Hi,
Why do batteries for mobile phones have three connections? And does the
charging current automatically stop after the batteries are fully charged in
common mobiles like nokia 3310, siemens c25, etc.

Thanks in advance.

Prasad.

prasad wrote:
Hi,
Why do batteries for mobile phones have three connections? And does the
charging current automatically stop after the batteries are fully charged in
common mobiles like nokia 3310, siemens c25, etc.

http://www.maxim-ic.com/ and look at the battery charger chips
http://www.cadex.com/ and look at the FAQs.

The third wire is typically temperature measurement or data communication
in larget cells.
For lithium-ion, it's basically once the battery has been charged to 4.2V
and sat there for a while.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
If God hadn't intended us to eat animals,
He wouldn't have made them out of MEAT! - John Cleese

In article , prasad wrote:
Hi,
Why do batteries for mobile phones have three connections? And does the
charging current automatically stop after the batteries are fully charged in
common mobiles like nokia 3310, siemens c25, etc.

Thanks in advance.
Prasad.

The Nokia 3310 I recently disassembled (it got dropped into the wet bilge
of a boat! ;-) has 4 connections on the NiMH battery. There is usually a
thermister inside battery packs like this to allow the charge controller
to detect increases in temperature which are one indication of end of
charge. Some laptop battery packs that I've seen also have a fixed resistor
which is used to sense the type of pack installed.

I'm sure the charge circuit will be "intelligent" and shut down when the
end of charge is reached, probably via a voltage gradient sensing approach
with the temperature as a backup. There's no shortage of CPU power to do
all this properly in a mobile phone...

Regards,
Mike.

The third terminal is usually the thermo safety sense. In some battery
units for sophisticated equipment, they have a microcontroler board.
At the factory, they test the cell characteristics, and write the
matched cell data in to the firmware of the controler. The parameters,
and temperature of the batteries is monitored by the controler, and
this information is sent to the uPC in the device that is being used.
This is to give the charger and phone accurate battery condition and
status.

In otherwords, simple batteries are getting too complex. But, they
are getting better performance out of batteries than ever before.

Jerry Greenberg
http://www.zoom-one.com

--


"prasad" wrote in message ...
Hi,
Why do batteries for mobile phones have three connections? And does the
charging current automatically stop after the batteries are fully charged in
common mobiles like nokia 3310, siemens c25, etc.

Thanks in advance.

Prasad.