as taken from the issue tracker ticket here
Vierlex and myself are researching the possibility to create a new addon for the Metalab in addition to the PowerZ: A five-port USB 2.0 version of it that is compatible with iPhone, iPad and all other devices that don't use the USB charging standard.
We looked into commercial solutions and were unable to find any that support more than one device (this could have been one: POP, but the device was canceled due to issues with Apple).
The iPad is the most demanding device for this application, and needs 1.5A-2A to charge, which means 10A in total. Thus, I propose the following power supply:
It uses convection cooling (thus is silent), has <300mW no-load power consumption and has 80% efficiency. These properties were deemed very important and aren't available on cheaper parts (or PC power supplies).
The iPad needs a specific setup of resistors to accept a charger for 2A charging:
both need 49.9kΩ to GND and the following resistor to 5V:
I'm not sure whether we're really capable of soldering a lot of 2mm SMD resistors… That's up for discussion. UPDATE: Meta and wizard told me that we have access to a reflow oven, so SMD is the way to go!
Additionally, we would like to add self-resetting fuses to the ports to avoid burning them down (by drawing 11A from a single port). This would fit the bill: Bourns MF-MSMF125-2
It would be cheaper to make multiples of these at the same time.
materials & costs
- Fuses: €0.461 × 5
- 49.9kΩ: €0.046 × 10
- 43kΩ: €0.023 × 5
- 75kΩ: €0.118 × 5
- Board (Conrad price): €0.80
- USB socket: €0.98 × 5
- Power supply: €35.63
- Molex 6pin: €0.27
- Molex 3pin: €0.107
- ICE power socket w/ 10A fuse: €4.62
- Power cable: €5.10
- Cabling: ?
- Casing: ?
total costs, except for the ones marked with “?”: €54.90 + €10.98 VAT