We are using some of the smallest SMD device you can buy in these days. For this reason you need good soldering skills. These instruction are not for beginner!
You are still there? Okay, let's talk about my Powerbox. It is a device for charging and discharging a lithium battery.
On this picture you can view the PCB and four lithiumbattery. It has 6000mAh. Not bad isn't? And it is small. Only 70mmx50mmx30mm.
The device depends on four parts.
pbox1.sch Eagle schematic
size 69kb
1. This is the charging part. It is made with a Texas Instruments
BQ24108. It can charge the battery with any external voltage between
6V and 16V. So you can use every stupid line-supply or a car adapter
to charge the battery. I charge the battery with 1A. It is also
possible to charge with 2A. But this depends on your soldering
skills. We will talk about this later.
Unfortunatly this device is really small. For this reason it needs
some special soldering skills, too. I use an old iron to solder it. :-)
pbox2.sch Eagle schematic
size 89kb
2. A boost converter for 5V and 1A. I use a Texas Instruments
TPS61032. This device is bigger than the BQ24108 but it is also
necessary to use an iron to solder because of the thermal pad at the
bottom.
pbox3.sch Eagle schematic
size 62kb
3. A safety circuit made with a Seiko S-8231. It checks the maximum and
minimum voltage of the battery and limits the current.
It is not easy to buy, so I took one from an old cell-phone battery. I also found
there a TPC8204. There are many different battery protection IC with
different names, but they are very similar. Please compare pinout if
you find a different one.
pbox4.sch Eagle schematic
size 4kb
4. Some boring transistor to check the batteryvoltage and indicate an
empty battery.
I made an mistake on the PCB. You have to cut the wire between
collector of T5 and basis T4. Then you need a small wire to basis
T3. The schematic is okay. Look on the first picture!
Now lets have a look at the PCB.
You can made it yourself. I draw it with the demo-version of Eagle 4.13 from cadsoft .
pbox.brd
size 50kb
I printed the layout with a 1200dpi laser printer and I think a lower
quality printer will not work.
It is a double-side PCB, but I made it myself and connect both side
with 0.8mm wire. But there is one problem. IC3, the BQ24108 need a
very good thermal pad. So I drill a bigger hole with 2.5mm and solder
a piece of copper between the bottom of IC3 and the bottom side of the
PCB. This is necessary or the IC becomes to hot! This IC needs the
copper at the bottom for cooling. It is impossible to use it with a
one side PCB.
If you are very good you can change R21 and charge the battery with
2A. Unfortunatly I was only good enought for 1A. :-)
Here you can see how I am using it. To tell the truth I did not try
how long I can use the C750 with this battery, but I expect more than 24h.
This are the data-sheet you should read:
Seiko S-8231 datasheet size 404kb
TI BQ24108 datasheet size 404kb
TI TPS61032 datasheet size 404kb
If you not read them, the goddess of electronic will kick your ass!