This is my fork of Stuart Pittaway's excellent diyBMS..
Principle differences between this fork and the main line are :-
- Addition of controller pcb containing
- ESP8266 processor ( Wemos D1 mini)
- Power supply derived from battery voltage
- Current, power and voltage measurement based on INA226
- Relay control to switch charger and inverter on/off
- Smoke alarm input.
- Addition of inverter controller pcb containing
- ESP8266 processor
- Filter circuit to turn PWM signal to a DC control
- Controller reports status via MQTT to NodeRed, EmonCMS etc.
- Both controllers receive commands from NodeRed via MQTT to set charging current, inverter power output, and inverter/charger relays.
- Several of Colin Hickey's enhancements.
I have a pre existing 4kW solar installation for which I receive a Feed In Tariff (FIT) for producing solar power. I get paid the same regardless of whether the energy is exported to the grid, or I use it myself. So the most cost effective course of action is to store excess solar energy in a battery using an AC coupled power supply, and then to feed the energy back in the evening using a grid tied inverter powered by the battery. This will be beneficial to the grid as a whole since it will reduce demand during the peak evening 'spike'.
My Powerwall layout consists of a 9S 44P battery with a nominal voltage of 33V. The battery is charged from the mains using a 24V 600W power supply via a 900W rated boost converter model BST900 manufactured by Ming He and easily available on eBay. The boost converter operates as a constant current/ constant voltage source. The output voltage and maximum current are both set using push buttons on the BST900. Alternate firmware is available for the BST900 to control it via a serial interface. See BST900 alternate firmware. In my system Node Red is used in conjunction with OpenEnergyMonitor to measure solar power production as well as electrical load to calculate how much excess solar energy is available to feed into the storage battery. NodeRed communicates the figure via MQTT protocol to the diyBMS controller which then controls the BST900 boost converter over the serial interface.
A solid state relay connected to the AC input of the 24V PSU allows the diyBMS controller to shut down the PSU when it is not required, or in the event of an error.
I am using a SUN-1000GTIL2-LCD grid tied inverter which produces up to 1000W of AC power. This inverter has a socket to attach a current sense transformer to modulate its output power. When the current sense transformer is attached to the grid inlet, the inverter will modulate its power to minimise power imported from the grid. In my situation this is not convenient because the grid inlet is too far away. Instead I have taken advantage of a hidden feature of the inverter to modulate the power using a digital potentiometer. On opening the inverter it will be seen that there is an unused white plastic 2 pin header.If the plug leading to the socket for the external current sense transformer is moved to this header, then by applying a suitable voltage between the pins of the socket, the inverter output can be modulated. Initially I tried using a digital potentiometer managed by the ESP8266 controller to set the inverter power output, but this was unsatisfactory because the inverters Ground was floating relative to chassis ground, and there was a potential difference to the ground reference of the charger circuit. So instead I use a separate ESP8266 processor to produce a PWM output voltage to the inverter. This ESP8266 is wifi connected to Node-Red and sets the inverter power as requested. A small modification is required to the inverter to break out 3.3V power supply for the ESP8266 processor
Stuart Pittaway's original README follows:-
Do it yourself battery management system to Lithium ion battery packs/cells
More discussion https://community.openenergymonitor.org/t/diy-lithium-battery-balancer-and-monitoring-bms/5594/10
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.
A large number of people have utilised the commercial BATRIUM BMS system in their powerwall devices.
UK based, with existing solar panel installation and “feed in tariff” - this is a grid tied install. I do not want to change/interfere with the existing installation as I get the maximum FIT rates for the next 20 years!
I may also install additional solar panels to a separate inverter in the future.
Therefore, I am looking at an “AC coupled” solution where excess electric generation is diverted to store in a battery rather than exported to grid. This energy is then released at night (or at peak costs) to reduce cost of importing energy.
I am NOT looking to go off-grid (or islanding) as UK power cuts are a rare event in my area.
Through the monitoring of my home electric usage using the emonTX and emonSD solutions I typically use around 9kW/H per day (excluding electric car charging). Apart from odd spikes, load it generally less than 500W for the majority of the day/night.
Install a DIY powerwall with the ability to supply a 1000W load to cover all regular home usage (excluding spikes which the grid will handle). A grid tied inverter would be required to convert the battery DC into mains level AC. A controllable charger would be required to charge the battery during the day (or at cheap energy times from the grid). Ideally the charger should be able to match the generation of export from the solar array(s) to prevent import. It may be possible to combine both charger and inverter into a single unit (so called hybrid units)
For obvious reasons, safety is critical, so care must be taken to ensure components are installed and certified as needed, along with the correct specification for cables, breakers and fuses etc.
Why am I doing this? For fun :slight_smile: I really must get out more!
I’m working to the the following design parameters, which are taken from research into the area (what most others are doing!)
Assumption that second hand 18650 cells are made into “packs” containing tens or hundreds of cells in parallel. Voltage of 18650 cell between 3.0V (empty) and 4.2V (full) 48V DC battery pack - running 14 packs/cells in series (aka 14S) this gives between 42V and 58.8V DC Battery expected to output (1000W) so produce up to 25A current (depending on battery voltage) Charger and inverter would be commercial products (not DIY) to comply with necessary approvals BMS Design Building upon my existing skill set and knowledge, and also building something that others can contribute to using regular standard libraries and off the shelf components.
- Design a hub and spoke arrangement, for a central controller and individual cell monitoring nodes on each pack (so 14 in my case)
- Use Arduino based libraries and tools (possible move to platform.io) **
- Use esp8266-12e as the controller - to take advantage of built in WIFI for monitoring/alerting and CPU/RAM performance
- Use AVR ATTINY85 for each node
- Ensure each cell voltage is isolated from other cells and that ground voltage is isolated
- Isolated communications between controller and node is needed
- Put everything on GITHUB
- Document it!
** There are better more capable CPUs than the 8-bit Arduino however they lack user friendliness and the community to support and nuture the development of code
Typical bill of materials for each cell module, costs and part numbers provided from Farnell (UK) so other suppliers may be able to provide better costs or similar products. The ADUM1250 unit is particularly expensive from Farnell and can be purchased for less than 1 USD if you shop around. Excluding the ADUM1250 chip the component cost is around £5.50 GBP.
| Quantity | Board Marking | Farnel (cost per single unit) | Make Model | Farnell URL |
|---|---|---|---|---|
| 1 | ATTINY85V-10SU SOIC-8 | 0.887 | ATTINY85V-10SU | http://uk.farnell.com/atmel/attiny85v-10su/mcu-8bit-attiny-10mhz-soic-8/dp/1455166 |
| 1 | REG710NA-3.3 | 1.20 | REG710NA-3.3/250 | http://uk.farnell.com/texas-instruments/reg710na-3-3-250/charge-pump-regulator-buck-boost/dp/1535743 |
| 1 | ADUM1250ARZ SOIC-8 | 4.51 | Analog Devices ADUM1250ARZ | http://uk.farnell.com/analog-devices/adum1250arz-rl7/digital-isolator-4-ch-1mbps-nsoic/dp/2758723 |
| 1 | M1 SI2312BDS-T1-E3 MOSFET Transistor, N Channel, 3.9 A, 20 V, 0.025 ohm, 4.5 V, 850 mV | 0.241 | VISHAY SI2312BDS-T1-E3 | http://uk.farnell.com/vishay/si2312bds-t1-e3/mosfet-n-ch-20v-3-9a-sot-23-3/dp/2396085 |
| 1 | D1 SE30AFG-M3/6A Standard Recovery Diode, 400 V, 3 A, Single, 1.1 V, 1.5 µs, 40 A | 0.306 | VISHAY SE30AFG-M3/6A | http://uk.farnell.com/vishay/se30afg-m3-6a/rectifier-esd-400v-3a-do-221ac/dp/2313878 |
| 1 | F1 MC36228 PPTC Resettable Fuse, 1.5A 8V | 0.08 | MultiComp MC36228 | http://uk.farnell.com/multicomp/mc36228/fuse-ptc-reset-smd-8v-1-5a/dp/1861169 |
| 1 | B57891M0103K000 Thermistor, NTC, 10 kohm, B57891M Series, 3950 K, Through Hole | 0.571 | EPCOS B57891M0103K000 | http://uk.farnell.com/epcos/b57891m0103k000/thermistor-ntc-radial-leaded/dp/2285471?ost=B57891M0103K000&iscrfnonsku=false&ddkey=http%3Aen-GB%2FElement14_United_Kingdom%2Fsearch |
| 1 | 1x GREEN LED 1206 SMT | |||
| 1 | 1x BLUE LED 1206 SMT | 0.12 | King Bright KPL-3015QBC-D | http://uk.farnell.com/kingbright/kpl-3015qbc-d/led-blue-200mcd-465nm-smd/dp/2426226?ost=KPL-3015QBC-D&iscrfnonsku=false&ddkey=http%3Aen-GB%2FElement14_United_Kingdom%2Fsearch |
| 2 | C1/C2 2.2uF Cap 1210 SMT | X7R | ||
| 3 | C3/C4/C5 0.1uF Cap 1210 SMT SMD Multilayer Ceramic Capacitor, 1210 [3225 Metric], 0.1 µF, 100 V, ± 10%, X7R, Y Series FF-CAP | 0.15 | KEMET C1210Y104K1RACTU | http://uk.farnell.com/kemet/c1210y104k1ractu/capacitor-1210-100nf-100v-x7r/dp/1520317 |
| 2 | C6 0.22uF Cap 1210 SMT | X7R | ||
| 1 | R1 3.3R 50W Wire Wound Resistor | HS50 3R3 J | ||
| 1 | R2 47R Resistor 1206 SMT | |||
| 1 | R3 20K Resistor 1206 SMT | |||
| 1 | R4 10K Resistor 1206 SMT | |||
| 2 | R5/R9 47K Resistor 1206 SMT | |||
| 1 | R6 470K Resistor 1206 SMT | |||
| 1 | R7 680K Resistor 1206 SMT | |||
| 3 | R8/R10/R12 2K2 Resistor 1206 SMT | |||
| 2 | J2/J3 JST_PH_S4B-PH-K_04x2.00mm_Angled | 0.10 | S4B-PH-K-S (LF)(SN) | http://uk.farnell.com/jst-japan-solderless-terminals/s4b-ph-k-s-lf-sn/header-tht-right-angle-2mm-4way/dp/9492488 |
| 1 | J1 S2B-PH-K-S (LF)(SN) | 0.07 | JST S2B-PH-K-S (LF)(SN) |