Fork me on GitHub

Project Notes

#503 imaxRC B3 Lipo Charger

Quick teardown and review of the imax B3 Pro charger for 2s and 3s Lithium-polymer battery packs.

Build

Notes

I bought the imaxRC B3 Pro to charger some HRB 3S1P Lipo 11.1V 2200mah battery packs.

I haven’t used it much except to top-up the packs. My initial observation is that the charger gets very warm to the touch (batteries remain cool); not sure what’s going on here.

This charger probably falls into the “too dodgy, buy a decent one” category per: Everything you need to know about LiPo Battery chargers

Specifications

Item Specification
Input voltage AC 100V-240V
Balance charge current 850mA
Max charger current 3*800mA
Display 3x Bicolor LED
Power plug EU Plug
Display Green & Red LED
Case material ABS
Dimension 90 x 55 x 35mm
Compatible batteries 2S/3S Lipo

manual-en

Quick Teardown

teardown-1-front

teardown-2-rear

teardown-3-board

The AC-DC rectification use the DK112 Switching Power Supply Control Chip:

teardown-4-smps

Charge circuit uses a AD4056ES or TP4056 equivalent. I don’t see any active re-balancing support, so not sure what would be generating so much heat.

teardown-5-bms

Circuit Design

The high-voltage side is a conventional application of the DK112, similar to Typical application #1 from the datasheet (12V/1A output offline flyback switching power supply).

DK114_example_schematic

The more interesting part is the low-voltage side and how the TP4056 has been used. Here’s a partial re-drawing of the circuit.

Essentially, there are three low-voltage windings that are half-wave rectified to power three TP4056 circuits (for each batter cell). Since the power supply is floating, these are stacked in series.

Main things to note:

  • regulation is a bit howsyourfather. Single bulk filter capacitor after the half-wave rectification and a 750Ω bleed resistor
  • they’ve skimped on the thermal regulation. There’s not NTC; the TEMP pin of the TP4056’s is permanently pulled low.
  • Rprog = 1.8kΩ, corresponding the a charge current (Ibat) of ~600mA (each cell).

imaxRcB3LipoCharger_schematic

Credits and References

About LEAP#503 PowerBMS
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.