Creating a 36v Ebike Battery with 18650 Cells: Understanding Amp Output

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Discussion Overview

The discussion revolves around the creation of a 36v e-bike battery using 18650 cells, focusing on understanding the amp output capabilities of the battery in relation to the load it will support, particularly a 500w motor. Participants explore the relationship between battery specifications, load requirements, and safety considerations in battery assembly.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on whether the amp output of the battery is determined by the battery's specifications or by the demands of the connected electronics, specifically a 500w motor.
  • Another participant notes that 18650 cells typically have a maximum discharge of 2-3 A.
  • A different participant explains that the amperage a battery can supply is based on its specifications, but the actual consumption depends on the load. They provide an example illustrating how drawing more current than the battery's rated capacity can reduce its effective amp-hour capacity.
  • A participant inquires about the potential output of a configuration using 40 18650 cells arranged in 4 parallel groups and 10 in series.
  • Another participant asks for guidance on obtaining and wiring a balance charging circuit board for their specific battery configuration.
  • One participant emphasizes the dangers of undertaking such a project without sufficient knowledge of electronics, warning about the risks of fire and recommending further education before proceeding.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and concern regarding the safety and technical aspects of building the battery. There is no consensus on the best approach or the safety of proceeding with the project as discussed.

Contextual Notes

The discussion includes assumptions about the capabilities of 18650 cells and the implications of load demands on battery performance. There are unresolved questions about specific wiring and safety practices for the proposed battery configuration.

Who May Find This Useful

This discussion may be of interest to individuals looking to build their own e-bike batteries, those studying battery technology, or anyone interested in the practical applications of 18650 cells in electronics.

needhelp194
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so i want to make a ebike battery out of 18650 cells, I've done all the research about series and parallel and balance charging but what is still unknown to me is i know i want 36v coming out of the battery and i don't know how to find the amps that the battery is capable of putting out, is the amps based off of the battery or how much the electronics it is wired to PULL from it. (so does the amps depend on the battery or how many amps the electronic, my motor 500w 36v, needs.
 
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Specs. on "18650" read 2-3 A max. discharge.
 
The amperage the batteries are CAPABLE of supplying at the output voltage is one specification. The load may or may not CONSUME all that current capability at the operating voltage.

So, if the batteries are CAPABLE of supplying 10amps at 36Volts, and the load only CONSUMES 8 amps at 36V, then the batteries will simply provide the 8amps that the load consumes. But, if the load needs 15A at 36V, then the batteries are under-rated for the load and something needs to give.

The Ampere-Hour rating of a battery is specified/measured at a specific load current. Drawing more current than that load will result in an actual lower Ah capacity (not just a shorter battery life)

For example, a 2400mAh 18650 is rated at 240ma. It will lose half its capacity if you discharge at 4A. It becomes a 1200mAh battery. That is in addition to the fact that it discharges faster because you are drawing higher amperage. Again, this is a actual reduction in Ah capacity,

Here is a curve from http://www.candlepowerforums.com/vb/showthread.php?84980-2400mAh-LG-18650-cell-discharge-graph

18650_2400mAh.jpg
 
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so if i get 40 18650 cells in 4 paralleled and 10 serial how many amps is that capable of pushing out.
 
and also a lot of people have a balance charging circuit board of some sort. where can i get one. and how do i wire it for my 36v, 4 paralleled, 10 serial 18640 cell battery pack
 
keep in mind i have a 500w esc and motor 36v
 
Wow. It is just too dangerous for us to encourage you to do this project with so little education in electronics. Best case you end up with a system that doesn't work very well. Worst case you start a fire that hurts you or somebody else. (Do not ask me how I know about fires in battery powered systems...)

This thread is closed. Please take a basic electronics class (in person or online), and learn the basics so you don't need to rely on Internet advice that you don't understand. Please be safe and smart.
 
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