Introducing SolPak for the Energy Harvesting Challenge!!

A project log for SolPak

Open Source Tesla style battery pack for EV, Robotics, and off the grid living. Modular design for multisize packs

AVR (lordKiCAD)AVR (lordKiCAD) 06/09/2018 at 20:370 Comments

SolPak is a rechargeable portable battery pack that can be charged via solar panels or AC mains voltage. The pack uses 18650 lithium ion cells and will be using the ADI LTC6813HLWE-1#3ZZPBF battery balancer/monitor chip suspected to be used by Tesla in the model 3 pack. SolPak will have modular output modules where different DCDC converters or DCAC converters can be swapped in based on end application use. The pack is intended for portable powering of devices, off the grid solar power, portable solar for camping longterm, and custom EVs. 

The overall system in the pack consists of the following:

- Battery Banks (x2)

- Batter balancer/monitor/charge controller board 

- Overall system control board

- Swappable output converter module interface

- Cooling system

The battery banks will consist of 18 18650 lithium ion battery cells, there will be two banks in the first prototype. The battery balancer, monitor, and charge control board will consist of two LTC6813HLWE-1#3ZZPBF for monitoring and balancing each bank, the chips can interface with each other to balance all cells together. The cooling system will be integrated in with each battery bank. Right now I am planing copper tubing attacked to copper plate pressed against and between the cells to cool them as loads of current is drawn. The liquid in the copper pipe will be pumped through a radiator or some passive heat exchanger. In the event of a radiator there will be fans.  I'm still developing a solution for the charge controller portion, be I'll have it ironed out in the week. The overall system control board will be based on a STM32 MCU, it will talk to the battery board and the converter module interface, it will run the main firmware that marries together all the subsystems. The swappable output converter module interface is meant to allow the user to choose the outoput voltage for the end application. Swap in a DCAC inverter for 120VAC power to run your laptop or xbox while camping. Swap in a DCDC converter to power your robot etc. 

All this good stuff is going to be mounted in either a custom case made from carbon fiber sheet cut on a CNC with brush aluminum panels here and there or I'll get some off the shelf flight case and use that. What I really want to do is build a frame out of 2020 aluminum extrusion with carbon fiber panels on the sides and to mount everything to the carbon fiber panels, then plat the outside with bushed aluminum sheet. Have holes cut for the radiator and fans to breath. 

So far I have ordered a bunch of 18650 cells and I'll be diving into the length datasheet for the LTC6813HLWE-1#3ZZPBF. Once I understand the balancer chip I can choose components and putt together a PCB to be made. Once I get the battery cells I'll be able to get a good idea for how to design the case. I have aluminum extrusion laying around and carbon fiber sheet has gotten cheap so we'll see what happens. Stay tuned folks! 

Happy Energy Harvesting Challenge Everyone!!