Project

General

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Introduction

Disclaimer

I am 44 years old and really started electronic 3 years ago to build my own home automation modules (commercial ones are too expensive). So, I have very limited knowledge, skills, experience, money and devices. I discovered kicad 2 years ago. This will be my second real project.

Special thanks

Before the actual story, design and materials, I'd like to thank specially people who helped me with their websites, videos or advices :

All of these helped me to design my own device, as I did want to understand and not to reproduce.

Process

Everything designed in
  • KiCAD
  • Arduino IDE
My approach is :
  • define the needs and specifications
  • design the global schema without component refs and values
  • read the datasheets and pick the components refs
  • calculate the resistors and capacitors values.
  • check and add decoupling and filtering components
  • eventually update the SPICE models and run some simulations
  • update all footprints and 3D models
  • design the PCB and order PCB+components
  • design the enclosure

Introduction

I design embedded PCB based on MySensors for my home automation system. I want some of them to run on battery and to use very low energy. Thus, I sometimes need to evaluate the power regulation part of my circuits. Some other circuits are powered from buck or boost components, or from mini switching power supply that I need to evaluate, too. I need an electronic load for that.

MySensors
MySNode

I am a subscriber of the French Cyrob's Youtube channel and facebook group. He often uses his commercial electronic load. Commercial products are quite expensive. I began to investigate electronic load few month ago and found Jasper's and its derivatives, or Wingman27's. There are not so many online. I also found a very old Elektor article to build one 1000W electronic load with 10 2N3055 transistors.

At the end, none of them were perfectly fitting my needs but I learnt a lot during this investigation. Thus I decided to design my perfect electronic load by myself (Schema, PCB, enclosure, firmware). This post serie describes this process and the build.

Needs and specifications

It was hard to precisely define my needs in terms of maximum ratings, thus I chose to use the same as Cyrob's Electronic load as a base : 150V, 30A, 150W. It is oversized and will give me some security headroom. My bigger bench power supply is 50V 20A, so I have very little chance to need a more powerful electronic load. Even if I manage to have only 50% of the specifications, this will satisfy my need. This is my very first complex project, after all !

Must have:
  • DC only
  • Max absolute ratings 150V, 30A, 150W
  • Constant current, voltage, resistor and power modes, battery test mode
  • Voltage cut-off and timer for battery testing
  • External temperature sensor and cut-off for battery testing
  • Autonomous thermal security cut-off,
  • Autonomous temp. controlled fan
  • Programmable
  • External driving signal (from DDS)
  • User-friendly interface
  • Cheapest possible
  • only with standard components easy to find
  • Easy to reproduce (not too many CMS)
  • Easy to calibrate
  • lot of probe/test points.
  • SDCard and/or USB data logger
Nice to have:
  • AC (very low priority)
  • USB monitoring and driving
  • Challenge : All components from LCSC and Banggood (to evaluate this chinese providers).

Regarding the providers Banggood, JLCPCB and LCSC, this post is NOT SPONSORED at all and is independant

I initially wanted to adapt Elektor's schema, but it has intellectual property rights and I would not be able to freely share my derivated work. Cyrob also made a very simple example, way too simple regarding my wishes and I wanted to design it by myself.

I wanted to use Chinese Voltmeter/Ammeter modules, but most of them dont support so many Amps and Volts. Furthermore, this design has to be reproductible, with standard components.

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