Samsung Galaxy Nexus S - run without battery?

[daneel]

Hi all,

I need to run my Samsung Galaxy Nexus S without battery, just from USB power. I need this for a robotics project, where weight matters.

I'm looking for a circuit which will not only trick my smartphone into believing that there is a battery present but will also tell it that the (non present) battery is full, so that it does not waste any USB power for trying to charge the battery.

This is probably a very basic question, so please forgive me. Any help / directions would be highly appreciated.

Many thanks and all the best,
Michael

 

[CocaCola]

You should be able to regulate a 3.7 power source directly to the battery terminals... I don't know exactly what the battery feedback pins provide to the phone, and what the phone will do without feedback, but there is one sure fire way to find out... Wire up 3.7 Volts to the battery terminals and see what happens... You can get the 3.7 Volts from your 5V USB supply using a low drop out regulator...

Worst case, I'm guessing that fooling the battery feedback pins state isn't all the difficult if the phone fails to work, but I wouldn't worry about it until you know you have to...

 

[daneel]

Hi Coca,

many thanks for the reply.

I found out some more information about the inner pin:
http://www.cpkb.org/wiki/Samsung_AB463446BU_battery_pinout

It seems to be a resistor telling the phone the capacity of the battery.

How do I avoid the phone to try to charge the faked battery? When will the phone believe that the battery is "full"? I guess this depends on the voltage of the power supply, right?

My perfect solution would be to not use the internal battery port at all (power comes through the USB port), but I guess there is no way to accomplish this without at least supplying power to the internal battery port, right?

Many thanks and all the best,
Michael

 

[daneel]

Hi again,

can't I just shortcut the + and - pins of the phone (not of the battery!), possibly with a resistor in-between, to trick the phone into believing that there is a battery present?

This is just a thought, I'm really a newbie with that stuff.

Many thanks and all the best,
Michael

 

[CocaCola]

My perfect solution would be to not use the internal battery port at all (power comes through the USB port), but I guess there is no way to accomplish this without at least supplying power to the internal battery port, right?

Take your battery out, plug the phone into the USB charger and see if it works (most won't) thus no matter how much you want to avoid it you are going to have to 'fake' the battery and the best way is to simply skip the USB port charging and go directly to faking the 3.7V battery itself...

can't I just shortcut the + and - pins of the phone (not of the battery!), possibly with a resistor in-between, to trick the phone into believing that there is a battery present?

No...

 

[daneel]

Many thanks for your reply,

using the phone without the battery does not work, that is what I tried first.

I cannot avoid the powered USB port. It's how the phone communicates with the robot. The port needs to be powered, otherwise the data communication won't work. So I'm stuck with powering the phone through USB.

I always thought that (from the battery chargers point of view) a battery is nothing else than a (variable) resistor. That's why I thought of simply connecting the + and - pins, possibly with a resistor in between to lower the voltage just to the point where the phone think that the battery is full (and thus stops charging it).

I will further read into how those LIPO chargers work. May that will help.

Many thanks for your replies and for your patience.

All the best,
Michael

 

[CocaCola]

Shorting the battery pins will short the negative and positive supply rails to the phone, not fool the phone into thinking the battery is charged but instead shorting the phone out... The extra tabs on the battery is how the phone monitors the battery charge, not through the + and - terminals... But these charging feedback tabs will not fool you phone into thinking that it has an actual battery attached so that it will actually boot... You have two issues to contend with...

 

[CocaCola]

Something further on this subject, now that my daughters have given me 5 mintues to take a breath and type.... The BSI pin on the battery is likely a thermistor, a variable resistor that varies with temp... The phone likely uses this to determine the charge of the battery, along with the voltage... The BSI pin is also generally hooked to a shut down circuit, so if that pin is not connected or functional the phone will no work... You can fool the BSI pin with a resistor between BSI and GND, I don't have the specs for your battery so I have no idea what value would work... With this fooled and 3.7 Volts to the + and - terminal the phone should function without a battery...

As for fooling the charging circuit, you will likely really have to tinker with the BSI resistor value as well as possibly increasing the 3.7 Voltage slightly (to a max of about 4.2) to simulate a fully charged cell...