Here are the great news:
at DealExtreme is a "8,4V power supply" for less than $5 available. It is a perfect "CC/CV" Lithium battery charger!!
Unfortunately the built quality of the charger is only "chinese standard", it didn't work out-of-the-box and I had to resolder some joints. But it is no "SMD-soldering", just normal sized components! And for $5 we can not expect it to have passed any "quality control"
Most important, the link:
Out of my curiousity I ordered the charger to test it on my original 2 cell battery pack:
Up to a voltage of 8,0V it charges the battery pack with 1000mA (like the original tablet's built in circuit!). As the voltage rises, it will "slow down" and decrease the current to ~30mA. Perfect CC/CV behaviour!
The charger has an indicator-LED that shows red while charging, and green when the voltage of 8,4V is reached!
The charger will be able to charge a big (2200mAh) battery in ~2,5-3 hours when the tablet is shut down (on standby it will take a little longer).
If you use the tablet while charging (yes, it will be possible!), it will take app. 5-6 hours for a full charge from 0% to 100%.
I made a chart for anyone who doesn't believe it. My battery pack was not completely empty, therefor the chart starts at a voltage of 7,8V, the tablet was not used while charging:
Charging 2-cell battery pack.jpg 48.04KB 160 downloads
If you'd have a working circuit in your tablet, it will do exactly the same thing, exept for the high voltage. It might be only my device to go up to more than 8,4V. It will not kill the battery, but might shorten the "lifetime" of the battery a little. If you use the indicator-LED, and disconnect the charger when the light is green, everything will be fine. Just don't leave it connected "overnight".
If you are willing to open your tablets back, and you know how to use a solder iron (only two wires and a small plug will be needed!), you will be able to fix the charging with the DX-charger! You might also use the original power plug of the tablet, but it is not as easy to do, as I thought. It depends on your skills!
No extra wires need to hang out of the tablets housing.
The order-to-delivery-time from HK to Germany took exactly 20 days: order now, and have your battery power back in ~3 weeks...
Now here is the news:
The idea to use the original tablet's plug with the DX-charger is very difficult and not recommended!
Trying to do it nearly killed my (still working) tablet's board, because I nearly cracked it!
I was very lucky, no electric traces seem to be damaged.
If your charging circuit in the tablet is completely dead (like Marcos' and Philip's) it might be possible to use the original plug, but I will not do any further tests, I will not damage my tablet for a this.
I will try to write my guide during the next weekend.
It will include three different ways to use the DX-charger:
1: the "easy way" with the original plug, that didn't work on my tablet, because my tablet's charger still works. My battery tried to charge itself, and I had a "green and red LED" at the same time! Like this the battery drained very fast, even with a switched off tablet! It might work for tablet's with a dead charger circuit, without mods on the board. You can also try it on tablets with a bad working charging circuit, it might work. It only needs the DX-charger and soldering two wires and I think, it's worth a try.
2: the very hard way, using the original plug, for tablet's with a "bad working charger circuit". It will need some modifications on the board (cutting two traces on the backside of the board!). I didn't finish it, because I don't want to "damage" my tablet.
3: the "not so easy" way with a secondary plug in the tablet's housing. You will need to drill a small hole to the housing and mount a small secondary two-pin "power"-plug for the DX-charger. I didn't do it, but it's easy to do and will work nice. I think it will be the best of the three possibilities.
Edited by eatatjoes, 06 October 2011 - 05:31 PM.