18650 for 48v ebike - what amps per cell needed?

Rocky1198

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Hello,
This is my first post here. New to ebikes. I'm a total beginner.

I am wanting to build a 48v battery pack for a 1000watt ebike kit from 18650s
I would like to have a range of at least 20 miles. My riding style is casual pavement use only.
I'm not sure yet how many will be in parallel and how many in series. But I'm thinking around 60 cells total.

But I'm pretty sure each battery must be able to carry a certain amount of amps current and I'm wonder what that minimum per cell would be or how to calculate it so that I can buy cells that are adequate. I was under the impression that if I use 3A cells, once in parallel the amperage of the pack will increase so if I use 5 of the 3A cells I would get the 15A that I need? Or does each cell need to be a 15A cell? I'm just not sure how it works yet.

I found this in the Battery Building information section and so I think it means that I should get batteries capable of delivering 15A ?

For high amps and good range, I like the 30Q which provides 3000-mAh, and 15A. If you want 20A per cell, check out the Sony VTC6, LG HG2, and Samsung 25R
If your pack is big enough that you don’t need the high amps of the 30Q, you can get more range by choosing one of the popular 10A cells, which are generally rated at around 3400-mAh

Also, how much can I expect a 48v pack to cost all total?
I will do a lot more research and learn more before I begin.
Thanks for any advice
 

Mike Ellis

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The following remarks are just basic engineering. Other folks on this forum can add much more nuance and experience....

1. Other things being equal, range depends on the amount of energy your battery pack can provide. To a first order, that's volts times ampere-hours. A reasonable estimate for typical energy consumption is 10 to 20 Wh per mile depending on speed and the pedaling effort you put in. Taking the higher number and using 50V as an average working voltage gives 20Wh/mile * 20 miles / 50 = 400/50 = 8Ah, so you'll probably want 3 cells in parallel. The 30Q's you mention would give 9Ah capacity and the 10A's would give 3*3.4 = 10.2Ah

2. The current rating is important for power, e.g. how fast will you be able to climb a very steep hill. Getting the full 1000W from your motor at 50V will require 20 A from the battery pack. With 3 cells in parallel, that's 6.67 A / cell. So the 10A's might be just fine.

Hope this is useful.
 

Hoggdoc

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Hello,
This is my first post here. New to ebikes. I'm a total beginner.

I am wanting to build a 48v battery pack for a 1000watt ebike kit from 18650s
I would like to have a range of at least 20 miles. My riding style is casual pavement use only.
I'm not sure yet how many will be in parallel and how many in series. But I'm thinking around 60 cells total.

But I'm pretty sure each battery must be able to carry a certain amount of amps current and I'm wonder what that minimum per cell would be or how to calculate it so that I can buy cells that are adequate. I was under the impression that if I use 3A cells, once in parallel the amperage of the pack will increase so if I use 5 of the 3A cells I would get the 15A that I need? Or does each cell need to be a 15A cell? I'm just not sure how it works yet.

I found this in the Battery Building information section and so I think it means that I should get batteries capable of delivering 15A ?



Also, how much can I expect a 48v pack to cost all total?
I will do a lot more research and learn more before I begin.
Thanks for any advice
Rocky the really simple answer is the more the better. My battery uses genuine Samsung 18650 cells 35E. See attached spec sheet.

My pack consists of 13 cells in series (13x4.2v) yields full charge of 54.6 volts. These series are strapped in Parallel 5 times giving 40 Amps maximum output. But remember the BMS circuits limit the current output as well so it is critical to choose a BMS that matches you battery pack.

Then you have to factor in the motor controller and it's specs. It has to match or exceed the maximum voltage and amps your battery can provide if you want maximum performance. Also you need to factor in your motors capacity to use the volts and amps the system can provide. Generally a quality brushless motor can handle much more than its rating for short periods of time, then heat becomes your enemy.

In my case my hub motor is rated at 750 watts continuous but my battery system (cells, BMS and controller) put out maximum 1200 watts. I have seen no heating problems thus far with this combo.

Then you need to consider the overall weight of your ebike and rider and the type of riding you will be doing. Flat paved roads requires far less power than hilly rough roads.

Like I said the more the better, over taxing your power train could and most likely will end poorly. My system yields me about 30 miles of combined hills/flat using pedal assist and throttle about equally. My bike weighs in a 72 lbs and I weigh about 200 lbs.

Hope this gives you some real world number to work with.

Just for the record I wouldn't want any less battery or power for my type of riding in my area. If I had it to do over I would get a bike with similar power but having a mid-drive motor
 

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