by Ken Torino
This is the second in a series of articles about human energy.
The best research was done in the early 1980’s by a group of scientists who were trying to develop human/pedal-powered cars and planes. To do this they measured the potential power output of typical humans over different conditions.
The simple answer is a human can generate 75 watts on a sustained, continuous basis. 300 watts is peak, the most, like a bike racer going up the Alps, but after an hour of this they were completely exhausted and needed to rest for 24 hours.
The largest muscles in the body produce human energy best. This means legs and pedaling is the best way to use them that has been found over the history of development. With this in mind, lets discuss the low end of human powered generators, hand crank, for the rest of this article. In subsequent articles we’ll discuss pedal powered generators and what you can do with them.
To use the biggest muscle you can with hand crank generators, use your arm to crank and hand to grip. We kept this in mind when designing our hand crank generator. Also, the longer the crank arm the easier to crank but the harder to turn fast. So we experimented and came up with what was the best compromise in crank length. Competitor models use the fingertips to grip and the wrist to spin the generator, not conducive to lots of cranking.
The size of the generator was driven by the most popular application, charging cell phones. K-Tor generators are many times the size of generators in competing products. Cell phones are no longer just phones. They are computers and their increasing data requirements have increased the power demands. Chargers used to be .5 Amp, then one Amp and now fast charges are 2.1 Amps. This works against hand crank generators because the human arm did not get any stronger. The K-Tor PS2 USB model picked the best compromise and charges at one amp which is the most powerful hand crank on the market but still not too difficult to crank.
There are many hand cranks on the market today and many are combined with batteries, flashlights and radios. The market drives the design of these devices. First of all low price. As a result, the generators are too small and are easily overloaded. This causes high mechanical stress on the unit and premature failure. The combined function units are a marketing success as the customer feels he is getting a bargain, multiple functions for a low price. The problem is the cost budget for all these functions is too low. If a multi-function product sells for $30 retail, the cost is one forth this or $7.50. For each of the three functions there is about $2.50 of cost available. So to make a flashlight, radio, or hand crank generator you have $2.50 in cost available each. This means you have to use very low cost components. From a generator standpoint a very small 2-3 watt generator with minimal regulation circuitry that will be overloaded when used. These devices appear to be working as the small batteries in them come charged but once the battery is depleted it is too difficult to recharge with the hand crank. They can really only be operated by recharging from a wall outlet. Flashlights and radio receivers use very little power so they can be used for short periods of time in these modes but they are not suitable for the higher demands of charging cell phones. The most demanding application is bring a cell phone back from the dead. We have a video showing a comparison of bringing a cell phone back from the dead with our hand crank and the leading combined hand crank, radio, flashlight. It shows the relative capability or lack thereof of these products.
Our experience has shown that if you want a hand crank get a good one, the K-Tor USB model, a flashlight get a good one and an emergency radio, get a good one. The three combined is a false economy.
On the subject of flashlights we were asked by many customers to recommend a hand crank flashlight. We tested many models and could not find one we would recommend. They were not bright enough and the hand crank generators on them were not powerful enough for them to be useful. We did come across a rechargeable flashlight we were impressed with and we now carry it on our store, the Cree flashlight. As a companion to the USB hand crank it is an effective solution. The illumination element is powerful so you can get enough light to see in any situation. It is zoomable and comes with three modes, high intensity, flashing and battery saving. It also has a good size battery that we tested to last three hours.
In the next issue, we will discuss pedal power all the applications it can support. Pedal power is our preferred solution as you can pedal comfortably for long periods of time and at higher power.