Maggie/Electronics/Accu

Maggie's Accu

The accu of maggie is a laptop accu. As this accus can easily be found in trashes, or on ebay, or other similar places, they are relly cheap. I choosed the older toshiba models, simply because I had some available, with charger, and for free! But i discovered that this model is really simple, unlike most modern accus, that have more complicated features inside, so that some are really a mess to interface. This is particularily the case with DELL models...

To be able to interface this accu properly, i did a bit of reverse-engineering, by opening one of these accus. Please do not unnecessarily repeat this, it is dangerous to simply open it.

Caracteristics

• Brand : Toshiba
• Model : PA2487U
• Nominal voltage : 10,8 V
• Nominal capacity : 4 Ah
• weight : 400g
• size : 70 * 19 * 175 mm
• Technology : Li-ion
• Cells : 9 * Sony Energytec US17670GR (3.6 Volt)
• wiring : 3 series assembly of 3 parallel cells
• current protection : 2 thermal fuses + 1 thermal switch
• voltage protection : comparators on each cell stage for overvolt and undervolt. Cutoff mos are external to accu
• Other logic : one i2c eeprom for storing infos. No other interface. Completely independant of accu circuitery
• thermal sensor
• contacts : 10 contacts, plus 2 contacts to be shorted for activating accu
• Found in laptop : Toshiba Satellite 4000 CDS, and many others.

Li-ion : DANGER !

The li-ion accus are dangerous ! They can explode, and the lithium can burn, at very high temperatures. You should really be aware when using this kind of batteries. Please use the prescripted protective circuitery, and a good charger. A good charger gives the correct output voltage within +- 1%. If a bit too much charging voltage is applied, the accu can explode ! The same can occur if it is shorted. Make your electronics shure. Make your electronics shure. Make your electronics shure. Your electronics is not shure enough. Make your electronics shure.

Accu wiring

Here is a schematic from the internal parts of the accu.

There are 3 series of 3 paralell cells. The midpoints are directly connected to the PCB.

3 different overtemperature fuses are wired in series with the plus. one is a reversible thermal switch klixon4MM70B1 : 70 °C opening, 7A @20°C, 4A @55°C The two others are marked : Microtemp KJFACA G4A TF 092(I guess, last part not very readable)

The two "top contacts" must be shorted to make the accu work. This is a security for not having the two poles of the battery on the same face.

This is the pinning of the accu :

• 1 : "+"
• 2 : NTC connection (second pin of NTC is connected to contact 9)
• 3 : UNDERCHARGE output (pin1 of the MM1309)
• 4 : eeprom VCC
• 5 : SCL
• 6 : SDA
• 7 : EEPROM GND
• 8 : OVERCHARGE output of the MM1309
• 9 : EEPROM write protection, apply "1" for enabling write operation. also second contact of NTC
• 10: "-"

protection circuitery

The main security IC is a Mitsumi MM1309. It contains all the necessary comparators, references, and so on. The two output pins simply go to two contacts of the accu, where (externally) MOSFETS are connected. See Level 2 Card for an example of external circuitery to add for protection.

EEPROM memory

The eeprom memory is a simple i2c eeprom: 24C046 from ST, probably equivalent to a 24C04. I did actually not investigate on the content of this eeprom, if you do something with it, please mail me your interesting results !

Charger

[Image:Maggie_accu_chargeur.jpg]

I found in a trash this wonderful accu charger !

It is a Toshiba model PA2488U, and has place for two accus. It needs a 15V PSU (same as the laptop). It does all what is needed to charge these accus properly.