Author Topic: creating a external phone charger  (Read 565 times)

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Offline vipulan12Topic starter

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creating a external phone charger
« on: September 19, 2013, 05:34:42 PM »
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?

Offline jwatte

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Re: creating a external phone charger
« Reply #1 on: September 19, 2013, 07:12:16 PM »
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."


Offline vipulan12Topic starter

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Re: creating a external phone charger
« Reply #2 on: September 19, 2013, 08:07:31 PM »
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
« Last Edit: September 19, 2013, 08:25:25 PM by vipulan12 »

Offline jwatte

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Re: creating a external phone charger
« Reply #3 on: September 20, 2013, 09:57:21 AM »
Quote
then what other battery source could i use?

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!)

Offline vipulan12Topic starter

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Re: creating a external phone charger
« Reply #4 on: September 20, 2013, 05:43:07 PM »
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?
« Last Edit: September 20, 2013, 05:44:50 PM by vipulan12 »

Offline jwatte

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Re: creating a external phone charger
« Reply #5 on: September 21, 2013, 12:00:50 AM »
The USB port has 4 pins. Normally, pins 1 and 4 are power/ground, and pins 2 and 3 are differential data.
The USB device will signal speed to the host/hub by using a pull-up resistor on one of the D- and D+ lines.
A device that charges through USB will not draw more than 500 mA when just connected, because this is the maximum allowed by the USB bus. In fact, to be conformant, the device should not draw more than 100 mA without negotiating with the host -- thus, there needs to be logic on the host side (that supplies power) to go to 500 mA.
Because plug-in chargers shouldn't need to be USB hosts, a standard was developed where the charger can short D- and D+ together. The device can then detect this using its pull-up resistors and some logic in the device, and this is a signal that the device can draw 1A.
No standard exists to signal that a device can draw more than 1A, so most phones do not. There are some special cases with USB 3.0, and with iPhones that use some resistance for the shorting circuitry, which are not well documented. Unless you are charging an iDevice, or can provide a USB 3.0 host, don't worry about this.


Offline Roman505

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Re: creating a external phone charger
« Reply #6 on: September 21, 2013, 03:36:23 AM »
will 1 A be enough?how can i increase that if i needed to?
Whether 1A is "enough" depends on how much current you wish to offer the charger wnd what effect it will have on your batteries. As jwatte points out, all that is signalled to the device being charged is that the charger can supply at least 1A. More than that is whatever you happen to supply. If your supply batteries have a small AH capacity or are discharged beyond their limits (depends on the chemistry) they may have a short life.

 


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