Electronics > Electronics

creating a external phone charger

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I am trying to build an external battery pack consisting of 8 rechargeable batteries to power my blackberry phone
their hooked up so that the batteries together have a voltage on 6 volts(other batteries are in parallel for storage)
using a 5 v regulator(or something ) i will get 5 volts out of the phone

will this work? also how can  I prevent overcharging( the phone battery i want to charge is a lithium ion battery)
do i need other components as well?

If you supply the 6V into the USB input of the phone, you will possibly destroy the phone.

If the phone expects 5V, then you need to get a 5V regulator. A LM7805 or similar would be fine, except it needs a 7V input minimum, and it also will "burn off" extra energy, so it will not be very efficient (60-70% efficient.)

I suggest that you wire all your batteries in series, and then get an efficient 5V buck converter. It can easily be > 90% efficient. The Murata OKI-78SR is under $5, and runs on 7V to 36V in. (You could also add a car battery input very easily here.)

The final thing to note is that 1.5V batteries will actually have a higher votage when fully charged, and a much lower voltage when discharged, so the "6V" you're suggesting will be more like "7.5V when full, 4V when empty."

then what other battery source could i use?
the port where i charge the phone is the same one used to connect the phone to a usb port on my computer
since the usb supplies 5v the port could be used


--- Quote ---then what other battery source could i use?
--- End quote ---

There is no battery that has constant voltage.
That's why you need a regulator.
I described how you can use the batteries you have in series configuration, with an inexpensive switching regulator, to provide the appropriate voltage, and this would work on the power pins of the USB port. You will likely want to short the two data pins of the USB port together, to indicate to the phone that your regulator is a "dump charger" and can provide 1A of current. (Assuming your batteries can actually provide that current!)

why exactly do i need to short the data pins-how does the phone pick up on this exactly?
will 1 A be enough?how can i increase that if i needed to?


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