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Current limiter add on

Discussion in 'General Electronics Discussion' started by goffery, Oct 11, 2013.

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  1. goffery

    goffery

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    Aug 4, 2013
    Dear Friends,
    I purchased a simple step-up converter (2.5-5V in, %V out) with USB output socket. My intention was to use it with 3 AA batteries for portable, on-time extender or charger for smartphone. This is the simplest circuit with no protections of any kind. When I used it, hooked to my HTC, it did the job: the phone was charging. However, after several minutes the batteries, as well as the converter became VERY hot. I'd guess that the phone draws too much current, although the DCDC converter is rated to 1 A.
    Now, what I would have liked to do is to add a simple, though energy efficient (if possible) current limiter. I don't know it it will be wiser to hook such a limited after the battery pack and before the converter, or after the converter, before feeding the USB. I found some interesting circuits based on L200C regulator, but I have no idea how to harness it to my needs. I thought of limiting the current to 800 or 700 mA, but I will have to tweak it for best results. Maybe better off to go simpler and add serial resistor, and loose bit energy.
    I will be happy to hear your comments and suggestions, of any kind.
    Best regards,
    Yossi
     
  2. hrishib

    hrishib

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    Aug 30, 2013
    Battery getting hot is not a good thing. If not charged properly they can explode. Also i've found that the best way to charge a phone battery is at about 200-300mA. The time required to charge the battery is inversely proportional to the charging current. Higher the current, lower the time. However, a high charging current can also reduce battery life. Looks like your HTC is set to charge at a lower voltage and current which is why its becoming so hot. Though your converter is rated at 1A actual max capacity ratings are higher (this is true for most voltage regulators). Looks like the converter is operating at max output capacity which is why its getting so hot. Can you share more detail about the step-up converter? Does it use an IC of any kind? Also how are you powering it? Can you measure the voltage and current when it is hooked to your phone?
     
  3. goffery

    goffery

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    Aug 4, 2013
    The converter uses an IC designated as c0303 HXN=AP, which I did not find reference to. The url below will lead you to its electronic circuit. It is powered by 3 alkaline AA batteries in series. Note that it is these batteries that get hot. Not the HTC's rechargeable pack. Sorry for not being clear enough.

    [​IMG]
     
  4. goffery

    goffery

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    Aug 4, 2013
    current limiter add on.

    The converter uses an IC designated as c0303 HXN=AP, which I did not find reference to. The url below will lead you to its electronic circuit. It is powered by 3 alkaline AA batteries in series. Note that it is these batteries that get hot. Not the HTC's rechargeable pack. Sorry for not being clear enough.

    [​IMG]
     
  5. hrishib

    hrishib

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    Aug 30, 2013
    Switch the alkaline batteries with NiMH rechargeable ones and instead of using 3 batteries for the input, use only 2. Looks the like the charger circuit is drawing way too much current for the alkalines to supply. Does it get hot when you connect something to the USB output connector? Or does it get hot irrespective of whether there is any load?
     
  6. goffery

    goffery

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    Aug 4, 2013
    Thanks for the reply.
    I'll give it a try.
    The DCDC converter and batteries gets hot ONLY when it is connected to load. I need also to see how it works with different load, like other smartphone (I need this portable only for long trips in the wild, when I have no access to power)
    I'll keep you posted.
    Yossi
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You can't use a current limiter. A current limiter operates by reducing the output voltage if the load tries to draw too much current; if you do that, the phone will think the charger has been unplugged. It will then stop charging, and the current limiter will then ramp up the output voltage. The phone will think the charger has been reconnected and will start charging, and the cycle will repeat. This is very undesirable!

    I suggest you first measure the charging current drawn by your phone from a proper 5V supply (a bench supply or a 5V wall wart). This will give you an idea of how much current you need to supply. I would guess it would be about 1A but it might be more.

    Then you need your circuit to be able to provide 5V at 1A. If the boost converter is only rated at 1A I would get a bigger one; it's not good to operate things at their limit, especially if they claim higher specifications than they can reliably deliver (did you buy it from eBay? LOL).

    You should also realise that three AA batteries are not an adequte power source for this application. First, three zinc-carbon or alkaline AA cells cannot deliver enough energy to fully charge a cellphone battery; they will run flat before the first charge cycle has finished, and second, if you try to draw more than a few hundred milliamps continuously from them, they will get hot, as you noticed, because of their internal resistance.

    For your application, your best bet would be to use a buck regulator powered by a bank of large lithium-ion or NiMH cells. For example, if you want to fully charge a 1500 mAh cellphone battery three times on one charge of the large battery bank, you will need to produce about 5W at your charger output for five hours, i.e. 25 watt-hours; this would require about ten D-size NiMH cells.
     
  8. goffery

    goffery

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    Aug 4, 2013
    Thank you so much for the answer.
    Very professional and educating.
    This sends me back to my desk to think.
    Thanks again,
    Yossi Gofer
     
  9. BobK

    BobK

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    Jan 5, 2010
    An NiMH D cell is about 10000mAH at 1.2V or 12WH, so more like 2 of them than 10.

    Bob
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Really? What brand claims 10 Ah for a D cell? Do you have a link to a data sheet?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Many seem to make that claim. Here is one (the datasheet is a little further down the page)
     
  12. davenn

    davenn Moderator

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    Sep 5, 2009
    far out!! didn't know such hi capacity ones existed
    Thanks Steve :)


    Dave
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Hmmm. AA Portable Power Corporation of China.

    Well, the data sheet does clearly make that claim - for the first three charge/discharge cycles, at least. And it even mentions one international standard. And they're pretty cheap - USD 54 for eight! I guess it's possible...
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Note that I said:

    I was just answering the question about claims. I'm not fool enough to vouch for their headline specifications :D
     
  15. BobK

    BobK

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    Jan 5, 2010
    Seeing as AAs are typically 2000mAH, I don't see why 10000 for a D cell is a stretch.

    Bob
     
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