[Stoves] Hand Crank Dynamo for Fanned Stove?

[Charlie Sellers]

Paul,

If you really are pulling the full 300 milliamps (.3 amps) at 12 V then that amount of "power" is just the product of these two, or about 4 watts.  For comparison a single ordinary LED will need MUCH less than one watt and the WoodGas stove fan needs a little more than 1 watt.  So your 4 watt need is quite a bit of power.  Are you sure that your PWM duty cycle is 100%, and not less than that?  As you turn it up from no power to full power the duty cycle (or percentage of time that the PWM turns the power on) goes from 0% to 100%, increasing the fan speed proportionately.  An ordinary multimeter will not tell you duty cycle, so you can't use it to determine the power you are consuming.

This got more complicated than I thought (so I deleted much of my discussion on LED circuits, units of measure, and calculating the energy per crank), but it was not a simple question.  The bottom line is what is the amount of energy that can be stored in the internal battery (voltage times the milliamp-hr battery rating) and how many cranks does it take to fully charge the battery?  Then determine how you will compensate for the lower voltage of the battery (perhaps much less than 12 V).  Some homework is required, and my gut feel is that all the LEDs in the latern take very little power, compared to 4 watts.

My issue with solar battery charging and similar gadgets is that these are just more pricey parts to break when you are in a developing country - and the batteries themselves are just more parts to be diverted to other applications (like radios, then new rechargeable batteries may not be available to replace them for the stove).  I carry a slim 110/220 VAC battery charger with me, but fan stoves just may not be suitable for many places because they are somewhat high tech for now.  Cell phones at least are priming the world for small appliance and battery charging. Internal thermoelectric power is one approach to less parts, if a lifetime can be predicted when used in the field.

Charlie


"Paul S. Anderson" <psanders at ilstu.edu> wrote: Stovers,

>> Jeff Davis wrote:

>>> Found an interesting product at Harbor Freight. It's a hand crank LED
>>> lantern.
>>> Crank for 60 seconds and get 20 minutes of light.

For the blower in my TLUD in India, I need 300 milliamps at 12 volts DC 
maximum
power, and I "turn it down" with a PWM (pulse width modulator) that has a 500
milliamps maximum.

Question:  How many minutes of 300 milliamps 12 volt power can I get from
existing hand-crank devices?




       
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