First Thoughts on Recharging a Battery during balloon flights

Warning … Warning … The following is unencumbered with a reality check – or even research.  You have been warned.


Schematic Fragment

My problem is that I would like to power a Raspberry Pi (5V about 0.8A) during a balloon flight (4 hrs) using an 11.1V LiPo battery maybe 300 to 800 mAhr, supplemented with a 15W array, instead of using a 4000 mAhr battery.  I try to size things to run 4 hrs.  And no, I don’t know if this actually saves weight.  However it would be cool to accomplish.

Some observations:

1)     My goal is more to supplement the battery power than to recharge it. Though some recharging may occur when if the battery gets depleted, most of the time the load will be powered by the array.

2)       I think the main purpose of the diode is to keep the array from shorting out the battery when array is dark.  On the balloon, there will be times when the array is not in full sun and would deplete the battery.  The diode prevents this.  So we want the array to supplement the load current, or recharge the battery with excess current.  But we do not want it to discharge the battery.

3)       [This is what worries me] I’m not sure what happens when the batteries are over-charged so  I think a regulator is needed across the array.   For my 11.1V Battery problem assuming a 0.5 V drop across the diode, I’ll need an 11.6V or 11.5V (and 1A) regulator across the array – maybe a 12 Regulator can be tuned to a lower voltage?

I’ve sketched out the rough idea above.  The diode and regulator have to be sized to handle the current, 1 to 1.5A.

© David B Snyder 2013