Control module

Control module will need a lot of Energizer bunnies to keep it going:

Component	Work cycle	Current draw
GPS unit	100%	30mA
Baro/Temp sensor	1%	15mA
Camera	100%	80mA
XBee	100%	215mA
Arduino	100%	20mA
TOTAL	–	360mA

I’m planning to run it on 8xAA Energizer Ultimate Lithium batteries, wired 4+4 in parallel. Total capacity will be about 6,000mAh at room temperature, reduced to ~2,000-3,000mAh at high altitude, where temperature drops to -40°F.

Lithium batteries are expensive ($2 each) so I did a test with standard alkaline batteries:

Battery voltage dropping to zero means the unit stopped functioning due to low voltage or battery protection.

Emergency Release

Burn wire requires a lot of current (1.5-2A @ 3V). It will use a dedicated lithium 123A battery, so that high current draw does not impact control module. I ran ten 5-second burn-wire tests from the same batter, it accommodated all of them with no problems.

Backup radio beacon

I tested Big Red Bee transmitter with standard and high-capacity LiPo batteries. Work cycle was set to 25%: 0.5sec beep — 1.5sec pause — call sign every 5 minutes:

Beacon kept going for 4 days!!! I think I might reduce duty cycle from 25% to 15%-20% to let it run for a whole week.

I will need to test LiPo battery in cold temperatures – I hope it will freeze and loose capacity during ascent, but regain it back as it warms up during descent. So far, I put beacon into freezer and it ran for 4 days – similar to test at room temperature.