Steps closer to more universal power supplies
Today I want to report we're getting a lot closer. A new generation of cheap "buck and boost" ICs which can handle more serious wattages with good efficiency has come to the market. This means cheap DC to DC conversion, both increasing and decreasing voltages. More and more equipment is now able to take a serious range of input voltages, and also to generate them. Being able to use any voltage is important for battery powered devices, since batteries start out with a high voltage (higher than the one they are rated for) and drop over their time to around 2/3s of that before they are viewed as depleted. (With some batteries, heavy depletion can really hurt their life. Some are more able to handle it.)
With a simple buck converter chip, at a cost of about 10-15% of the energy, you get a constant voltage out to matter what the battery is putting out. This means more reliable power and also the ability to use the full capacity of the battery, if you need it and it won't cause too much damage. These same chips are in universal laptop supplies. Most of these supplies use special magic tips which fit the device they are powering and also tell the supply what voltage and current it needs. The magic tip system is good, but the vendors have overdone it. I called several and none of them would just list the tips based on voltage. If you have uncommon equipment and just want to know, "What tip of size X will give me 12 volts" they refuse to answer the question. You can get all the tips and put a voltmeter on them, but I did not find a web site where anybody had done that. They just don't trust the public to figure out what to do, and I guess there are enough stupid people out there who might put a totally wrong voltage on a device and screw it up, and blame the power supply vendor. (Of course, more and more devices also will work with a wrong voltage but may not be perfectly happy with it.) The good news is these supplies are really dropping in price. Got one on eBay that takes all ranges of AC power, plus 12-18 volts of DC to work in cars and airplanes for under $50. Pure AC ones are dirt cheap now.
The tip system isn't ideal for meeting rooms, as tips will be lost and may be hard to apply. A smart data+power system is ideal but not yet ready. A special "tip" which is actually a wheel of tips that can be spun until the right one is in place could serve most laptops.
(I've also found that quite often at meetings I see people pull out devices that charge from mini-USB. So I also suggest conference tables all be equipped with a USB power hub with retractable mini-USB cables. Any powered USB hub will actually do this with a plug in power supply, and they are cheap.)
So now on to the device I want to be able to buy -- cheap of course -- for power needs. It's a universal "Use any source, power anything" box (within reason) that will let you plug into not just wall power, car power and plane power, but also other power supplies and all sorts of batteries. This box would come with the selectable tips and output power of course, but also would have a variety of input tips. Powering one laptop from another's supply would be cute (if it's small enough) but since it can probably just plug into the wall (using both the standard 2-prong and 3-prong power cords) you won't need this.
However, it could have "input tips" for all the common laptop batteries. Laptop batteries are plentiful, lightweight and you're already carrying a charger for them (your laptop.) They come in various voltages (usually from 7.2 to 14 volts) but usually can deliver lots of current. This universal box, given an input cable that clamps onto your laptop battery, could let you use your laptop battery to run your ipod, or a different laptop, or a DVD player.
Of course, you can get custom chargers and batteries for these other devices. The goal here is that for travel (or the meeting room) you only have to have one device, and one type of battery, and one cords to connect to that battery and the other power sources you might encounter. You could get battery packs for AA, C or D cells and use those to power any device for as long as they have power.
With alkaline batteries, you actually do want to have a switching supply that will suck every last bit of juice from the batteries as there is no chance of "damage." On the other hand, alkaline batteries' useful life varies greatly based on what current they deliver. A typical one might deliver 10 amp-hours at a low current like 100ma, but only 2 amp-hours at 1 amp. (Those "ultra" batteries are ones that can do high current better, and they cost more.) What this means is that if you need 6 volts at 1 amp, you will do far better having an 8 pack of batteries delivering 12 volts at 0.6 amps, and converting it to 6, than to have 2 4 packs and change the batteries half-way. (Of course an 8 pack doing 6 volts is even better but must be custom wired.)