[Stoves] Powering a TLUD Fan

[Phil Hughes]

I see Paul Oliver's work to be excellent and appreciate how a variable
speed fan can offer excellent control over TLUD operation. My reservation
is that there are many places where even the small power requirement (Paul
says 1-2 watts) just isn't available. Lots of people here in Nicaragua are
totally off-grid and don't have reasonable access to a way to charge a
battery. So, I am been thinking about options. Being, among other things,
an electronics geek, here is what I have been thinking about.

Running the TLUD 8 hours a day at "average" fan speed means 12 watts per
day. At 12 volts that's one ampere hour. I have been thinking about a
couple of approaches. One is "higher tech" but may be a better solution at
an equivalent or lower cost. In both cases I am just thinking of a
photovoltaic panel to charge the battery. The difference is the battery
voltage.

Small PV panels are pretty common on the surplus market. For example,
Electronic Gold Mine (http://www.goldmine-elec.com/) offers an assortment.
The specifications vary from 7 to 35 volts open circuit with output power
in the range of 1-3 watts. Prices are from $4.50 to $15. As this is
quantity one retail price information, it is likely the could be found at
significantly lower costs.

As any PV-based system will need some sort of charge controller for the
battery and what PV cells (in particular, what voltage) will be available
at the best price point, I am thinking that using a single-cell Lithium Ion
battery (3.7 volts nominal) would make the most sense. Units with a
capacity of 2.2 ampere hours and more are commonly used in laptop
computers. They offer reasonable life, low cost and the possibility of
finding them on the surplus market. The cells can be paralleled if higher
capacity is needed.

A switching "up-converter" would be needed to supply the 12 volts needed
for the fan. The speed control could be incorporated into the up converter
which would reduce the cost and increase the efficiency.

The alternative would be to use a more or less 12 volt battery (three
Li-Ion cells in series) so that the up-converter could be eliminated. My
initial guess is that the reduced electronics cost would not be as much as
the increased battery cost but it is a viable alternative as long as higher
voltage surplus PV panels are available.

While this sounds like a lot of electronics, this is all very common stuff
that you find in, for example, cellular phones. There is some design work
needed but the actual component costs will be very low.

Comments?
-- 
Phil Hughes
nicafyl at gmail.com
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