#503 imaxRC B3 Lipo Charger
Quick teardown and review of the imax B3 Pro charger for 2s and 3s Lithium-polymer 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
|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|
|Dimension||90 x 55 x 35mm|
|Compatible batteries||2S/3S Lipo|
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.
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
- Everything you need to know about LiPo Battery chargers