Li-Ion battery capacity meter: Difference between revisions

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Power supply:
Power supply:
analogRead(INTERNAL2V56) should do the trick as reference to get a stable voltage reading.
analogRead(INTERNAL2V56) 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.
If not a calibrated external power supply may need to be added to the project. ([http://www.skillbank.co.uk/arduino/measure.htm])


FET:
FET:

Revision as of 20:36, 27 February 2017

Li-Ion (18650) battery capacity meter
Heapof18650cellsnew.png
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

Heapof18650cellsnew.png {{#if:No | [[Tool Owner::{{{ProjectParticipants}}} | }} {{#if:No | [[Tool Cost::{{{Cost}}} | }}

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(INTERNAL2V56) 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. ([1])

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.

Liion checker raw.jpg IMG 20170227 184502.jpg

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