residence's aggregate power factor.

More realistically, washing machines and tumble-dryers may sometimes have lousy power factor, because different loads of washing mean different loads on the motors. But you'd, again, have to do rather a lot of washing for this to make a significant difference to your home's aggregate power factor, and even if you do, it won't cost you any more money, because residential customers aren't billed by power factor. (Just in case you forgot that.)

Shortly after the cheap-electricity-meter demo, A Current Affair's piece on the Oz Power Saver suddenly switches to an update on a story from last year, about some blokes who make a whole different power-saving thingy, the "Futurewave Energy Saver". Which I immediately, of course, assumed would be another box of pure uncut pixie dust. But which I suspect is actually kosher.

The Futurewave device is alleged to reduce the power consumption of swimming-pool pumps, and some other similar motors. It isn't a magic power-factor box, though; it's a speed-control device, that according to the FAQ saves actual real power, instead of confusedly-described apparent power, by just running the pool pump at reduced speed for most of the pool-cleaning cycle, when full power isn't actually required.

This seems as if it might actually work. I don't know if it does, but it seems to have no arguments with the laws o' physics, or of electricity billing.

Next, the ACA story whiplashes back to the Oz Power Saver, and cheerfully informs us that the Oz Power Saver will "do the same" for "anything with a motor".

So presumably you'd be a total idiot to buy the Futurewave product, that only works for pool pumps.

God, I'd be irritated if I were the Futurewave people. It'd be like taking the time to build a comfortable and safe 80-mile-per-gallon car, and then finding yourself lost in a vast mob of hucksters selling cars that run on water.

I'm not holding my breath for a regulatory agency to do anything about the Oz Power Saver. It is, for a start, not actually on sale yet, and the regulators are overworked and understaffed. Scams that don't actively kill people often don't get a very high priority.

Here, to cheer us all up a bit, is the Australian government slapping down one of the many plug-in power savers, called the Enersonic Power Saver, which I mention here and here.

The Australian Consumers' Association were so impressed with another plug-in power saver, the "Reegen Micro-Plug" that they gave it a Shonky Award. And here are those nice people who sold one of these things until they realised it was a scam, then said sorry. They, along with some non-Australian examples are mentioned at the end of this old post.

My offer from the end of that post still stands. If the Oz Power Saver people want to contact me about installing one of their boxes at my house, preferably with a nice Frankenstein knife switch so I can switch it in and out of the circuit at will just as they do in their demo, I will test it with various household motor loads and will immediately recant all of the above if the Oz Power Saver turns out to do a damn thing.

Posted in Electricity, Scams. 15 Comments »

Self-adhesive super-science!

4 November 2010 — dan

A round of applause, gentle readers, for Stephen Fenech, "Technology Writer" for the Daily Telegraph here in Australia, for his unflinchingly courageous presentation of the "Q-Link Mini".

The Mini is a tiny self-adhesive object which, Mr Fenech assures us, is "powerful enough to shield us from the potentially harmful electromagnetic radiation generated by mobile phones and other electronic devices". (Q-Link themselves delightfully refer to the Mini as a "Wellness Button".)

Not for Mr Fenech the mealy-mouthed objections of hide-bound so-called "scientists", who've observed that there's no good reason to suppose that low-level exposure to non-ionising electromagnetic radiation has any deleterious effects, and that there's also no good reason to suppose that there is even a theoretical basis for low-energy EMR to harm us, and that if you block the radiation coming out of a mobile phone, the phone won't work any more.

Mr Fenech is similarly wisely unconcerned that Q-Link's most famous product, the "SRT-2 Pendant", contains a copper coil that isn't connected to anything, and a surface-mount zero-ohm resistor, which is also not connected to anything.

I'm sure Mr Fenech disregards doubts raised by this discovery because, of course, Q-Link's products are unconstrained by the foolish fantasies of orthodox "science", which has somehow come by the idiotic idea that the existence of microwave ovens, GPS satellites and personal computers might indicate a more accurate understanding of the principles by which the universe operates than that possessed by the manufacturers of mystic talismans supported by testimonial evidence, uncontrolled user tests and the sorts of studies that cause spikes in the blood pressure of "scientists" who work so hard to get their own papers published because, of course, their papers are mere tissues of lies that never mention "biomeridians" or "Applied Kinesiology"...

...which is here discussed in a way clearly calculated to underhandedly attack Q-Link's products!

If you buy something that's meant to operate by "Sympathetic Resonance Technology™" or "non-Hertzian frequencies", you should of course take it back for a refund if it turns out not to contain seemingly-meaningless components that aren't connected to anything. Those components are where the magic happens, people!

Now, I know that some of you are the sort of raving "science"-worshippers that won't take Mr Fenech's word by itself as proof that the Q-Link Mini is worth $US24.95 - or even $AU48, which for some reason is what it costs here.

Rest assured, all you Moon-landing conspirators and Nazi doctors, that Mr Fenech has diligently secured supportive quotes from the entirely unbiased CEO of Q-Link Australia, and also a naturopath called Daniel Taylor, who appears to be a practitioner of the "Dorn Method", which regrettably does not seem to have anything to do with being knocked out to demonstrate how dangerous the latest threat to the Enterprise D is.

I don't believe a study's yet been done to determine what happens if you use one of those antenna-enhancing stickers at the same time as a Q-Link Mini. Be warned that adding a battery-enhancing sticker and a Guardian Angel battery may result in headache, irritable bowels or time travel.

Posted in Electricity, Scams, Science. 10 Comments »
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