Nexus Mosaic, providing constant power to 24 android tablets  - Page 1
Forum section: electronics / projects

author: sean87
author_rank: Regular Contributor
timestamp: November 19, 2013, 12:54:17 pm
content: Hey guys,In last few weeks I was busy making an Android app that plays a movie divided in 24 devices. I am running the demo succesfully on 24 Nexus 7 tablets.No I am facing a challenge! all this time I had to charge the tablets, and they usually last for few hours. Now I want to mount them on a board, so I need to find out a way to constantly provide power for them.EachThe option of removing backplate and connect directly to a PSU is a no go, since I don't want to void the warranty, and the wifi antenna is on the backplate (The videos get synced through WiFi with a time server). Now I have some very thin right angled USB plugs that allows the tablets to be close to each other, so now I have to find a way to power up all tablets using usb port.I did a search, and found a power supply like this:http://nl.farnell.com/tdk-lambda/ls150-5/psu-enclosed-5v-26a-150w/dp/1657459?Ntt=1657459So my question is, is going for 2 of those supplies, and ordering some PCB mountable usb jacks and connect all them to that power supply in parallel (current divider?) a good idea?What you would suggest in this case!? please let me knowThanks!

author: Clint
author_rank: Regular Contributor
timestamp: November 19, 2013, 01:04:43 pm
content: Out of interest do you not have the supplied PSU's ?

author: sean87
author_rank: Regular Contributor
timestamp: November 19, 2013, 01:09:51 pm
content: Well yes, but I am thinking of a ultimate solution

author: penfold
author_rank: Frequent Contributor
timestamp: November 19, 2013, 01:18:10 pm
content: It doesn't have to be a USB port, you can drive them all from a 20A 5V supply or two.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 19, 2013, 08:23:27 pm
content: Easiest solution would be to just use the supplied chargers and a few power strips. A neater solution would be to use a PC power supply wired to a bank of USB sockets. Just tie the data lines to each other to enable full speed charging.

author: Balaur
author_rank: Unknown
timestamp: November 19, 2013, 08:49:49 pm
content: Are the tables 2012 or 2013?If 2012, maybe you can use the pogo charging port (left side of the device).If 2013, you can use QI wireless charging pads (if you find them at a good price)

author: dannyf
author_rank: Super Contributor
timestamp: November 19, 2013, 11:19:56 pm
content: Wireless charging if the device supports it.

author: DavidDLC
author_rank: Frequent Contributor
timestamp: November 20, 2013, 05:32:11 am
content: http://www.engadget.com/2013/11/19/nexus-wireless-charger/

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 20, 2013, 08:23:52 am
content: You can buy somewhat decent QI compatible charge pads for about $20 USD each.Then grab oen of these;http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_123394_-1

author: mobbarley
author_rank: Regular Contributor
timestamp: November 21, 2013, 01:08:13 pm
content: A couple of powered USB hubs?

author: strangelovemd12
author_rank: Regular Contributor
timestamp: November 21, 2013, 06:55:09 pm
content: You might need to clean up the signal from the linked PSU to protect the Nexus devises and/or get them to function properly. I am not sure how well everything is regulated these days, but many older USB devices would smoke if fed anything outside of spec. Speaking of which, checkthisout for helpful general info.Also be wary of using USB hubs. USB spec says 5v 500ma per rail, so daisy chaining a bunch of hubs is bound to fry something.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 21, 2013, 07:22:23 pm
content: Any good PC PSU will work just fine for that application. If anything, it would likely be better than the supplied chargers.

author: ddavidebor
author_rank: Super Contributor
timestamp: November 21, 2013, 07:30:02 pm
content: A GOOD QUALITY switching power supply 5v will do that.Absolutely not a chinese crappy one. If it fails you will have a lot of dead tablets.You should Buy something for industry of a reputable brand and from a reputable distribuctorSome extra protection can be a good idea, like a lot of zener in parallels and a overcurrent protection.Also, you will need big cables, the current you need is not a joke and the voltage drop may be unaceptable.