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Cell Phone Battery Backup Charger

Discussion in 'Power Electronics' started by jeffhoward001, Apr 13, 2011.

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  1. jeffhoward001


    Apr 13, 2011
    Hello -

    I purchased a battery-backup pack for my cell phone, and I'm not happy with the performance thus far. Here's a quick break-down of what it is - It contains 4xAA cells, with special "tips" which I assume contain some voltage regulating electronics as difference cell phones will be expecting different voltages. I'm sure many of you have seen these devices, there are many on the market.

    On the wall charger, the phone charges up pretty fast. I did some testing, and the phone will charge from 50 -> 98% in under 2 hours. On the battery pack charger, with fresh Alkaline or hot-of-the-charger NiMh cells, it will charge the phone from 50 -> 98% in 3-4 hrs.

    And to make the scenario even more irritating, if the cells aren't hot-off-the-charger, then the phone charge time is even longer - sometimes slower than the stand-by discharge rate of the phone! Meaning even if the cells still still show as "good" on my battery tester, and still work great in my digital camera, it doesn't charge the phone.

    So I did some testing, and this is what I found - The wall charger puts out about 5.75V and the battery backup about 4.7V. So thinking this was the problem, I wired another 1.2V NiMH cell in-line to bump up the voltage but that didn't seem to make much difference.

    Can you think of any reason why the battery pack is having this problem? From my basic understanding of batteries, they should dish out as many amperes as the circuit demands, unless the circuit limits the draw. Do you think that something in the "tip" portion of the battery pack is limiting the current as well as the voltage? Unfortunately there isn't an easy way to test this without destroying one of the "tips", and they are a bit spendy.


    - Jeff
  2. Resqueline


    Jul 31, 2009
    I don't think there's anything electronic in those tips (although it'd be easy to measure). On the other hand, what kind of cellphone is it?
  3. jeffhoward001


    Apr 13, 2011
    It's a Palm Centro. I have a "tip" for my wife's iPod as well. I suppose I could do a side-by-side test to see who well it works on the iPod, although I really need it for my cell phone in the long run.

    Is there's something rudimentary I'm missing, or does this seem silly to you as well?


    - Jeff
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Certainly in the case of the iPod, it can detect the current available from the charger and draw an appropriate amount of current.

    This is why some USB leads will not allow charging of certain apple portable devices from third party USB chargers.

    In this case it looks for certain voltages to be present on the USB data lines to indicate the type of device.

    I'm also aware of Dell PCs that have a third connection in the charger which has some signal that tells the laptop it i connected to a "genuine" dell charger. If it fails to sense this signal it will not charge the batteries to "protect you".

    It's not beyond the realm of possibilities that other devices do tricks like this.

    However, it is far less likely (but not impossible) with devices that have 2 pin charger connections.

    In pretty much ALL cases the magic (other than extra connectors) is in the power supply, and no the plug itself.

    The only exception I've seen is this. I have seen a similar gadget that is 2 connectors without the cable, so it just looks like an adapter "tip".
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