T&L Publications

Here's an interesting story that shot across my radar today:
An inventor created a backpack that generates electricity while walking... 7.4 watts actually; enough to power a multitude of small electronic devices.<p>The really interesting thing is that researchers found through testing that the backpack altered the gait of the wearers causing them to walk more efficiently and thereby used less metabolic energy than expected.<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>By carrying a load weighing from 44 to 84 pounds (20 to 38 kg), Suspended-load Backpack testers were able to generate up to 7.4 Watts--more than enough electricity to simultaneously power an MP3 player, a PDA, night vision goggles (or 3 LED headlamp), a handheld GPS, a CMOS image decoder, a GSM terminal in talk mode, and Bluetooth. The electricity can be used while it is being generated, or it can be stored in a lightweight rechargeable battery for later use, greatly reducing the need to haul and use heavy replacement batteries.<hr></blockquote>

Interesting idea - this stood out at me:
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>By carrying a load weighing from 44 to 84 pounds (20 to 38 kg), Suspended-load Backpack testers were able to generate up to 7.4 Watts <hr></blockquote><p>Uh, I don't think I'll be toting that around...<p>This is not a new concept. In the 60s some electric watches had a small, internal generator. I believe it was a magnet on an arm which would move back and forth past a coil with the normal motion of the wearer. This was apparently enough to keep the watch battery charged. Bad news if you put the watch in a drawer for a few weeks, though. The advent of much more efficient motors and lower power digital watches made them irrelevent.<p>I've always though that something could be done with shoes to generate power. The heel takes a lot of shock in normal walking.<p>It might be fun to experiment with.

There goes my idea of a helmet-mounted wind powered generator for joggers!

Who jogs with a helmet?

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Matt Nuzum:
Who jogs with a helmet?<hr></blockquote><p>GIs in Irag...

7.4 Watts - thats' 7.4 N.metre/sec = 2.475 kg.metre/sec = 5.47 ft.lbf/sec = 327.5 ft/lbf/min. It dosn't matter how you produce this - if you do it with a suspended oscillating 44 + lbf weight then the 327.5 ft.lbf/min which is being absorbed by the 7.4 Watt generator has to be replaced by work done by the operator i.e. the guy carrying the backpack or whatever. That means that the operator has to be doing equivalent work of lifting one 327.5 lbf weight EVERY MINUTE - like Phil, I wouldn't want to be doing that either.

Sorry . . . .by lifting one 327.5 lbf. weight . . by one foot every minute

Well, I misunderstood that statement at first, sorry if I miscommunicated it. The article doesn't say its free energy, just that they originally estimated how much extra work would need to be done to create the electricity with their backpack instead of using a regular hiking backpack, but they were surprised that because of the ergonomics of the pack, the work was less than expected.<p>This pack is designed for campers and hikers, not school kids. So people on long trips presumably carry lots of gear and not having to worry about electricity or carry replacement batteries is a bonus supposedly.<p>Now, when I was a kid (born in '75), I had to walk 13 miles to school and carry a 52 pound backpack full of books and homework... and instead of a TI84 I had to carry a PDP11 with me...

Unfortunately they don’t mention if it’s a watt second, watt minute, or watt hour, ....as in Horse power. <p>Just 7 watts? <p>This could be accomplished over a longer period of time. <p>A watt unlike the horse power is not a time based unit. It’s a work or quantitive unit, with out time. <p>But with the loads they mention, 44 to 84 pounds, 5 pounds per second jumping around is nothing. <p>At 84 pounds your load would only have to move up and down 3/4 of an inch,... per second to make 7 watts, per hour. <p>That’s what any back pack wiggles on your back any way.

"Unfortunately they don?t mention if it?s a watt second, watt minute, or watt hour, ....as in Horse power." <p>"A watt unlike the horse power is not a time based unit. It?s a work or quantitive unit, with out time."<p>Both statements are inacccurate.<p>Both the watt and the horsepower are units for the rate of delivery of energy. Energy (in joules, ergs, calories, or other units) is not time dependent. A watt is 1 joule per second. A horsepower is approximately 746 watts. These are units of work, not energy. Work is basically the rate of energy transfer.<p>Describing the generator output as 7 watts is entirely accurate.

Carrying the PDP-11 wasn't so bad. The real killer is carrying the Model ASR-33 Teletype. At least the PDP-11 was made of aluminum.

Incorrect Steven. <p>There are “equivalents” for the watt, all of which include time, but the watt has no time frame attached to its actual meaning. <p>The joule per second, is a “equivalent” and the “horsepower” is also a Equivalent rating, neither represent the actual watt. <p>A watt is a electrical unit, having to do with electrons, amps, and volts. <p>There are many Equivalent structures to measure a “equivalent” amount of power, but again, the watt is none of the above. <p>The watt (symbol: W) is the SI derived unit for power. It is “equivalent” to one joule per second (1 J/s), or in electrical units, one volt ampere (1 V·A).<p>The present definition, adopted by the 9th CGPM in 1948 is: "one ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2 נ?10-7 newton per metre of length". The definition for the ampere is equivalent to fixing a value of the permeability of vacuum to μμ0 = 4πp נ?10-7 H/m. Prior to 1948, the so-called "international ampere" was used, defined in terms of the electrolytic deposition rate of silver. It is equal to 0.99985 ampere.

--Edited by Positronicle--

My mistake, work and energy are the same thing. Both can be measured in joules (MKS), ergs (cgs), newton-meter (MKS), dyne-cm (cgs), calories (metric), British Thermal Units (english), kilowatt-hours (english), foot-pounds (english), or inch-ounces(english).<p>Power is the rate of doing work or transferring energy. It can be measured in watts (MKS), newton-meters per second (MKS), foot-pounds per second (english), or horsepower (english).<p>The watt is not limited to electrical use. If you look at the web sites describing aircraft engines, you will find the outputs given in both horsepower (english) and kilowatts (metric). There are few things more mechanical and less electronic than the output of either a reciprocating engine or a jet engine.<p>Defining the value of the permeability of free space defines the ampere in terms of the standards of length, mass, and time. Once the ampere is defined, the ohm and volt can be derived.<p>Originally, the ohm was defined as a physical column of mercury and the volt and ampere can be derived from this. In any case, the objective has been to choose the electrical units such that the unit of energy is the same whether the energy is electrical or mechanical. (ie, one newton-meter is equal to one watt-second which in turn is equal to one joule) By 1948, the match seems to have been made to about 1 part in 10,000 or better. It has probably been improved considerably since then.

The portable generator is properly rated as 3000 watts. There is no time dependence.<p>It is also fairly common to see servo motors with their mechanical output rated in watts rather than horsepower. This makes it simple to calculate efficiency, since efficiency will be watts output (horsepower times 746) divided by watts input (volts times amps).