Dan's Data letters #197
Publication date: 31-Mar-2008.Last modified 03-Dec-2011.
Household Renovation Of Doom
I was wondering if you have any expertise in the building construction area, regarding the safety of materials used. There are two areas of concern:
1. Australian kitchen makers kicked up a big fuss about the formaldehyde content in the cabinetry of their overseas competitors. This was in the media at one stage, with people quoting the Chinese-made kitchens as containing twice as much formaldehyde as the upper limit of the Australian Standard, so it could cause cancers when the smell of the freshly installed kitchen is inhaled.
This caused many people grave concerns and many sleepless nights - those who installed cheap Chinese made kitchens instead of Australian-made ones ($7000 vs $20000 for essentially the same configuration).
But it seems that the Australian standard is specified on the amount of formaldehyde "per volume of cabinetry". So really, one is not at much greater risk of cancer from formaldehyde if installing a smaller Chinese-made kitchen compared with one who installs a large Australian-made kitchen, assuming ventilation is adequate. Is this a fair assessment?
2. There were also concerns about Chinese stones used for benchtops containing some sort of radioactive substance (naturally embedded or not). I wonder if this extends to Chinese made quartz wall tiles as well. Do you have any thoughts on this?
Is this just a case of local craftsman trying to discredit overseas competition, or is there possibly substance to this radioactive stone/quartz business?
Jin
Answer:
I wouldn't be at all surprised if the "Chinese
Poison Train" turned out to be delivering loads of unusually toxic building materials,
but I agree that it doesn't sound like a major risk to most home-owners.
Formaldehyde is indeed bad for you, and it is indeed used in the manufacture of all sorts of "pressed wood" products. But the dose makes the poison. Even if your kitchen is packed with cabinets made from the most toxic fibre-board the Poison Train has ever managed to deliver, your formaldehyde dose may still be trivial if you don't spend a lot of time in the kitchen, or if you just leave the kitchen window open.
There's also a big difference between the dosages received by people who work in the kitchen-installation industry, working with bare panels of the stuff and drilling and sanding it into dust all day, and the dosage received by people who just have such a kitchen in their house. If the maximum formaldehyde content is calculated to keep people with serious occupational exposure safe, then the limit is likely to be vastly lower than is necessary to protect people who do not have such exposure.
And, as you say, six double-outgassing cabinets would probably give you the same dose as twelve regular-outgassing ones.
Some people insist that doses of various substances far below those scientifically known to be harmful can cause all sorts of ghastly diseases. This is connected with the phenomenon of "Multiple Chemical Sensitivity", an ailment which I do not believe has been persuasively demonstrated to actually exist.
Personally, I wouldn't worry about this at all. If your new kitchen smells funny, leave the window open, and in due course, the outgassing of formaldehyde and any other volatiles from the materials will subside.
It's perfectly possible that there is a readily provable health risk, here, but we're surrounded by readily provable health risks every day. No reason seems to have been presented to suppose that there's any significant risk here, compared with everyday killers like motor vehicle accidents and heart attacks which most people do not spend much time worrying about.
Regarding radioactive kitchen counters - it's normal for granite to be slightly radioactive, essentially because it's got uranium in it. The uranium levels are very low, though; even if you decide to start eating powdered granite as a health tonic, you'll be long dead from other problems connected with the eating of rocks before you accumulate a significant uranium dose.
I suppose it's possible that someone has sold seriously radioactive stone for building purposes, but I haven't heard of it. "Engineered stone" counters and tiles made from powdered rock mixed with resin would be the most likely candidate, because the aggregate the "stone" was made from could be contaminated with something highly radioactive. Stranger things have happened.
If all people are worrying about is counter-tops that read five times the local background radiation, though, then they're fretting over nothing. Coffee, because it's grown at high altitude and thus catches more cosmic radiation, is about as radioactive as natural granite, gram-for-gram.
Unexpected resistance
I have read some of your headphone reviews and found them very useful. I have chosen to get Beyerdynamic DT 770 Pro headphones to use with my iPod, but I've got the choice of 80 or 250 ohms. What do recommend me getting if I am mostly using them from my laptop and iPod?
Sam
Answer:
The
lower-impedance version is indeed the one that's meant to be used with portable
players, and other things that have relatively weak headphone outputs. The 80-ohm DT
770s still have considerably higher impedance than everyday portable 'phones, though;
an ordinary set of cheap earbuds will probably be 32-ohm.
All things being equal, lower impedance means more noise from a given voltage, or volume-control setting. But the headphone outputs from portable players often have very low power output limits, and behave badly (like, losing a lot of bass) if you push them too hard. They often work very well as a line out if you connect them to a separate amplifier (which will have far higher input impedance than any normal headphones), but the more power you ask for, even the mere tens of milliwatts needed for headphone listening, the worse they sound.
So if you plug 250-ohm headphones into a typical portable player, your maximum volume won't be very high, but the sound quality will be higher than the much-louder same volume control setting for 80-ohm headphones.
In Physics Experiment Land, if you adjust the volume control to equalise the loudness of different headphones, they all ought to be getting the same signal and will therefore (ignoring differences in fidelity between different kinds of headphone) sound just as good. In practice, this is likely to only apply for very low volume levels; it's very easy to exceed the clean output power limits of a lot of headphone connectors.
The solution to this problem is a separate headphone amplifier of some sort, strapped onto your MP3 player or laptop (or a separate USB audio adapter for the laptop with stronger headphone output). If you don't want to go that far, then the lower-impedance headphones will probably work better than the higher-impedance ones. But don't expect miracles.
240V to 48V to hydrogen to a flywheel to compressed air to 110V
Recently, I bought this wonderful alarm clock from the USA. Filled with glee I opened my package this evening when I got home from work... only to find that the battery backup abilities the unit boasts are more of a keeping-the-internal-processor-a-tickin’-kind of feature rather than the powering the clock off batteries.
So it would seem I need a step-down transformer of some kind to run the clock here in Australia.
After careful examination of the power requirements (i.e. the sticker on the bottom) it appears that the input voltage is 110V and a whopping six watts. Now I see Jaycar and Altronics have appropriate models, but at more than the cost of the clock, I think they’re a bit of a waste of my hard-earned dollars. Seeing as the cheapest Altronics transformer is 65W, I feel this approach is overkill.
So my question is, is it feasible to make my own step-down transformer, or am I going to end up spending four to five times the cost of my clock in the process?
Cam
Answer
Yes, it is perfectly possible to make your own mains voltage converter. Making a SAFE
one can be a bit more challenging, though, and you may find it hard to make one for
less than the price of the smallest step-down adapters, especially if you value your
time at more than $0 an hour.
Off-the-shelf step-down and step-up adapters are always autotransformers (which aren't the safest things in the whole world either). You could wind one of those yourself, though it'd be tedious at best.
Alternatively, you could just take a 230-volt-to-X-volt transformer and an 115-volt-to-X-volt transformer, connect the X-volt windings together, and you'd be done. That's a bad solution if you need a lot of power (small affordable transformers have small current ratings; two bare back-to-back transformers that can pass the fifty volt-amps of a $50 step-down converter will cost you at least as much as the whole off-the-shelf converter), but in this case you don't. The back-to-back technique will also give you the same 115V 50Hz output as a normal step-down adapter.
If you do this, insulate the heck out of everything in sight and it'll be fairly safe - though probably still break a few electricity authority rules; all usual disclaimers apply. Your clock presumably only has a two-pin plug anyway, so it's not as if you'd be committing the cardinal sin of running gear that's meant to be earthed without an earth.
There are other, kinkier possibilities you might like to try, though. Small inverters meant for automotive use are easy to buy on eBay, and it's easy for Australian shoppers to find 110VAC versions as well as Australian-voltage ones.
One of those would run perfectly happily from any 12V source, including a plugpack. If your plugpack is only a 12V 1A unit then you shouldn't, of course, expect to be able to run more than about a ten-watt load from the inverter's output, but that'd be plenty for just the clock.
The only really elegant solution, of course, is to convert the clock itself to take Australian-voltage input. This is not necessarily very difficult; if the clock's internal electronics run from only one DC voltage (which is quite possible in this day and age) then you can just yank the standard power supply and replace it with an AU-compatible version, either tucked inside the casing or an outboard plugpack.
[Cam later e-mailed me because he was concerned that 50Hz power for a clock from a 60Hz country might cause it to run at 5/6ths of its proper speed. Old "synchronous" electric wall clocks, based on a synchronous motor, certainly do work this way; the exact frequency of mains power varies significantly during the day, but electricity authorities try very hard to make the number of cycles per day even enough that you can use mains frequency, over time, as a very effective timekeeping system. But modern electric clocks almost invariably use the same quartz mechanisms as modern battery-powered clocks; I'd be very surprised if any fancy five-alarm digital clock these days had a synchronous motor in it. Cost and complexity aside, such a design would prevent the battery backup feature from working.)
A solution in search of a problem
USBCELL USB rechargeable batteries may not be new, but when I saw them I thought they were a great idea. They don't need an actual charger. You just pop the top off, and plug it right into a USB port.
I don't know about the quality of the actual cells used, and the price is a tad chunky (Looks to be about ~$17-$20AUD/pair at Thinkgeek/Jaycar). But being able to whack them into a USB port without need for a charging unit is just damned handy.
Andrew
Answer:
Yeah - the USBCELL people wanted to send me some for review, but I declined. Here's
what I said:
It seems to me that the minuses of your product greatly outweigh its plusses. You can get a four-slot charger and eight off-brand 2.5Ah NiMH cells for less than the price of two of your 1.3Ah batteries. The going rate for a four-slot charger by itself is $US10 or so, which means it's hardly difficult for most people to put one wherever they want to go. USB-powered chargers (which let you fairly slowly charge four cells from one USB port) are only slightly more expensive.
If your cells had low self-discharge chemistry then their low capacity would matter less, but I don't think they do (am I wrong?), so it does. And the charge rate is low, and it's difficult to charge more than two cells at a time from many computers.
[They didn't reply to this e-mail, so I presume the USBCELLs do indeed have standard, high-self-discharge chemistry, and will go flat on the shelf quite quickly.]
Heck, I can get a pack of four 2.1Ah low self-discharge NiMH cells from the supermarket now, for $AU15.
So there's really no way I can recommend your product to anybody who's not planning to climb a mountain or be shot into space. The tiny extra bulk of a separate mains/USB charger is otherwise very well worth all of the advantages it gives over the USBCELL.
Sorry about that, but better I tell you now than sucker you into sending me review product and then spring my true opinions on you.
UPDATE: Right after this page went up, a PR person from Moixa Energy, makers of the USBCELL, contacted me to carefully avoid addressing any of my actual problems with their product, and allege that it was in fact better because regular rechargeables "are on average only re-used less than 10 times". Something that can be recharged more easily would, presumably, therefore be a good thing.
I asked them whether they had an actual reference for this claim that people are throwing their rechargeables away after hardly using them at all; they've not yet replied. Oh, and apparently the USBCELL has received a few "green" awards; I told them that at this stage I regard environmental awards as something that counts against a product's plausibility, since they're usually only about feeling as if you're doing something. I think this may have made them angry.]
Give my crappy 80s music... LIFE!
I don't get it - how could this work?
Can you move that much air by varying the plasma "energy"?
Chad
Answer:
Plasma loudspeakers work just fine, and have
been well-known for a long time. An electric arc makes a noise; modulate that noise
and you can make it play music. Because the arc has essentially zero mass, it can in
theory be an extremely high fidelity device.
You're quite right that an arc can't move much air unless it's unreasonably large, though. This means that any arc-speaker that wouldn't impress Nikola Tesla is restricted to treble frequencies only.
People have made "musical Tesla coils" that have response down at least into the midrange...
...but the high-powered driver hardware is made to create square waves, not reproduce music, so the result is extremely heavily distorted, like a transistor guitar amplifier in hard overdrive. It'd be perfectly technically possible to make a very musical huge arc, though, if you were willing to use much more expensive, much more power-hungry drive hardware.
There are, of course, practical problems with this idea. One of them is that any kind of safety screen around the hilariously dangerous arc will damage the sound. Another is that an arc in air will create a constant flow of ozone and, I don't know, probably nitrogen oxides as well. So in a poorly ventilated room, air-arc plasma loudspeakers will poison you. The only way around that is to feed the arc area with a stream of some inert gas, like helium.
