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Old 19th June 2006, 08:47 PM   #1
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Default Ingeneous Cell Battery charger

I wanna know if it's possible to charge a cellphone battery (3.6V Ni-MH)
directly from the 3.6V output of a standard (3.6Voutput) battery charger?,
or will i just cause more harm to the battery.
  • i've measured the output from the charger which actually turned out to be 9v and not 3.6v !!
    is this annything to be concerned of?
  • Also should the max charge current be of any concern
  • and lastly, how whould i know once battery is sufficiently charged,
    since there wont be any DISPLAY unit to confirm this.

reason for asking: in need of project running off a Cellphone battery
(which must be charged without popping the battery back into the cellphone for recharging).

Has anyone came accross a project similar to this?
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Old 19th June 2006, 09:00 PM   #2
es44 is offline es44  Denmark
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I'm pretty sure Nokia has an internal charging circuit in the phone.
So what you are proposing will harm the battery if done like that.
Sorry, i don't have the skills to guide you further, but maybe someone can

Best regards
Ebbe
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Old 19th June 2006, 09:12 PM   #3
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DON'T charge the battery directly....

While I'm not sure it wuold do damage (because the voltage usually will drop as the battery is charged and will be less than 9V), don't try it!

It could be hazardous. The battery and charger may overheat!!
The battery may even explode.

Ni-MH batteries should be recharged with a constant current (usually) and knowing the right capacity of the battery.

If you want I can further guide you... but I think you had better using another kind of battery.... I would use three AA cells...
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Old 19th June 2006, 09:29 PM   #4
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seeing as that is to dangerous...

my origional intension was to create a similar project as this.
snoop

But these IC's are either extremely expensive or not in stock. Since the 1.5v cells are easilly come by (as well as their chargers) ,
but not the IC's, I thought i'd improvise...
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Old 19th June 2006, 09:54 PM   #5
jc2 is offline jc2
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To properly charge a cell phone battery or any Lithium Ion battery in general you need to use a Constant Current Constant Voltage charge method. You need to have a tightly controlled 4.1-4.2V output voltage and limit the current to less than 1C rate, preferably around 0.7C. On a 1000mAh cell, 1C would be 1000mA, 0.7C is 700mA.

To determine end of charge you wait for the charge current in constant voltage mode to drop below a specified level. Most cell phones have 50mA as the end of charge detection.

Too much current, too much voltage, high temps, and other malfunctions can cause a lithium Ion battery to explode. Cell phones have extensive circuitry to monitor all the parameters to make sure charging is done properly.
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Old 19th June 2006, 09:55 PM   #6
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you want to charge from USB??
or simply charge some kind of battery??
It's not clear the purpose
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Old 19th June 2006, 11:22 PM   #7
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Quote:
Cell phones have extensive circuitry to monitor all the parameters to make sure charging is done properly.
Most of the time,I have found that this circuitry (the "watchdog" as I guess it is called.) is inside the battery pack.
On most of the NiMh and all of the Li-Ion packs I've taken apart,the "watchdog" was inside the battery part. If you were to take one apart,there would be the cell(s) and a small circuit board with a couple SMD IC's and whatnot on it -this monitors the charge and discharge cycles,usually also has have overcurrent protection (incase you short the output,as I did. -it 'reset' about 10 seconds later. DO NOT short the battery by itself!) and low-voltage cut-off,and other features..(the 'battery meter',for instance.)
Note there's usually atleast 3 or 4 pin connectors on Cellphone/laptop battery packs.

It is possible to hack them,I've done it several times (both cellphone batteries,and laptop batteries)..
But DO be careful!
Read up about the proper charging methods,etc..
Don't overcharge them,or short them out,etc.
Exploding batteries can really Fubar your day.
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Old 19th June 2006, 11:51 PM   #8
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Cell phone battery packs will have the safety circuitry inside, to protect form over voltage, undervoltage, and over current. But in the vast majority of cases the charge control, fuel gauging and secondary safety monitoring is done inside the phone itself. It costs too much for a manufacturer to add an IC to handle those things inside the battery pack when you can use the power management IC inside the phone to handle those chores. When I referred to the monitoring done in the phone I was speaking of actually monitoring and controlling the charge current and voltage, making sure that the battery temperature is in range, having timers to make sure charging doesn't continue for too long, etc.
5 or so years ago "smart" batteries were more common than they are today. Back then you would have 1 or 2 pins used for some sort of serial communication between the battery pack and the phone. Now the extra pins on those batteries are used primarily for a thermistor for the phone to know the temperature of the battery pack.
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Old 20th June 2006, 03:32 PM   #9
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firstly, Thanks for all your input sofar...

iv'e measured the i/p Charger Voltage = 8.3V
o/p pins of phone to battery = 3.7V
so nokia does provide some kind of DC/DC converter before
giving power to battery pins, but...
----------------------------------------------------------------

For Cell outputs to battery

pin1 (gnd) = 3.71V
pin2 (Btemp)= 2.18V
pin3 (BSI) = 0.92V
pin4 (+) = 3.7V

----------------------------------------------------------------

On Battery itself [all wrt pin4 (+)]:

pin1 (gnd) = 3.71V
pin2 (Btemp)= 3.69V
pin3 (BSI) = 3.70 to 3.71V

thus showing there is voltages to be taken into concern from pins other than pin1&pin4.

So how can one then "hack" the battery to be able to use it with a homemade project charger?

I think the following image will give some more light on my idea.
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File Type: jpg charger2.jpg (14.9 KB, 308 views)
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Old 20th June 2006, 04:09 PM   #10
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Just as a matter of interest, this is what someone else has done.
ps. doesnt look like he worried to much with pins 2&3 ?????
digital power supply and set it at 4.2 V's to charge any 3.6 or 3.7 Volt battery.
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File Type: jpg desk top charger.jpg (20.4 KB, 320 views)
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