Power router for mobile computer

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Overview

As always this is, above all, an educational project.

• based on ESP8266
• and sla5073

For a mobile computer project I need to manage a set of power sources

• 2-3 power banks
• solar panel
• wall-plugged power supply
• 12V car adapter

and a set of loads/consumers

• 2-3 power banks (charge ports)
• Single-board-computer
• powered USB hub (for 2x Wifi and 2x GDM modem)

  protection mechanisms

• measurement of power consumption (amps) of each consumer
• various temperature sensors

  Additional Inputs

• charge level of batteries (that's typically indicated by 0-4 LEDs when a button on the power bank is pressed
• voltage on power sources
• serial link to host computer

  User Interface

The ESP8266's independent Wifi is used to serve up a simple web-based user interface that uses REST routes to display and manipulate the system state.

Displays

• charge level of batteries
• temperatures
• power consumption (with history) of sub systems
• power sources history (useful for solar)

  Power management

• picks best available power source (wall>car>solar>battery)
• manages charging of batteries
• powers on/off subsystems on host computer's request

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Basic circuit ideas

Analog sensors

• sensor input is multiplexed to the ESP's ADC pin using CD4051B and ~2B
• voltage metering (sources)
• amp metering (consumers)
• temperature sensors

Digital outputs

• the power matrix (2x 6N channel MOSFET H-bridgey thing) is controlled with shift registers
• or i2c port i/O expander (like the JeePlug uses)
• it's a 6x6 matrix, so we need 12 digital outputs

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Current status

• sourced shift registers, mosfets and analog mux/demux ICs in SOIC packages from DigiKey
• SOIC ICs soldered onto DIP adapters using hot plate reflow method with solder paste )
• got PSF A85 module from ebay
• installed ESP 8266 open source tool chain on raspberry pi
• connected A85 module to FTDI adapter from modern devices
• set boot mode pins to boot from internal flash and tried the default firmware
• loses serial connection after initial boot, so I could not try the AT commands :(
• could be a problem with my wiring?
• also: after a firmware update to the Pi, the Pi does not boot any more :(

break out board for A85 module

To make life easier, I designed a breakout board in Eagle.

Next steps

• build two breakout boards
  • transfer PCB design onto copper (laserprint/ironing method)
  • etch
  • surface-mount module
  • try AT command demo again
  • try to flash some blink demo
• make RPI boot again
• play with mosfets and muxers

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Batteries

the batteries are 3 sets of 6 to 8 18650 Lithium-ion Cells I took out of discarded notebook batteries.

I put them into cheap power bank enclosures with charging/protection circuits.

• from amazon.de Power Bank Case Kit 18650 mAh mit Lightning für Handy
• from ebay.de 5V 3A Dual USB 18650 Power Bank Batteriebox Charger For iphone6 Plus S6

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Battery interface

A plug with pins for

• 5V input at 1A (charge)
• 5V output (design for 3A)
• temperature sensor
• charge level indication (or unregulated cell voltage?)

Questions/Research topics

• do we need isolation between the power banks? (different "GND" potentials?)
• inputs are typically on mini or micro USB connectors, outputs on Type A connectors. How can we make a space-efficient connector w/o too much modification to the power bank circuit board?
• is it worth while to design our own charging/protection circuit with a nice connector instead? (it's risky – potential fire hazard)