Dan's Data letters #17

Publication date: 15-Dec-2002.
Last modified 03-Dec-2011.

 

Battery malarkey

I have a question about my lithium ion laptop battery. I use it all day at work, and was wondering what is best for it - to keep it plugged into the charger all day, or to let it drain down to about 10% then charge it up again and repeat this cycle?

Geoff

Answer:
Unless the charger's lousy and slowly barbecuing the battery - which is possible, but unlikely - it's a much, much better idea to run the laptop from its mains adapter whenever you can. Your LiI battery will only be good for some hundreds of full cycles (discharging to 10% then recharging pretty much counts as a full cycle), or rather more partial cycles; leave it plugged into the mains and the battery shouldn't be cycled at all.

All rechargeable batteries wear out when you cycle them, and wear out faster when the cycles are deeper, all things being equal. Lithium ion batteries have good energy density (watt-hours per kilogram) compared with NiMH and NiCd batteries, but their finicky charging behaviour means they're more prone to be damaged (slightly) at the end of each charge; LiI batteries can be killed faster by a bad charger than any other popular rechargeable technology.

So rechargeable packs can be damaged by bad chargers, and LiI packs are the most fragile of them all, and that's what's led to some people getting the impression that a 1% top-up charge will wear out a LiI pack as much as a full 100% from-flat charge - see this page, for instance, which says "If you run your Laptop on the mains power all the time you may ruin a perfectly good battery within 6 months."

That's a bunch of hooey, unless the laptop's charger is crummy. Which it might well be. Even if it is, though, if the laptop's plugged into the mains all the time, so the charger doesn't keep restarting its charge unnecessarily, the battery ought to be fine.

Lithium ion charging is complicated. If you just want to throw most of a charge into a lithium ion battery, you can do it quite easily with a bench power supply and an in-line resistor. I know, because I've done it. If you just set the open-circuit charge voltage so that it's below the nominal voltage of the battery, and pick the in-line resistance so that the charge current isn't very high (starting at "0.2C", say; that's 200mA, for a 1Ah LiI pack), you'll never fully charge the pack, but you ought not to hurt it either.

(Since LiI packs are quite fond of exploding if they're charged poorly enough, by the way, it pays to be confident about what you're doing if you want to try this yourself.)

Picking the end of a lithium ion charge is really tricky, though. Overcharge is extremely bad for LiI packs (because of that explosion problem, again), which is why a crummy charger can murder a battery pack fairly quickly, if you keep letting it try to charge an already-full pack.

A good LiI charger should start at a low constant current (varying the applied voltage to maintain a particular current flow into the battery), wind up to a high constant current as the pack charges, and then switch to a carefully picked constant voltage at the end - which'll cause the charge current to taper off as the battery finishes its charge and its terminal voltage creeps up towards the applied voltage, without ever going into overcharge. Getting all of this to happen in a charger for a $100 gadget is quite difficult, but expensive laptops really ought to have chargers that can manage it properly, and which won't do anything untoward if you plug the laptop into the mains when its battery is already charged.

 

P4 prodding

I have a Pentium 4 1.8a processor that uses 100MHz FSB. According to some documents there is a way to cover the "BSEL0" pin on the CPU to make it into a 133FSB processor. I know the CPU will do the OC, so that's not a prob. The problem is, what would I use to cover a pin that small to make it non-conductive? I'm looking for ease of use, as I have not a microscope of any sort to aid my hands.

Ben

Answer:
Try lacquer. If you want to feel all technical about it, go to an electronics store and get a can of spray-on circuit board lacquer (known in my circle of friends as "banana spray"; you'll understand why when you smell the volatile ester that seems to make up a large portion of the stuff). Spray a blob of it onto a disposable surface, dip a toothpick in it, and coat the pin with that. I'm pretty sure the ZIF socket won't grab the pin hard enough to be able to make contact through the lacquer.

If you want to do it the ghetto way, you could try nail polish instead. The circuit board lacquer shouldn't attack plastic, though (unlike acetone-based nail polish), and it'll probably also be tougher than nail polish.

 

Disco sunburn?

I've noticed that the latest mod craze seems to be UV lighting. Paint enough of your case with that fluorescent stuff and install a UV light and bingo, a fairly effective, and fairly cheap mod.

However, I was wondering about the risks of a UV light, and more specifically, is it possible to get sunburnt by having the case close to my face for a few hours everyday?

Tristan

Answer:
No.

I talk about why this is in my review here.

 

Mystery card

I am having trouble getting 256 colours or better on my PC, and would like a bit of advice from you.

I had Windows 95 on the computer, and all seem to be going well until I decided to upgrade to Windows 98. Yeah, I know I'm a bit behind the times and all, but a mate of mind said it would be no problem. Well once I loaded 98 I found that I could only choose 2 & 16 colours. I did have 256 colour mode before.

The video card in the machine has on it Butterfly; other lettering on the card says AGD FO2, 94v-05290. N272, 0003001121, AGP-S3-307-8M.

Peter

Answer:
You need new video drivers. The question is - what chipset does the card have?

From the information you provided, I think, but don't know, that it's an S3 Savage4 card. The last ID is the only thing that means anything to me - AGP card, S3 chipset, 8Mb memory. You'd think the "307" would indicate the chipset model, and I presume that it does, but I don't know of any S3 chipset ID numbers between 298 and 325. Different Savage4 versions have the numbers 394 to 399.

Anyway, S3's rather strange driver download login page (you need a username and password, which they give you at the bottom of the page...) is here. There are a couple of utilities on that page that should ID the card chipset for you. Do that, then proceed to the download site and grab the appropriate driver.

 

Magnetic jewellery

I just read your article on magnets and cool things that you can do with them. I was just wondering if you could suggest some magnets to make a wrist band out of. You mentioned that you could hook up 12 of those small babies and spin them around your head, so I'm thinking they'd be all right for the situation.

Also, are there any foreseeable problems with doing this? Since all my work is on a computer, I guess it could mess with the screen, but I'm willing to overlook that, just for the sheer coolness factor.

Answer:
Little spherical magnets would do it. You'd need quite a few of them, though, and if you wore the bracelet all the time the magnets would quite quickly wear through their protective metal plating at their contact points. You could re-protect them by dipping them in epoxy or something, though.

Anyway, if you want to try it, Forcefield's 1/4 inch spheres would be quite suitable. I'm thinking you'd need at least 30.

Half inch spheres might do the trick, too; Forcefield have those here, and Amazing Magnets have them here.

A ring of neodymium-iron-boron sphere magnets, especially quarter-inchers, has a very small external magnetic field. Disconnect the ring into a line and it'll affect a monitor from a reasonable range (especially if you're using half-inchers or bigger), but the ring configuration keeps the field small.

 

Network niggle #4293

I just set up a network which connects my home computer to my laptop. I used an Ethernet crossover cable. My laptop can see and access the files on my home computer fine. I am trying to use the laptop to run applications which are only on my home computer, but receive an error message every time I click on the shortcuts through the Ethernet connection. Can you please tell me if this is possible? I no longer have the install disks for some of the software I have on my home computer, but need to use it every day.

Don

Answer:
You won't be able to run a lot of programs this way. They depend on stuff other than the program file, which is installed when the program is. A computer lacking the extra libraries, registry entries and so on will not be able to run the software. Non-trivial detective work is needed to find all the stuff a program wants and move it to a new computer, if you can't just reinstall the software.

 

Light hunting

I've seen these LED Christmas lights, but balked at the price/ugliness of them. I was wondering if, in your weird and wonderful collection of LEDs, there were any Christmas lights. It's something that you may not appreciate Down Under, but here in the Great White North Christmas lights seem to be one of the greatest scams around. Every year you buy new ones because they've changed the sockets so you can't replace bulbs. That's if you can find the ONE BULB in the string of SERIALLY WIRED lights that's burnt out/loose/broken. Not to mention the hassle of untangling them. It seems that most people crack and buy new lights instead of messing with the old ones. Trust me when I say putting up a new string of lights in our weather is NOT FUN.

The long life and low power consumption of LEDs would seem to be the solution to this problem. We use those LED traffic lights so the weather here (-40 degrees C for a few days every year; 2 years ago we hit -30 or below for 30 days - oh and don't forget wind chill) can't be too much of a problem.

Cameron

P.S.: I tried my best but I bow before the master of placing links in his articles. How do you find so many great and appropriate link sources?

Answer:
I've never actually reviewed any LED Christmas lights (which can more politically correctly be referred to as "holiday lights", though that becomes a little tricky if they're a string of light-up Santas), but I bought some for my sister a couple of years ago. I hope that counts.

Check around your local electronics stores. Cheap no-brand LED Christmas lights, complete with multi-mode controller that lets them flash and chase and twinkle and such, have been around for some time now, and I'm pretty sure you'll be able to find them where you live. Hardware stores commonly have them as well, here in Australia at least.

Jaycar in Australia has sets almost exactly the same as the one I bought from them (the new ones have star-shaped lights; the ones I got were plain) for $AU25 ($22 Canadian). They're catalogue number SL2840, not that anyone's likely to want to buy them from the other side of the planet, of course.

There was a discussion on this subject on Slashdot recently, by the way; it's here.

How do I find esoteric links?

I guess I'm just special.

 

Scan-spotting

You may already have seen this, but thought I'd send it anyway!

I ask you, would anyone but a true Daniel Rutter fan be able to identify his idol's work sans credits or references?

Jarkko

Answer:
Actually, yes, I have seen it. That is, indeed, a scan from the issue of Atomic magazine in which the letters column that's now reprinted here first appeared.

Naturally, I found it while I was, um, zapping channels.

No, wait - my, uh, girlfriend, see, was looking at those horrible pictures, and I happened to look over her shoulder, and, um...

No, no. It was my evil twin. From the universe where Spock has a beard.

Ahem.

Oh my god! Look over there!

[receding footsteps]

If you want to ask me a question, feel free - but please read this and this first.

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