3500-mAh NCA cell, Samsung, LG, Sanyo, Panasonic
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smeagol222
100 W
I think thats his youtube trademark thing hehe
Sorry I'm learning all this - can you explain how Amps are divided when bulk charging vs balance charging (full pack) vs single cell charging
As an example using MJ1 cells (0.2C standard charge = 1.7A per cell, max charge 1C = 3.4A per cell)
Example pack 72v 20s10p
Going by the number for this packs discharge (10A per cell in 10p config = 100A discharge)
Can I use this same calculation for expected max charge and standard charge settings?
ie. standard charge 10x 1.7A = 17amps max charge 10x 3.4A = 34amps
This math seems pretty off, but surely 10 cells in parallel the amps that are applied to charge get split between the cells?
Sorry I'm learning all this - can you explain how Amps are divided when bulk charging vs balance charging (full pack) vs single cell charging
As an example using MJ1 cells (0.2C standard charge = 1.7A per cell, max charge 1C = 3.4A per cell)
Example pack 72v 20s10p
Going by the number for this packs discharge (10A per cell in 10p config = 100A discharge)
Can I use this same calculation for expected max charge and standard charge settings?
ie. standard charge 10x 1.7A = 17amps max charge 10x 3.4A = 34amps
This math seems pretty off, but surely 10 cells in parallel the amps that are applied to charge get split between the cells?
cycborg
1 kW
If it's a 3400 mAh cell, then 0.2 C is 0.68 A, not 1.7 A. But yes, then you multiply by the number of cells in parallel to get the pack charge of 6.8A.smeagol222 said:
Bulk charging and balance charging are the same, except for balancing you hold the pack at balancing voltage so the BMS can bleed the high groups. As for single-cell charging, you can't charge the cells individually but you can charge the parallel groups individually; the current limits are the same as for the whole pack, but obviously the voltage would be in the single-cell range.
smeagol222
100 W
Sorry I made a mistake - not sure where I got 0.2C from its meant to be 0.5C
the cell nominal is 3500mah, minimum is 3400mah. They seem to use this minimum number to come up with the below from the PDF
https://www.nkon.nl/sk/k/Specification%20INR18650MJ1%2022.08.2014.pdf
just looking at this spec document, on page 4 it says "standard charge current 0.5C (1700mA)" and "max charge current 1.0 C (3400mA)"
I thought to get the charge amps you just mulitply the C rating by the mAh?
0.5C x 3400mAh = 1700mA or 1.7A standard charge rate
1C x 3400mAh = 3400mA or 3.4A max charge rate
so the 20s10p pack max charge 1C pack to 100% 4.2v per cell is 84v at 34amps?
standard charge rate 0.5C pack to 100% 4.2v per cell is 84v at 17amps?
That seems like a lot of amps to charge at, I guess I'm still calculating it wrong. Either way I suppose it doesn't matter since my multi charger only does max 5A anyways
which would mean 0.5A per cell in a 10p pack
After all that my practical use is the modular battery I'm building. Four 18v 5s10p packs that get plugged together in series when under load to make 72v pack. These don't have a bms but use four CellLogs with alarms. I plan to bulk charge most of the time all four in series, but when I need to balance the plan is to connect them in parallel and use a balance charger and JST parallel harness all 4 of them in 5S
let me know if this sounds right, I don't fancy blowing myself to smithereens
the cell nominal is 3500mah, minimum is 3400mah. They seem to use this minimum number to come up with the below from the PDF
https://www.nkon.nl/sk/k/Specification%20INR18650MJ1%2022.08.2014.pdf
just looking at this spec document, on page 4 it says "standard charge current 0.5C (1700mA)" and "max charge current 1.0 C (3400mA)"
I thought to get the charge amps you just mulitply the C rating by the mAh?
0.5C x 3400mAh = 1700mA or 1.7A standard charge rate
1C x 3400mAh = 3400mA or 3.4A max charge rate
so the 20s10p pack max charge 1C pack to 100% 4.2v per cell is 84v at 34amps?
standard charge rate 0.5C pack to 100% 4.2v per cell is 84v at 17amps?
That seems like a lot of amps to charge at, I guess I'm still calculating it wrong. Either way I suppose it doesn't matter since my multi charger only does max 5A anyways
which would mean 0.5A per cell in a 10p pack
After all that my practical use is the modular battery I'm building. Four 18v 5s10p packs that get plugged together in series when under load to make 72v pack. These don't have a bms but use four CellLogs with alarms. I plan to bulk charge most of the time all four in series, but when I need to balance the plan is to connect them in parallel and use a balance charger and JST parallel harness all 4 of them in 5S
let me know if this sounds right, I don't fancy blowing myself to smithereens
cycborg
1 kW
This is correct.smeagol222 said:
5 A is definitely a safe charge rate (0.15 C). I guess the manufacturer specs are what they are, but 0.5 C standard and 1.0 C quick charge sounds like a recipe for short battery life to me. But that's what we're talking about - usable cycles, not "smithereens".
Charging strategy sounds fine except that when you parallel them for balance charging, keep in mind that the reason for doing this is that they're out of balance, meaning that the cell groups you're paralleling won't be at the same voltage. That means that when you connect them, charge will flow through the balance wires until they do reach the same voltage. This may not be a problem if they're close, but if not you could get sparks, heating, vaporized wires, etc. Safest thing would be to balance charge the modules separately. An alternative would be to connect them through resistors to keep the current to a manageable level until they equalize, then remove the resistors and connect them directly.
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