Energizer Wiimote Induction Charger Teardown

Energizer Wiimote Induction Charger

An inductive charger is a type of wireless energy transfer system, it can also be called an air core coil transformer. It works by passing alternating current into the coils and air acting as a medium between them, the interacting electromagnetic field helps to induce inductive coupling. Wikipedia does a much better job of explaining it: Inductive Charging.

In this teardown, I’ll be featuring the Energizer Wii Inductive charger (model # PL-7581) and try to figure out how it works internally. This will be a challenging on-going project since some key IC components have been blackened for a reason to keep their functionality secret. I would like to add that throughout this teardown, I have come to appreciate the complexity of this device and commend Energizer for a job well done, they did their homework.

Now, this inductive charger works in the same way as the wireless charging toothbrushes. This schematic of the Interplak Model PB-12 electric toothbrush (although rough) is a good example of a simple inductive charger, and yes, it does indeed work nicely. Here is another example of a toothbrush induction charger at the picaxeforum.co.uk. Hack a Day has featured this technology in the past, “Inductive charging going mainstream“.

Readers are encouraged to help with this project, I’ll need information on capacitor values (since I do not own a capacitance meter) and help identifying any unknown IC’s and passive components (would the bus pirate help while cycling through charge on/off modes?).  Alternate uses for this project have been posted at the bottom. Also, clarification or explanation of the theory and operation is also encouraged. Posting comments or emailing (teamubermodder(*at*)gmail.com) us works.

I should first explain the various operational modes that are noticeable upon using the device. Placing the Wiimote and connected Energizer battery pack onto the charging dock, the red symbol lights up, when charging is complete, the symbol turns green. If the battery pack is not connected to the Wiimote and placed onto the dock, the red symbol flashes red in error and will not charge the pack. Just the charge peak detection through inductive fields alone is noting some incredible built in intelligence circuity.

To start, I removed the myriad of screws holding the bottom cover, then I opened it up and went straight to the good stuff.

Let me backup to the wall-wart transformer. It’s a 100 to 240 VAC 0.3 Amp 50/60 Hz (model # JSD-2710-050200, energy star rated device), quite capable since they only need to make one model to support the European and American markets.

As expected there are two inductive coils taped to the underside and a magnet resides in the center. The magnet appears to help the WiiMote stay on the charging dock since the accompanying battery pack also has a magnet. If designed properly, ferrite magnets can also improve the inductive coupling of the electromagnetic field between the coils, however I don’t think Energizer had that in mind for this application. The planar inductive coils appear to be wound in one layer (rectangular shaped) with about 16 windings. There are also two rectangular weights to keep the charging base properly weighted.

Top side of the circuit board exposed. The circuit board is basically divided into two, a side to manage each inductive coil. Model # shown on circuit board: HC-Q-0712 V4, built on 2009.09.01. Two large red ceramic capacitors reside in the middle (154J), 0.15 uF 250 volt. Various resistors and capacitors reside below the large capacitors. Note that the circuit board is double sided and the inductive wiring connected on the right and left.

Bottom side of the circuit board exposed.   I’m assuming that the IC, SO14 package, in the center is a microcontroller to manage the charging modes and various functionality. Could the IC be a Microchip or an Atmel product? Maybe the readers can help! The other two IC’s, SO8 package, have to be some COT’s (commercial-off-the-shelf) based devices, maybe power managment IC’s like battery chargers or current/voltage monitors to help the microcontroller judge battery charging characteristics. The large black capacitor is a 470 uf electrolytic, used to condition the dock’s power source coming into the black connector. There are two SOT23 6 pin IC’s towards the center of the board, I can’t find an explanation for those at the moment, these may be measurement IC’s of some sort. Two SOT package transistors, both are beside the SOT23 IC’s, the markings on them are illegible.  Beside each of the red capacitors is what looks to be a Zenier diode. Scattered around the board are various passives like capacitors and resistors, all surface mount. Lastly, note the indicator LED’s on either side.

The inductive charger comes with two battery modules, each are rechargeable. The rechargeable batteries are Nickel Metal Hydride AAA, 500 mAh in series to produce 2.4 Volts overall (but the voltage was not measured through a multimeter, so it must be connected through a power management circuit board). Here what’s inside of them…

Each module has an inductive coil taped to the backside and a magnet resides in the center. The planar inductive coils appear to be wound in two layers (rectangular shape) with about 17 windings per layer. Also, the coil is backed with stainless steel foil, this must help reduce the inductive field that would normally be absorbed by the batteries and the wii-mote. The coil is somehow connected to the + and – of the 2.4 series battery setup (noting again my theory of a connected power management circuit board).

Upon turning over the battery module, I noticed that the shell can be popped off. The two AAA batteries can be easily removed as they aren’t even soldered in, this may open the door for higher capacity NiMh AAA batteries! Where the batteries previously resided, there was masking tape covering up wiring and a small double sided circuit board. I carefully removed the tape, let’s take a look…

The circuit board have a few noticeable features, a small black bead temperature sensor monitors the temperature of the batteries during charging. There is a small SOT-23 6 pin package off to the side, looks to be the temperature sensor receiver (reads LM75 variant, check out Maxim IC’s information on these variants), the only SOT23 packed temperature sensor information that I could was at Maxim IC’s website (MAX6625). What looks to be a red Zenier diode nearby. Also, the typical blackened IC with no legible identification, I really think this is a microcontroller, same as what is in the base. Four diodes on the right hand side to turn the AC component of the inductive field signal into DC (Wikipedia: rectifier), they look to be 1N400X series diodes (rated for low voltages, small signal rectifier, 1N4001 would do). Four SOT package transistors, the two beside the IC have the same marking (431), the other two different markings (KL3P0) and (A1SHB). Lastly, the two wires from the inductive coil is in parallel with a small surface mount capacitor, leading into the diode rectifier circuit.

For the sake of my time on this project I’ll have to leave you here for now. To conclude, here are some of the things I’d like to look into:

• Measure all pins on the nameless blackened IC’s in both the base and the battery module. Monitor record all waveforms while invoking various charging and on/off modes, post pictures. Try to produce an IC pin diagram with functional pin descriptions. It would help us understand what’s going on here.

• Figure out what activates the charging dock into battery charge mode, if it’s a waveform from the Wiimote, more simply a resistance measurement or current draw prerequisite. If this is solved, the charging station can be used for alternate projects.

• Alternate uses for charging station:

1. Roomba or robot charge dock, the Let’s Make Robots! community would be interested in this.
2. Mousepad charger for wireless mouse.
3. Cell phone/Ipod charger (although li-ion charging characteristic must be taken into consideration, risk of fire!).
4. Or contribute with your own idea, let us know!

This will be stamped as a reader contributed on-going research project, stay tuned!