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TinotopiaLog → ‘Universal’ DC Power Supply ( 5 Jun 2001)
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Tuesday 05 June 2001

‘Universal’ DC Power Supply

At home, my desk sits out in the middle of the room. I can’t deal with a desk that’s pushed up against the wall. I like to have something to look at, even if it’s only a wall that’s five feet away.

Anyway, the desk is in the middle of the room. One good thing about this is that it gives me ready access to all the wires dripping down behind (i.e. in front of, that is to say on the side I don’t sit on) the desk. One bad thing is that all these wires are out in plain sight. Here’s what it looks like:

You can see my toes (in socks) at the bottom of the photo.

Roughly speaking, from left to right: Toshiba DC adapter for scanner (which is an HP); 100 mb Ethernet hub; USB hub; UPS, into which are plugged: Sony DC adapter for laptop; unbranded Chinese DC adapter for Ethernet hub; unbranded Chinese DC adapter for speakers; Toshiba DC adapter for laptop; Archos DC adapter for CD-R drive; Viewsonic DC adapter for flat monitor.

This mess behind my desk is bad enough, but it’s a real nightmare when I’m travelling. I have to carry power supplies for my computer, my cell phone, my CD drive, my digital camera, and who knows what else. The exact inventory varies depending on the purpose of the trip.

It occurs to me that I am not alone. All this electronic stuff runs off DC power; if you don’t plug a brick into the wall to power your electronic device, it’s because it’s doing its power mojo inside. The only electronic items I know of that actually use the AC power itself for anything are TVs and VCRs. Everything else is purely DC.

Most manufacturers of DC-powered consumer electronics, though, seem to believe that their products are unique; so every device comes with its own power supply, one that’s usually incompatible with nearly everything else on Earth.

Radio Shack (among others) sell switchable power supples (like the one at left), that will produce any one of a number of voltages on command. These usually come with an assortment of plugs, one of which will probably fit the thing you need to power.

The biggest problem with these, though, is that you can’t power more than one thing at a time. I often need to charge my cell phone while I’m using the computer, or my computer and CD drive, or even all three at the same time.

The adapter shown above will not power most laptops, which usually like to see around 16 volts. Radio Shack sells a power supply that will power a laptop, but it’s a completely different animal, and comes with different plugs (so it won’t also recharge your cell phone, for instance).

And, adding insult to injury, these switchable power supplies are almost always of the very cheapest manufacture. There’s not much to the things, electronically speaking, so they’re pretty reliable nevertheless. But the cables are incredibly cheap — and pretty long — and they will break before too long.

I’ve written about this before, and even suggested a possible solution. Unfortunately, that solution has at its base the assumption that I am the Absolute Monarch of The World. Since we are still living in the interregnum, I propose another solution, to be used until I can force DC power supply manufacturers to bend to my will.

This solution is a modular DC power system, meant to be used behind a desk, on the road, or wherever it’s needed. It doesn’t use any radical new technology, it just repackages existing technology in a more useful and convenient form. Here’s an illustration:

The whole thing is about the size of a largish laptop power supply of current vintage.

There are a few basic components:

1. AC plug. Available in all major world standards. When you leave the country, you shouldn’t need to use those clumsy adapters that are always falling out of the wall.

2. AC cord. Available in a number of lengths, to suit your needs. Possibly there should even be an automatically-rewinding version for tidy packing.

3. AC/DC adaptor. The heart of the system, it accepts AC input on one side, offers it on the other, and outputs DC power in between. You can thus plug it directly into the power cord (see 16V module above), or you can plug it into another AC/DC adaptor (like the 3.6V and 12V modules in the drawing). The drawing shows three adaptors plugged together, but in practice the number that you could connect would be effectively limited only by the space you have available (AC/DC adaptors don’t use enough power, generally, for electrical limitations to be much of a problem). Most of the adaptors would probably have receptacles for two DC cords, should the user have two devices that use the same voltage.

4. DC cord. This is standard across the range, and available in a number of lengths. You might want a three-meter cord for powering your laptop while you sit on the sofa, but only a 10cm cord for charging your cell phone, since it wouldn’t be subject to tangling.

5. DC plugs. DC plugs would be available for everything under the sun, because this is where the modular power system meets the devices made by any number of manufacturers. Since some manufacturers will perversely use impossible-to-duplicate or very rare connectors, there would be a kit that would allow the end user to connect any DC plug to the system without too much trouble.

The main point here is that everything unplugs from everything else. This makes packing a lot simpler, and it allows the user to customize the lengths of the cords to the particular purpose — cutting down on tangling and bulk.

And the modular design lends itself to other uses, too! A UPS module (much larger, of course, to hold batteries) could hold a number of DC modules, eliminating the tangle of AC cords. An inverter module with a cigarette lighter plug on it would allow the things to be used in cars, boats, and RVs.

The main market, though, would definitely be the traveller who wanted to cut down on bulk and tangles, while maximizing convenience.

Posted by tino at 10:18 5.06.01
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