The objective of the project was to create a case for a single cell Li-ion battery with built-in charger. Charging will be via the USB port, while the case will include a flying lead for connecting to MCU modules that can run at 3.3v via a regulator.
Alternate versions with a 5v buck converter or a 3.3v regulator included would be extremely useful.
Required components are are the charging module and a battery holder, together with whatever is needed for the flying lead. The case was designed to be a tight fit for the battery holder, with a separate compartment for the charger module and a cutout at the end for the USB port. The charger module is not designed to power the load, so the user is required to remove the load before applying power through the USB port.
The charge control nodule is based on the 4056 chip. This module comes in two versions - with and without over-discharge limiting. The version without over-discharge limiting is shown here - it is suitable for use where the device being powered turns off when its supply voltage is too low. The version with over-discharge limiting is slightly larger and can be identified by the additional control chip (DW01A) and the dual mosfet (eg, 8205A) used to disconnect the output if the battery voltage is too low. The version without discharge protection is used when this protection is included with the battery or when the device being powered turns itself off at low voltage. Note that both versions will have a small quiescent current, so batteries should not be left uncharged for long periods or they may be discharged below their recovery value.
The flying lead ends in a two-pin female socket that can be connected to a solderless breadboard or directly to the module using Dupont leads. A small inductor core with the lead looped through it serves as the strain relief, while a rubber plug is used to to provide a clean border for the hole in the case.
A short length of clear plastic rod, rounded at the top and lightly polished at both ends, is inserted into a raised section in the lid of the case so that the light from the charger LED is visible. The plastic piece is actually a section of sprue from a plastic model kit.
The lid is a simple press fit on the base. Two holes were molded into the bottom of the base so that the battery can be pushed out of the holder if required. The base also includes a locating peg for the holder.
This site was last updated 27th
January 2022.