Version 4 of the diyBMS
Do it yourself battery management system for Lithium ion battery packs/cells
If you are looking for version 3 of this project take a look here https://github.com/stuartpittaway/diyBMS
Videos on how to use and build
This is a DIY product/solution so don’t use this for safety critical systems or in any situation where there could be a risk to life.
There is no warranty, it may not work as expected or at all.
The use of this project is done so entirely at your own risk. It may involve electrical voltages which could kill - if in doubt, seek help.
The use of this project may not be compliant with local laws or regulations - if in doubt, seek help.
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A DIY Powerwall is the DIY construction of a pack of battery cells to create an energy store which can be used via inverters to power electrical items in the home. Generally cells are salvaged/second hand, and typically use Lithium 18650 cells.
Lithium batteries need to be kept at the same voltage level across a parallel pack. This is done by balancing each cell in the pack to raise or lower its voltage to match the others.
Existing balancing solutions are available in the market place, but at a relatively high cost compared to the cost of the battery bank, so this project is to design a low-cost, simple featured BMS/balancer.
- Build upon my existing skill set and knowledge.
- Building something that others can contribute to using regular standard libraries and off the shelf components.
- Build something that is inheriently safe
- Use platform.io to manage code and libraries
- Use Arduino based libraries and tools
- Put everything on GITHUB
- Document it (always gets left to the end!)
How it works
Controller provides human interface over Wifi/Web and also integrates with other systems like MQTT, emonCMS and Grafana.
Controller is esp8266-12e (NodeMCU v1) - although could be upgraded to ESP32 if really needed.
Controller should be able to take action on alerts/events to shut down inverters/chargers/fuses.
Each cell in a battery pack has a monitoring module. This uses AVR ATTINY841 linked together by optoisolated serial ports for communication.
- internal temperature monitoring
- external temperature monitoring
- Spare input/output for 3rd party use
- autonomous cell voltage balancing - it should still work even if controller is down
How as v4 improved over v3?
- Code is better!
- Controller provides outputs for integration with relay boards and switch gear
- Rules to control relay outputs
- Cell modules use ATTINY841 chip which provides more pins and lower power usage
- Removal of 3.3v regulator and ADUM chips lowers current usage significantly
- v3 module uses 10-12mA current constantly and v4 uses <1mA
- Dual temperature monitoring board + cells