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

Fri May 31 06:54:53 EDT 2013

I'd be interested in ddwrt on tp-link 2030's, primarily because of the
Nepali data, that they can handle 25 clients, and because they run on 5v.

Add to that a DC-DC buck converter to 5v at the remote end of poe. I'm
testing
http://www.amazon.com/gp/product/B00A71CMDU/ref=oh_details_o07_s00_i00?ie=UTF8&psc=1which
in the spec has 8-23v input capability, and 3A output ($8)

Let's analyze the worst case for an ethernet cable at maximum distance. (24
awg wire at 70C has resistance of 29 ohms/1000 feet, poe has 2 wires per
leg, but we have drop in each leg. So my guess is worst case loop
resistance of 300 feet * 29 ohms/1000 feet * 2 legs / 2 wires/leg = 8.7
ohms loop resistance.

If the minimum input voltage for the DC-DC is 8, then we only have 3 volts
of drop to play with. The current input spec for the tp-link is 1A. So if
300 at 1A would dorp 8.7 volts, and we can only afford 3 v drop, we can
only extend the AP 100 feet from the server.  I suspect that the current
draw is much less than the spec,  worst case battery discharge,ambient
temperature, are not likely, so more than 100 feet is likely.

This solution, would probably work for 3 or 4 adjacent classrooms, and
75-150 students -- but needs to be reality tested.

George

On Thu, May 30, 2013 at 12:47 AM, <server-devel-request at lists.laptop.org>wrote:

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> Today's Topics:
>
>    1. Re: 12 Volt power system for School Servers. (James Cameron)
>    2. Re: 12 Volt power system for School Servers. (Sameer Verma)
>    3. Re: 12 Volt power system for School Servers. (David Farning)
>    4. Re: 12 Volt power system for School Servers. (Anna)
>    5. Re: 12 Volt power system for School Servers. (Adam Holt)
>    6. Re: 12 Volt power system for School Servers. (Tony Anderson)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 30 May 2013 08:26:32 +1000
> From: James Cameron <quozl at laptop.org>
> To: David Farning <dfarning at activitycentral.com>
> Cc: server-devel <server-devel at lists.laptop.org>,       Tony Anderson
>         <tony_anderson at usa.net>
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID: <20130529222631.GB20168 at us.netrek.org>
> Content-Type: text/plain; charset=iso-8859-1
>
> 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
> 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/
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 29 May 2013 15:48:48 -0700
> From: Sameer Verma <sverma at sfsu.edu>
> To: James Cameron <quozl at laptop.org>,   David Farning
>         <dfarning at activitycentral.com>,         Jerry Vonau <
> jvonau at shaw.ca>,
>         server-devel <server-devel at lists.laptop.org>,   Tony Anderson
>         <tony_anderson at usa.net>
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID:
>         <CAFoGK8G3ZRQdj+1qyCiv8=
> pUTnSCh5+7b4LevAhWr-zsxBB1cw at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> 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.
>
> cheers,
> Sameer
>
> > 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/
> > _______________________________________________
> > Server-devel mailing list
> > Server-devel at lists.laptop.org
> > http://lists.laptop.org/listinfo/server-devel
> >
> >
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 29 May 2013 18:01:11 -0500
> From: David Farning <dfarning at activitycentral.com>
> To: Sameer Verma <sverma at sfsu.edu>
> Cc: server-devel <server-devel at lists.laptop.org>,       Tony Anderson
>         <tony_anderson at usa.net>
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID:
>         <CAOGko=8F5TydsQwNcK-QB267BfyTF=
> oX8dfXvqVq7nA+qoqDsg at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Thanks guys,
>
> I'll start playing tonight.
>
>
> On Wed, May 29, 2013 at 5:48 PM, Sameer Verma <sverma at sfsu.edu> wrote:
>
> > 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.
> >
> > cheers,
> > Sameer
> >
> > > 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/
> > > _______________________________________________
> > > Server-devel mailing list
> > > Server-devel at lists.laptop.org
> > > http://lists.laptop.org/listinfo/server-devel
> > >
> > >
> >
>
>
>
> --
> David Farning
> Activity Central: http://www.activitycentral.com
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> ------------------------------
>
> Message: 4
> Date: Wed, 29 May 2013 19:46:12 -0500
> From: Anna <aschoolf at gmail.com>
> To: James Cameron <quozl at laptop.org>,   David Farning
>         <dfarning at activitycentral.com>,         Jerry Vonau <
> jvonau at shaw.ca>,
>         server-devel <server-devel at lists.laptop.org>,   Tony Anderson
>         <tony_anderson at usa.net>
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID:
>         <
> CAFM0qr1sZg2HJQemRKNuu1SqSncZpdHnFchC9UWc7T+hpqJYcg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On Wed, May 29, 2013 at 5:26 PM, James Cameron <quozl at laptop.org> wrote:
>
> >
> > If the AP was USB powered Wifi dongle, the problem goes away.
> >
> >
> Speaking of, and this would only be appropriate for extremely small
> deployments, but I started messing around on the XSCE with hostapd with a
> wifi dongle this very afternoon.  It's been on my wishlist for a long time,
> but earlier kernels didn't have support and it is such a PITA to compile
> the XO kernel.
>
> Anna
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> ------------------------------
>
> Message: 5
> Date: Thu, 30 May 2013 00:05:48 -0400
> From: Adam Holt <holt at laptop.org>
> To: server-devel at lists.laptop.org
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID:
>         <
> CAHaBuGcuj_PHoPaZ9aFETq5CvbRGGXzhV4mjdMPqUswnRO1bkg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Just a reminder to include power at lists.laptop.org if this discussion
> advances, the tightly focused electrical/energy list run by Richard Smith
> for many years to come God willing =)
>
> http://lists.laptop.org/listinfo/power
>
>
> On Wed, May 29, 2013 at 8:46 PM, Anna <aschoolf at gmail.com> wrote:
>
> > On Wed, May 29, 2013 at 5:26 PM, James Cameron <quozl at laptop.org> wrote:
> >
> >>
> >> If the AP was USB powered Wifi dongle, the problem goes away.
> >>
> >>
> > Speaking of, and this would only be appropriate for extremely small
> > deployments, but I started messing around on the XSCE with hostapd with a
> > wifi dongle this very afternoon.  It's been on my wishlist for a long
> time,
> > but earlier kernels didn't have support and it is such a PITA to compile
> > the XO kernel.
> >
> > Anna
> >
> > _______________________________________________
> > Server-devel mailing list
> > Server-devel at lists.laptop.org
> > http://lists.laptop.org/listinfo/server-devel
> >
> >
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> ------------------------------
>
> Message: 6
> Date: Thu, 30 May 2013 06:47:26 +0200
> From: Tony Anderson <tony_anderson at usa.net>
> To: Anna <aschoolf at gmail.com>
> Cc: server-devel <server-devel at lists.laptop.org>
> Subject: Re: [Server-devel] 12 Volt power system for School Servers.
> Message-ID: <51A6D9DE.6060804 at usa.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi,
>
>
> 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.
>
> Tony
>
>
>
> ------------------------------
>
> _______________________________________________
> Server-devel mailing list
> Server-devel at lists.laptop.org
> http://lists.laptop.org/listinfo/server-devel
>
>
> End of Server-devel Digest, Vol 73, Issue 17
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