Portable, Battery Operated USB power supply [Home made]

Impotence

Impotence

May the source be with u!
The Problem:

My mp3 player, with its lovely -internal- battery cannot simply be replaced when it dies!

The Idear:

A cluster of batteries, attached to a USB Socket (a FEMALE plug)

Basic Spec:

a USB port on your computer supplys 5V with a maximum current of 400 mA [anything above and the computer refuses to power the device]

The batteries im planning to use are rated @ 1.2V 2300 mAH (didgital camera battery's). I'm planning to use 8 like this:-

/--[BATTERY]-[BATTERY]-[BATTERY]-[BATTERY]--\
---< >---
\--[BATTERY]-[BATTERY]-[BATTERY]-[BATTERY]--/

(If the above diagram doesnt format correctly, its two lines of batterys in series, and then the lines connected in pararlel)

Which SHOULD supply 4.8V.

4*1.2 = 4.8, and the other 4 batteries are in parrallel (which will double the available charging time).

What i have done so far:

Cut a USB cable in half, I found 4 wires..... Power[+], Power[-] and two other wires, Data to and from the device at a guess (But there unimportant, as the wont be connected to anything!)

Found a *possible* Battery holder, but it was designed for Cybot (Real Robots :P)... and is also two separate battery packs in one so it might need some modding!

What needs to be confirmed:

V = IR, so I = V/R

V = 4.8
R = X
I = ?

I BELIVE that Resistance, X, Ω is dependant on the device.... and that is how a manufacturer sets the current drawn by the device. The problem is, if I'm wrong then I'm about to unload 18,400 mA of current through my mp3 player in a couple of seconds! :x: which would NOT be good!

I Might also add a method of charging the battery's without having to remove them from the holder. When i get this made, it should be suitable for any usb device that can charge itself off the power supplied by the computer (IPOD's etc)

What im worried about, is why has no1 else done this? it just seems a bit too simple and im worried theres a good reason it hasnt been done!

*edit*

I have thought of a way to limit any damage to my mp3 player (if any) when i test it, If i include a variable resistor with a range of 0-XΩ [and insert a multimeter into the circut to test voltage and current values) i would be able to reduce the resistance slowly.... and keep an eye on on things!

*edit*
 
where is the problem?........lol

All you have written seems to be very good. Reason which I believe why people dont want to do this is.................. Scare of damaging their own computer, Not have enough knowledge like you, not a requirement(they might be using charger or smthing for charging their batteries).

Take me as an example. Everything you have written is going above my head~! SO I will never gonna try this in my life time unless I have nothing to do and have extra money.
I think its physics and I havent done physics.
 
I Have the charger :P Just i need somewhere to plug it in!

also forgot to mention that There rechargeable battery's, and they cost £10 for 4 out of a camera shop :eek:

I have one final question!

If each battery can supply a mA for 2300 hours, and my device draws 200 mA... how long will the battery pack last?

I know that adding the extra battery's in parallel will double the time.... but I'm unsure about how long just 4 battery's would last! i just cant get my head thinking along those lines (but i know the reply I'm going to get will most likely insult me :P)

I'm thinking about getting a big leather trench coat... and wiring it up with a usb hub + cabling so i can plug phone, etc + battery pack in..... so it will all charge! (and it would rise me to a, omg..... that guys such a geek :D)

Of course, i would also have a retractable usb cable inside the jacket! [sit down, plug in the jacket!]
 
Impotence said:
but i know the reply I'm going to get will most likely insult me
Click to expand...

How dare you think like this? You must 've heard that line "Different People doesnt do different things, they do things differently" Which you have done.
 
Karanislove said:
How dare you think like this? You must 've heard that line "Different People doesnt do different things, they do things differently" Which you have done.
Click to expand...


I was meaning, I do Tec studies @ Higher (Which would be an A-Level in england) but i cant get my head around battery life!

@Ninja.... are you sure its 11 hours? it looks like you did 2300/200 = 11, but there is an extra set of batterys in pararlel.... so would it be about 22 hours?

Both the I-Hacked & Hack-A-Day projects use 9V batterys with a 5V regulator :/ But im planning to use my method, as i have seen voltage-time graphs for lithium-ion batters and there bloody good! I cant find it now but first bit fo the graph is 1.3/4V, and then it hits 1.2V and stays constant untill the end of the batterys life (and then it drops to 1V before giving up!).

If Voltage drops then:

v = IR
--------------
V = 5
I = 0.2
R = ?

v = IR
R = V/I
= 5/0.2
= 25Ω < Resistance of the device
--------------

max voltage from cells = 1.4 * 4 = 5.6 V (Allthough i belive its more likely to be 1.3 * 4 = 5.2V)

V = 5.6V
I = X
R = 25Ω

V = IR
I = V/R
I = 5.6/25
= 0.224 A
= 224 mA

--------------

Min Voltage from cells = 1 * 4 = 4V

V = 4V
I = Y
R = 25Ω

V = IR
I = V/R
I = 4/25
= 0.16 A
= 160 mA
--------------

that gives me a voltage range of 5.6 - 4V & a current range of 224 - 160mA(charged - dead). I think some sort of voltage regulation is a need!

Im off to see what parts i can borrow from my school! :P
 
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