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

James Cameron quozl at laptop.org
Wed May 29 18:26:32 EDT 2013

On Wed, May 29, 2013 at 04:51:47PM -0500, David Farning wrote:
> Any thoughts on powering the AP? 

They are all different.

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

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

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