Project Idea : portable power for a portable station
This battery pack idea started after I carried a sealed lead acid battery up to a mountaintop for my first SOTA (Summits On The Air) activation of Pinkham Mountain in northwest Montana. I determined, after less than 10 feet from my truck, that I had made a bad choice.
Since then, better cells and battery management systems have appeared on the market, leading me to devise a plan to build a more powerful and lighter battery pack suitable for many portable ham radio activity, including SOTA and emergency communication situations.
The most important thing to do when setting out to build something like this is to determine and document your use cases and specific requirements. What weight and form factor do you need for portability.
The capacity of the battery pack is probably the most important characteristic to select from the beginning. Consider things like operating parameters of the consumption devices, and their duration in use. Are you operating multiple radios? QRP or high power? Other accessories?
Defining the functional requirements:
Easy portability and moderate weight
Separate charging input – provides correct charge voltage and constant current
12v output with boost converter
“Raw” battery output jack
“Boost” battery output jack
Power switch – controls USB jack, raw output and boost output
Volt/Amp meter – measure all loads
25 Amp/hour capacity to run one or two radios at up to full power for hours
Rough out a design:
Working from those requirements, I started on a schematic of the battery pack, as well as the physical layout within the enclosure, both for safe and easy wiring, as well as for the ergonomics of the pack.
Obtaining the components:
Shopping on the usual sites, I located all the components in the sizes, capacities, and quantities needed.
Pay attention that the Battery Management System (BMS) you select supports the cell chemistry and capacity you are building. The one I selected is a 4S 12V 40A LiFePo4 BMS.
“4S” represents the number of cells in series.
All bits have arrived, so it’s time to start mocking everything up and measuring…