Electronics > Beginners
Effect of switching current on Li-ion battery packs
VEGETA:
--- Quote from: BravoV on February 08, 2020, 08:08:50 pm ---
--- Quote from: VEGETA on February 08, 2020, 07:49:14 pm ---Well, at 15A max we got 7.5A per cell which is doable even for Chinese 18650 batteries.. which is my aim. To be able to use this thing with any battery.
--- End quote ---
:palm:
Seriously ? Especially using those "firey" brand 18650 cells like SureFire, MustFire and etc. :scared:
--- End quote ---
we don't have these brands that you mentioned but rather other brands that performs good. They are cheap and good, not good as panasonic that is.
I am working on implementing protection and charging circuitry to make sure even the unprotected cells can work without problems. Now the performance is another story since it depends on the batteries but my point is that the device should work with any battery. It is the user's fault for getting a cheap battery that lasts for a short time.
ogden:
--- Quote from: VEGETA on February 08, 2020, 07:49:14 pm ---So the question is: should I use 2S2P or 4P? since they are using same current per cell (~7A) -> at maximum ever state.
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This part was already answered:
--- Quote from: GeorgeOfTheJungle on February 08, 2020, 06:12:37 pm ---In general the rule (for 18650s) has always been more current (max A) => less capacity (Ah/Wh), and in this sense 4S is better than 2S2P, and 2S2P better than 4P, because 4S lets you get the same watts with less amps.
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For DC-DC converter also it is better to minimize input current because you minimize losses in the switches, rectifiers and inductors.
VEGETA:
--- Quote ---This part was already answered:
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I get it but it is as this:
2S2P: max current from battery is ~15 amps but per cell battery is about 7A.
4S1P: max current from battery is ~7 amps which is the same as per cell.
What you mean is 15 amps of total current is worse since more current means more heat... thus per cell current is not the lone factor?
--- Quote ---For DC-DC converter also it is better to minimize input current because you minimize losses in the switches, rectifiers and inductors.
--- End quote ---
this makes sense. I wonder if adding bigger caps will enhance the system... but without hindering the speed. I remember once I tried to add an inductor after the battery (not the 50nH wire one) but circuit didn't work.
Concluding from all this that 4S is the correct choice here with making sure enough capacitors directly after the battery. Correct?
ogden:
--- Quote from: VEGETA on February 08, 2020, 09:17:36 pm ---I wonder if adding bigger caps will enhance the system... but without hindering the speed.
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Sooner or later you get diminishing returns. You balance caps for ripple_voltage vs cost/size.
VEGETA:
--- Quote from: ogden on February 08, 2020, 09:34:46 pm ---
--- Quote from: VEGETA on February 08, 2020, 09:17:36 pm ---I wonder if adding bigger caps will enhance the system... but without hindering the speed.
--- End quote ---
Sooner or later you get diminishing returns. You balance caps for ripple_voltage vs cost/size.
--- End quote ---
I've modified the simulation a bit to consolidate some parts and so on... I also made ESR for each passive part as much as I could. Kindly see it.
Is this ripple good enough?
Also, see the very first +40A overshoot thing... I couldn't fix it even by putting 4.7u inductor.
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