Archive for the ‘iPhone car charger’ Tag

Cheap DIY iPhone External Battery

The beauty of this design is that you can take a box of AA batteries with you on a trip and not have to worry about your phone dying and you can buy AA batteries just about anywhere.

Use your existing docking cable to connect the iPhone to the battery. I prefer this method to the one where the battery attaches to the phone directly. The battery can be in your pocket or purse while you use your phone normally with just the cable connected to it.

Caveat: I did this and tested it on my first generation iPhone!!! Should work on new 3G iPhone but I haven’t even seen one yet.

Radio shack sells a 4 AA battery holder with on/off switch for $1.99.
Radio Shack 4 AA battery holder

Radio Shack 4 AA battery holder

I prefer rechargeable batteries but any AA will do.

Type A female USB connector

Type A female USB connector

You will need a female Type A USB connector. I had one laying around that came with the last motherboard I bought.
USB A Male to A Female Extension Cable

USB A Male to A Female Extension Cable

You could also buy  a cable from Amazon.com or cablestogo.com and cut off the male end. (OUCH)


Computer end of USB cable

Computer end of USB cable

I cut off the end that was intended for the motherboard.
Type A female USB connector

Type A female USB connector

Now you would think that all I needed to do was connect the Red (VCC) and Black (GND) to the  battery and it would be done. I tried that and it didn’t work.

To make a long story short, the iPhone wants to see some voltage on the data pins or it will not start charging. I created a voltage divider with a couple of huge resistors (100K) and tied both data pins to the junction which yields half of the battery voltage which seems to satisfy the iPhone. The current drawn by those two 100K resistor is 30 microamps at 6V.

Wiring Diagram

Wiring Diagram - pin colors = wire colors

Resistor divider under shrink tubing

Resistor divider under shrink tubing

I forgot to take a picture of the resistors before I put the shrink tubing on but believe me, the resistors are in there.
You can tie the shield to the GND wire but I didn’t bother since there is no data being transmitted over this cable.
External iPhone battery for less than $10.

External iPhone battery for less than $10.

Here is the finished product. I pasted the diagram on the box because 2 weeks from now I won’t remember what the hell I did to make it work!

I suggest you turn off the off the switch on the battery holder when not in use to prevent the resistor divider from draining the the batteries. (Do not despair if you don’t have an on/off switch, it will take a long time to drain the batteries with a 30 microamp load.)

WARNING: There are no guarantees and I will not be held responsible for you damaging your phone.  I only tried this with my phone using 4 NiMH batteries that were putting out about 5.2 volts.

I would love to hear from you if you found this article useful or if I made a glaring misteak!?!

7/24/2008
I just ordered a car charger for the iPhone for a nickel plus $2.98 shipping. It has the iPhone specific connector that I can use instead of the female USB connector. I will update this blog when I have tried it.

iPhone car charger

7/29/2008
I just received the above charger and although it works it is not what I was looking for.

Charger circuitry

The board contains 4 capacitors, 5 resistors, 1 diode, 1LED and the regulator IC.
Two wires connected to Firewire power pins.

Two wires connected to Firewire power pins.

Unfortunately the cable only has two wires in it and the are attached to pins 19 & 20 (Red, Firewire power +12 VDC) and pins 29 & 30 (Black, Firewire ground).
This charger supplies approximately 9 VDC to the Firewire power pins and it seems to do the job.
I also ordered the following cable for 33 cents plus $2.98 shipping.
Retractable USB to iPhone cable

Retractable USB to iPhone cable

This one should do the trick. When I receive it I will cut of the USB end and wire it directly to the battery pack.

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