parts:
U1 NE555 timer IC
R1 2.2k ohm resistor
R2 15k ohm resistor
C1 0.01 uF ceramic capacitor
C2, C3 220 uF electrolytic capacitor
C4 470 uF electrolytic capacitor
D1, D2 1N4002 diode

all resistors are 5 or 10 percent tolerance, 1/4-watt
all capacitors are 10 percent tolerance
this circuit rougly doubles the voltage of the input, however the current output is low. doubled output is at 'V source.'

I think this is what i've been lookin for... a couple questions though:

Where can i get these parts? The ic in particular... i think i can get everything else at radioshack

This is what I plan on doing...

I want to create an external battery pack for my ipod. The ipod's specs are 8-30v, 1A max

The oem charger outputs 12v's via firewire 6pin adapter
orginally, I was thinking about using 8 aa's (1.5v) in series to get 12v's... but this is incredibly bulky... so i was hoping for a way to get 12v's with less batterys. This circuit will allow me to do so with 4 batterys right?

Also, it's bad to mix battery sizes right? I shouldn't be combining 9v';s and 1.5v's in my circuit?

Also, I'm not sure how the charging circuit works inside my ipod... I'm not sure if there will be charge sharing going from my ipod to the external pack, can i solve this with a simple diode? Or is the problem more complex?
For example, if the voltage of my ipod is higher than that of my external pack, would all the charge leave my ipod (bad) and go to my battery pack?

Is there anything else i should consider?

thanks
Henry

also... what happened to pin 5?

Hey,

actually I think this circuit will not give you any more voltage than you supply the 555 timer chip with. the 555's have an opamp inside of them, and that's how the op-amps work..

you can pick up these 555 chips at radioshack as well.

I don't think there's anything wrong with connecting different battery sizes together in series.

I think to actually double the voltage beyond what you have already, you'd need a transformer and be willing take a loss on current. But transformers wouldn't work on anything portable very well..

Andrew is wrong.
The 555 creates a pulsating DC that goes through a diode to double the voltage and then through a capactor or two to smooth the pulse.

But, I am not sure that you can get 1A with a 555. Maybe you can squeeze 50ma out, but that may not be enough.

Take a look at other sites that provide power supply theory about voltage doublers, triplers, etc. These have been around for quite some time.

I'm a little late with my reply, so I guess this is for anyone else that may be considering a similar portable power pack.

The thing that needs to be considered here is 'energy' or 'power output over time'.

"The oem charger outputs 12v's via firewire 6pin adapter
orginally, I was thinking about using 8 aa's (1.5v) in series to get
12v's... but this is incredibly bulky... so i was hoping for a way to get
12v's with less batterys. This circuit will allow me to do so with 4
batterys right?"

First let me say that I know nothing about ipods power requirements. So I will use your supplied info with a worst case scenerio, that is; 12 volts @ 1 amp.

A typical alkaline AA battery is rated at 2700 mah, or 2.7 amp hours. That doesn't mean that it will produce 2.7 amps for an hour, What it does mean is that it SHOULD produce 270 ma for a period of 10 hours. That's way short of your required 1 amp.
A typical alkaline 'D' cell battery is rated at 18000 mah, or 18 amp hours. Ok so here we have a battery that has the capacity to supply the needed 1 amp. Now string 8 of them in series and you will have a portable charger that will last approx 18+ hours at 1 amp load. But this really doesn't fit your desire to make it small. Nevertheless for a moment let's say that you would be content with a size of 4 'D' cells = 6 volts -> voltage doubler circuit -> 12 volts into ipod. Problem solved right? Wrong! You can't get energy for free.

12 volts at 1 amp = 12 watts. This is what your battery pack will be required to produce (assuming for simplicity that you used a perfect, 100% efficient, lossless voltage doubler), regardless of the number of cells or their voltage.

Therefore, using 4 'D' cells, you have 6 volts from which you must draw 12 watts. Ohms law tells us that 2 amps will be required, which once again puts the power draw over the battery's rating. Though the batteries can supply 2 amperes, their useful life decreases severely with the increased current.

The bottom line is that there is no way that 4 AA's will do what you want. Your best bet is to make a car cigarette lighter adapter to charge your ipod, unless of course you are a hiker or mountain climber (or have a phobia of cars), in which case it would not be practical to carry your car along with you.

Hope this helps somebody.



Rod Frary
* Be who you are and say what you feel; 'cause people who mind don't matter, and people who matter don't mind.