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A Universal Power Bus?
mjpalm21 asks: "A friend of mine recently sent me this story on a new universal power technology that charges devices through your desk. This is a cool idea, but it seems complex. I have long wondered why there isn't a universal power bus (UPB) along the lines of universal serial bus (USB). UPB would work like this: You would buy a n port UPB hub for your desk, and then all of your electronic devices (cell phone, PDA, computer speakers, modem, phone, hubs etc.) would plug into the hub via a standard UPB cable. I would think that the device manufacturers would be all over this as it would reduce their product cost (no need to bundle a power brick), reduce their packaging cost (smaller box), increase customer satisfaction (I know I would be happier), and give them another device to sell (the UPB hub and all those cables)! Why hasn't this happened yet and what would prevent it from happening?"
Hmmmm.... lets see here.
115V * 30A = 3450W
Monitor
150W=High 17inch usage
Computer
1100W=enermax 460W power supply
Speakers
100W=decent sized computer speakers
network hub
10W
pocket pc
35W=HP Jornada
cell
35W
laptop
200W
for a grand total of:
1645W
even with a 25% error it still is 2056W. Thats a lot of extra room for mor things on one outlet
Do not go gentle into that good night. Rage, rage against the dying of the light.
However, things still get murky, even in a 5V standard world. You run into issues
- Over current protection of the source
- Transient protection both ways
- Accidental polarity inversion
- Ground loops
- Noise
- Devices supplying power inapropriately
The easy (cheap) way around this is to specify a standard charger that is specifically NOT interconnectable to anything else, thus resulting in the plethora of incompatible devices that frustrate you.My choices for a standard
- 5 Volts, TTL standard power with a new connector
- 13.8 Volt lighter plug, perhaps a mini version
- Standard plug/polarity/voltage sizes for barrel connectors.
- A new 5 volt, 3 phase 10Khz standard power connector
3 Phase power is cool, too bad it doesn't make it into more homes.--Mike--
Technically, he's correct. Unfortunately, since device manufacturers also specify all characteristics of the power supply, some are planned around very specific voltage/current profiles, in other words, actually planning on a certain voltage drop at a certain current draw. This is most common with rechargers, wherein at the start of the charge cycle, the device relies on the power supply sagging under the load to prevent charging the battery too fast. Give it a more robust supply, and you overheat the battery.
This, however, is only an excuse, and applies to only very simple and inexpensive devices, and not even many of them, any more. The real reason is forced incompatibility. Batteries and power supplies commonly have elaborately-keyed connectors, both physically and electrically. Even though the device reqires only some minimum current capability within some voltage range, in some cases the connector actually has to provide power and ground on some undocumented combination of the pins, and has to turn on and off some pins based on power sense in others, provided by the device. This is just to prevent aftermarket replacements. Did anyone ever try to buy a replacement dongle for an ethernet or modem PC card? It's commonly barely cheaper than to purchase a complete replacement for the device. open up one of those automotive power adapters for a cell phone, and see what it is. I've never seen one yet that did any voltage or current modification. THe phone just lives with whatever voltage it gets, as long as it's not too little to run on, or too much to handle. The cost is in the needlessly-complicated and fragile connector. Power to portable consumer devices is still largely closed-source.