#503 imaxRC B3 Lipo Charger

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

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

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

• High Quality iMaxRC iMax B3 Pro Compact 2S 3S Lipo Balance Battery Charger For RC Helicopter 6.17
• 2pcs HRB 11.1V 2200mah Lipo Battery T Deans XT60 XT90 EC5 3.5mm EC3 30C For HPI Racing Cars Monster Truck Boat Airplane RC Parts
• DK112 info and datasheet
• AD4056ES
• Everything you need to know about LiPo Battery chargers