Continuous discharge

[Freshblood]

Hi,

Short discharge question . If I place cells in parallel, I increase the Ah but do I also increase the maximum discharge current? For example, 4x4.2V 3000mA 10A (continuous discharge current) cells in parallel. That makes 4.2V 12000mA 40A battery or a 4.2V 12000mA 10A battery?

 

[indianajo]

Each individual cell has a discharge limit. Since all cells are 18650 and nobody will tell us the actual part number or datasheet of the cell they used, this varies around. Another poster has noticed some battery builders are using samsung laptop cells to build bike batteries. Those don't have the high discharge rating of the bike cells. So those batteries are cheap, but not very useful for e-bikes.
But, if you put cells in parallel, then the discharge rating adds up. Theoretically. However, because LiIon batteries act weird when they are in parallel, the BMS has to manage all the stacks to keep them discharging evenly. In that case, you can add up the discharge rate. If you take two LiIon batteries with two different BMS boards, and parallel them, eventually one of them will supply all the load. So in that case the discharge rate of the single battery actually supplying the load rules.
Actually, I've bought two batteries rated at 50 A discharge where only 1 of 14 stacks was working at the BMS board. So 3 A discharge would make the battery voltage collapse to 1/3 the nominal voltage. Got my money back for one of them, the other would work long enough I thought it was the motor overheating until the battery warrenty expired. The acid test that proved I had garbage was a resistor load that tried to draw 3.5 A from the battery, no motor or controller involved.
Your question has some jumbled numbers IMHO. 3000 ma sound reasonable discharge rate for a 4.2 v cell. I don't know where the 10 A came from, unless they are allowing you 4 x 3000 ma in parallel but downrating to 4 x 2500 ma because they know things aren't perfect when paralleling celles. The 50 a batteries I bought had 14 parallel stacks, which is fairly conservative.
If your talking lead-acid batteries, they do parallel with fewer problems than LiIon cells.

 

[Freshblood]

Each individual cell has a discharge limit. Since all cells are 18650 and nobody will tell us the actual part number or datasheet of the cell they used, this varies around. Another poster has noticed some battery builders are using samsung laptop cells to build bike batteries. Those don't have the high discharge rating of the bike cells. So those batteries are cheap, but not very useful for e-bikes.
But, if you put cells in parallel, then the discharge rating adds up. Theoretically. However, because LiIon batteries act weird when they are in parallel, the BMS has to manage all the stacks to keep them discharging evenly. In that case, you can add up the discharge rate. If you take two LiIon batteries with two different BMS boards, and parallel them, eventually one of them will supply all the load. So in that case the discharge rate of the single battery actually supplying the load rules.
Actually, I've bought two batteries rated at 50 A discharge where only 1 of 14 stacks was working at the BMS board. So 3 A discharge would make the battery voltage collapse to 1/3 the nominal voltage. Got my money back for one of them, the other would work long enough I thought it was the motor overheating until the battery warrenty expired. The acid test that proved I had garbage was a resistor load that tried to draw 3.5 A from the battery, no motor or controller involved.
Your question has some jumbled numbers IMHO. 3000 ma sound reasonable discharge rate for a 4.2 v cell. I don't know where the 10 A came from, unless they are allowing you 4 x 3000 ma in parallel but downrating to 4 x 2500 ma because they know things aren't perfect when paralleling celles. The 50 a batteries I bought had 14 parallel stacks, which is fairly conservative.
If your talking lead-acid batteries, they do parallel with fewer problems than LiIon cells.

Hi

Thanks. It is 18650 2250mA cells with high discharge 10A capacity. I built a 13s4p battery and just wanted to confirm if the maximum discharge current is also 4x10A. That means my battery is good to power a 2kw motor. Currently powering a 750W motor.

 

[harryS]

Well, you went from 3000maH cells to 2250 mah.

Let's get the units correct. The measure of capacity for batteries is amp-hours. It would be 3000maH, not 3000ma. An ma is 1/1000 of an amp, so 3000 ma is 3 amps, and 3000 mah is also 3 aH. So 2250 maH is 2.25 AH. Four of them is 10AH, You built a 48V 10AH battery. That's a little battery, as ebikes go. How long can you do 10A per cell?

Your cells can put out 10A for a finite time, which is figured by
2.25 Ah / 10 amps = .225 hour which is about 12 minutes.

The cells will not sustain 4.2 volts at max current. You will have to refer to the datasheet to see what they can do. A quality cell might drop .5 volts. Cheaper ones might drop .8 volts. Voltage sag in a battery is a headache with low quality cells. A cheaper13S pack could drop 13 x .8 or almost 10 volts under a heavy load.

Your max current is also limited by your BMS, if you installed one. If someone was selling a battery like yours, he would probably limit it to 25A on the BMS.

I think you might need like a 8P battery to run a 2000W motor.

 

[Freshblood]

Thanks. The first thread was just as an example and therefore the 3000mA. I then used my own specs of 2250mA cells in the second thread to get more precise data. My battery works great thanks. Gets 40kms on a charge at full tilt and its done 1500kms with it. Got a nice fancy bms as well. .

I just wanted a short answer to whether the max continuous load of 10A per cell is added together when in parallel. Nothing more. 4p makes 40A ??

Currently my motor has a 15A limit and my bms actually has 30A limit. I just asked is this battery could possibly run a 2kw motor in the future. 40A x 54.8V = well over 2kw.

As a side note some of these 18650 cells get like 30A continuous discharge. They are used for vaping. My 10A is perfect for ebike battery.