Tim,
thank you very much for the quick reply. I ordered everything today so hopefully I should have everything in about 5 business days.

I now need to start designing and building the physical dock.

Ken

\@ timothyb..
good day! im a newbie trying to experiment here. i followed your drawings and managed to charge my ipad2 at a rate of
around 12- 15 % per hour versus around 25 % per hour charging of the original charger of ipad. i used and old atx power supply to get a 5v since i cant find a local supplier here in the philippines
that of 7805 with 2amps output.
my questions are:

1. when i measured that current im pulling from the atx power supply i got a reading of only around 500ma
is it this normal? or the source ( atx power supply ) cant supply the 2 amperes i need?
2. i tried to use the normal 7805, the cheap one, but the same result and it was very hot when i hooked it up
with the 12v output of the atx power supply.
does anyone know any replacement / or alternative to the old 7805? preferably a cheap one....
3. i have an old original sony psp charger that specified that it can give 2amperes of 5v
do you think this will increase the ampere of this circuit?

update:
i hooked it up with an original sony psp charger/adaptor 5v 2000ma/
got at 600- 660ma current which charges my ipad2 at a rate of 18% per hour

raffy/manila philippines /november 29, 2011

Tim,
I am wondering if you can help me.

I finally built the circuit board. I have 6 USB ports connected to the circuit board. The problem I have is as soon as I connect two ipads to the system the power supply shuts down. This is completely confusing me since I purchased a 5 volt, 8 amps, 40 Watts Max power supply.

Any ideas?

Also my voltage on my pins are a little different than yours even with using the same resistors.

Pin 1 = 5.2 V
Pin 2 = 2.091 V
Pin 3 = 2.976 V
Pin 4 = 0V

Please note it does not happen right away but it does happen 15 to 20 min later.

Any thoughts?

How much power does the iPad require to charge?

Originally Posted by markdevoll

How much power does the iPad require to charge?

5.1volts at 2.1amps

Originally Posted by Killerken

Tim,
I am wondering if you can help me.

I finally built the circuit board. I have 6 USB ports connected to the circuit board. The problem I have is as soon as I connect two ipads to the system the power supply shuts down. This is completely confusing me since I purchased a 5 volt, 8 amps, 40 Watts Max power supply.

Any ideas?

Also my voltage on my pins are a little different than yours even with using the same resistors.

Pin 1 = 5.2 V
Pin 2 = 2.091 V
Pin 3 = 2.976 V
Pin 4 = 0V

Please note it does not happen right away but it does happen 15 to 20 min later.

Any thoughts?

The voltages will can vary depending on the accuracy of the resistors. In other words, the actual resistance as opposed to the stated resistance. It is a simple voltage divider circuit and using the same calculations I did you could select some different resistors based on what you may have in stock. You may want to confirm the voltages on the original apple iPad charger under full load conditions. That is when the iPad is connected and charging. Compare the voltages on each pin to the values that I measured.

To get pins 2 and 3 to match the apple iPad charger exactly, you could use a variable resistor (potentiometer) to get the resistance just right to provide fine adjustment on the pins 2 and 3 voltages to get them just right. I am pretty sure that all the power for charging the iPad comes from the 5v on pins 1 and 4 and the current draw on pins 2 and 3 should be very small. I am not sure what the allowable voltage tolerance that apple requires on pins 2 and 3 to allow the iPad to charge as apple does not publish this information as far as I am aware.

The bottom line, once charging begins, your iPad should charge at the maximum rate and your PS should not shut down and your charging rate should be the same as the OEM apple charger.

If you continue to have trouble after you try all this let me know and I will give it some more thought.

Good luck.

Tim

Originally Posted by Killerken

Tim,
I am wondering if you can help me.

I finally built the circuit board. I have 6 USB ports connected to the circuit board. The problem I have is as soon as I connect two ipads to the system the power supply shuts down. This is completely confusing me since I purchased a 5 volt, 8 amps, 40 Watts Max power supply.

Any ideas?

Also my voltage on my pins are a little different than yours even with using the same resistors.

Pin 1 = 5.2 V
Pin 2 = 2.091 V
Pin 3 = 2.976 V
Pin 4 = 0V

Please note it does not happen right away but it does happen 15 to 20 min later.

Any thoughts?

Another comment- your power supply should have a trimming potentiometer or adjustment on it main board that will allow you to adjust the output to 5.0 as opposed to 5.2. This will also slightly change pins 2 and 3.

Another thought came to my mind. The iPad will only charge at when on under two conditions. 1> when connected to the apple wall charge that came with the iPad, 2> when connected to a high power USB port.
So how does the iPad know what type of USB port it is connected to? Figuring this out may be the answer to maximizing your charging rate.

Check out this link. They explain the different power charging capabilities of different USB ports. Sorry I only had time to skim this.
http://en.wikipedia.org/wiki/USB#Power

Also these guys have some good information that leads me to believe that the voltages on pins 2&3 tell the device how much current the USB port can supply.
http://voltaicsystems.com/blog/choos...nes-and-ipads/

This appears to agree closely with the voltages that I measured. I would use the 2v and 2.75v as my target for the data pins and make sure that the voltage divider can supply enough current to maintain these voltages. Verifying the pin 2 and 3 voltages under full load and adding a potentiometer to adjust the resistances on the voltage divider to get the precise voltages on pins 2 & 3 is the way to go.

Also, check the current draw on the PS after hooking up 1 iPad. Then hook up the 2nd iPad. The current should approximately double. If not, you may have wires something wrong and you may have a short or a current leak some where that is causing your power supply to overheat and eventually go into thermal shut down or into over current mode which requires cycling the power to your PS to reset.

Good luck and let me know how you make out. My schedule prevent me from always answering promptly but I always try to check and answer my emails and posts as best I can.

Tim