[Peripherals] Charging the XO off a bicycle dynamo

[Richard A. Smith]

Nick Foster wrote:

> and it would go dead on you. LA batteries do not like to be stored empty 
> for any length of time (the plates will sulfate and the battery will 
> eventually fail to charge and discharge). Thus, some sort of indication 
> of battery life might be useful. This might be a chicken-and-egg 
> problem, but Holden, you have been using the oscilloscope feature of the 
> OLPC to measure voltages; this facility could be very easily harnessed 
> to determine the approximate charge state of a lead-acid battery. Of 
> course, this presumes that the laptop isn't already dead!

LA batteries hate deep discharge cycles period.  Even so called "deep 
cycle" batteries.  Deep cycle really means that the battery won't die if 
you happen to drain it completely a few times.  The rule of thumb on 
using LA batteries in solar setups is to design around a 50% discharge 
depth.
Which means that you need approx double your load in battery capacity. 
Only going to an 80% discharge depth has a large impact on the life 
expectancy of the LA battery.

-- 
Richard Smith  <richard at laptop.org>
One Laptop Per Child