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Ebike battery help
#1
Hi everyone!! I am making a ebike battery for a 1000w motor. I am making with 18650 recycle of laptop batteries. At full throttle it consumes 26A. My question is, if it is 1,8A per cell a very high current for a 2000mAh recycle 18650. I know that when less current to the cell, more cycles can have, but i dont know if 1,8 is soo much. Apart of that 1,8A is only when i go full trhottle. Only sometimes. At medium throttle was like 0,9-1A per cell. It is a good option? Thank you for reading and sorry for my bad english XD.
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#2
Depends on the cells chemistry and manufactured design.

Some are rated at .5C, others at 2C. If the cell was originally a 2400mAh cell, then it's rating is 2.4A. That would make .5C 1.2A. But, you'd need to consult the cell database to find the ratings of the cells you are using. Then use the lowest ranked one.

Alternatively, you could go LiFePO4's as they can handle higher amps. Or, if you want to stick with recycled cells, use power tool cells as they are designed for high amps discharge as well
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#3
Thank you for answered again. I aprecciate very much.

I have some of this cells:

https://secondlifestorage.com/t-LG-LGABB...ifications

It says standar current: 500mA. What means "STANDAR", And below says "MAXIMUN" 5000mA

So... Can i use the cell for a bit more of 1A. Im a bit confuse.

Thankyou and sorry for my ignorance!
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#4
Standard is the rate that is used to specify the cell. This is usually a small figure because it's used to determine the capacity that is then stated in the specification. And the manufacturer wants this to be as high as possible obviously.
Maximum is the highest continuous rate that the cell has been designed for. It will have lower capacity and will get warm but it can do it in a way that is still worthwhile and won't damage the cell so it can be repeated. It will lead to increased wear though, so while it can be repeated it will shorten its lifespan.

But these figures are only true for new cells. If they have been used then these figures aren't valid anymore, that's why you have to test it. Using reclaimed laptop cells is already a bad start for an ebike battery because they are always low power high capacity cells. What you want is more like power tool cells with high power and low capacity. Or at lest something in between.

Also, 26A divided by 1.8A isn't an even cell number. It's close to 14.5, so either 14p or 15p. Assuming the cells can't do it then you might even have to double it, at 48V (I guess it's a 48V motor) this means 14s30p = 420 cells. That's almost 20kg of raw cells without any connections or case. It might become a bit large and heavy for an ebike battery, don't you think? With 2000mAh cells it will be over 3kWh.
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#5
Yes, i was thinking to make a 15-16p battery. I understan all that you said but i dont understand why you said to put doble battery pack 30p. I suposse that with 30p was more good for the cells but i dont know...

I repeat that only was 26A when 100% thottle, and in the most time i go with 16A (low speed mode). And that its like 1A per cell. 

Thank you for answer my
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#6
30p was just an example. You could end up in this area though with used cells that sometimes are barely able to do 1A at decent capacity and energy.
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#7
1 year ago i make a battery only to test the motor kit. I make a 13s6p battery from recycle 18650 with an average of 1700mAh. (yes i know is a very bad battery kit with many fire risk and fails) but was ONLY to test the kit. In the 26A mode, the voltaje drops a lot of and the controller cutoff the motor power. But with the 16A mode was very nice. The voltage doesnt ddrop a lot of and it was pretty well (in plain, no slopes). This ebike was for only having fun, no for any transport. But i want to be SAFE
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#8
Well, this isn't about safe or unsafe. This is about a properly working bike or an unreliable bike. If you want to use reclaimed cells and calculated the battery sizing in such a way that you need 1.8A per cell then test the cells at 2A.
Headrc likes this post
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#9
(01-20-2019, 10:40 PM)DarkRaven Wrote: Well, this isn't about safe or unsafe. This is about a properly working bike or an unreliable bike. If you want to use reclaimed cells and calculated the battery sizing in such a way that you need 1.8A per cell then test the cells at 2A.

Okey. But even if it 1,8 was a safe battery. With 4A fuses per cell. Thank you
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#10
It sounds like you want to draw 26A from a 6P pack. That peak draw will be roughly 4.3A per cell. There are 2000-mAh cells that are made for high discharge, and there are also some 2000-mAh cells that are made for low cost. Laptop cells are the low cost version, and they will get hot at 4.3A

I understand your desire to save money by using cells that are available at very low prices, but I recommend that you focus on cordless tool cells, which are made for high current. If there is no room in your budget for cordless tool cells, you would need to use a much larger pack of laptop cells.

At 13S, a 6P pack is 78 cells, and that might be a large pack to try and fit it into your bicycle frame. This is why you should use cordless tool batteries, even if it costs more. You can get very high power form a 5P pack, and the cells will not get hot.
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