Introduction: Convert a Battery Charger From Mains to USB Input

About: My Name is Daniel Aeschlimann. During the day I am a Mechanical Engineer. During the evenings I tinker with witn my 3D-Printer, my CNC router and with Arduino. Some projects i record on video and upload them t…

In this project, I will show you, how to convert a main voltage battery charger to a USB Power input.

Project Video: (German spoken language)

I needed this project, to be able to charge my camera battery from the solar panel, which I have introduced in my last instructable.

I will remove all the electronics of the charger and replace it with a single electronic module form Ebay.

The charger I used to modify:

Step 1: The Right Charger Module for Your Battery

The chargers which I have modified are all for Li-ion batteries.

A Li-ion cell has a final charging voltage from 4.2 Volts. Depending on how many cells your battery has, you need a module with 4.2 or 8.4 volts output.

The charging current is also important. In general, I recommend going with a lower charging current than the original charger electronic provides.

When you use a battery with more than one cell, you have to think about balancing the cells. Some batteries like my two cell camera battery have an integrated balancing circuit. With this you are fine. If you don't have a balancing circuit, I recommend lowering the final charging voltage to 4.1 Volts per cell. To ensure that the cells remain balanced, charge them periodically with the original charger.

For a one cell battery, I recommend this module:

For a two cell battery, I recommend this module:

The further steps are appropriate for the two cell battery. the usage of the one cell version is even simpler.

Step 2: Solder the USB Cable to the New Circuit

You need:

  • The step up module
  • spare USB cable

First, you have to strip the USB cable.Then you have to measure on which cord ground and 5V is present. (There are some color codes, but I never trust them.

Afterwards, you can solder the cords to the corresponding solder pad on the module. Make sure that the spare cords are isolated from each other.

Step 3: Make a Wire Connection to the Charging Contacts

Now you need your battery charger which you want to modify to USB power.

As explained in Step one, you have to remove all the existing charging electronic.

Then make a connection from the module to the charging contacts. It is very important to have the polarity the correct way. Double check this before you insert the battery. The same with the charging voltage.

Step 4: Close the Charger Case - With a 3d-printed Part

Now we are done with the electrical part of this project.

I made a new case part to close the back side of the charger with my 3d-printer.The *.stl files are attached.

If you like to make some adjustments, you can download my Fusion 360

The 3d-model I made has also a feature to attach the case to the pipe of my solar panel stand.

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