SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project
SolarMAX2 - Solar Power for your Raspberry Pi Project

SolarMAX2 - Solar Power for your Raspberry Pi Project

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SolarMAX2 Solar Power For Your Raspberry Pi Project!

  • Tired of building solar power projects that just don't generate enough power to cover your cloudy days?    
  • Tired of building systems that end up destroying your Raspberry Pi SD Card?   
  • Tired of building systems that don't give you the solar power data you crave?
SolarMAX2 is a brand new design with open source software that costs 1/2 as much as the last version and improves the performance dramatically of your solar power system.  And you get lots of data!

SolarMAX2 Waiting for Sunrise!
SolarMAX2 Waiting for Sunrise!

SolarMAX2 is for you!

Most Raspberry Pi solar power systems shown on Instructables and other forums are seriously underpowered.  If you are building projects that require a significantly larger amount of power than small solar cells can provide, the SolarMAX2 is for you.   Open Source Software puts you in control.   We use SolarMAX2 in our SkyWeather2 projects.
NO SOLDERING!   SolarMAX2 is a SwitchDoc Labs designed system to charge batteries from Large Solar panels in order to provide more power to small computer systems. SolarMAX2 is designed to collect and return data about the solar panel system to the powered (or even other computers) computer via a 433MHz wireless link.  SolarMAX2 collects and transmits the following data via 433MHz Wireless Radio every 30 seconds.  No data cable needed!  It transmits:
  • Battery Voltage
  • Battery Current
  • Solar Panel Voltage
  • Solar Panel Current
  • Load Voltage
  • Load Current (to your Raspberry Pi!)
It also supplies the following about the inside of the SolarMAX2 box:
  • Inbox Temperature
  • Inbox Humidity

SolarMAX2 Block Diagram
SolarMAX2 Block Diagram

SolarMAX2 uses a 433MHz wireless module which can transmit up to 100 meters or much further with larger antennas and uses very little power.   You plug a USB Software Defined Radio (SDR) into a Raspberry Pi or a 433MHz receiver Arduino and read the data on the computer with the provided software drivers for the Pi, Arduino, ESP8266 and the ESP32.   This is really yummy!

SolarMAX2 Ready to be Wired!
SolarMAX2 Ready to be Wired!

This is a perfect system for powering SwitchDoc Labs SkyWeather2, Raspberry Pi, Arduino and other small computer systems.
And, BTW, this is compatible with SkyWeather2 and WeatherSense sensors.  Same hardware used to transmit and receive.

What does the SolarMAX2 do that Other Solar Controllers Don't?

  • SolarMAX2 sends all the data from your solar panels to your Raspberry Pi for you to use and to learn about solar power.   Great for educational institutions and teaching about solar power!
  • SolarMAX2 includes hysteresis which protects your Raspberry Pi SD Card from the dreaded "Slam on, Slam off, repeat" problem when your system recovers from too many cloudy days.
  • SolarMAX2 protects your Raspberry Pi from turning on too soon after the battery reaches a good value by incorporating a delay in those conditions
  • SolarMAX2 provides turn-on current sufficient to start all Raspberry Pi systems, including the Raspberry Pi 4B.
  • SolarMAX2 gives you all the source code the controller and the software used to send an receive all messages.   All Open Source.  All available.

SolarMAX2 Beta Test at a new Winery in Virginia
SolarMAX2 Beta Test at a new Winery in Virginia

Can I Build This?  I'm new to Maker Projects

We have designed the SolarMAX2 system to require no soldering to build.  You have grove connectors and cables (Grove cables are keyed so you can't plug them in backwards!),  jumpers and some wires to cut and place in screw terminals.   This is an easy kit to assemble. NO SOLDERING!

Why is the  SolarMax2 system for me?

This isn't too complex of a  question.
Do you need lots of power (Like a Raspberry Pi 3B+ or Raspberry Pi 4B)? - Then SolarMAX2 is for you.
Of course, you still need to think about not just the processor, but what else you are driving (like Fans or giant radio transmitters, etc.)  Before we give some guidelines, let us show you some numbers behind our thoughts.  

SolarMAX2 Specifications

Form this table, we can see SolarMAX2 provides a maximum of 25W.
More questions to ask to decide which is for you:
1) How much current does your project need?    Note that if you are using a Raspberry Pi,  you need to think of the "startup current" too.   See this SwitchDoc Labs article.   Most small solar power systems fail to even start a Raspberry Pi 4B.
Arduino. ESP32 or ESP8266 based system?  SolarMAX2 will run these for a very long period of time, even without sunshine.
2) How long do I want my project to run without enough sun?
The bigger the battery, the longer your project will run without the sun.   Twice the Ah (Amp hour) capacity will run your project twice as long.

Want to do a little more math on this problem?  Check out this article:
3) I want to use a 3.3V solar powered system like the ESP32.  Which do I use?
Either you can power your project thorugh a USB connection (which is generally 5V on your device), or you need to use a power converter to drop 5V or 12V to 3.3V.   Lots of these are available on Amazon and Adafruit.

SolarMAX2 running SkyWeather2 in Palm Springs.   Lots of Sun!
SolarMAX2 running SkyWeather2 in Palm Springs. Lots of Sun!

SolarMAX2 Kit

What is in the SolarMax2 Kit?
  • Mini Pro Plus Low Power Computer
  • INA3221 High Current with Large Screw Down Terminals
  • 18V Solar Panel Charger for 12V Lead Acid Battery
  • HDC1080 Temp Hum
  • 433MHz Transmitter and Antenna
  • MC4 Solar Plus Female (and Pin)
  • MC4 Solar Minus Male (and Pin)
  • USB Weatherproof Plug
  • USB Plug w/terminals
  • 20cm Grove Cable
  • 30cm (or 50cm) Grove Cable
  • Grove Connector to Female Pin Headers - 1 Cable

What else do I need to make SolarMAX2 work?

WeatherProofing materials (see the SolarMAX2 assembly kit manuals for details) - Also available as an Add-on Reward
Here is what we recommend for WeatherProofing of both kits.   There are many other options!    The WeatherProofing SolarMAX2 Plus reward contains all of the below.

Solar Panels

You may be able to get away with 35W 18V Solar Panels in your area, but we recommend 100W 18V panels because of their superior performance in cloudy and dim light conditions (and partially covered panels by snow!  The snow is coming in the near future!)
There are many panel options, but we have tested this one.   Also, whatever you buy, make sure it has MC4 connectors on it so you can easily plug it in!


SolarMAX2  - 12V Lead Acid Batteries
You can use any 12V Lead Acid battery with SolarMAX2.  But remember, bigger batteries only help so far.   They have to be charged up too!
The Lead Acid battery we are using is the ExpertPower 12V EXP1270 Rechargable.   It *perfectly* fits in the Bud Box we recommend.
ExpertPower - -7Ah ~ $25 for more capacity (also fits!)
Interstate Battery - - 10Ah ~$40 (fits too!)
Less than half the price of equivalent LiPo technology batteries and lasts just as long.

Software for the SolarMAX2

There are three pieces of software that will be available - all Open Source - (released during the Kickstarter - currently in development for SolarMAX2)
  • WeatherSense Software (reads and Graphs SolarMAX2 using SDR on Pi)
  • Arduino IDE Software for the MiniProPlus in the SolarMAX2 system
  • SkyWeather2 Support for SolarMAX2
  • Arduino Drivers for Receiving SolarMAX2 Data
The WeatherSense software reads and decodes the incoming 433MHz data from SolarMAX2 using an SDR plugged into the Raspberry Pi.  It stores all your solar data into a MySQL database on the Raspberry Pi and displays a web based graph of the last 7 days (easily changed to a different time span in the Open Source Python3 software).

WeatherSense Display
WeatherSense Display

See the gap in the data on August 25th?   We turned off the Raspberry Pi gathering the data by mistake.  Whoops!   The SolarMAX2 system merrily went on generating power anyway.

SkyWeather2 Displays

SkyWeather2 SolarMAX2 Display
SkyWeather2 SolarMAX2 Display

Note we turned off the Raspberry Pi to upgrade to the latest SkyWeather2 software and forgot to reboot the Raspberry Pi on August 22nd!  Note we recorded all the data on August 25th that was missing above.   Two different Raspberry Pi systems.  One just reading the data from all the instruments and then the SkyWeather2 Raspberry Pi actually running off of the SolarMAX2 solar panels.

Status Panel on SkyWeather2.   Note the green status of the SolarMAX2 system.  Happy Computer.
Status Panel on SkyWeather2. Note the green status of the SolarMAX2 system. Happy Computer.

As part of the SkyWeather2 package, you can also use Blynk to give you data about your system on the go!

Blynk display during the day.  Fully charged!
Blynk display during the day. Fully charged!

Fully charged!  Happy SolarMAX2 system.
Fully charged! Happy SolarMAX2 system.

What are the Differences between SolarMAX2 and SolarMAX (the first generation SolarMAX)?

SolarMAX2 has a higher level of integration and a new architectural design that makes the SolarMAX2 less expensive and more reliable than the first generation SolarMAX products.   The hysteresis and reporting has also been improved in SolarMAX2.   Due to the high level of integration in SolarMAX2, there is no reasonable way of upgrading from SolarMAX to SolarMAX2.   We managed to reduce the cost of the SolarMAX2 to 1/2 the cost of the previous generation and eliminated 40% of the wiring!   Good stuff.

How SolarMAX2 works

SolarMax2 consist of  a solar power controller (and then a Grove Mini Pro Plus (Arduino based) computer) that reads all the sensors, deals with the solar panel control and manages the 433MHz radio link.   The radio broadcasts a set of data packets, protected by a CRC including the protocol number, message ID and all that good data.   
Here is a example of the JSON (easily readable!) data that is transmitted.

Power Management and Pi Protection in SolarMAX2
A standard solar power controller will not correctly protect your Pi and the SD Card.  One has to avoid brown out conditions and the power turn on and off rapidly.  This kills SD Cards.

There are three major components to the SolarMAX2 software power management system (these numbers are current as of Version 015 of the SolarMAX2 MiniProPlus Computer software:
  • Hysteresis - Hysteresis is the first line of defense for your Pi and your SD Card. Basically, SolarMAX2 will turn the on the USB Power (to the Pi) at a higher voltage than it will turn on.  The criteria for turning on (subject to the timers below) is: battery voltage 11.8V and 100mA of solar current.   The criteria for turning off is: battery 10.86V or Pi Load Voltage of less than 4.76V.
  • First Time On Timer - Delays a turn on of the USB Power (to the Pi) when SolarMAX2 has determined that it is time to turn on the USB Power.   Doesn't occur on power on to the SolarMAX2 computer, but only after the Hysteresis function has determined that it is time to turn on the USB Power
  • Ten Minute Timer - Used to prevent a quick turn off and turn on on a well discharged  battery.   If SolarMAX2 turns the USB Power off (to the Pi) then this timer prevents it from turning on again for 10 minutes.

The AuxA variable (which is on the Solar Voltages Graph) has the following meaning:

// AuxA has state information
// coded in the long integer
// 00000000 00000000 00000000 000X ABCD
// X - undefined (0)

// A = undefined (0)
// B = 5V Load Power state
// C = 1 - Ten Minute Power Off / On Timer
// D = 1 - First Time On Timer On, 0 First Time Timer Off

Want more information about sizing your Solar Power system?  Check out this article, "Tutorial: Solar Power - Sizing your Solar Panels for your Raspberry Pi."