Zaps and bangs

A reader writes:

Hi, Dan! 

Though I didn't follow all of the details, I did enjoy your writing about electrocution and car batteries.

Do you know the odds of getting electrocuted if one is standing in a wet shower with wet skin using a cordless (battery-powered) sander? I don't know what kind of power I'll need to work on residential showers for hours at a time, but the electric chorded sander I WAS using (until I decided that I'm tired of risking electrocution) says it's a 120 Volt, 10 Amp model. 


There's probably no danger, but there could be some.

Cordless tools all run from low-voltage DC, although the voltage has risen in recent tools that use one or another flavour of rechargeable lithium battery. Higher voltage is better, from the tool-makers' point of view, because a given power from a higher voltage requires less current. This means thinner wires, less beefy switches, and generally speaking a cheaper, lighter tool with the same power.

Cordless tools are also, in general, significantly less powerful than corded versions. It's normal for corded drills and saws and sanders and such to draw peak power of at least several hundred watts. The ten-amp 120-volt rating of the sander you mention makes it a 1200-watt unit (so I presume you're talking about a belt sander, not an orbital one), though it'll only draw that much when it's working hard. You can expect even big heavy cordless tools to have no more than half the power rating of a similar corded tool.

Discovering exactly what that rating is can be difficult, partly because cordless tools can have a larger range between their "spinning freely doing nothing" and "working so hard it's barely turning at full power" power consumption than corded tools do. Mainly, though, cordless power ratings are harder to find because consumers think more watts are always better. So a cordless tool that costs three times as much as the wall-powered version, yet has a third the power rating, won't sell well, unless the manufacturer conceals that latter number.

I'm telling you all this just to explain my original wishy-washy "possibly dangerous" statement. If you're using a 12V tool then you probably won't be able to do yourself any electrical harm with it, even if you smash the thing on the wall until it breaks and then smack yourself in the chest with the pointy bits.

A 36-volt tool, on the other hand, is edging up toward the kind of voltage that actually can harm you, if only indirectly. (Direct harm: Current through your heart stops it, you die. Indirect harm: Current through some other part of your body causes you to spasm and dig a tool into yourself, fall off a ladder, flop out of the shower recess and smack your head on the toilet, et cetera. This sort of secondary injury following a non-fatal shock is a lot more common than injury or death caused directly by electricity.)

In the real world, even crappy bargain-basement cordless tools have enough plastic between you and the wiring battery terminals that no matter what voltage they run at, you pretty much have to make a specific and deliberate project out of killing yourself with one. Working in a wet environment is still dangerous, but only because it makes it easier to slip and then drill, saw or sand yourself instead of the workpiece.

Brand-name tools are generally safer still, and adding water to the situation may ruin the tool but is unlikely to hurt the user. Even the commonly-recognised-as-lethal "dropping a hair-dryer into your bath" situation is actually not terribly likely to kill you, though I don't recommend you try your luck.

If it's possible to electrocute yourself with cordless-tool gear in any way at all, here is I think your best chance of doing it without specifically running wires from the inside of the tool to nails driven into your chest. There are plenty of battery designs with exposed terminals of one kind or another, so suppose you eject the battery from the tool by accident, and then somehow grab that battery with both, wet, hands, so positive is touching one hand and negative is touching the other.

Even then, the resistance of human skin is way up in the tens of thousands of ohms - I found the resistance between two closely-spaced points on my tongue to be 70,000 ohms. So even with a 36-volt battery it'd be surprising if one whole milliamp managed to flow across your chest, and not all of that would go through your heart. I think you'd be an easy order of magnitude away from enough current through the heart for there to be any risk at all.

(I'm sorry to say that I'm not about to conduct heart-stopping experiments on myself. I have, however, previously zapped my arm for science.)

If both of your hands had bleeding cuts on them then 36 volts might be enough to at least give you a shock you could feel and it might have cardiac consequences, but this is really pushing it. And any sort of work gloves not made of chain-mail would erase the risk completely.

And, of course, back in the real world it continues to be downright difficult to actually touch the positive with one hand and the negative with the other. If you just grabbed both terminals of a 36-volt battery with one wet bleeding skinless lightly-salted hand then it'd sting like a bugger, but once again the only real health risk it'd present would be if the pain startled you enough that you then hurt yourself in some other way.

I won't be surprised if cordless-tool voltages rise further, though. There are already cordless mowers that run from 48-volt packs, for instance. So it's possible that a few years from now there'll be cordless tools running from voltages high enough to pose real electrocution risks.

It'll still be a lot less dangerous than it was in the olden days of corded tools, though, when casings were still commonly made of shiny cast aluminium. Then, the user's life was in the hands of the manufacturers and electricians who're meant to keep earth wires connected, and prevent live wires from touching the tool chassis.

With modern plastic casings and other construction improvements, even a theoretical 96-volt cordless tool is not likely to be an electrocution risk, even if you use it in the rain or, more realistically, get all hot and sweaty while working.

There's a lot of energy in a cordless-tool battery, though, and they definitely can hurt you if that energy is released very quickly because of, say, a short circuit...

...or severe over-charge...

...or physical damage...

The reason why drills and laptops and iPads aren't exploding all over the place is that the naturally excitable personality of lithium-ion technology, in particular, is kept calm by strong casings and protection circuitry ranging from simple fuses to smart current limiting:

If one of your cordless tools manages to puncture the battery of another, though, your life may still become quite exciting.

So I suppose I've allayed your fears of one kind of injury and then given you a new one to worry about.

There's no need to thank me.

Psycho Science is a... sort of... 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.

My ever-vigilant Perpetual-Motion-Claims Patrol

A reader writes:

OK so this looks really cool:

Alabama-Based CMR Demos Programmable Magnets That Changes Polarity And Strength On A Whim

As long as they don't violate the laws of physics that is. What do you think, scam or not?


Correlated Magnetics Hoverfield demonstrator

I don't see any reason to think that Correlated Magnetics are doing anything snake-oil-y. They've just got a way of making single magnets which contain multiple differently magnetised regions.

Take the above "Hoverfield" demonstration unit gizmo, for instance...

...which you can buy for a hundred bucks if you like.

Clear acrylic and magnets doing odd things do indeed instantly start some red flags waving among those of us who're accustomed to independent thinkers like Steorn who, as you say, claim to break the laws o' physics but never quite manage to actually do it. But Correlated Magnetics are not in the physical-law-breaking business. You can make a less elegant contraption that does the same thing all of their products do, at home.

Take the "Hoverfield" thing, for instance. To make your own ugly version, all you need is a couple of large relatively weak magnets, plain ferrites, for instance, and two or more small strong rare-earth magnets.

Now glue the rare-earth magnets onto the faces of the ferrite magnets so that when the ferrites are facing and attracting each other, the rare-earth magnets are facing and repelling. The large ferrite magnets have a big, weak field; the small rare-earth magnets have a little, strong one. So the ferrites attract until they're close enough that the stronger but smaller repulsive force of the rare-earth magnets equals the attractive force of the ferrites, and provided your contraption prevents the magnets from slipping sideways and ruining the demonstration, it'll oscillate to stability with the magnets close, but not touching.

Correlated Magnetics can make a magnet array that does this, but looks like an ordinary single magnet. They produce various other one-piece arrays too. "Coded" magnets that have matching pseudo-random pole patterns so they lock together very strongly but only in one orientation, for instance, and other patterns that reduce the size of the field but strengthen its holding force. (This is also how rubber fridge magnets work - rub a couple of them over each other and you can easily feel the "ridges" of polarisation that make the weak magnetic material able to actually stick to a fridge.) Correlated Magnetics have a few other such creations.

Calling these magnets "programmable" is I think a bit of marketing puffery, since they've got nothing to do with true programmable matter. If these things are really "programmable", then so are those big Edmund-Scientific-type junk-fishing magnets that you can "turn off" with a handle (which moves the magnet inside away from the external field-concentrating pole piece that the junk sticks to).

There's no perpetual motion claims here, though. leave your pitchforks stuck in the haystack, and your torches unlit.

Psycho Science is a... sort of... 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.

"I will not buy this record, it is the wax tadpole."

As a dedicated, to the point of self-destructive obsession, follower of the DealExtreme New Arrivals feed, I read a lot of very strangely translated product descriptions.

For a while there, for instance, they were regularly adding new "Gypsophila" laser pointers. There are about twenty of those listed now.

That one was pretty easy one to figure out. Gypsophila is the genus of flowering plants whose most famous member is "baby's breath", and baby's breath is known for its large number of tiny flowers. A laser pointer with a diffraction grating built into it will project tons of tiny dots in one pattern or another. "Tons of tiny dots" is in some way connected in Chinese or at least whatever translation software they're using with baby's breath flowers. And there you go, Latin plant name instead of "grid of dots".

Sometimes it takes a little more thought, though. Like when I found glasses and a clock in a shade of black called "Dumb".

DealExtreme aren't alone in using "dumb black" as a colour description. There are plenty of other Chinese dealers who do, too.

I briefly wondered whether this could have something to do with direct or accidental racism and/or survival outside English of racist archaisms, like that whole "nigger brown" thing. Then I thought a bit more laterally, and came up with this:

We, the Chinese sellers of inexpensive mass-produced objects, have a product which we describe in our complex language as having a glossy, shiny black finish. We wish to sell this product to those English-speakers who'll buy bloody anything.

None of us speak English, so we'll hit up our highly unreliable translating software, in which we have the same faith that awful tattoo artists have in those gibberish Asian fonts, for a suitable word.

What, context-not-understanding translation software, is an English word for whatever the Chinese is for "glossy/shiny"?

The software spits out several words, in an alphabetical list, and we take the one at the top: "Bright".

Hang on - we've got some matte-black products too. Not shiny, not bright - dull. So while we're here, we'd better find what the English for "dull" is.

Out comes another list, again alphabetical, and we again take the top result: "Dumb"!

Hm, better be careful, wouldn't want to look silly here. Forget the translation software, let's ask an English thesaurus what the antonym of "bright" is. Whatever that is, it will surely mean "matte".

Oh look, there's "dumb" again! So it must be exactly right!

Result: Descriptions of matte-black objects as being "dumb black" in colour.

(A plain Google search for "color dumb black" OR "colour dumb black", that extra word being there to filter out racists, currently turns up "About 84,800 results". But that's because Google reduces server load by not actually accurately counting hits for string-searches until you click on past the first page of results. There are actually only 30 results not counting duplicates. If you search for "dumb black" on eBay, you get several more examples of this mistranslation, along with various rude T-shirts.)

(P.S.: This post's title is of course partly this, and partly that.)

Small ridiculous object du jour

Crank-operated fan

This is a fan.

I am delighted to say it is every bit as demented as I had hoped it would be when I slapped down $US3.40 at DealExtreme to buy it.

(There's a green one as well, but that costs three dollars and sixty cents. What am I, made out of money?)

It is not a big fan. The diameter of the see-through rubbery blades when they're spinning is about seven centimetres (2.75 inches). The blades fold back at rest, and can thus get in the way of the crank a bit on start-up.

Crank-operated fan

The blades spin fast, though; they're heavily geared-up, and turn something in the order of 110 times per crank of the handle.

I think this fan may actually have a substantial calories-expended-to-air-moved advantage over a simple paper fan. Both cool your face while they warm up your arm muscles, but I think the crank-fan requires less effort.

It also takes up less room, both in your bag and when you're using it.

I wouldn't expect this plasticky little thing to last a whole summer of frequent use, though. But it's probably more durable than similarly tiny fans that run off batteries or USB power; no motor brushes to wear out or solder joints to let go.

I think the principal purpose of this device is to make other people smile when you use it, though, and on that count it seems entirely successful.

And yes, you can turn it to point away from you and crank the handle the other way, and run about pretending you're an aeroplane.

EDIT: I just opened it up.

Crank-fan gears

Black plastic gears on metal shafts, and a couple of actual bushings for the output shaft. The bushings are only plastic too, but should wear slower than if there were only holes in the casing plastic for the fan-shaft to go through. This trinket was not just thrown together.

(The gears were dry; I added some fancy plastic-safe oil, and now I think the fan turns more quietly. This may be a complete fantasy.)

Even if it breaks after a month, it's difficult to complain when the thing costs very little, including delivery, for this orange one, and very little plus twenty cents, including delivery, in green.

(DealExtreme have bulk-buy discounts as well; you pay an extra $US1.70 for the whole order to use the "Bulk Rate" feature, then pay less for three or more of any given item in that order. The three-unit prices for these fans are only two cents more than the ten-unit prices.)


An excuse to use that spider photo again

Here's yet another Reddit-comment transplant, this time from this thread about scary animals in the USA, in the opinion of...

Huntsman spider


I opined:

1: The house centipede. Perfectly harmless, but practically a prototypical creepy-crawly, and very common.

2: The toe biter. Apart from the egg-carrying creepiness, toe-biters have that name for a reason, and their bite may be the most painful of any insect. Won't kill you. May make you kill yourself.

(Most insect-bite-pain-scales, like the not-entirely-serious but well-researched Schmidt one, don't cover large swathes of the arthropods. The Schmidt scale, for instance, only covers the stinging Hymenoptera - wasps, bees and ants.)

I regret I have been unable to locate a YouTube, or even LiveLeak, video of someone deliberately getting bitten by a toe biter. All those marvellous videos of people eating staggeringly hot peppers (or just straight capsaicin), or volunteering to be tased, or shooting each other with fireworks, or engaging in the various other things that only other drunk 20-year-olds used to get to watch... there are even voluntary Irukandji jellyfish stings! But no toe biters.

If you can't find me video of some idiot being turned into a flowing puddle of agony by a toe biter, I of course welcome your suggestions of even more terrifying American fauna and/or flora.

Dead kids, dead animals, and other such jollity

Here's another post that was about to be a comment on a Reddit thread that no bugger'd read because the thread is five whole hours old.

The thread is about this picture of some Chinese doctors (disrespectfully translated versions here and here) bowing in respect to the body of a terribly young organ donor. She donated pretty much everything, and was only eight years old.

Needless to say, the Reddit conversation immediately wandered as far and fast from the topic as it could, thanks to someone noting the similarity between the doctors' respect for the dead girl and a hunter-gatherer's respect for the animal he's just managed to kill.

(Put like that, it sounds as if it's about half an inch away from turning into 4chan dead-baby jokes. The thread isn't actually like that. Well, no non-deleted comments with a score above minus 50 seem to be, anyway.)

This comment in particular pressed one of my personal Talk Buttons, so now that I've spent a couple of hundred words explaining the background, here's my Canned Rant on the subject of carnivores who never see an animal killed:

I don't think it's bad that people don't see where their meat comes from any more, but I think everybody who eats meat should at least visit an abattoir once. Not watch a documentary, visit one, so you get the full experience - sights, sounds and definitely smells. The smell of blood cooking on the steam pipes, the smell of various useful components of animals that people aren't going to eat, the smell of the hair being burned off the hog bellies by a guy with one of the safest, and least interesting, jobs in the whole awful place...

Talk about your "life leaving the eyes..."; how about seeing a pig screaming, thrashing around, managing to get its back feet off the hook and then flapping on the concrete floor, still fettered but no longer hung, as the blood fountains out of its throat and its dog-level brain may actually realise it's now every bit as fucked as it thought it was going to be if it got shoved up that ramp with all the rest...

(Sheep and cows don't seem to have any idea what's coming, thanks partly to clever feed-ramp design. Pigs figure that shit out, though, and do NOT want to go into the building. Perhaps that problem's been cracked now with even more animal-psychology; I saw all this, including the unexpected Porcine Murder Show, on a school trip more than 25 years ago.)

I still eat ham and bacon. But only occasionally.

(I also don't know whether it was normal, back then, for slaughterhouses here in Australia to hang up very-much-conscious pigs and cut their throats, without stunning them first. The usual reason for hanging and bleeding conscious animals is to comply with kashrut and/or halal rules, but obviously there's no such thing as kosher pork, so that couldn't have been it. If an animal's stunned or brained before being bled, then this sort of drama's only ever going to happen, with or without an audience of rather alarmed Agricultural High School kids, if the stunner-guy manages to miss.)

Wibbly-wobbly WTF

The Name of the Doctor

Do you enjoy Doctor Who episodes that are almost entirely free of events that make sense?

You'll love The Name of the Doctor, then!

(Spoilers below.)

Never mind the standard weirdness of having a machine that can go anywhere in time and space but, if your friends are being abducted, never just goes to the moment of the abduction so you can open the door and pull them in.

No, in this episode you've got the whole universe's timeline being rewritten and people fading out of existence like in Back to the Future, while other people... don't. Whole star systems are vanishing by the dozen, friends become enemies but for unexplained timey-wimey reasons stay in the same location... but the people necessary to get the plot to where it needs to be retain their previous memories, just because.

(Oh, and Clara can visit Tom Baker and help him out, but she is powerless to de-interlace him. I suppose it's fair that she seems to have been poorly green-screened in, though. I bet some effects guy really wanted to interlace her, too, but it didn't happen.)

And there are more blokes with weird faces to add to the surprisingly long list of New Who's Nattily-Dressed Scary Dudes. And there's some more gratuitous weapon-like use of the sonic screwdriver.

Three out of ten, if you are foolish enough to watch it sober.

This week's minimalist Doctor Who recap

This one was perfectly decent, too.

Highly suspicious Doctor

Good casting including non-annoying kids, at least two dumb solutions to problems being shot down as such, and a much-needed villain upgrade for the Number Two Doctor Who Major Baddies. I think Matt Smith dropped the ball a bit in his Gollum-and-Smeagol number, but that was good enough too.

OK, perhaps they could have done a little more to blunt the distracting similarities between the New And Improved Cybermen and a certain other iconic sci-fi cybernetic-baddie-race, beyond "but our ones have blue lights on their heads!"

But I think that's entirely compensated-for by Cybermen that are, one, not avoidable by anybody capable of jogging, and, two, now able to "upgrade" any other sentient life.

Given the Cybermen's numerous previous extremely bad strategic decisions, they will of course now be making a beeline for the nearest repository of Kaled genetic material.

Or just somehow upgrade an actual Dalek. The result would surely be-

Cyberdalek v1.0

OK, the first attempt might not be terribly impressive. But I'm sure they'd get it right after a few iterations.