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

Sameer Verma sverma at sfsu.edu
Wed May 29 18:48:48 EDT 2013

On Wed, May 29, 2013 at 3:26 PM, James Cameron <quozl at laptop.org> wrote:
> On Wed, May 29, 2013 at 04:51:47PM -0500, David Farning wrote:
>> Any thoughts on powering the AP?
> They are all different.

Yep. The one we use in Bhagmalpur (India) and in Jamaica is the
Ubiquiti Picostation2 unit that runs off a PoE injector. Ours run off
110/220V AC, but an AP that can run over 48V PoE can use a DC-to-DC
PoE unit to power it from a 12V battery source.


> First, select an AP that says it has a 12V input.
> I would record the voltage without load emitted by the power supply
> supplied by the manufacturer.  This is a known maximum voltage that
> the AP can take.
> Then I would record the voltage on load.  This is a known minimum
> voltage.
> Then I would record the input voltage specifications of the access
> point using the manufacturer's documentation.  This is usually a
> typical voltage, but sometimes they include a maximum or minimum.  If
> there was no documentation, I'd ask them, though perhaps with no great
> expectation of success.
> Taking the minimum and maximum of those three values, I'd compare them
> to the lead-acid battery charge cycle operating range of 10V to 15V.
> If there remains any doubt (e.g. they haven't specified a maximum), I
> would attach the AP to a variable power supply and gradually ramp it
> up to 15V, checking for sudden drop of current (a blown fuse), or
> excessive operating heat.
> Once I'm happy, I would cut the cable as far from the device as
> possible, and reterminate it there.  Before cutting, I would discharge
> the power supply capacitors ... saves wear and tear on wire cutters.
> If the AP was USB powered Wifi dongle, the problem goes away.
> --
> James Cameron
> http://quozl.linux.org.au/
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