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Powering Mobile Phone from Leisure Battery

Discussion in 'Power Electronics' started by ChrisXenon, Mar 20, 2013.

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  1. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Hi,

    I'm trying to use an old LG GT540 Android for surveillance on my allotment (garden away from my house, for those who don't know the term), which is off-grid, so I've got solar panels charging a leisure (Lead acid) accumulator.

    My first thought was to leave the Lithium Ion battery, and plug in a car charger and power the charger from the lead acid battery. However, that apparently ruins the lithium ion battery and rapidly flattens the lead acid battery.

    So I turned to stepping down the voltage from 12 - 14 volts to the 3.7V required for the phone. Research suggested that a switch mode regulator would give far greater efficiency so I set up an L200C to do the job.

    The mobile battery ("LGIP-400N") contains protection circuitry. One component of that is a "strap battery device VLD P 220 SLF". The datasheet is not clear to me but it looks like a thermal shutdown device to protect things if the battery gets too hot. There are also two ICs and 7 resistors - they have no symbology and I don't know what they do. I tried leaving all this in circuit by connecting the battery terminals to the mobile via soldered wires and connected the regulated 3.7V to the place where the lithium ion battery used to be. I reasoned neither the phone nor the electronics would know the battery was... not what it used to be. However, it doesn't work; the phone does nothing.

    So I removed the battery circuit components, and routed the 3.7V power from the regulator straight to the two outer pads in the mobile phone; the middle pin is ignored. Well, it works, and the phone comes all the way up and works fine.

    However - two things:

    1. There is an 80mA current drain from the leisure battery, even with the phone switched off
    2. With the phone on, the regulator is too hot to touch and about 300mA is drawn, implying a 4 Watt consumption!

    This is not going to fly with the meagre PV charging I have going, and anyway - it suggests something is worryingly wrong.

    I wonder if anyone can shed any light on what if anything I'm doing wrong. I'd appreciate any help you can offer.

    Regards,
    Chris
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Switched off as in completely off or in standby?

    If it's in standby that is about right and expected...

    Yep, normal most new smart phones draw quite a bit with the screen on and the CPU crunching, this is an expected drain amount for a smart phone when in use...
     
  3. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Switched off - so it should be drawing nothing. And when on, I know that network activity and other specific functions can be very heavy on power, but it sits there in airplane mode doing nothing.

    Should the regulator get hot? I thought switch mode regulators were efficient.
     
  4. davenn

    davenn Moderator

    13,582
    1,869
    Sep 5, 2009
    give us a link to the switching regulator you are using

    also a sharp well lit photo or 2 of the way you have wired things up
    particularly at the phone end

    Dave
     
  5. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Well I have never seen a current smart phone with physical on/off switch, every one I have see has a momentary switch that puts the phone in 'standby' mode, not truly off... Now standby current could be next to nothing or it could be as high as you are reading it all depends upon how it was designed... I suspect that the designers were not overly concerned with dropping standby to next to nil, 80mA was probably perfectly acceptable for them...

    If you want a true on/off with no power drain install an on/off switch on the power lines going to the phone...

    Airplane mode shuts off the radios, it doesn't mean the phone is doing nothing, in fact it might be doing quite a bit, and is certainly almost always doing something as the OS has overhead CPU requirements...

    Efficient yes, perfect no... So yes depending upon the design it could get hot or warm..

    Personally if it was me, I would have just dropped the battery down to 5V and used the phones internal USB charging circuit to charge the battery and run it light that vs hot-wiring it to the battery directly...
     
  6. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Dave I am using the L200C which you can read about here http://www.hqew.net/datasheet/L200C-datasheet-pdf-download-197577.html. It quotes a max junction temp of 150c but my concern is not self destruction (it's got protection inside anyway) but rather efficiency.

    No photo - it's just two wires soldered directly to the outer 2 pins in the battery compartment, which I feed from the regulator circuit output.
     
  7. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Thanks CocaCola. You are correct of course. The phone has a push-button which isn't a physical electrical cutoff switch. When you said "standby" I thought you meant the phone is on, but not in a call. So yes, 80mA in standby. Still seems vast. If the phone took that current continuously when normally powered, it would die after less than 19 hours on a full 1500mAH battery, whereas it doesn't.

    And it's worse than that becuase this 80mA is being drawn from the Leisure battery side of things, so the power isn't 3.7 x .08 but 13 x .08 = 1Watt. And the fact that the regulator is so hot is the killer. Right there, that heat is a big dissipator of power I don't have to waste in the leisure battery.
     
  8. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Looknig at the phone spec here http://www.gsmarena.com/lg_gt540_optimus-3081.php they quote stand-by (which most people take to mean the phone is ON but the screen is off and it's not in any calls) of "up to 500 hours". Allowing for the bull factor, let's say 300 hours. For a 1500maH battery, that's FIVE milliamps, with the phone on. I'm seeing 80 with it off. So I think smething is clearly wrong. No?
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,385
    2,772
    Jan 21, 2010
    The regulator you're using is not a switching regulator, it is a simple linear regulator. And its efficiency is inversely proportional to the ratio between the input and output voltages (i.e. the larger the difference the worse the efficiency).

    We need to know which 2 pins are connected to what, and where you get the output from. Even a linear regulator shouldn't be getting too hot in this arrangement unless you have a very high voltage battery or a very small device.
     
  10. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    Steve you're a star and I'm a moron. Thanks. The store I bought it from described it as a high efficiency switching regulator, and though I have been through the datasheet and the design guide a lot, I never spotted that it really isn't.

    The leisure battery is just nominal 12V - fully charged it's around 13.5V, so it's dropping 8.3V.

    Given the nature of my error I'm inclined to just junk this effort and start again with a (cough) switching regulator. Apologies for wasting anyone's time & thanks for your help.

    Chris
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,385
    2,772
    Jan 21, 2010
    I still think you have another issue. The regulator is going to draw some current, but it shouldn't be as high as 80mA. Are you sure the battery in the device isn't being charged? Or have you removed the internal battery?
     
  12. ChrisXenon

    ChrisXenon

    7
    0
    Mar 20, 2013
    You may be right Steve. The internal battery is removed, so it's not charging that, I have purchased a switch mode regulator from China for £4 and I'll see how that performs. If it works fine and draws sensible current, then job done. If not, then I may be forced to look at whatever this other issue may be again.

    But until that's proved, I'm going to move on. Thanks again for putting me on the right track with this.

    Cheers,
    Chris
     
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