This is a discussion on iPad 2 DIY Charger within the iPad DIY forums, part of the Apple iPad Discussions category; Originally Posted by Killerken Question: since I am thinking about using a 8 amp power supply do we need to regulate the power going to ...
And how do I build it into Tim's circuit?
I am now wondering if I can use a smaller power supply? I originally was going to use 5V, 5A, 25 watt power supply but this is to small based on my calculations. So i think I will keep the power supply that I mentioned earlier. I know that not every time every space on my charger will be filled but at night I could be easily charging 2 iPads and three iphones at the same time.
I saw on a circuit website that you can use at JFET current regulator but I don't know if this is the right device to use. On another site I saw the use of transistors to do the same thing. The key to the design that I want to make is small, compact and efficient.
The other thing that I would really like to add is a way to introduce led's into the circuit. So that when a device is pluged in a led light comes on and when the device is fully charged the led light goes out. This is not necessary for my first design but this is a wish for future designs.
As for the LED, I don't think it can be done. You would have to build another device for each iPad/iPhone that can tell the difference between fully charged and charging.
In theory, when the device is fully charged, it won't be pulling the same voltage and amps as it does when it is charging. So, if you could build a device that could tell the difference, it could be possible.
But this is just me speculating.
No need to regulate current to each device. Each device will draw the current it needs. Just make sure your power supply can accommodate the total current needed It is as simple as 5vdc through the USB cable outer pins and the voltages that I show on the inner pins of the USB.
Keep in mind that there is a tolerance on the 5vdc for USB. I am not sure the exact number but it can vary +/- somewhat and still work properly in spec. Typically +/-5% in industry. You should be able to look this up in Wikipedia.
The lambda power supply will do it but 8A may be a bit overkill. Double check the current draw on your devices. I believe the iPad only draws 2A when it is powered on and charging at the same time at full brightness. Getting a bigger power supply won't hurt you but streamlining this may save you some $$$$$.
Now that I understand your goal, then I agree a separate PS will make the most sense. Keep in mind that the PS will get hot when pumping out a full 8A. If you use a circuit board to make this neater, make sure the trace width and thickness is enough to carry the current that will travel on each trace.
Yay! Someone who knows what to do.
Timothy,Originally Posted by timothyb1969
Thank you for letting me know that i don't need to regulate current.
So let me understand this correctly :
1) Since I am using a power supply I don't need to use the voltage regulator that you had in your circuit.
2) I can used your resistance part of your circuit in one of two ways:
a) create one circuit and wire it to each of the usb connectors
b) create 6 circuits one for each usb port.
Am I correct in what i am stating?
Based on your EE knowledge which method would you take?
In a earlier email you spoke about building the power supply into the unit, how hard would this be? could we make it rather small?
Problem is current vs size. If you decide on a 8A power supply then the PS will be large. I think sticking with your idea of a inline power pack you can lay on the floor behind would be best. Then just buy a thru mount pc board style plug to detach the PS from the PC board for transport, etc. That is how I would do it. You could consider building the PS onto the board if you made a separate board for each device so you could locate them in different areas.Originally Posted by Killerken
1> bread board your circuit with the PS to verify all is working as expected before spending money on the final PC board.
2> Before you hook your iPhone or iPad up, double check the voltages on the 4 pins. Check them again once device is plugged in. That is check them each under full load to insure your 5vdc is being maintained
See my comments above.