ChinaPhil wrote:I use an iPhone 4 for navigation and have been trying to power / charge it with one of these converters set at 5V and powering a USB charging cable - cannot get it to work, any suggestions?
The iPhone 4 needs to sense voltage on the USB data pins. Its wall charger definitely outputs 2V & 2.7V on the two USB data lines, as well as the 5V on the USB Pwr pin.
If you have some electronics experience, follow the instructions below to construct your own charging adapter cable.
If you never soldered before, then donâ€™t try. If you connect things wrong there is the potential risk of damaging the phone.
As usual, if you do make your own cable, you do it entirely at your own risk. If your phone dies, do not blame me. Mine is working fine, so the procedure does work if done properly.
READ ALL STEPS BEFORE STARTING WORK!
The USB has 4 wires:
Red-5V, White-Data, Green-Data, Black-Gnd.
They are numbered Pin1 to Pin4, in the same order, ie Red =Pin1.
1. Cut the USB EXTENSION lead, trim both pieces to a shorter size, but make sure you leave enough length to work with !
2. Cut off the foil-shielding on both pieces, twist the braided wire shielding into a single â€œwireâ€ on each piece.
3. On the female piece of the lead solder resistors as follows:
R1=2K2; R2=680; R3=2K2
4. Trim resistor legs as short as possible. Make sure you put some insulating tape between all the exposed bits of wire and resistor legs. You want to pack the resistors as tight as you can, and you do not want any metal bits touching!
5. On the male end of the lead, cut off the white and green wires; you DO NOT want to connect them to anything! If they were connected it would feed power back to the car adapter, which could conceivably have those pins grounded as theyâ€™re usually not used (hence the iPhone 4 charging problem).
Even worse, you might one day accidentally plug this new DIY adapter cable into a USB port on your PC, and it may take offense at having power coming in on the data lines.
So cut the green and white wires on the male end.
6. Cut a piece of large-diameter heat-shrink and slide it over the male piece of the lead. It should be long enough to later cover the area where the resistors are. Hence the male end of the lead needs to be at least as long as the length of heat-shrink you need!
7. Join the two pieces of lead by soldering the male red wire to the female red, male black to female black, the shields to the blacks.
8. Carefully compact all the resistors together, ensuring there is insulation between adjacent metal parts, and that nothing comes lose. You might need to think about how you want to pack the resistors BEFORE YOU SOLDER!
Then slide the heat-shrink over the resistor assembly until it overlaps the untouched part of the the USB cable on both sides of the resistor assembly.
Heat up heat-shrink to make it grip.
* If the assembly is bigger than the heat-shrink you chose, remove heat-shrink and tightly wrap the entire cable with electrical tape instead. Done!
9. WAIT! DO NOT CONNECT iPhone, yet!!!!
10. Connect your new adapter cable to the DC-DC converter.
With a multimeter (and thin probes, or bit of stiff wire soldered to the probe tip) measure the voltages you get on the female end of your new adapter cable.
Put the Gnd-Probe on the plug shield, and be extremely careful with the other probe not to touch both the shield and a pin at the same time.
You should have ~5V on Pin1, ~2.8V Pin2, ~2V Pin3, 0V Pin4.
If you do, Congratulations, you now have a USB adaptor cable that will turn any plain USB voltage adaptor into an iPhone 4 charger.
If you have no voltage, you might have forgotten to solder the shield to the black. Put Gnd-probe on Gnd-Pin4, then measure all other pins and shield. If the pins measure ok, and the shield is still 0V, you are probably ok too.
All other results, and you need to re-do your cable!
11. IF YOUR CABLE MEASURES OK, at your own risk (!) you can now connect your iPhone to the adapter cable, and then into the DC-DC converter. It should now charge.
Note: Apple states that the iPhone should only be connected to authorised chargers,etc. Using the DIY adapter cable could potentially void your warranty.
Please be careful though :
When cutting an USB extention cable : Do not rely on the wire colours !!!
Mine had red colour connected to pin2, black wire connected to Pin 3, green (5V) connected to pin 1 and white connected to Pin4 (GND)
Measure twice !