Dan's Data letters #96
Publication date: 20 March 2004.Last modified 03-Dec-2011.
Something for nothing
I read with interest the following statement in letters #95:
"Reverse cycle air conditioning in heat mode can, in fact, have heating efficiency above 100%; you can get more watts of heat pumped into your house than you've expended, in watts of electricity."
How does this work? I thought this sort of thing was impossible according to rules about the conservation of energy.
Stuart
Answer:
Air conditioners, like refrigerators, are heat pumps; they move heat from
one place to another. When you're using them for cooling, you're pumping
heat from inside the house to outside (something you'll be acutely aware
of if you stand next to the condenser outside...); if you've got a reverse
cycle unit, that means you can switch it to pump heat from outside to inside.
No laws of physics are violated, here; heat is not of itself flowing from a cooler body to a hotter body. Because air conditioning's sealed, its operation is a bit confusing, but you could make a far less efficient but more comprehensible version of the same thing with an air compressor and a pressure cylinder.
Imagine compressing air into the cylinder outside. The cylinder would get hot, as the air was squished into it. Now cool the cylinder down to ambient with a fan (which is what the big fan on the outside portion of the air conditioner is for), and when it's cool, carry it inside and uncork it. The air howling out of the cylinder will be much colder than ambient, thanks to the pressure drop, and it'll cool the house down (somewhat). Now carry the empty cylinder outside and start again. Or move the compressor indoors and repressurise the cylinder there, for "reverse cycle" operation.
Sealed vapour phase refrigerant systems just take this impractical process and put it all in a simple, reliable pipe loop with radiators on each end for efficient transfer of heat in and out of the system. The Second Law of Thermodynamics remains unperturbed.
R201 hunting
Thank you for the review of this unique case.
After seeing your review, I wanted to see if I could go out and buy one of these things, but as you said in the review I was unable to find anyone selling them under this name outside NZ. (I'm in the USA.)
However, I thought you might like to know that this case is marketed under the name "Ahanix Plasma" in the US and possibly elsewhere. It appears that Ahanix sells several other 3R cases as well.
For reference, I found this by Googling for some of the English phrases in the manufacturer's description of the case, so if there's someone reselling this case who didn't just rip the manufacturer's English text for their own stuff, I wouldn't find it.
yet another Daniel
Suspiciously speedy
Is there any reason to be leery of this Digipower battery/charger combo? The battery roundup at imaging-resource.com indicates that Digipower's NiMH cells are up to snuff (the 1600mAH ones, at least), but at the same time mentions a one hour Rayovac charger that damaged any and every cell tested with it. The Digipower combo pack also claims a one hour charge time, and if there's any danger with current one hour chargers and I'd just as soon get a slower charger.
Tu
Answer:
I'm unconvinced that any one hour charger for regular NiMH cells
is going to be able to avoid boiling the batteries. You can charge that
fast if you're using super-tough NiMHs made for radio control applications,
but you can only get those in sub-C size. Also, Rayovac's special integrated-controller
I-C3 cells genuinely
can be charged
in 15 minutes by their own special charger. Not regular cells, though.
High quality lower capacity AAs - brand name 1500mAh cells, for instance - are likely to deal better with very hard charging, but you can throw about the same amount of energy into newer 2000mAh+ cells in about the same time, without getting up to that dangerous point around the end of the charge where the damage is usually done.
All-day dumb trickle chargers won't hurt the cells even if you let them go into considerable overcharge, but who's got that kind of spare time. The common three hour chargers are generally perfectly fine, though I dare say there are some that don't correctly monitor for temperature rise and voltage peak and beat the cells to death. Even the cheap three hour chargers I've used, though, seem not to hurt the batteries; lousy ones usually just stop charging too soon. The three hour charger that came with my old Olympus C-2500L, in contrast, has never missed a beat.
The red line for safe fast NiMH charging is, I think, 90 minutes. That's what a few models of Maha charger do, and the cells come out piping hot even at that rate. I've got a Maha C-401FS that they sent me for review some time ago (four AAs or AAAs, with an individual circuit for each cell; it's better than the C-204 that Imaging Resource like so much), and it's great; I'm ashamed every time I look at it that all I've done is mention it here and there in letters columns. It's never overcharged, and it's never given up early. The only quirk it has is that sometimes, when you plug it in, it freaks out, lights one of its status lights and just sits there. When that happens, all I have to do is unplug the cable and let the charger sit for a minute, then plug the cable back in. Then it'll go back through its show-off flashing-red-and-green-lights startup sequence and will be ready to receive cells for charging.
As I've said before, you should get whatever the heck brand of NiMH cell offers a decent amount of milliamp-hours per dollar, which generally means off-brand plain-shrinkwrap ones - but get a good charger.
Ajax and steel wool!
My girlfriend uses methylated spirits with a silky cloth to clean her eyeglasses and it seems to do the job well. But I'm hesitant to try this on my camera lens, as I'm not sure if the metho would be good for it.
I'm wondering, what do you use to clean your camera lenses?
Minh
Answer:
Alcohol (ethanol, denatured ethanol, isopropanol, whatever) is not Instant
Death to coatings on glasses and camera lenses, but it's not good for them
either. It's fine for old uncoated lenses, but if you clean a coated lens
with alcohol all the time, there's a good chance the coating will be patchy
after a while. The same goes for cleaning lenses with dry tissue or your
T-shirt, by the way - either is acceptable in a pinch, and who cares if
it's just a $10 pair of sunglasses, but you shouldn't make a habit of it
with valuable coated lenses.
I use microfibre cloths (available cheaply all over the place, these days), and a "lens pen" for heavier duty cleaning. The pen has a slide-out brush in one end (for removing dust; you should obviously always get possibly-abrasive dust off a lens before you rub it with something) and a chemical-coated pad under a cap on the other end. The pad magics away gunk, leaves no residue, and can be rejuvenated by just putting the cap back on it and giving it a bit of a turn.
Any photo store should have lens pens, and they're not expensive.
RAMbling
About two years ago I purchased a Dell Inspiron 8100 with its at the time stock configuration of 128Mb of RAM. Running Windows XP Professional, I immediately found it a bit sluggish, but shrugged it off. Today, I find myself not being able to run more than one session of IE before I get endless accesses to virtual memory and everything grinds to a snail's pace.
So I've decided to purchase another 128-256Mb of RAM. I have asked around and Googled to find out whether Dell notebooks require proprietary Dell memory or not. Some have said yes, others were unsure and Google didn't turn up much. I am quite sure if I order an additional 128-256Mb of non-Dell RAM, I'll save a decent amount over the price of "Dell Certified Memory", but I am not sure if the notebook will accept it or whether it will cause problems working with the notebook's existing RAM.
I took out the existing RAM in the notebook and examined it, and there no brand markings or any other printing on it aside from a "Dell Certified Memory" sticker.
Simon
Answer:
I don't think any laptop that has standard memory slots requires a particular
brand of RAM.
Some laptops, however, are a lot more finicky about their RAM than most desktop machines, giving rise to those magic moments when you put perfectly good PC133 RAM in a PC100-RAM laptop and find the computer's unable to figure out what it is.
Dell's specs for your laptop don't say it needs anything special; just PC133 SODIMMs, CAS Level 2 or 3 (maybe a CAS 2 module wouldn't like running with a CAS 3 one; I dunno). The Crucial Memory Adviser agrees; it suggests plain PC133 CL2 modules.
So I'd bet a small amount of money that you'd be fine with any quality 256Mb PC133 CAS 2 module. You might as well get 256Mb; the dollars per megabyte are likely to be rather lower than for a 128Mb module, and XP will be able to make good use of the extra 128Mb.
Help Me Spend Money
Three years ago, my wife and I jumped into the whole digital photography thing, and now, over 4,000 pictures later, we are getting ready to upgrade. My wife is thinking of using this new camera (in addition to the current family pictures she has been taking) in a new small business where she will do some sports photography for the local children's hockey league. I know that I need at least a solid prosumer camera for this, but I don't know what I should be looking for feature-wise.
Basically, the camera needs to be able to take a non-blurry picture of a kid (4-6 foot tall) skating full speed (25+ mph) on the other side of the rink (about 80 yards maximum distance). Additionally, the pictures need to be able to be blown up to 16 by 24 size posters without being too grainy.
How can I translate this into camera specs, so I can purchase the lowest priced camera that can get the job done without breaking the bank? Could a mid-level camera like a Kodak EasyShare DX6490 handle this, or will we need something nicer?
Greg
Answer:
Welcome to the world of Big Glass and Big Dollars. There's a reason why
the photographers you see around football fields are all toting cameras
with howitzer-barrel lenses on 'em, and it's not sexual inadequacy. Well,
not just that, anyway.
For sports photography of any kind, you want shutter speeds of about 1/500th second, at most; 1/1000th or faster is preferable. It's also a very good idea to have rapid burst-of-shots capability and fast image saving, unless you've got an Olympic skeet shooter's target acquisition skills.
Pretty much any camera that can do 1/1000th at all (which is everything half-decent) will produce fine results at that shutter speed in daylight, but even quite bright indoor lighting is a lot dimmer than direct sunlight. A brightly lit skating rink might manage better than 1000 lux (reflection from the ice will help a lot), but indoor sports venues can have various light levels; you can't tell without measuring it.
If you assume ISO 400 sensor sensitivity (about as far as you can push most digital cameras these days before they start giving grainy results), and typical bright-indoor-sports light levels, then you'll juuuuust be able to get down to 1/500th of a second, if you've got an f2 or better lens on a digital SLR.
The f2.8-at-best lenses that point-and-shoot digicams come with do better than DSLR lenses (because they're focussing the light down onto a smaller sensor; I explain this stuff in my photo tutorial), and may be able to cut it; it depends on the light level. If it's not pretty darn bright, you'll be at 1/125th or slower, which is not good enough. And this is not where your troubles end.
To get a human figure at 70-odd metres to fill a decent amount of the frame, you need a lot of magnification. A 500mm lens on a 35mm camera has, at 70 metres, a field of view about 5 by 3.3 metres in size. That'd do it, but I don't think any integrated-lens cameras can manage 500mm-equivalent zoom. The 10X-optical-zoom brigade generally top out around 400mm (380mm for most of them, actually, including the DX6490 you're considering). That means a field of view (for a 35mm frame shape) of more than six by four metres at 70 metre range.
Now, you can crop the image, of course, but this reduces your resolution; for 16 by 24 inch prints at even 100 dots per inch you want, surprise, 1600 by 2400 pixels. This doesn't give you much breathing space, even if you've got an eight megapixel fancy-cam. Poster prints can look surprisingly acceptable with rather less than 100dpi, but it depends on the viewing distance.
A digital SLR with one of Sigma's surprisingly good 50-500mm zooms on it would be about as good for this job as you're going to get without making like a pro sports shooter and investing in multiple cameras, but the Sigma is f6.3 at full zoom, which sinks you again unless the rink's very brightly lit indeed. And you'd have to buy a DSLR, which wouldn't be cheap.
Even if you went for second hand film gear, you'd end up spending large-ish dollars; long lenses with reasonably low F-numbers just aren't cheap. Or small. Or light.
I think your wife may just have to resign herself to only photographing players on the near side of the ice.
Item, Ridiculous, One
I am writing on behalf of the furry critter who occasionally graces us with her presence, often referred to as the cat of our house.
Have your cat(s) reviewed the Panic Mouse, as linked to from here?
Scotty
Answer:
He has indeed; I bought one on eBay a while ago.
The Panic Mouse's standard black-pom-pom-with-a-tail dangly thing interested him not at all. He will, literally, lie in front of the Panic Mouse allowing the pom-pom to bop him on the nose over and over, and not care.
He has, however, a weakness for ordinary brown jute string. Replacing the dangly thing with some string turned the Panic Mouse into a source of considerable entertainment for him.
Ideally, an electric cat toy should scurry around the house, because it's a huntable thing going around a corner and out of view that really excites most cats. The Panic Mouse does work as well as a stationary string-wiggler is likely to, though, and doesn't seem to beat its batteries to death very fast. The only flaw I can find in it is that the pink level knob that also serves as a power switch is rather smooth, and a little hard to turn; if your hands are greasy, or you've got arthritis, you won't be able to work it.
Kaboom!
A friend and I who like to dabble in an amusing explosion or two recently began designing a water powered firearm (firearm in that it fires a projectile by way of Newton's third law, and water powered in that water will be the explosive propellant). We're thinking of using something like a car battery to split the oxygen and hydrogen of the water, and a spark plug to ignite the gasses in a combustion chamber of some kind. I was wondering what kind of energy the device will have to be able to withstand. Will PVC pipe be able to contain an explosive reaction between the two constituents of water (in a 2:1 ratio)?
a different Dan
Answer:
No, it won't, if you actually manage to get a decent amount of fuel mixture
in there. The combustion pressure of hydrogen/oxygen is very high. Cheap
PVC tubing potato guns commonly disintegrate even when using low energy
fuels (the canonical hairspray and air, or alcohol and air); you'd need
much more serious engineering to handle oxy-hydrogen, or (even worse) oxy-acetylene.
If you under-loaded the cannon you might get away with it, but in that case
you might as well be using a safer fuel.
Here's a page that mentions this problem.
Oh, and disclaimer, disclaimer. Disclaimer! Disclaimer disclaimer disclaimer. That ought to do it.
Widgets wanted
Finally, in a blatant attempt to mine my readership's collective knowledge:
A friend of mine is looking for linear bearings and shafting in Australia (for the CNC mill he's making, as you do). He'd buy from the States, but shipping for shafting from the USA is hilariously expensive.
He needs 12 linear bearings, and appropriate shafting, around 12 to 25mm diameter. If'n you can help, e-mail him.
