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.



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


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


Quick Teardown




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


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.


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).


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).


Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

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

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - 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
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.