[Stoves] Powering a TLUD Fan

[Phil Hughes]

Let me toss in a few more factoids.
http://www.batteryspace.com/li-ioncylindricalcellseries.aspx will give you
a decent sample of the common LiION cells. The most common size in laptop
batteries is the 18650 which is typically from 2.2 to 2.78Ah. When you see
a laptop with a higher capacity battery it is typically cells in
series-parallel. For example, a 6-cell battery is generally two strings of
three 18650 cells in parallel.

The explosing fist is real. The good news is that there are very
inexpensive chips designed to charge these cells. You will find one (for a
single cell) in all cellular phones. They will deal with maximum voltage
and maximum charge current. They are also low drop-out as a typical use is
to output 4.2V from a USB (5V) supply.

In a typical laptop, you find other chips (generally more than just a
single component) to charge the "almost 12V" string of LiIon cells from the
typical 16 to 20V AC adapter. The disadvantage here is that you need to
monitor the voltages of each cell in the string. Not complicated but that
is what makes the 12V solution potentially more expensive than the 3.7V one.

A 5V fan is an interesting possibility. First, if may operate fast enough
from say 3.5V so a single LiIon cell would handle it. If not, a flyback
converter to step up 3.7 to 5V would be cheap and high efficiency (because
most of the power comes directly from the battery rather than needing to be
"converted").

On Thu, Aug 30, 2012 at 9:36 AM, Frans Peeters <peetersfrans at telenet.be>wrote:

> Phil,
>
> 3x LiION  =3,7Vx3=11,1V  Charger needs 4,2x3=12,6 maximum or EXPLOSION RISK
> 2W motor at 12V-------->0,1666 A
> 8h xO,166A =1,8Ah
> Laptop cells are 3,6 Ah and more
> Sun cell 15,6V---------> 12,6 V +3V for charging  regulator LM317
>
> PC  uP fans exist at 5V x0,2A=1W you could power with 2 cells;
> Also a dual fan of 2x 1W
>
> Regards
> Frans
>
> 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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-- 
Phil Hughes
nicafyl at gmail.com
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