Homebrew USB charger - won't charge iPhone

[pointAndy]

I had some spare parts lying around so decided to turn them into a solar powered iPhone charger. The problem I have is it seems to charge / power any USB item I throw at it except an iPhone / iPad. If I plug in an iPhone it doesn't register anything at all, no charging icon, no complaint, no lighting up when it detects being plugged in. Any suggestions?

Basic set up is: solar panel -> solar/battery charger -> 12v battery -> 5v step down converter (not a linear voltage converter as I wanted to reduce power loss) -> USB jack (black and red wired, data lines currently floating) -> standard iphone cable -> iPhone / iPad

• I've checked output voltage, it's keeping 5v out on the USB side no matter what's connected
• I've checked current output. With nothing connected the voltage regulator consumes about 16mA from the 12V battery. With an iPhone connected that increased by about 50mA. With any other device connected it goes higher (max I read was about 350mA on the 12V side).
• I've tried two iDevices (one iPhone 7 and one iPad Mini) both with lightning cable ports.
• I've tried more than one lightning cable.
• All devices charge on all cables when plugged into a computer or usb charger (including non apple chargers)
• I thought maybe my power converter was generating a lot of line noise so I tried a capacitor across the 5v and gnd but that didn't make a difference either.
• I've tried powering a USB hub through it's 5v power port and charging via that; again, works for everything that isn't an iPhone.

I've read that the data lines can need resistors across them. I figure that's only if I'm making an iPhone cable right? Shouldn't a cable that works when you plug it into any USB port or charger work with my setup above? I'm not the first one to try this but all the other projects I've seen don't mention having any difficulty getting the device to charge when they've done the above. Anyone have a suggestion to try or better yet, had this issue yourself and fixed it?

[NiHaoMike]

The data lines should either be connected to each other or biased to certain voltages. I suggest just connecting them together since that's what the official USB spec says to do for a dedicated charging port.

[Decapitator]

Apple chargers incorporate a handful of resistors to bias the USB data lines (D+ and D-) to specific voltages that identify the capacity of the charger.

https://electronics.stackexchange.com/questions/177788/how-do-i-design-a-2a-or-more-power-supply-for-my-consumer-usb-devices/177792
http://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/

[floobydust]

You need bias resistors so the device knows how much charging current is available. It's a mess between manufacturers as a few chose to be unique.
Lately I'm trying an auto-bias IC like Prolific MT5887/9 which looks after the mess.
There are a few part that do this, although the IC's from Asia are simpler in a SOT-23-6.

[pointAndy]

Ok, you were all right. The resistors are needed after all.

I tried connecting the two data lines together and this at least gets the iPad to the 'not charging' 500mA charge rate. So I'm pretty sure once I fish around for the correct resistors it will happily charge at the full rate.

Thanks for the help!