DIY Charging Base for BF-888S HT

The BF-888S “walkie talkie” radio came with an AC only charging base.  This model is for constructing a DIY charger using DC voltage as the supply.   This charger can charge a battery by itself or while installed on the radio. 

The electrical contacts used in this model are the Keystone SMT Contact-Tin Nickel Plate P/N 5231.   They are available from sources like Mouser (https://www.mouser.com/ProductDetail/Keystone-Electronics/5231?qs=U32tdPngY%2FzD9hIzRVKITw%3D%3D) and Digikey ( https://www.digikey.com/en/products/detail/keystone-electronics/5231/316380 )

This charger is based on a TP5100 charging management module, like these:   https://www.amazon.com/dp/B09QKW6FBV

Some versions of the circuit board are not as well labeled as others.  Here are the major landmarks:

Use of this module required configuration for 1S charging at a 1A rate.  See picture for reference.  You remove one R100 surface mount resistor (see circled resistors above) to change charge rate from 2A to 1A.   The module came configured for 1S operation, with the two jumper pads that control charge voltage (see circled solder pads above) open, which is appropriate for 1S (4.2v) charging.  

See picture below for a board configured for 1A charging.  The circled area shows the removed resistor location.

There is a two color LED on the charging module that changes color between idle (blue) and charging (red).  Being inside the bottom housing makes this hard to see.  There are three contact positions on the board for using either one two color LED or two mono color LEDs.  The common (center) position is for the anode, the two outer are for cathode connections.  If using a two color LED you need to use a “common anode” version.  The feed beside the +VIN pad is the “idle” circuit.  The feed closest to the GND pad is the “charging” circuit.

I used 3mm discrete LED's and the holes in the electrical box were sized to fit.  Green for charged/idle, red for charging.

Silicon coated,  20awg stranded copper wire is probably the largest size for attachments to this board.  Silicon coated, 24awg stranded copper is an easier fit for small through holes.

Contacts are attached to the “socket” component with M2.5 cap head screws. I attached the wire leads by soldering directly to the back of the contacts.  If there is insufficient engagement between body & screw, you can always use a longer screw & a nut for retention.

The remaining assembly of the components is done with M3 cap head screws.   The “bottom” component houses the charging module, LED's and power input.  The charging module is held in place with servo tape. The cap should be a slip fit, but a couple of dabs of CA glue can be used if desired.

For the power input, I used a USB-C connector like these:   https://www.amazon.com/dp/B0B24SXXP3   to provide a 5 volt source.  You could also use something like a pigtail 2.1mm x 5.5mm barrel connector for use with a wall wart transformer.    The TP5100 module is advertised as accepting 5 - 15 dc volts as input, as long as the input is higher than the charging voltage.