Mobile Charger...Slow Charging problem..

Discussion in 'General Electronics Chat' started by qaisershah, Nov 29, 2015.

  1. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    Respected friends!
    I have little bit knowledge of Electronics, i have built a mobile charger but it is charging the smart phone very slowly...what to do for fast charging...details are as below:
    Smart phone = Nokia lumia 520 (1430mAh).
    homemade charger=
    Transformer = 2Amps (12V)
    Bridge= 5 Amp
    Capacitor= 4700uF 35V
    Transistor= 7805 ( for output 5V).
    plz reply me any suggestions for improvements in circuit...
    this charger gives only 120mAh charging and mobile phone takes too long to charge...
    help me out plz friends..
    thanking you in anticipation.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Use a deadicated charger, the phone dictates the charging rate, not the charger, so it will charge at a safe rate for that battery.
     
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  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Make the charger identifiable to the phone.
     
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  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    ... which may mean supplying certain voltages to the data lines of a USB connector.
     
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  5. AnasMalas

    Member

    Nov 27, 2015
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    Sometimes its the phone that limits the charging for safety! Iphones for example need 2 volts through the data pins. some androids need data pins to be shorted.
    I have no idea about the lumia phones however...
     
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  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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    On a side note and in deference to the foregoing comments regarding data pin requirements, often when a dedicated fast charger starts acting like a generic slow charger, it's due to a break in the wire or connector on one or more of the data pins.
     
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  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    So, let's analyze this using math.

    You have a 12 V source and a 5 volt regulator. That means the regulator drops 7 volts at 150 mA = 1 watt.

    These little 7805 regulators have a thermal shutdown. So it is likely throttling back the current as it heats up. 1 watt is a lot for a 7805 without a heat sink. If you are expecting a full 2-amp charge rate (based on transformer rating), then the little 7805 would need to dissipate 14 watts. You need better heat sinks and maybe a purchased charger based on a switching power supply.
     
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  8. AnasMalas

    Member

    Nov 27, 2015
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    this may be the case(i dont know much about voltage regulators). if it really is wouldn't a 12 v to 5 v transformer work? these typically aren't that big... and not that expensive.
     
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  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Or better still, use a switchmode psu, like they do in Normal phone chargers,......(dejavu)
     
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  10. qaisershah

    Thread Starter New Member

    Nov 21, 2014
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    i have added four 7805 and all are connected with heat sinks...actually i have four smartphone at home (family), i want to charge all of them through single charger....let me add the the above mentioned 120mAh charge rate was from one port while other port where not connected with load (phones).

    Can i use computer power supply as it has 3.3V,5V and 12V output for phone charging?
     
  11. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    I didn't see anyone mention it but in the past for me I get different charge rate depending on the wire diameter of the USB cord..
     
  12. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    check where the D+ and D- pins are connected on the stock charger and what is the resistance to GND and VCC.
     
  13. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can use 5V from a computer psu, as long as your cables are thick enough, i think your problem is the charger lead.
     
  14. Willen

    Member

    Nov 13, 2015
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    12
    Or add a current booster transistor too to divide down the the huge power dissipation/heat or to boost currents. Search for 'current booster circuit for 7805'. However it wastes lots of power if you are using 12V battery as power source.
     
  15. marcf

    Member

    Dec 29, 2014
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    I probably do not need to point out that there is a big difference between a charging circuit and a power supply. Connecting a PS capable to supplying 20 Amps at 5v to a battery could have bad results.
     
  16. bertus

    Administrator

    Apr 5, 2008
    15,638
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    Hello,

    In a lot of usb charger schematics there are resistors on the D lines of the USB connector.
    This search query will give you some examples:
    usb charger schematics with resistors

    Bertus
     
  17. marcf

    Member

    Dec 29, 2014
    136
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    I understand that point, but I just thought it would be good to point out that it can be a very bad idea to charge a battery with a power supply. A battery charger is not a power supply, it is a device for charging batteries that contains a power supply and is designed to properly charge batteries. Some of the designs in this post do not seem to take this into account.
     
  18. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    But the battery charger circuits are in the phone itself. and even in the battery in some cases. you dont pump 5 volts to the battery. you regulate the voltage down...
     
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