The Solar Power Expert Blog

Free Charge Controller Kit – Part 2 – Preparing to Assemble the Power Circuitry

by Chris - March 15th, 2012.
Filed under: Charge Controller.

This is the second part of a multipart series of articles describing how I constructed the v4 Free Charge Controller kit from Jameco. The first part covered setting up your computer to work with the Arduino. This section covers some basic hardware preparation and soldering on the initial components to the board.

I built the buck converter circuitry first as it’s the heart of the circuit. I took pictures as the assembly progressed and I am posting them here with descriptions. This in not necessarily the best way to build the kit, it’s just how I went about it as a first attempt. You mileage may (and probably will) vary. Before doing any soldering, I verified the Arduino was working properly first. I recommend you complete part 1 before moving on to part 2.

A Note on Copper Braid

Whenever I do serious soldering, I make sure to have plenty of solder wick on hand. Many people learn to solder with suction guns, but I’ve never gotten the hang of it. If you make an error in your soldering, the copper braid will suck up solder when heated, through capillary action. Just place the braid over the solder mess, and press down with your soldering iron until the braid is saturated with solder.

Fixing a mess with solder wick

A Note on Bridging

In order to wire together the components on the Arduino protoboard, you’ll need to create solder bridges. You can do this one of two ways:

  1. If you’re experiences with a soldering iron, you can heat up the top layer of solder on the board and create a bridge from a ‘blob’ of pure sodler. However, it’s always better if your bridge has a copper core, so I recommend the second way if you have the patience.

  2. Use a piece of 20 or 22 AWG and create a core for your bridge, like in the picture below. This significantly decreases the resistance of your bridges as copper is a much better conductor than solder. It takes some patience, and you’ll probably want some helping hands to hold the wire for you.

Using 22 AWG wire as a 'core' for solder bridges

A Note on Jumper Wires

In order to save time and keep my wiring connections clean, I decided to use pre-made jumper wires. It’s easy to make your own jumper wires, so these are certainly not required. They do make prototyping a little cleaner and easier though.

I usually try to use a red wire for power and a black wire for ground, but the pre-made jumper wires are different colored based on their length. To help, I used black and white Uni Paint Pens to color in the ground wires and add information to the prototype.

Paint pens can help you add information to your prototype

Assembling the Power Terminals

Many people recommend soldering based on height of components – e.g. start with the wires, resistors, and other low profile components and end with the taller components like capacitors and terminals. That works fine when you know exactly what you’re doing. Instead, I decided to build based on debugging. I decided to build the power circuitry first since it’s the heart of the charge controller. If it doesn’t work, the best programming won’t fix anything.

Jumpers J1 and J2, with two wires for each power path.

I also wanted to be careful in building the charge controller because I want a low resistance path for my power circuitry. For that reason, I used two pieces of 22 AWG wire for each node of the power path. For example, the pictures above and below show the two headers (J1 (right) & J2 (left)) and eight jumper wires. I’ve got two wires for each power and two for each ground wire.

Tying power wires together with solder bridges

For the rest of the assembly, I’ll only use one wire for the power path until the board is fully assembled and debugged. Once I know that everything is running properly, I’ll go back over the board and add additional wire if I think it’s necessary.

The maximum current the charge controller is designed to handle is only 4 to 5 amps, so additional wiring may not be necessary. I’ll be able to determine if it is or not by viewing the board with a thermal camera during the final stages of testing.

Installing the Current Sense Resistor

After installing the headers, gather the MOSFETs, heat sinks, and current sense resistor. Install the heat sinks to the MOSFETs.

Collect the MOSFETs, heat sinks, and current sense resistor. Mount the heat sinks to the MOSFETs.

The next step is to install the current sense resistor. Solder one end to the power input track and jumper it to the prototyping area where the majority of the circuitry will be located.

Use the current sense resistor to jumper power to the prototype area.

At this point, the board is prepared for assembly of the power circuitry, which I’ll cover in Part 3.

3 Responses to Free Charge Controller Kit – Part 2 – Preparing to Assemble the Power Circuitry

  1. What is the ratio betewwen panel power and battery power ?
    This is the efficiency of the DC/dc Converter.
    I really need this information.
    Thanks alot.

  2. In my testing, it’s between 85% and 90% efficient.

  3. Heyy,

    Thanks for such a well explained guide.

    My problem here is with the current sense resistor and an additional current sense IC to be sent to the Analog pin for current monitoring.

    Why didnt we use Hall Effect Sensors to sense current ??

    Im on the building stage. Will keep you posted.

    SolarPV providing 26V here in India, much sun. :)

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