Battery Selection Help - Page 1
Forum section: electronics / projects

author: mgwalker95
author_rank: Contributor
timestamp: January 02, 2021, 07:35:10 am
content: I am having trouble selecting a battery for a project that I am working on. What is the best way to go about battery selection?My requirements are Li-po battery with only 1 cell that I can pull 16.5 W out of the battery or ~4.5A @ 3.7 A also the battery's voltage cannot go below 2.7V when I am pulling the 16.5W(~4.5A) from the battery. The problem I am currently running into after testing a few different batteries is that many batteries fully charged with 5000mAh capacity output voltage will fall below 2.7V when I try applying my max load. I have also tested a larger capacity batterie(8000 mAh) and found that the batteries internal protection limits the current below the needed current. Has any one run into issues like this that can give me some suggestions to try or helpful resources to check out?What is the best way to find batteries that can meet my specifications? I have searched Amazon, Aliexpress, Digikey and Mouser are there other places I should look for batteries? should I contact battery manufactures to get a battery that will meet my requirements?Thank you for your help in advance!

author: Hiemal
author_rank: Regular Contributor
timestamp: January 02, 2021, 07:52:43 am
content: It sounds like you might just need a larger battery. Batteryhookup.com (I'm not affiliated with them, nor am I being paid by them) have a decent selection of batteries, you might want to try one of the headway ones... though that's LiFePO4 chemistry. Is there any reason why you wouldn't want to parallel cells? It might help give you more oomph since the cell's internal resistance would be paralleled.

author: mgwalker95
author_rank: Contributor
timestamp: January 02, 2021, 08:01:47 am
content: Thanks for the suggestion, I will check out Batteryhookup.com. What is the advantage of using LiFePO4 vs Li-Po? The reason I want to use a 1 cell battery is because the form factor that I am building the project for can only fit 1 cell batteries. If I really need to switch to 2 cell batteries I will but, that would many redesigns both electrical and mechanical which I would like to avoid.

author: elektrolitr
author_rank: Contributor
timestamp: January 02, 2021, 10:36:50 am
content: Which type (size) of battery is suitable for your project?Is it 18650 or something smaller? From capacities you've mentioned (5000mAh+) I assume it can be even biggerLi-ion batteries are usually optimized either for large capacity, or for large discharge current. It's possible than your 5&8 Ah batteries are meant for low power devices only and can barely deliver the current. Give some high discharge rate 18650 a try and these will deliver you 20+A from 2Ah cell.You can start looking at discharge curve from datasheet or testing results which are plenty on the Web.Like:Sanyo hi-cap 3400mAh battery:This is high capacity element and voltage drops significantly when loaded but it can still deliver more than 3V at 10 A for about 70% of capacity and easily go above 3V to the end with 5AHave a look at another cell:This is closer to high-current ones, with 25A rated discharge (10C) and it can easily stay above 3V even at 25A, and your 5A is a child's play for the cellPlease note that the voltages are measured at battery terminals, and poor connection/thin long wires can easily take 0.5V or even more.

author: mgwalker95
author_rank: Contributor
timestamp: January 02, 2021, 07:12:27 pm
content: Thank you for your informative suggestions.My size requirement is that the battery must be slim so I am currently testing out pouch cell batteries rather than cylindrical shaped batteries. The 5000 mAh battery that I tested was the LP735977JH. Do pouch batteries typically have higher internal resistance than cylindrical batteries?What are some good ways to find pouch shape batteries that have this type of information? I am finding it hard to buy batteries to test, do you have any recommendations for Li-po pouch battery distributers/resellers?

author: mgwalker95
author_rank: Contributor
timestamp: January 02, 2021, 08:56:38 pm
content: After doing more research it might just be easiest to buy RC car/plane Lipo battery packs and disassemble them/modify them to what I need. RC car/plane Lipo battery packs seem to have a high discharge rate and are the proper shape and capacity.