The major problems with my unit was the total lack of quality into the assembly: defective wires, less than perfect solders were the main problems.

I'm working now in refining the circuit traces and perform some more testing

Well, I'll post the final trace of the circuit in a short time (aka.. when I can finish it), even if some details does seem to not match (starting current, final current) - I think my multimeter is defective, especially in current mode, its serie resistance in affecting the measure.

Yes, at battery voltage 4.2 it is still pushing 13mA - the battery is able to reach 4.22V (and beyoind) but I stopped the charge and did not yet measured the current.

Charge current is slow though, limited by a 10ohm resistor; it starts at 180mAh and goes down in a strange way.

The RED led goes off.. the control ciruit for it is a dirty PNP with the base connected to the input line for the current going to the battery. While the charge current decreases, the base voltage increases until it reach 4.3 - at that moment the PNP is slowly turned off, because base voltage must be 0.6V (depends on transistor model) less than Emitter voltage (which is connected to +5).. a dirty trick :\

The only good part, is the TL431, which safeguard the final battery voltage and block it from going over 4.25V by turning off the base of the final transistor.

The first mod would be to half that 10ohm value, and thus increase the initial charging current. I'll also tweak the output network o lower the final voltage threshold to 4.22, which is more than reasonable - I might check the final voltage of the battery when charged by the original Nokia adapter.

When the RED led is off, the battery is still far from being fully charged - mine the red led is dimming until you can see the red "dot" inside the green led.



Full size Diagram

If you need the schematic file to use in LTspice just drop me a private message - at now still I don't want to post it straight to the public, I don't feel satisfied yet (accuracy is somewhat random..).

My cheapo RC-Charger i use for my phone is luckily good at shutting of at the limit of 4.23V, since you are new here you can check it out, link in my signature (the battery test one )

The other thread is over 70 pages long! gosh

Did you post some schema/circuits? I've read the first posts, nice work with those batteries - I was thinking that the 5800 was subdimensioned respect it's battery, but sseing the N900 with the *same* one.. well, someone at Nokia played dirty

However, before coming in hsi forum, I started collecting (so far) 5 fake BL-5J batteries, circa 2.5$ shipped from various eBay seller and trying them too.

The charger was more for the curiosity, than real need.

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Back to the charger: the schema is cheap, components cheap, cables.. cheap! there's really nothing, up to now, to do to improve that charger.. at the moment I lowered the charge threshold from 4.25 to 4.22V and I'm feeling alredy safer now (I can "literally" go to sleep with that thing ON).

To improve it.. that circuit is a lie in every part! it's almost impossible to hack it without loosing some functionality! the way even the RED led is connected, it helps the battery to charge.. and the "main line" where the charge should come, it's just used to provide little current to keep things running, but nothing more. I couldn't even hook to it some kind of current control, cause.. ther's no clear point of control

There were at least a dozen ways to assemble it.. they did it in the worst possible way. At this point, either, I keep it "as is", or I start with a new design. Well.. to let the steam off (I'm frustated!) It just costed 2,3$ shipped

Well im my thread post 1-3 are the most relevant, else i link to other mods etc.

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And on the cheap charger i also link to a cheap DX 18650 charger which also like the one you submit goes a bit higher then it should, but it will take many hours before it will go critical (>4.23V)

Generally speaking of cheap chargers they are all the same in the sense that they all do float charging in the end, and this is not generally good for Lithium battery's.

But good work here on the circuit, there are other users here like you and me that makes electronic mods to accessory's or the N900 it self

Like 'Wonko' with his modded wireless charging

The battery would be full when floating at 4.20V and current dropping to less than C/20.

True! I was reading that when charge current drops below 3% of C-rated, the battery is full - where C is the amp/hour capacity of the battery.

So 3% of 1320mAh is 39mAh.. but this ""charger"" (double quotes needed) is arriving at 4.21V @ 3mA so so.

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..
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I'm already designing a custom charger

Some other updates.

Before starting the design of a new charger (just for phun) I found a nice trick to pimp this charger.

I was stuck in increasing the efficiency of the circuit given fixed the input voltage!

With the charger, arrived also another cheap e disposable 5v adapter with usb port output, so I could charge batteries even without a computer. The v_output of the PSU was little disappointing, 5V when open circuit, 4V and something under load.

A quick inspection of the internal circuit revealed a common technique of using a 5V1 Zener to stabilize the output to 5V.. BINGO - Applied immediately a dirty trick, not having a zener with nearly 6V of reverse voltage, I soldered in serie to the zener but, in reverse direction, a 1N4148 to get an additional .6~.8 reverse voltage barrier.

So the output of the charger is at 6.1V open circuit, 4.9 someting under 100mA of load

Now the charger has reached a satisfactory level of functionality.

I should apply, more often, that "anything worth doing, is worth overdoing" rule

so the charger you are making is also a "dumb" charger or is it a shut off when done "intelligent" charger?

A smart one!! the smartest-never-seen-before...

I've read some suggestion here and there, nothing of professional but:

_there are several IC that would already do the job, one over all the Microchip MCP73831/2 (http://ww1.microchip.com/downloads/e...Doc/21984e.pdf) - order, configure, solder-5-pins, plugs for cable --> done!

But that would take out all the phun!!!

Right now I'm deciding a current sensor, then a constant I/V source, finally I'll model something around a PIC, something like:

_ check cell voltage, if below 3.6 charge at 100ma
_ then constant current 500ma up to V=4.15
_ constant V_charge until I<40ma (3% of 1C).

Basically that's all is needed; I'll add some other safety checks, some charge holding logic (connect the battery and forget it until use) and bells and whistels as the opportunity will dictate.

ETA? ..none!