Design Question: PSU for a high altitude baloon (HAB) - Page 1
Forum section: electronics / projects

author: kml183
author_rank: Contributor
timestamp: June 26, 2023, 05:55:05 pm
content: Hello!I am working on a HAB project and I am not sure what is the optominal battery/dc-dc converter to select for this. The max height would be 100,000 ft. The batteries will be store in a temperature controlled box, and they shouldn't get to bellow 40 degrees C. I need a 5v at 1.5 A rail and 3.3v rail at 1A for my avionics. In total I need a 5AH capacity. NiCD batteries look like the cheapest option that would work at the pressures at 100,000 ft so that is what I am going with. I am also not going to discharge them at that capacity past 75% so the voltage should be relatively the same for the cells.My two ideas for the PSU are:- I can use a 1.2 or 2.4V NiCD battery pack and boost it to get the voltages I want.- I can use a 7.2 or 8.6v NiCD battery pack and buck to get the voltages I want.It seems like a toss up to me, I am not sure if there is anything else I should consider to make this decision. Thoughts?Thanks!

author: Benta
author_rank: Super Contributor
timestamp: June 26, 2023, 07:47:20 pm
content: Why NiCd? They are bulkier and heavier than lithium cells, and finding a ready-made IC for the voltages you need is easy today.Either as a 1-cell buck/boost or a 2S stepdown.I expect the electronics will be inside the heated battery enclosure?

author: kml183
author_rank: Contributor
timestamp: June 26, 2023, 08:59:02 pm
content: Quote from: Benta on June 26, 2023, 07:47:20 pmMy understanding was that NiCd are less likely to fail when experiencing low pressures versus lithium based batteries.Ya if lithium ion or a lithium polymer battery can survive at 100,000 feet. That would probably be battery. I thin in that case a buck/boost for a 2C off the shelf battery would be the easiest.

author: Zero999
author_rank: Super Contributor
timestamp: June 26, 2023, 09:13:45 pm
content: Do they need to be rechargeable? If so, how and when?What's the service life?Will it be a single use device?

author: kml183
author_rank: Contributor
timestamp: June 27, 2023, 01:27:39 am
content: Yes I would be rechargeable. I would like to launch the module multiple times. I have a charger that can charge multiple battery types so I would probably use that between flights. The device would not be single use.

author: globoy
author_rank: Frequent Contributor
timestamp: June 27, 2023, 03:49:55 pm
content: FWIW, I was part of a team that flew a HAB during the 2017 NA eclipse. We had several payloads that worked successfully up to around 100k feet using different battery technologies. A 360° camera and a GoPro both used LiPo batteries. These cameras generated quite a bit of heat during operation so we figured that would help the batteries. An APRS tracker and a couple of Raspberry Pi Zero based devices ran on Primary Lithium AA batteries since these have good cold ratings. We considered the primary batteries as just part of the consumables expense for the launch. I can't remember what the other Pi device did but in my Pi-based package I basically mounted the Pi right over the batteries so any heat it generated would help warm the batteries.Interestingly we didn't consider altitude effects on the batteries - and fortunately weren't bit by it (all batteries looked fine at the end of the trip).

author: kml183
author_rank: Contributor
timestamp: June 28, 2023, 06:44:36 am
content: Quote from: globoy on June 27, 2023, 03:49:55 pmAll very cool!Ya I think I am going to take an off the shelf lipo from hobby kind and run with that. Buck it down to the voltages I want with a SMPS. That should work!Do you have a link to any documentation about your teams' project?Thanks!