Charger il 97% done, I've lost some time with a differential amp with a soul on it's own, voltage trimming here and there and some issue with an old Lithium cell with an higher than expected resistance due to wearing that was causing trouble to the threashold system regulating chrge current.

At the moment the charger is:

_ precondition the cell @50ma if voltage detected is lower than 3.4V
_ Full charge current @500ma from 3.4v to 4.10v
_ Top charge @150ma from 4.1v to 4.2v
_ Finalize charge @50ma from 4.2v to 4.23v

Actually I was measuring cell voltage when applying current, but it turned out to give only false reading, so now I'm modifying the structure of the code - but then I hit the memory limit of the PIC16F690... so now I'm back at optimizing code before continuing :\

Update: I was getting false reading of the voltage due to too high input resistance seen by the PIC, lowering it solved the main problem.

Another issue is present here, the sensitivity: there's a 10bit ADC reading a 5V span: 5/1024 = 0,004mV step, so it's quite a guess distinguishing anything in between, 4,19..4,23 is a hit and miss job. Even with filtering, hardware and softeware, I end up slightly off target.

98% ready!

Here's the pic of it charging a standard cell, on the left, the grey thingh.



Full size

The charger.. simply grew up on it's own.. and sure, it looks more complicated than it really is.. really!

Add this, add that, fix, improve, expand.. wiring is also messy, never intended to be a final setup.

The core is a PIC16F690 and the true charger is the program written for it; hardware consists of a Pic, couple of opamps, a power mosfet, a small power transistor, 2 power resistor, a differential amplifier, LM317, 7805 and a nice display

The battery is treated like a motor, push it from one side and discarge itselft, push it on the other side and you can charge; check voltages, check temperature and regulate current. I might pots a video of it.. or not, it's nothing special about it.

The final pad for the battery will be that "black" thingh you see on the left side, near the LCD, it has embedded a LM35 to sense temp, and the battery will stay there when in charge.

Code is 98% done, I've still to fine tune the mAh count when discharging, so I can know the true capacity of the various batteries.

See you nexxxxt!

looks good, can you make a simple charge only with monitoring of battery voltage and no display.

Then i would make one myself.
Not that i need chargers.

Uhmm.. the answer to your question would be: copy the chinese charger - it has just 2 transistors and the voltage reference IC, it works only looking at the voltage, the finalizing charge current is unregulatet and is damw cheap to produce.

My charger seems big, ugly and with a lot of uneeded parts.. but they are are all essentials.

Voltage monitoring is done via a differential amplifier, current sensing involves just a resistor and NO opamps. Current control allow me to run this circuit with voltage from 9 and up. Removing current sensing (removing 1 resistor) makes impossible for the PIC to know or limit the charge current..

Disaply again, is just wired to the PIC, I can remove it straight on, but then it's like flying in the fog

It would be possible to remove discharge features, you'll save 1 transistor, 2 resistor and 2 caps.. again.

You could remove temp sensing too, but it's the *only* safety external loops/barrier available, I wouldn't do

Really, the cheapest charger is the one on the first page

By the way, I'm tuning it more and more and I'm taking out those false voltage reading when in charge caused by various contacts resistance that are causing increased sensed voltage.. I might.. build a board for it after all the work that's been done to now.

Still, I've to fix mAh metering :\

Hey, that was most interesting blog/thread about reverse engineering thread I've gone by in ages Not that this Chinese charger was so interesting, it's rather about style and passion, I think?

Anyway, what about our "cold fusion" battery? Have You measured it? It's like waiting for new episode of "to be continued" science/criminal serial

Thanks!

Ooppss! Sorry! the summer was good enough to scramble all my habits - but I kept working on it in a steady manner

The charger has reached a decent working stage! Hardware hasn't changed since the beginning, software went to about 30 major "releases" and is currently in stage v1.01.

Every release added functions, Monitor, Charge and Discharge cycles. The biggest problem was the small program memory of the PIC in the way that floating point operations are not used because when just one decent division is programmed, the compiler sucks 18% of program memory.. so, all integer inside!

Or better, only fixed point math is used and some tricks are done trying to optimize all the various calcs..

The discharge cycle now is trying to meter mAh spent, I know, it would be better to measure Wh, but believe me, there isn't enough (or yet) space to datalog V and I for every second with the right precision.

At least, at the end of discharge cycle I know the starting and ending voltage of the battery; if I remember right, the nokia 5800 turns off at v_batt of 3.3V (or not?).

The discharge cycle if done:

_ @150ma until 3.6V
_ @75ma until 3.4V
_ @40ma until 3.3V

It's clearly not a real discharge profile, but I just want to measure the capacity of my cheap batteries.

The charge cycle works by:

_ v-batt<3.3v precondition @50ma
_ v-batt<4.1v charge @500ma
_ v-batt<4.22v charge @200ma
_ v-batt<4.23v charge @50ma
_ v-batt<4.24v charge @25ma

Each stage works by pumping the constant current for 10s, pause 500ms, sample v-batt for 500ma and take the average, then compare v-batt with the current stage and so on.

I've done this way because when you push current throug the battery AND sample voltage it gives obviously a false reading. The 3 final stages are done because even pausing after pushing 200ma inside the battery it still isn't enough, the battery looks like it's charged, but the voltage then drops to 4.13 like; so my profile is still time-un-optimized, but nice enough to fully charge the battery at the end

Also, I've checked the nokia battery during recharge inside the phone and with the standard nokia adapter it looks pulsed too, like each second charge, stop, sample and pulse again the current.

Give me a couple of days/week, I can start to get out some battery numbers, see if they a reasonable, then I'll post the final hw schematics and the source code of the charger (C lang.). I don't think it would be ever usefull to anybody, but who knows!

So, long time no see

Here (link to google sheet) you can take a look at the performances of different batteries, tested with the charger, read the notes to get more info.

The charger: the hardware is the same, the software went throug various tuning but the main ideas remain (charge profiles and so on), I've done some fixing, counting mistakes, cicles and little else.

Temperature: I've got a IR thermometer, now I'll measure why (some) od those batteries are colder than the others. It only happens after a full charge, with my charger.

Sooner or later I'll ran the remaining test of how much is the Nokia charger charging vs my profiles.. but now life has changed a lot since my last post, moved out, found a job, paying my bills and got a QWERTZ keyboard and a lot of accents to deal with :>

My time is now shared among job/survival/hobbyes - being the first one quite compulsory, and the last two thread locking each other out :> - I could survive without food/cleaning for up to 1 week however... better not try

Good Nickel Cadmium cells do cool down slightly when charging actually, then warm up when they are full. Because of this, some chargers detect the temperature change to tell when the cells are full. Though NiMH also warm up when full, they don't cool down as notably as NiCd during charge.

I don't think you could get away with running NiCd batteries in the N900 or with a Li-ion charger, however.

old thread, but anyway: experimenting with this is extremely dangerous!
i had 2 examples in my neighborhood:
1 burned his bed because of a battery starting to burn while loading, he only noticed, because his dogs began to bark
the other one burned down his house, because of an exploding battery while he was sleeping.

better spend 20 bucks more on your battery and charger, it can save your house and your live.

just my 2 cents

While you are correct, messing around with Li-ion batteries is EXTREMELY dangerous, foxontherun has proven he knows exactly what he is doing.