You have 4 lipo batteries. They are wires 2 pairs of two each are wired in series and the resulting two batteries are wired in parallel. Isn't his considered a 2S or 4S battery?
Thank you for the reply. That raises another question however: How do I wire it up for balance charging? It seems to me that would be effected. Every cell is supposed to be charged in parallel but you can't do that now since each cell is actually 2 cells. But without putting it on paper, in my head it seems like it creates a cross-wiring issue if you try to wire all 4 cells in series-parallel and in parallel for discharge and balance charging. Can you split the two series stacks and wire them to charge as 2 separate 2S batteries?That is called 2S2P, which should give about 7.4V at twice the capacity of a single cell. That is, two, 2S in parallel.
Admittedly, my tech depth on balance charging needs polishing. But I seen a diagram of how Lipo batteries were wired for balance charging. The best way I can describe the the diagram is thet each battery shared positive lead but each had their own ground lead. And I know for fact that other 2S and above lipo batteries, specifically used for RC devices, do have a discharge lead and a balance lead. The balance lead for a 2S is 3 wires, a 3S is 4, etc etc. Which fits the idea that each one shares one lead with an individual ground. So I believe it is not only possible but is necessary for these type of lipo batteries in order to ensure that each battery charges equally to prevent one cell reaching full charge before another and becoming damaged from overcharging as it will still receive a charge current waiting on the other cell or cells to reach full charge.Balancing parallel cells is a problem. Being parallel means that the voltage for each cell is the same. Check here: https://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations
Scan down to Parallel Connection. Note the comment that balancing is less important in parallel-connected cells.
Balancers are made for series-connected cells. If you want to balance individual cells in parallel, you must disconnect them from each other at one end. I would just treat the pack as a 2S pack. That is, the cells in parallel would be treated as a single cell.
As for splitting cell packs, sure that can be done. But is it worth the effort? You will eventually be putting them back parallel, presumably without using any protective device between them, like a resistor.
Hm. Thank you for that information, sir. Appreciate it!Just as a thought experiment. Let's assume you have 2 cells in parallel, but you disconnect at one end (doesn't matter which end) and charge balance them to +/- 20 mV. They could be 40 mV different. You then connect them in parallel using connections, say 2 mohm (which may be high). Now, you connect them in parallel. E=IR (Ohm's law). 40 mV/2 mohm = 20 A! Of course, a better connection would give even more current. They would quickly reach some state of charge that gives the same voltage for each cell.
That is why I suggested that balancing "good" cells that are to be connected in parallel is worthless. Now, if one cell is shorted, of course, you will detect that while charging individually, but I suspect you will also detect it when charged in parallel too. Battery University discusses that scenario (I think).
Outstanding. Thank uou very much, sir! You've been very helpful!No, even simpler and use a 2S balanced charger
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Whoop. Pump the brakes. Something has to be in series to get the voltage right. If everything is in parallel I end up with a 3.7 volts and 20,000mAh. I was targeting 7.4 voltd 10,000 mAh so I didn't have to constantly be boosting the voltage when using it. I'm not even sure my module can boost from 3.7 to 12V now. That T I think about it.No, even simpler and use a 2S balanced charger
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This is exactly what happened to one of the battery packs in my MIL's oxygen generator. A 4S4P setup was allowed to rest at a low voltage resulting in a few failed cells. Those failed cells dragged other cells down. In the end I disassembled the pack and removed all the batteries. Charging them individually I found four out of the 16 that were charged to 4.2 volts and in four months have not dropped below 4.12 volts. Those are the ONLY four batteries I'd consider reusing - but ONLY in a single cell configuration such as an LED flash light. JP suggests balancing "good" cells for a good reason. One bad cell in parallel with one good cell can harm the good one by dropping its voltage below 2 volts. At which point the battery starts undergoing chemical changes that lead to internal shorts. And those shorts can cause fires.That is why I suggested that balancing "good" cells that are to be connected in parallel • • • if one cell is shorted, of course, you will detect that while charging individually, but I suspect you will also detect it when charged in parallel too.
I usually use recycled cells in my projects. With a little care they can be a very inexpensive source of power.I'm new to Li-Ion batteries myself, so I'm learning a lot too. The biggest lesson I've taken to heart is to recycle cells that show any signs of failure. Even then I might still find it risky to reuse old cells.
Charge and discharge characteristics of Li-polymer are identical to other Li-ion systems and do not require a dedicated charger. Safety issues are also similar in that protection circuits are needed. Gas buildup during charge can cause some prismatic and pouch cells to swell, and equipment manufacturers must make allowances for expansion. Li-polymer in a foil package may be less durable than Li-ion in the cylindrical package.
by Duane Benson
by Jake Hertz
by Jake Hertz
by Jake Hertz