Making a mega multi-port usb rapid charger?

I'd like to build a usb rapid charger with a minimum of 8 ports (but the more the merrier, 16 would be ideal) that can provide a minimum of 1A per port (2A preferred for rapid charging).  I'm thinking, for a smaller foot print, that I could use a 250W mini ITX power supply, but I don't know how much I can get away with putting on the 5v rail alone.  I'm willing to build circuits to use the other voltage outputs if necessary, but I know very little about circuit design and would need to be able to find appropriate schematics at the least, if not actual pcb kits.  Each usb needs to provide stable power, regardless of how many other devices are plugged in, for picky devices.  The devices to be charged are all Samsung.  If I'm not mistaken, I should be able to put them in rapid charge mode by connecting the two data lines on each port, but I'm open to suggestions, in case the charger is later used for Apple products.  I plan to have a fuse for each port, perhaps 3A.  Would I need a bigger fuse further upstream for the whole charging circuit?  Say, 24A?  Also, if any other outputs will be used besides the built in 5v, I'd like to find the most efficient means of using these, the less waste-heat produced, the better.  I feel like there is probably enough information on the webs to put this together, but I'm finding conflicting info, and since the device will not always be under my direct supervision, it needs to be fool-proof and safe.

Thanks, in advance,

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Get a decent PC power supply and attach the USB jacks directly to the 5V rail. The 5V rail needs to be rated at no less than 20A if you want each port to have up to 2A available per port. To keep compatibility with apple and other devices you'll want to set up a couple of resistors in a voltage divider arrangement on each data line so the data lines are being fed about 2V to 2.5V each. This enables apple products and some other products to start charging.

tinkerist (author)  mpilchfamily3 years ago

The more I look at this problem, it seems that there might be other, more appropriate power supplies. I've found some 5v 40a LED drivers that I think will do the trick. Most of them seem to have 3 v+ and 3 v- rails. I assume that that 40a rating is using all rails, but do I use the v- rails the same way as the v+, only backwards? Does the ground go in between?

if im not wrong led drivers are constant current drivers so i think they will try to rise voltage to enforce current. that might blow up your devices. i use a 25W power supply. i tuned it to 5.32V. i use that with 10 port usb hub. it is connected to computer so i wont mess with data pins but i strengtened power and ground lines with some copper wire. i wouldnt mess with led drivers :)

The -V rails are of no use in this project. Get a pair of the power supplies and split the USB ports between them.

tinkerist (author) 3 years ago

i've seen a usb mega-hub that will charge something like 26 devices, but it's obviously way cooler to build one. 12 tablets in rapid charge mode would draw about 126 watts, i'm going for 16, which would draw about 168. with internal resistance and inefficiencies i think i could get by with less than 200W for the whole contraption, but i'm aiming for a power supply that can handle 220 or more, just to be on the safe side. after a bit more study, i think i'm going to either get an LED driver or just build a supply from scratch. I really don't think it will be all that difficult, but my main concern is making sure the voltage is as "clean" as possible, even when things are being plugged and unplugged all the time, so that the devices don't reject the charge as "not supported". i'm thinking that this will require a sort of power supply within a power supply arrangement, where i'm supplying perhaps 10 or 12 volts to pairs of ports with a regulated 5v supply at each port.
there's also the problem of potentially offering rapid charging for different devices, which will require either switchable modes, or a little internal computer (perhaps an arduino or raspberry pi) that can detect the type of device and give an appropriate signal on the data lines. for example, samsung goes into rapid charge mode when the data lines are shorted to each other. the samsung sees a data "echo" and assumes that it is a proprietary charging device. this is true of most devices. however, i think apple has multiple charging modes, and for maximum charging speed a low current 2v is supplied to the data lines.

When the device says the charge is not supported its connected to a cheap charger that is only providing current to the power lines of the USB port. Those devices are looking for the 2V to 2.5V on the data lines like i said before.

tinkerist (author)  mpilchfamily3 years ago

yeah, that was a copied and pasted comment from elsewhere. some of it didn't really apply. but thank you for your responses!