pgrovetom1
Member
There is some work Jack Rickard has one at evtv.me regarding communicating with the BMS integrated into the Tesla Modules.
I have thought about the need to increase the battery capacity of a Tesla PowerWall. That was one reason I cancelled my Powerwall deposit because I wanted a system that I could increase the storage capacity. My choice of a hybrid inverter has not given me the programmatic choices that a PowerWall would have and therefore my need for additional battery capacity has not been needed. I will follow your project with interest.
Its not difficult to implement the BMS functions except balancing the cells by just controlling charging, discharge and a temperature monitor. It may not need balancing except initially and it would be easy to monitor the cells using the A/D and a 6:1 analog selector. Then it can be reported. If necessary, cell balancing modules for a high current 6s battery are available without messing around with the Tesla interface details. I would just remove it and bring the cell wires over to the controller.
I don't think adding 5KWhrs will make a huge difference plus the arbitrage is small stuff .... but it could be entertaining. The whole thing can be in the garage away from the outside environment. Only the radio based current monitors for the solar, PW2 and the home would be out at the service entrance. My service entrance ( and the PW2's and their stuff) is about 50 feet from my house.
The cost should be very reasonable at about $900 plus $1000 per 5.2KWhr battery pack - A wild guess!
1) 240VAC to 18V Power supply is about $100
2) The DC to DC 1800W constant current power supply is about $30
3) 2 good Micro inverters $500-$700
4) Raspberry Pi 4 Model B - 2GB RAMabout $40
5) DIY AC current monitors using Arduino and a LoRa transceiver plus misc $50-$100
6) DIY Variable current limiters $25
7) Tesla Model S Battery Module 24v 250ah 5.2kwh 444 Panasonic 18650 3200mah $900-$1200 each 5.2KWhrs
5.2KWhr - $2000
10.4KWhr - $3000
15.6KWhr - $4000 etc... very roughly
If there are no gotchas! Like the PW2's somehow can detect whats going on and complain! The trick is be invisible to the greatest extent possible.
Power injection - looks just like a reduction in home power load.. no more and no less
Charging - Looks like a home load.
By using a UL 1741 complaint micro-inverters, it looks just like the solar inverters. The power injection at transitions of home power ( an oven or high power appliance is turned on and then off) and the MI's must raise and lower the injected power from zero to maximum ( 500W in my example) without having the voltage spike. Since injection cannot be done while the PW2's are fully charged and the 60Hz has been raised, at all other times the PW2 can soak up any excess power being injected during on/off appliance transitions - I hope.
The radio link needs to be quick so the control loop doesn't have any problems. If the radio goes down, the system disconnects and the limiters are set to zero.
Last edited: