Power

19 December 2011 ~ 0 Comments

Power Supply

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Here are the requirements we had for our power supply:

  • We needed enough power for the whole electronics for more or less 2h30m; more is better.
  • The batteries must be able to work under very rough conditions, including negative temperatures of about -50ºC and very low pressure. Both are problems for regular commercial batteries.
  • Lightweight. The payload can’t exceed more than 1.5Kg, including boxes, parachute, electronics, motors, cameras and batteries.

Extreme negative temperatures and very low pressure was our main problem. Most commercial batteries can’t handle less than -20ºC (-4ºF) and would probably expand and explode under very low pressure.

After lots of reading we concluded we had to use Lithium based batteries. There were reports of teams using surplus military batteries that you can buy online in the US but those seemed too difficult for us to get hold of. We ended up using the amazing Energizer L91 Ultimate Lithium batteries. They’re made of Lithium/Iron Disulfide (Li/FeS2) which is good under low pressure, they’re not too heavy, can handle -40ºC and boast 3000mAh of power, max 2A, which is more than enough for our 2 hour flight.

They’re not too cheap but not too expensive either and if you look online you can get good deals for quantity packs.

 

We used 18 batteries distributed by 3 parallel modules for extra performance. The power supply has a DC voltage regulator and outputs 5V and 3.3V for the electronics and radio comms. We used:

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