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My Battery powered Ipod charger

Discussion in 'Power Electronics' started by hyudryu, Mar 30, 2010.

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  1. hyudryu

    hyudryu

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    Feb 24, 2010
    Hi, i am making a Ipod charger using 4 AA batteries and a LM317 regulator. But which pins on the USB is connected to the battery?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
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    Jan 21, 2010
    That's pretty easy to google for, but there is another problem. You need to do something with the data pins. The ipod doesn't like to charge from USB unless it sees something on the data lines.

    Look here for something similar. (Note that I would not recommend opening up one of these power supplies to do this -- I'd connect the jack to the wires that come out of the wall wart).

    Another problem you will have is that a 317 will need more than 6V to generate a regulated 5V supply. And as the batteries start to discharge it will get worse.

    You could look at a low drop-out regulator (e.g. LM2940CT). They are available with the same pinout. They are often a little more stringent in their requirement for input and output capacitors.

    The specs of the LN2940 say it requires a minimum of 5.5V to generate a 5V output. For an LM317 you'd be looking at an input voltage of 7V under the same conditions (25C and 1A). At lower currents the required voltage is lower, but not substantially.
     
  3. hyudryu

    hyudryu

    64
    0
    Feb 24, 2010
    No im regulating from 6Vdc to 4.2V
    And i tried measuring all 4 pins on the USB after plugging it into my ipod but nothing came up on my voltage meter... Because im assuming the pins 1 and 4 connect directly to the battery in the ipod thats why it can charge. Standard is 5V right?
     
    Last edited: Mar 30, 2010
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You need 5V for USB. 4.2V is wrong (where did you come up with that?) Measure between pins 1 and 4, and don't short out the pins. I just measured mine and got 5.04V

    Look at the link I gave you. You need to do more than connect +5V to the correct pins.

    And don't connect it backwards or bad things might happen.
     
  5. hyudryu

    hyudryu

    64
    0
    Feb 24, 2010
    I just tried pumping 5VDC into my ipod with a power supply and it actually was charging but it only took in 100 mA... Thats going to charge VERY SLOWLY
    And can i use a Zener diode as a regulator?
     
    Last edited: Mar 30, 2010
  6. hyudryu

    hyudryu

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    Feb 24, 2010
    When i measured it, Nothing. But when i connect it to power supply, it charged at 100 mA
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yeah, you can increase the voltage to 12V. I suspect the ipod will then draw more than 100mA. But then smoke will start coming out of it and it will never play music again.

    You can use a zener diode to regulate the voltage, but unless your power is coming from a solar panel, it is extremely wasteful of power. A low drop-out regulator is the way to go (a good alternative would be a switchmode regulator, but then I would advise using 6 1.5V batteries)

    hahahaha, It sounds like you're measuring the wrong end. Measure at the end that the power comes OUT of, not the end that the power goes IN to.
     
  8. hyudryu

    hyudryu

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    Feb 24, 2010

    Thats what i did. Oh well. So zener diode just converts the rest of the energy to heat?
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
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    Jan 21, 2010
    Don't tell me you connected it to 12V.

    What value series resistor did you use with the Zener, and what power ratings did they have?

    edit: oh, you measured the wrong end. That's OK :)

    A zener is a bad idea. It's a shunt regulator. Look that up. You want a series regulator (like a 317) but because your input voltage is so low in comparison with the output voltage you want, you need a low dropout regulator.

    If a zener was a good idea, I would have suggested it to you. :)

    For any linear regulator, the excess power is converted to heat. Switchmode regulators don't, but they are more complex.
     
    Last edited: Mar 30, 2010
  10. hyudryu

    hyudryu

    64
    0
    Feb 24, 2010
    I didnt connect it to 12 V but my ipod has some sort of digital circuit breaker or something.
    When i charged it using 5V, i slowly raised the voltage to see if it would charge faster, but surprisingly, It blocked the input power at 5.7V...:eek:
    But even if i was measuring the wrong end, the voltage meter should at least go backwards... Not stay at 0
    Oh BTW, do you know if there is any Touch switches in existance? Like an ipod touch, but just 1 switch inside. Its either on or off. Its turned on by your finger pressing it.
    And charging my ipod at 100 mA, If i use batteries and charge it with say, 1A, will only 100mA go in or will all of the 1A go in and smoke comes out and no more music?
     
    Last edited: Mar 30, 2010
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    :eek: is right. I won't even try to explain to you how stupid it is to power something designed for 5V from a higher voltage.

    Bwahahahaha. No it shouldn't. Why don't you place a voltmeter across the prongs of the plug attached to a toaster. Do you expect -110 VAC? The power (in this case) comes from a wall socket. You don't expect to be able to read some voltage suck on the toaster when it's not connected.

    What is a negative AC voltage? Interesting concept.

    I really don't know what you're asking for here.

    At 5V the ipod will draw as much current as it wants (providing the power supply can supply it). If the power supply can supply 10000000 amps, it will still only draw 100 mA because that's what it's designed to do.

    If you change the voltage, the current *may* change, and you may fry your ipod.

    Look, here's a simple explanation of voltage and current:

    Imagine your battery is a tank of water. The voltage is like the pressure in the pipe coming from the tank. Current is a measure of how fast the water flows along the pipe.

    With this particular tank, it can maintain the pressure (voltage) at up to a certain flow rate (current). After that, if you try to draw water faster (more current) then the pressure (voltage) drops. Of you try to draw water *really* fast, then the tank will implode.

    Now, imagine your ipod is a magic box connected to the pipe. At a given pressure (voltage) the ipod will allow a certain amount of water to flow (it will draw a particular current). If the tank (battery) can't supply water that fast (excessive current draw), the pressure (voltage) will drop. However if the ipod is connected to a huge tank (battery) with the same pressure (voltage), it doesn't matter that it can supply water at a high rate (high current) because the ipod will only draw water (current) at the rate it's supposed to.

    A battery or other power supply's ability to supply current is a property that determines the maximum current it can supply, not the rate it will supply current. Voltage, on the other hand, IS the voltage the battery will supply (under normal conditions)

    Please, Please, Please, go and learn about ohms law. It will really help you understand the very basics of electronics. And I mean the really really basic stuff. If you are not conversant with that then you are really doing yourself no favours.
     
  12. hyudryu

    hyudryu

    64
    0
    Feb 24, 2010
    Well, i finished it. Thanks for everything especially the diagram that shows which pins of the USB is 5V and ground. I finished it using a L7805CV Fixed Voltage regulator at 5VDC. I power it using 6 AA batteries and i attached a heatsink to the regulator
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
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    Jan 21, 2010
    Good job. I doubt that you'll need the heatsink though. It will only be dissipating a couple of hundred milliwatts at most.

    I presume it remains pretty cool to the touch?

    Did you read the datasheet?

    That regulator is really not appropriate. It will fall out of regulation as soon as the batteries get even a little flat. Once the voltage per cell falls below about 1.75V (and that is higher than they are brand new) The regulator won't regulate any more.

    I may have mentioned this before, but you *really* need to replace that with a low dropout version of the 5V regulator.

    This would be a far better option.
     
    Last edited: Mar 31, 2010
  14. hyudryu

    hyudryu

    64
    0
    Feb 24, 2010
    My charger can provide 1.5A at max. Will , for some strange reason, the charger pump 1.5A into my ipod and start smoking and no more music?
     
  15. mav2

    mav2

    5
    0
    Apr 14, 2010
    ipod power

    why go through the hassle, buy a cheap cord the kind you can take the plug apart, put a positive wire on pin s 19 and 20, and a negative wire to pins 29 and 30, hook them up to 12 volts, and the ipod does the rest, those pins are the firewire +,and -, which is 12 volts, i did this for my motorcycle, works great, add a 10 meg resistor between pins 21 and 29, and when you shutignition off the ipod will pause.. also the analog out of the ipod plug is 1and 2 are ground, 3 and 4 are right and left audio,
     
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