Why doesn't a mobile phone work with the battery removed, but charger connected?

Discussion in 'General Electronics Chat' started by mishra87, Jul 15, 2016.

  1. mishra87

    Thread Starter Member

    Jan 17, 2016
    170
    2
    Dear All,

    How can be implemented the above mechanism .
    I want to implement the same for my application .
    Could anybody guide me .


    Thanks !!!
     
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    The guess is there a high peak currents to support and there's no room for a big capacitor. Capacitors typically are a large component.

    The cell can easily determine if the battery is present by looking at the temperature monitor which is typically a thermister. In my phone, the two outer pins are the battery and between - and one of the middle pins there is about 10K. Total of 4 contacts.

    Some packs for the same phone have the polarity marked on them. Some do not.

    MY GUESS is replacing the battery with a supercapcitor e.g. http://www.mouser.com/ds/2/87/Bus_Elx_DS_4393_PB_Series-479424.pdf and a resistor for the thermister might work.

    I doubt you would have to add a supercap charger. e.g. http://www.linear.com/product/LTC4425

    If your battery pack has three terminals it could have one of these ICs https://www.maximintegrated.com/en/products/power/battery-management/DS2703.html in them or something similar. Apple uses the 1-wire serial number IC for their magsaf batteries, but it contains a lot more info.
     
    mishra87 likes this.
  3. mishra87

    Thread Starter Member

    Jan 17, 2016
    170
    2
    Is it possible if battery is removed and one want to operate with charger, It should not work .
    As i already told smart phone application.
    which device i need to put to achieve the objective.
     
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,147
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    If the battery pack has some sort of battery IC in it, your really going to have trouble.

    IF it consists of a thermister (10K is typical) and power pins, then replacing the battery with a supercap AND emulating the thermister MIGHT work.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,804
    1,105
    Typically the charger provides 5V, the battery is 3.7V, the phone operates at 3.7V or less and there is circuitry in the phone to control the charging and discharging of the battery. That circuitry will recognise the absence of the battery and may well then prevent use of the phone. If so, you would have to fool it somehow. The easiest way would be to insert a battery :).
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
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    Because of the current capacity. Your charger can not supply the needed current.
    If you replace charger with a power supply, it still may not work. It will depend on the internal circuitry.
    The internal charge circuits might not pass the required current.

    Does your phone work with battery installed and charger connected?

    If it does, there's your solution.
     
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,147
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    BR-549: Mine does somewhat.

    It needs about a 10% charge before it will. I tried tethering and charging and i was unable to get it to work 100%. The battery discharged faster than the charging rate. I even tried a USB isolator (second power source) and that didn't work either.

    I had another phone and it worked fine. The Motorola Razr. That was a cool phone.
     
  8. BR-549

    Well-Known Member

    Sep 22, 2013
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    Your right. Then the solution is a power supply connected to phone battery terminals.
    I have never owned a cell phone. I probably shouldn't comment.
     
  9. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    A traditional power supply. Maybe not. A 4-quadrant power supply possibly. They are able to source and sink current. I would at least put a diode or ideal diode controller in series with a conventional power supply for protection. Some bozo plugs in the USB charger.

    You still have to deal with the possible battery ID IC and charging thermister.
     
  10. BR-549

    Well-Known Member

    Sep 22, 2013
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    Unless your battery has more than two poles, your comment makes no sense to me.

    If I pull the battery, and connect the proper voltage and current capable power supply, to the battery terminals, I would expect no problems.

    What am I missing?
     
  11. BR-549

    Well-Known Member

    Sep 22, 2013
    2,004
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    Cellphone batteries have a control connector?

    OK, as I said, I have never owned a cell phone. I'll keep my mouth shut.
     
  12. mishra87

    Thread Starter Member

    Jan 17, 2016
    170
    2
    I think discussion has moved somewhere else..

    Actually I have a battery operated instrument-

    1. In my applications instrument works with charger if battery is removed. Only charger alone can operate the instrument.

    2. It also work with battery if charger is removed provided battery has charge. Only battery can operate the device.

    3. If battery is being charged . My instrument is working.

    Now I want my device should not work as per case no 1. Means if battery is removed and customer want to operate it with charger. it should not work .

    How it can be implemented.

    Hope i was able to make u all understand properly.
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
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    Show us a picture of the battery.

    The discussion will go where you lead it.

    You said mobile phone. Now you say instrument.

    SHOW US.
     
    Last edited: Jul 15, 2016
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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    You post title implies you want a charger only operational mobile phone.

    Post #12 implies the inverse of this. You want a charger only, non-operational instrument.

    Which is it?
     
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  15. mishra87

    Thread Starter Member

    Jan 17, 2016
    170
    2
    Yes..

    We have got 3 terminal in battery
    +, - and open.
     
  16. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,147
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    I'm out.
     
  17. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    This is a duplicate thread that you asked before. You were given options, such as a comparator circuit to detect the presence of a battery.

    Please don't start threads on duplicate topics just because you didn't like the responses.
     
  18. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    The peak current draw might be an important issue.

    Once I tried salvaging the top of a dud battery and hot wiring an external 18650. Any electronics and the thermistor were in place as if the battery was in - I assumed the refusal to work like that was because the phone saw too much cell internal resistance.

    There was probably enough space for an adequate capacitor in there - but not the pointy end of a soldering iron without taking the phone apart.
     
  19. Tonyr1084

    Active Member

    Sep 24, 2015
    539
    86
    I don't think so. My cell phone can run on the battery, and charge from the charger at the same time. So if you're thinking the battery is capable of delivering sufficient charge to run the phone but the charger can not - then how can the charger charge the battery while the phone is in operation? So I have to disagree with the statement "your charger can not supply the needed current".
     
  20. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,147
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    Ian:

    A 18650 does not have a thermister. Your battery contacts in the phone were more than 2.

    Mine will too. It's just won't keep up if continually transmitting in tethering mode and the battery needs "some charge" before it will even turn on.
     
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