| Li-Ion (18650) battery capacity meter | |
|---|---|
 | |
| Participants | |
| Skills | 1337 Skillz, Arduino, Coding, Hackery |
| Status | Planning |
| Niche | Hardware |
| Purpose | Infra |
| Tool | No |
| Location | |
| Cost | |
| Tool category | Electronics |
Li-Ion (18650) battery capacity meter
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As of many hackerspaces we rescue 18650 cells from old laptop batteries and other sources
We do have a charger but no good way of testing the capacity of each cell before it goes into the parts pile
Making a capacity tester would solve this. One could buy a chinese unit from fleabay but where is the fun in that? :)
Component considerations:
Controller: Choosing the Arduino Pro Mini for this project, because it is small, cheap and easy to use, and I have several in my partsbin that need using.
Power supply: analogRead(INTERNAL) should do the trick as reference to get a stable voltage reading. If not a calibrated external power supply may need to be added to the project. (Precise voltage measurement with the Arduino board) (Arduino analogRead pitfalls)
FET: Using Dave Jones (EEVBlog) DC constant current load as reference, I have selected the IRL540 logic level FET. The advantage of this FET is that at 5V the Gate will be completely driven open, whereas normal FET's require higher gate voltages to be driven open completely. I could have chosen other ones but this one seems easily available and the specifications meet my requirements.
Resistor: Given that the max power the resistor will dissipate is 2.1 Watt (4.2 Volt at 500mA discharge current) 10 10Ω 1/2 Watt resistors should do the trick which make up a 1Ω 5W resistor. There is enough overhead might a discharge of 1A be chosen later which will be 4.2W tops.
Using a relay for switching the load on and off. Could have used a high level switching FET but a relay is easier and has less resistance, and less hassle.
partlist:
- Arduino pro mini - Display - Button - TP4056 module - 18650 battery holder - 5v relay - DC current load \ - Logic level N chan mosfet - lm385 opamp - 50k 10 turn pot - 1 Ohm 5 Watt resistorrrr