Overview:
I decided to start doing POTA, (Parks On The Air), so I started building a portable station. One of the first items I needed was a battery pack I could trust. I did a bit of research and after chatting with a few of friends, I elected to purchase a BioEnno 6AH battery for my POTA station. I also purchased an item I have wanted for a long time– a dynamic load from AliExpress to test my new battery. Owning a dynamic load allows me to test rechargeable batteries for their discharge capacity– showing me just how beat up, or how good a battery really is. I decided to test my new BioEnno 6AH battery. While I was doing this, a buy one, get one free sale came up on BioEnno 9AH batteries that I could not resist, so I bought a set of 9 AH batteries, based on the promising results from tests on Bioenno’s 6AH battery.
I am very happy with all three of these batteries. Why did I want a Lithium Iron Phosphate battery as opposed to a Lithium Ion battery? All the exploding scooters, and cars are sending messages about the safety of batteries in general, and I would like to sleep at night, not worrying about my POTA station exploding… Further, the Lithium Iron batteries take more charges across their lifespan than Lithium Ions do. They are slightly more expensive up front, but I suspect over the life of the battery the Lithium Iron battery will be cheaper, and safer. Here is an interesting article on the difference between the two types of batteries.
What is a dynamic load:
In this case my dynamic load is used as a device that will present a variable resistance load to a battery, in such a way as to keep the current draw the same across any voltage change as the battery is discharged. The Dynamic Load came from AliExpress, and is actually a fairly decent piece of equipment. I have a friend who used to design power supplies for HP, (HP holds three of his patents based on his designs of switchers), he knows far more than I do about power supply design and testing, and he bought one of these as well, so I am confident the unit is useful.
Battery Life, and how to test:
There are a many ways to test a battery, one can just drain it until there is nothing left, one can drain it until it reaches some preset voltage, (maybe the lowest voltage your radio works at, probably damaging your battery in the process), or one can be responsible, and test the battery in a way so as to not damage it. I set about understanding the Lithium Iron Phosphate chemistry, and how to handle it by reading everything I could find, from textbooks, and the manufacturer of the batteries.
There are a number of articles on how to manage Lithium Iron Phosphate batteries, I liked this one. Suffice to say, what I found was that I do not want to drain my battery to lower than 80% of full charge, I can, but from what I have seen in the literature, I don’t want to go below 80% of full charge in order to maximize my battery lifespan. For my 12 volt POTA application this means that when I reach the 12.8 volt point, under load, (which most folks consider the 80% mark for a Lithium Iron Phosphate battery), I have reached the 80% discharged point, and need to cease using that battery.
Test Criteria
I set up my new Dynamic Load, for 1 A draw, and 3 amp draw, with a cut off at 12.8 volts, or 20% of full charge. I then proceeded to run each of the batteries to 20% of full charge, graphing the voltage drop vs. time. In a perfect world, if I draw one amp from a 6 AH battery, that is fully charged, it should take 6 hours to totally discharge it. So using 80% as the test mark, I would expect to see the 80% point happen after 4.8 hours, at one amp draw from a 6 AH battery, and 7.2 hours later for a 9 AH battery. Take a look at the curves below:
Bioenno 6AH battery to 80%
Note: Approaching the 80% discharge state at around 5.5 hours. The 20% point should have happened at 4.8 hours, the Bioenno battery lasted almost an hour longer than expected! Click chart to expand.
Bioenno 9AH battery to 80%
Approaching the 80% discharge state at around 8.5 hours. The 20% point should have happened at 7.2 hours, the Bioenno battery lasted just under an hour longer than expected! You can click either of these graphs to see an expanded version…
Heating/Cooling
After reading a bit more I discovered that battery heating can be an issue during charge/discharge. An even heat is classed as good, while having non evenly distributed warm spots can be classed as bad. Why? If one cell is taking more charge than another, then I might end up with unevenly charge cells within the same battery pack, some taking more current than others, and some taking less… Not a good thing I read! I expect to see some warmer areas, as individual cells will tend to warm an area, while the space between them will be cooler, what I don’t want to see is areas where some cells are cooler, while other cells are warmer than each other. I want to see an evenly distributed hot/cold pattern on the pack. I took a calibration image showing the battery during high current discharge, with a warm, (not hot), cup of coffee in the same frame, you can see it in the upper left. While this is not scientific, it does give me an idea of just how warm the battery is relative to something I understand– coffee!
Note the lack of hot/cold spots. This is at the beginning of a high rate charge cycle. The battery looks to be cool, and with no hot/cold areas. This is as I would expect it to be before applying a 3 A discharge rate to it. The FLIR camera will show any warm vs. cool areas on the battery with the warmer areas being lighter in color than the cooler areas.
Note the nicely distributed warm/cool locations across the top of the battery pack. This does not concern me, as I would expect the cell areas to get warm as the cells are charged. What I am not seeing are single cells that are far warmer or far cooler than other single cells. I like seeing that the warm areas, (shown as lighter white across the top of the pack), are evenly distributed, and not unlike each other in temperature. To me, this indicates an even current distribution within the cells in the battery pack. Note in the top image that the warm coffee cup is far whiter, and thus, warmer than the areas on the top of the battery pack being warmed by the charging cells. The battery pack is just barely warm enough to tell by placing my hand on it. The FLIR camera is exquisitely sensitive to temperature changes. I can walk barefooted across my wood floor, and see my footprints for a few moments afterwards using the FLIR camera.
Conclusion
Do I think these battery packs are what they are being sold as, yes, I do! I am very happy with my three Bioenno battery packs, and at some point, I will purchase a larger pack and test it as well.
