I bought days ago this cheap external battery charger (I have a 5800xm, BL-5J battery):



I think they are all the same, the price was right, 1.99 Gbp (inc shipping), and it is the only thing which is right with this unit.

The quality is next to nothing:





The screw was already broken, both two wire fell off as I opened the unit, the plastic assembly feels (is) very cheap.

So, before letting it torture my batteries in a unspeakable way, I was wondering about it's regulation circuit.. so I opened it and took a couple of photos:




I know that "reverse engineering" is not good, in some places this leads to bad things.. but with this cheap object, I think I can still sleep thigh in the night, so I tryed to trace back it's circuit:




And produced this schema!



http://img641.imageshack.us/img641/8428/circuits.png

(I inserted the full link to the image of the circuit, handy).

Now.. Much work is still to be done, currently I have a terrible split-by-two headache, so I'm going to link the last file, is the archive with everything inside:

_ images
_ models
_ datasheets
_ circuit file (LTspice)

Link --> http://www.megaupload.com/?d=7EYM531E <--

The circuit actually is simuable, it tends to a voltage of 4.4 circa. I do not know if it is right (the simulation!), I measured with a multimeter the output (before wires broke up) and it was around 4.2 - must check later.

First thing to do is:

1. Verify traces and plotted circuit, the two images (PNGs - in the above archive) are overlappable, one of them is mirrored so it is easyer to check traces; can someone help me veryfing them? reports here all the suggestions, rights and wrongs.

Then:

2. Find reliable substitutes for the original transistors or reliable models.

3. Find correct component value I'm 90% they are correct, there are some normal 4 band resistors, a couple of 5 bands resistors and one ceramic cap which reads "104" -->180pF?

The very-very-very last step will be to... err.. improve the design

Now, I must really go to sleep, aber I'll pass out

I was inspired in making this post by a thread on replacements batteries BL-5J where battery capacity was verified - playing around this charger could be usefull to many people around here

See you later!