[Server-devel] 12 Volt power system for School Servers.

Tony Anderson tony_anderson at usa.net
Thu May 30 00:47:26 EDT 2013


The setup at the Kokobe Primary school in Lesotho has a small solar 
panel (too small) which attempts to charge two car batteries (deep cycle 
would be better but not available).

The router (Belkin) runs directly from the battery (we cut the cable). 
Linksys and other routers I have used all run on 12vdc at 1A.

The MSI server does not run on 12vdc because of the design of it's power 
supply which requires a higher voltage (15vdc works). I purchased a 
Zotac which also uses an Atom processor but houses a 2.5in drive. It 
requires 19vdc.

Most standard laptops require 19vdc at 3.2A (maximum) to charge the 
batteries. I suspect the MSI and Zotac simply use laptop hardware for 
the power supply even though no battery is involved.

The router problem is that most home routers ($30 variety) can handle a 
limited number of connections (less than a classroom of XOs). OLE Nepal 
has found that a TP-Link router with DDWRT handles 25 connections (15 
with the delivered firmware). In any case, a school really should have a 
router per classroom to provide enough connections (not to increase 
signal strength). OLE Nepal powers all of the routers in a school from 
the same UPS that powers the server so that the network will continue to 
operate in a power failure. Since the routers are also connected by an 
ethernet cable, PoE would be quite useful.

This discussion is relevant because 12vdc does not travel well over long 
distances. It may be necessary in a school with multiple classrooms to 
use an inverter to provide 110 or 220vac to the routers via PoE.

So far in Lesotho, the laptops have been used in a single classroom next 
to the server and router so I don't have live experience in distributing 
routers. We will face that problem next year at the Nohana school which 
has two classroom buildings about 50m apart and where the teachers want 
to use the laptops in their own classroom.


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