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Things worth knowing about


This page is about those little power-sources in portable electrical devices. (We'll talk about crazy things it's possible to do with truck batteries later!). Some of the stuff is technical, and some of it isn't. Some of it may help you save money, so it might be worth reading...

* If the batteries in a device go flat, you throw them away, don't you? This isn't as obviously rational as it seems. Part of this is that "flat" is different for different devices. For example, a portable cassette recorder was go very slow and fade out and the batteries seem flat, but if you take them out and put them into a radio or a clock it'll work for several weeks, or months! The reason this can be done is because some machines require a much higher current than others. The highest current requirements are on motorised devices such as cassette recorders, and on some cameras. The lowest requirements are on radios and clocks, which can utilise the last drop of energy in the battery. If you see some "fool" pick up and pocket a discarded battery in the street, it's best not to mock them, as they're no more foolish than someone picking up a luckily found coin.

* Rechargeables. Are they cost-effective? It depends on the application. For a portable CD-player, YES! Definitely worth it! For a calculator, it's less obvious. The way to decide is to work out how much a set of rechargeables will cost versus how much expendable batteries will cost. Divide the results and you have a number representing how many sets of dry batteries you'll have to throw away before you have paid more than if you'd had rechargeables in the first place!

Also, on rechargeables, some devices say in the instructions "you must not use rechargeable batteries". Manufacturers putting this on the pack are doing so usually because of advice not by electronics engineers but by solicitors. There is usually no problem with using rechargeables even if the pack says "NO" apart from the fact that the machine may not work within rated operating parameters. If it's a portable computer it might go flat in a different way, for example with less warning. Does this matter? No, not if you are aware of the fact. Dry batteries go flat like a long-distance runner getting tired, whereas rechargeable NiCd batteries go flat like a car running out of fuel.

* Non-rechargeable batteries; how to recharge them: Before reading this, it has to be understood that the recharging of non-rechargeable batteries is not recommended by those who sell them and also it can be dangerous, especially if you're not sensible about it. If you attempt this, it is at your own risk!

Well I've recharged loads of non-rechargeable batteries and they very seldom explode! The method (at own risk remember) is to use a 12volt car battery charger and to hold the battery and the wires on the ends. Plus and minus have to be the right way round of course, and I always make sure I hold the body of the battery. This is so I let go when it gets hot! That way, it doesn't get so hot it explodes. Having said that, I always make sure that neither end of the battery is pointing in my face, or at anyone else. I'll recharge a battery for a few seconds, perhaps up to a minute, not long anyway. On hearing-aid type battery THREE SECONDS is plenty! And the results, quite good. If the batteries weren't totally dead to start with then the life can be prolonged quite a lot. The results are a bit unpredictable though, so it's best to avoid using the recovered batteries in life-critical equipment such as the smoke alarm. But for the television remote-control, calculator, spare torch, that's another matter. It is possible to save money by this method, batteries being a thousand times more expensive per unit of electricity than the 12v from a charger plugged into a socket on the wall! Helpful correspondents have commented that they have had some success using slow charging of non-rechargeable batteries. This is good, but I recommend caution with leaving such experiments unattended!

* How to test a battery: Put it across a meter, or in a torch, or some other device to see if it works. But what if it's one of four, or you haven't got a meter or a torch? Put it across a hi-fi speaker, just momentarily. The amount of click is a good subjective measure of battery voltage. It also tests the speaker, incidentally, in case you were wondering if the speaker had been burnt-out by playing the music too loud!

* Mythology of the battery-specific: devices claiming to be "battery only" or to require a special battery of some unorthodox size that costs a lot of money, myth! Diabetes meters, cameras, toys, etc can be adapted to run off standard batteries by connecting wires up to where the battery should be and to any battery of a compatible voltage and current capability. Generally the larger batteries are cheaper per capacity, so you can save money by buying D-size Batteries and using wires to connect them up to the battery holders of devices that use AA size or AAA size batteries. Plus, it is possible to run battery-operated machines off a power supply deriving its power from the mains. In general these step-down the voltage and then rectify it (AC becomes DC) and then sometimes smooth it with a big capacitor.

* AC battery: This is a mythical device. All batteries are DC. The notion of the "AC battery" was thought up some time ago by amateur radio enthusiasts just for fun. No-one has yet managed to build anything of the ilk of an AC Battery!

* The "Power Tube": This device, made by Zyra in the 1980's, is not an AC battery but is a 240volt battery. It's a copper tube 54 inches long with a 240volt UK 13A socket on one end. Contains 210 x 1.2volt NiCd batteries. Capable of powering AC/DC mains devices such as table lamps, electric drills, BBC Computers, etc in wild situations, this generates more normal-reality defying interest than electricity.

* It's possible to make a battery using cat food! To do this, open the tin preferably without the cat being near otherwise it'll expect to be fed. Put a fork into the middle of the food so the fork stands up and doesn't touch the can. Now there is a voltage between the fork and the tin can. This is because the fork and the can are made of different metals and the cat food becomes an electrolyte and conducts electricity to some extent. The amount of electricity generated by a catfood battery is not great and won't light a bulb, but it is measurable and will drive "solar" motors.

For a different way of thinking about the term battery. Please visit STAMP DEMON's page Battery.

Following the publication of this page on Issue47, I have received this useful money-saving advice about NiMH Batteries

If you're looking for batteries for sale, it's worth having a look at MDS, Laptops for Less, Battery Mountain, Batteries.com, MDS Battery USA, Brooklyn Battery Works, Budget Batteries, Battery Force Ltd, Optima Batteries, and other Battery Shops