Dan's Data letters #196
Publication date: 24-Feb-2008.Last modified 03-Dec-2011.
Taser kaboom?
I have a question related to your "Avoiding Electrocution" article.
I am wondering about the safety of Tasers (the new tool security guards and police officers like to use). They deliver 50,000 volts and they puncture the skin; so, based on the info from your article, I would estimate at least 100 amps using the 500 ohms figure.
Can a capacitor in a Taser deliver that many amps? With the two puncture probes being so close, I would think that the resistance would be a lot lower and it would do a lot of damage to the muscle tissue and skin in that area.
But also, if you are shot in the back only a few centimeters from the heart, how many amps could be delivered to the heart?
The police keep saying no one has ever died from a tasering, but there are those who claim otherwise (some people who have been tasered up to 20 times).
Do you have enough knowledge to expound a bit on these questions, or do you know where I might be able to find the answers I'm looking for?
Doug
Answer:
Yes, 50kV into the 500-odd ohms you get across a human body when the skin's been punctured
would indeed be a hundred amps, but only if your 50kV source can deliver that full voltage
into any significant load. If it's a 50kV high-tension power line, it can. If it's a
Taser, it can't.
Which is just as well, because that much energy being dissipated in your body would blow a chunk out of you, at the very least. 50,000 volts at 100 amps for even one millisecond would be 5000 joules, which is the muzzle energy of two .30-30 bullets, or a single shot from a pretty serious big-game rifle.
Stun guns of all sorts are actually, fortunately, fairly low-current sources. They're 50kV or whatever when they're open-circuit and so can spark menacingly over a pretty wide air gap, but their current delivery is tightly controlled, specifically to prevent them from just killing people dead.
The spec sheet for the X26 Taser, for instance, says it delivers 19 100-microsecond pulses per second that each deliver about 0.07 joules into the "load", also known as the "unfortunate recipient". That doesn't quite line up with the somewhat confusing volts and amps specs, but the "peak loaded voltage" is specified as only 1200V, not the 50kV open circuit figure.
And although I'm sure some police have said that nobody's ever died from being Tasered, many others make clear - officially, at least - that electroshock weapons of all sorts are "less lethal", not "non lethal", since it's obvious that they've at least been strongly associated with deaths. And even if the shock from a Taser was 100% certain to never kill even the weakest-hearted of targets, falling down and hitting your head on something hard sure can kill you, and that's the kind of thing that can easily happen when you've just been Tased.
(That sort of thing is also a large part of the risk from ordinary household electric shocks. The shock itself often does no significant damage at all - but spasming and leaping off the ladder from which you were using your poorly-earthed power drill, and then whacking your head on the coffee table, can be a quite different matter.)
Police are generally supposed to only use a Taser when the alternative would be at least beating someone, and possibly even shooting them. Some may have rules that allow stun-gun use when the alternative would just be one of the physical "compliance methods", like choke holds, that they're trained to use; I don't know. Even if that's the case, though, Tasers certainly do seem to get used rather more often than you'd think. Especially when relatively unregulated electroshock weapons (Tasers and even the simpler handheld stun guns are illegal for private ownership here in Australia...) get into the hands of undertrained rent-a-cops, or their equivalents in the regular police forces.
Generally speaking, though, Tasers and stun guns are not horribly dangerous. I'm more concerned about authoritarian cops using them as a dead easy high-powered compliance technique to enforce not-necessarily-legally-required obedience than I am about people dying after being shot with one.
A Taser gives a thug a way to inflict the pain of a beating on someone without, as far as an onlooker can tell, doing much of anything to them. It's a phonebooks-and-rubber-hoses treatment that you can use right out in the open with the public watching. I think that's the real problem.
Worrying Hard Drive Noise #1
I have a 40Gb laptop drive in an external enclosure that draws its power via the USB connector. This is about my second or third one of these as they keep going flakey on me.
On my home machine I periodically have to "hunt the USB port" that works, often connecting/reconnecting until I don't get the tick tick tick of annoyance that indicates the drive not starting.
It didn't start out like that though. When I first put it together (to replace the previous one that failed to start) it worked perfectly every time and over a period of about 6 months, started the ticking. The ticking got worse and now I have to try all of my six front USB ports before I get a connection. I'm not sure if it's the USB cable or it's not getting enough juice or what.
Strangely enough, it doesn't appear to happen on my work machine. My home rig has a DFI Lanparty NF4 motherboard with lots of USB ports and drives etc being run by a 450W Antec power supply. My work machine is a HP small form factor box with a 230W power supply, all generic.
Answer:
The drive is unquestionably not getting enough power to spin up. A ticking noise is
the invariable symptom of this problem. Hard drives use considerably more power when
they're spinning up, and "consumer" drives invariably spin up quite fast, to minimise
wait time when they're woken up from sleep mode. All things being equal, a "server"
drive with slow spin-up will take less current (over a longer period) to get itself
spinning.
Now, why the drive's not getting enough juice is open to question. It's possible you've got a flaky voltage regulator feeding your motherboard's USB ports, or something; my personal policy for all things USB is to resign myself to the fact that you'll be able to find some USB devices that don't work with pretty much any USB controller, and just install a cheap PCI USB card in the PC. Anything that doesn't work with the motherboard ports will probably work with the add-on card, and vice versa.
So you could try that.
You could also try a powered hub, which has its own 2.5-watt (or a bit more) plugpack to run it.
Many cheapie USB hard drives also come with a "double-header" cable, with two USB plugs on it. One plug has all pins connected, and the other one only has the power pins hooked up; if you plug that cable into two root ports, you ought to have twice as much power, which is enough to spin up practically any laptop drive and at least a few desktop models.
The last and simplest option is to use a really short USB cable, one foot or less, so there's less resistance in it and a little more current can make it to the drive. Short cables can also fix some other marginal USB communication issues; they're a good thing to have in your collection of Random Computer Bits.
It's also possible - though I wouldn't say likely, since the drive is fine with your work computer - that there's nothing wrong with the PC, and you've just got unusually bad luck with hard drives. A sticky spindle bearing will make it hard for a drive to spin up; the problem's known as "stiction", and is uncommon but not unknown with modern drives. The classic presentation is a drive that's like the Land Rover in "The Gods Must Be Crazy"; it's fine when it's running, but it's very difficult to start.
It's possible to loosen sticky drive bearings by changing the drive's temperature, or by holding it in your hand and turning it sharply in the plane of the platters, so the platters' inertia keeps them still while the drive turns around them. Doing this is extremely unlikely to make the drive worse. Turning the drive a bit too sharply, so it flies out of your hand and clatters onto the hardwood floor, is another matter.
(Actually, some laptop drives will survive even that. Even a short drop onto a hard floor is usually fatal for desktop drives, though.)
First, crimp RCA plugs onto some coat-hangers.
Having just been to the record shop the other day, I came home with some new vinyl, quite a rare and enjoyable experience these days. At any rate this means I'll need to hook up my turntable again, and as the receiver sits high up on the wall now as I recently installed some groovy floating shelves, the turntable is further from the receiver than its own leads will let it connect.
I know from experience that you cannot use extension leads to connect it from across the room, but will an extra meter or so hurt anything? What is the maximum I can expect?
Sean
Answer:
Actually, connecting from across a small-to-medium room ought to be pretty much fine.
Phono-level signals are very weak and so you'll lose some readily measurable level with
every foot of ordinary RCA extension cable (moving-magnet cartridges have a higher output
level, but are more sensitive to cable capacitance, and will thus give you a bit less
treble if you add quite a lot more cable), but adding two or three metres shouldn't
make any noticeable difference.
You shouldn't need super-special RCA extension leads, either. If you use poorly shielded dollar-store cables then you're asking for interference at these very low signal levels, but some chunky Chinese cable or other from the local electronics shop should be perfectly adequate.
If the standard cable has a separate earth wire that hooks up to the amp as well, then you should extend that too, with a bit of speaker wire or something.
The elegant way of dealing with this problem is to put your phono preamp next to the turntable, so you can run line-level cables across the room instead. Some turntables have a preamp built in, which is particularly helpful now that phono inputs are no longer standard equipment for integrated amplifiers.
Splitters!
There are four ports on the back of my router for cable connections. There are eight contacts in the ports and eight wires in the cable. I know only four of the wires are used. A long time ago I heard you can run two computers off of one cable. Is this true? And how is it done? I'm thinking of a splitter like the one you use for a phone (just that small connector).
Matt
Answer:
10BaseT and 100BaseT Ethernet
do indeed need only two wire-pairs of the four that normal network cable (which, these
days, means Category 5 or
better) provides. Gigabit Ethernet,
however, requires all four pairs. Cheapo two-pair wiring will not work for Gigabit.
T-splitters are a pretty standard piece of network wiring hardware, and they are indeed little phone-adapter sorts of things. All they do, though, is let you split a run of four-pair cable into two two-pair connections, so you can use a run of four-pair cable to connect two 100BaseT-or-slower computers and not have to pull another cable.
Splitters won't work if you plug them straight into the back of a normal router, which is only expecting two pairs if it's 100BaseT or slower, and will only expect four-pair from a single Gigabit connection, if it's Gigabit-capable.
Someone's unsecured FTP server still the cheapest option
I'm looking for a place to host my pictures. I do underwater photography (personal, not a business), and wanted to do my own site for them, as I'm finding Picasa/Google a bit frustrating these days. I'm not worried if it's US or Oz based; I just want reliable, cheap, makes coffee etc. Traffic is unlikely to be high, and I'm thinking 5-10Gb as the kind of storage space I'm after.
Jonathan
Answer:
If all you want is image hosting, you might as well use a "Pro"
Flickr account. $US24.95 a year gets you
basically unlimited hosting of images of basically unlimited size, with as open or as
restrictive a use license as you like, and you can easily display those images on any
other page you like. So you can make your own quickie site on
Google Pages or whatever and put your Flickr
thumbnails and/or full-size images on that, and then upgrade to something else later
if you like.
The advantage of putting pics on Flickr is that people searching Flickr for stuff will be able to find them, which gives you more chance that they'll offer you money to use them elsewhere. It also gives you more chance that they'll rip 'em off for their own use without paying you, of course, but I think the ratio of paid-use to rip-offs remains much the same wherever you put pics online, unless you disfigure them with obnoxious obvious watermarks.
If you're not interested in selling your pictures, the Flickr interface by itself is about as good as anybody's. You can add tons of text to go with each picture if you want, lots of metadata, as many or as few "albums" as you like, et cetera.
Let's see if we can get another lawsuit threat
What do you think of the Pulstar pulse spark plugs? Will they work as advertised?
It could only be a good thing to use less fuel and emit less CO2. But there have been so many claims in the past that I am sceptical about these.
Chris
Answer:
There have been, as you say, dozens if not hundreds, of novel spark plug designs, all
sold with much the same claims as these ones. Magic plugs have been around for, oh,
at least seventy years. Probably more.
And yet those fools at Bosch, Champion, NGK, Denso, Motorcraft... EVERY billion-dollar spark plug manufacturer, actually... keep making plugs of conventional design.
Clearly, it's a conspiracy!
The Pulstar plugs seem to be a spark intensifier, similar to a spark gap gadget, which has been built into a plug. This page on fuelsaving.info mentions the other kind of spark gap gadget, that you install in the HT lead instead. It also points out that there is no reason to suppose that the fuel/air charge in a modern engine needs to be ignited any more effectively than it is already.
And if the Pulstar plugs actually do make the charge burn faster, all they're going to do is put the engine under more stress. Unless you change the ignition timing, making the charge burn faster will be like advancing the timing, which will increase the chance of knock.
I remember another recent magic spark plug called "Greenfire", which was feted on the Australian Broadcasting Corporation's New Inventors show back in 2004.
Greenfire promised to reduce toxic emissions by between 20 and 40 per cent, plus give more torque and I forget what else - the usual magic-plug claims. The judges were very impressed, and this amazing new product was obviously certain to revolutionise the automotive industry within months.
Needless to say, Greenfire actually dropped straight off the map pretty much immediately. This could have something to do with the fact that the plugs were claimed to cause fuel to "burn for longer, and more completely"... than the 99%-plus that normal spark plugs in modern engines manage?
Greenfire.com.au no longer exists.
(Greenfire was nothing compared with the New Inventors' Invention of the Year for 2006, though. That was the Exhausted Air Recycling System, which promised to revolutionise the whole pneumatic tool industry but, as far as I can see, actually violates physical laws.)
UPDATE: I returned to the subject of Pulstar plugs, and what effect users have managed to measure from them, in this letters column.
Eldorados for everyone!
I was wondering about fuel economy. I've been told by a number of sources that fuel use in your car is 100% dependent upon the revs of the engine at any given point.
The root of this came from a family member buying a new Holden V8 - everybody commented on the car being a fuel guzzler, but he has found the opposite. He hardly goes through any fuel at all (he says), because he can travel at 120km/h in 6th gear while his engine is idling at 1.5kRPM. Contrast this to our gas-hog Subaru that needs about 3.2kRPM to do 120kph.
Is this rule (fuel use = RPM * CCs of fuel per cycle) correct? Is there any more to it than that?
It leads me to a second part of the same question: If this is true, then using my engine brake coming down a hill would do terrible things to my fuel consumption! Wouldn't it be better for me to put the car in neutral and use the brake?
Eric
Answer:
An engine's fuel consumption depends on, duh, how much fuel you pump into it, and the
fuel pump is not just connected to the crank by a belt. Fuel flow is, instead, carefully
metered, so the engine only gets as much fuel as it needs to match a given throttle
setting.
If an engine is spinning rapidly but very little fuel is going into it - which will be the case if you're engine braking down a hill - then you won't be consuming much fuel. The spark plugs are still firing, but there's little to nothing for them to ignite. I think modern engines don't actually consume any fuel at all while you're engine braking - well, that's what Jeremy Clarkson said on that episode of Top Gear where he drove a diesel A8 from London to Edinburgh and back on one tank of fuel, anyway.
This zero, or near-zero, fuel consumption will of course change if you so much as dab at the throttle. But it stands to reason that it won't change much. If your engine's spinning at some high rate while you roll down a hill, and your dab at the throttle suddenly started feeding it as much fuel as it'd need if you were accelerating hard up a hill at the same high engine speed, that fuel will have to go somewhere. It will either have to be burned in the engine (causing you to suddenly accelerate very hard indeed down that hill, under both engine power and gravity), or it'll have to spray out of the exhaust pipe. That'd be a bit of a pollution no-no, though the afterburner effect would probably be cool.
High-performance cars that blow flames out of their exhaust on the overrun do so precisely because they've still got a lot of fuel flowing to the engine, I think often just because it helps with engine cooling.
What actually happens when you're engine-braking down a hill and dab at the throttle is that you speed up... a little bit. What has happened is that the throttle has let a little more air flow to the engine (because that's what throttles do), and whatever hardware handles the engine's fuel-air mixture has, in turn, admitted enough fuel to make the right mixture. Modern cars with electronic fuel injection and numerous sensors can handle this very efficiently indeed; only a couple of per cent of the incoming fuel, if that, ever escapes the engine unburned.
You certainly can cruise economically in a car with a big powerful engine - as long as you practically never do anything that requires a big powerful engine!
If an engine doesn't have enough power, so you always have to flog the hell out of it, then it's possible - though still not very likely - that you may actually find that you manage to use more fuel than you would if you'd bought the same car with a bigger engine. The same applies if a car's gearbox doesn't have a high enough ratio for proper highway cruising, as seems to be the case with your Subaru. And a smaller-capacity engine with higher power can easily consume much more fuel than a bigger, lower-powered engine, for pretty obvious reasons. Nobody would suggest that a 165-horsepower 3.8-litre V6 out of a 1988 Holden and a 480-horsepower 3.8-litre V6 out of a 2007 Nissan GTR can both be expected to give you the same mileage.
Honestly, though, there's almost always an obvious fuel consumption penalty that comes with any significant increase in engine capacity. That penalty just may not be as large as you think.
