<div dir="ltr">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.<div><br></div><div>Add to that a DC-DC buck converter to 5v at the remote end of poe. I'm testing <a href="http://www.amazon.com/gp/product/B00A71CMDU/ref=oh_details_o07_s00_i00?ie=UTF8&psc=1">http://www.amazon.com/gp/product/B00A71CMDU/ref=oh_details_o07_s00_i00?ie=UTF8&psc=1</a> which in the spec has 8-23v input capability, and 3A output ($8)</div>
<div><br></div><div style>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. </div>
<div style><br></div><div style>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.</div>
<div><br></div><div>This solution, would probably work for 3 or 4 adjacent classrooms, and 75-150 students -- but needs to be reality tested.</div><div><br></div><div>George<br><div class="gmail_extra"><br><br><div class="gmail_quote">
On Thu, May 30, 2013 at 12:47 AM, <span dir="ltr"><<a href="mailto:server-devel-request@lists.laptop.org" target="_blank">server-devel-request@lists.laptop.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
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Today's Topics:<br>
<br>
1. Re: 12 Volt power system for School Servers. (James Cameron)<br>
2. Re: 12 Volt power system for School Servers. (Sameer Verma)<br>
3. Re: 12 Volt power system for School Servers. (David Farning)<br>
4. Re: 12 Volt power system for School Servers. (Anna)<br>
5. Re: 12 Volt power system for School Servers. (Adam Holt)<br>
6. Re: 12 Volt power system for School Servers. (Tony Anderson)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Thu, 30 May 2013 08:26:32 +1000<br>
From: James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>><br>
To: David Farning <<a href="mailto:dfarning@activitycentral.com">dfarning@activitycentral.com</a>><br>
Cc: server-devel <<a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a>>, Tony Anderson<br>
<<a href="mailto:tony_anderson@usa.net">tony_anderson@usa.net</a>><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID: <<a href="mailto:20130529222631.GB20168@us.netrek.org">20130529222631.GB20168@us.netrek.org</a>><br>
Content-Type: text/plain; charset=iso-8859-1<br>
<br>
On Wed, May 29, 2013 at 04:51:47PM -0500, David Farning wrote:<br>
> Any thoughts on powering the AP??<br>
<br>
They are all different.<br>
<br>
First, select an AP that says it has a 12V input.<br>
<br>
I would record the voltage without load emitted by the power supply<br>
supplied by the manufacturer. This is a known maximum voltage that<br>
the AP can take.<br>
<br>
Then I would record the voltage on load. This is a known minimum<br>
voltage.<br>
<br>
Then I would record the input voltage specifications of the access<br>
point using the manufacturer's documentation. This is usually a<br>
typical voltage, but sometimes they include a maximum or minimum. If<br>
there was no documentation, I'd ask them, though perhaps with no great<br>
expectation of success.<br>
<br>
Taking the minimum and maximum of those three values, I'd compare them<br>
to the lead-acid battery charge cycle operating range of 10V to 15V.<br>
<br>
If there remains any doubt (e.g. they haven't specified a maximum), I<br>
would attach the AP to a variable power supply and gradually ramp it<br>
up to 15V, checking for sudden drop of current (a blown fuse), or<br>
excessive operating heat.<br>
<br>
Once I'm happy, I would cut the cable as far from the device as<br>
possible, and reterminate it there. Before cutting, I would discharge<br>
the power supply capacitors ... saves wear and tear on wire cutters.<br>
<br>
If the AP was USB powered Wifi dongle, the problem goes away.<br>
<br>
--<br>
James Cameron<br>
<a href="http://quozl.linux.org.au/" target="_blank">http://quozl.linux.org.au/</a><br>
<br>
<br>
------------------------------<br>
<br>
Message: 2<br>
Date: Wed, 29 May 2013 15:48:48 -0700<br>
From: Sameer Verma <<a href="mailto:sverma@sfsu.edu">sverma@sfsu.edu</a>><br>
To: James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>>, David Farning<br>
<<a href="mailto:dfarning@activitycentral.com">dfarning@activitycentral.com</a>>, Jerry Vonau <<a href="mailto:jvonau@shaw.ca">jvonau@shaw.ca</a>>,<br>
server-devel <<a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a>>, Tony Anderson<br>
<<a href="mailto:tony_anderson@usa.net">tony_anderson@usa.net</a>><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID:<br>
<CAFoGK8G3ZRQdj+1qyCiv8=<a href="mailto:pUTnSCh5%2B7b4LevAhWr-zsxBB1cw@mail.gmail.com">pUTnSCh5+7b4LevAhWr-zsxBB1cw@mail.gmail.com</a>><br>
Content-Type: text/plain; charset=ISO-8859-1<br>
<br>
On Wed, May 29, 2013 at 3:26 PM, James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>> wrote:<br>
> On Wed, May 29, 2013 at 04:51:47PM -0500, David Farning wrote:<br>
>> Any thoughts on powering the AP?<br>
><br>
> They are all different.<br>
><br>
<br>
Yep. The one we use in Bhagmalpur (India) and in Jamaica is the<br>
Ubiquiti Picostation2 unit that runs off a PoE injector. Ours run off<br>
110/220V AC, but an AP that can run over 48V PoE can use a DC-to-DC<br>
PoE unit to power it from a 12V battery source.<br>
<br>
cheers,<br>
Sameer<br>
<br>
> First, select an AP that says it has a 12V input.<br>
><br>
> I would record the voltage without load emitted by the power supply<br>
> supplied by the manufacturer. This is a known maximum voltage that<br>
> the AP can take.<br>
><br>
> Then I would record the voltage on load. This is a known minimum<br>
> voltage.<br>
><br>
> Then I would record the input voltage specifications of the access<br>
> point using the manufacturer's documentation. This is usually a<br>
> typical voltage, but sometimes they include a maximum or minimum. If<br>
> there was no documentation, I'd ask them, though perhaps with no great<br>
> expectation of success.<br>
><br>
> Taking the minimum and maximum of those three values, I'd compare them<br>
> to the lead-acid battery charge cycle operating range of 10V to 15V.<br>
><br>
> If there remains any doubt (e.g. they haven't specified a maximum), I<br>
> would attach the AP to a variable power supply and gradually ramp it<br>
> up to 15V, checking for sudden drop of current (a blown fuse), or<br>
> excessive operating heat.<br>
><br>
> Once I'm happy, I would cut the cable as far from the device as<br>
> possible, and reterminate it there. Before cutting, I would discharge<br>
> the power supply capacitors ... saves wear and tear on wire cutters.<br>
><br>
> If the AP was USB powered Wifi dongle, the problem goes away.<br>
><br>
> --<br>
> James Cameron<br>
> <a href="http://quozl.linux.org.au/" target="_blank">http://quozl.linux.org.au/</a><br>
> _______________________________________________<br>
> Server-devel mailing list<br>
> <a href="mailto:Server-devel@lists.laptop.org">Server-devel@lists.laptop.org</a><br>
> <a href="http://lists.laptop.org/listinfo/server-devel" target="_blank">http://lists.laptop.org/listinfo/server-devel</a><br>
><br>
><br>
<br>
<br>
------------------------------<br>
<br>
Message: 3<br>
Date: Wed, 29 May 2013 18:01:11 -0500<br>
From: David Farning <<a href="mailto:dfarning@activitycentral.com">dfarning@activitycentral.com</a>><br>
To: Sameer Verma <<a href="mailto:sverma@sfsu.edu">sverma@sfsu.edu</a>><br>
Cc: server-devel <<a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a>>, Tony Anderson<br>
<<a href="mailto:tony_anderson@usa.net">tony_anderson@usa.net</a>><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID:<br>
<CAOGko=8F5TydsQwNcK-QB267BfyTF=<a href="mailto:oX8dfXvqVq7nA%2BqoqDsg@mail.gmail.com">oX8dfXvqVq7nA+qoqDsg@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Thanks guys,<br>
<br>
I'll start playing tonight.<br>
<br>
<br>
On Wed, May 29, 2013 at 5:48 PM, Sameer Verma <<a href="mailto:sverma@sfsu.edu">sverma@sfsu.edu</a>> wrote:<br>
<br>
> On Wed, May 29, 2013 at 3:26 PM, James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>> wrote:<br>
> > On Wed, May 29, 2013 at 04:51:47PM -0500, David Farning wrote:<br>
> >> Any thoughts on powering the AP?<br>
> ><br>
> > They are all different.<br>
> ><br>
><br>
> Yep. The one we use in Bhagmalpur (India) and in Jamaica is the<br>
> Ubiquiti Picostation2 unit that runs off a PoE injector. Ours run off<br>
> 110/220V AC, but an AP that can run over 48V PoE can use a DC-to-DC<br>
> PoE unit to power it from a 12V battery source.<br>
><br>
> cheers,<br>
> Sameer<br>
><br>
> > First, select an AP that says it has a 12V input.<br>
> ><br>
> > I would record the voltage without load emitted by the power supply<br>
> > supplied by the manufacturer. This is a known maximum voltage that<br>
> > the AP can take.<br>
> ><br>
> > Then I would record the voltage on load. This is a known minimum<br>
> > voltage.<br>
> ><br>
> > Then I would record the input voltage specifications of the access<br>
> > point using the manufacturer's documentation. This is usually a<br>
> > typical voltage, but sometimes they include a maximum or minimum. If<br>
> > there was no documentation, I'd ask them, though perhaps with no great<br>
> > expectation of success.<br>
> ><br>
> > Taking the minimum and maximum of those three values, I'd compare them<br>
> > to the lead-acid battery charge cycle operating range of 10V to 15V.<br>
> ><br>
> > If there remains any doubt (e.g. they haven't specified a maximum), I<br>
> > would attach the AP to a variable power supply and gradually ramp it<br>
> > up to 15V, checking for sudden drop of current (a blown fuse), or<br>
> > excessive operating heat.<br>
> ><br>
> > Once I'm happy, I would cut the cable as far from the device as<br>
> > possible, and reterminate it there. Before cutting, I would discharge<br>
> > the power supply capacitors ... saves wear and tear on wire cutters.<br>
> ><br>
> > If the AP was USB powered Wifi dongle, the problem goes away.<br>
> ><br>
> > --<br>
> > James Cameron<br>
> > <a href="http://quozl.linux.org.au/" target="_blank">http://quozl.linux.org.au/</a><br>
> > _______________________________________________<br>
> > Server-devel mailing list<br>
> > <a href="mailto:Server-devel@lists.laptop.org">Server-devel@lists.laptop.org</a><br>
> > <a href="http://lists.laptop.org/listinfo/server-devel" target="_blank">http://lists.laptop.org/listinfo/server-devel</a><br>
> ><br>
> ><br>
><br>
<br>
<br>
<br>
--<br>
David Farning<br>
Activity Central: <a href="http://www.activitycentral.com" target="_blank">http://www.activitycentral.com</a><br>
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<br>
Message: 4<br>
Date: Wed, 29 May 2013 19:46:12 -0500<br>
From: Anna <<a href="mailto:aschoolf@gmail.com">aschoolf@gmail.com</a>><br>
To: James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>>, David Farning<br>
<<a href="mailto:dfarning@activitycentral.com">dfarning@activitycentral.com</a>>, Jerry Vonau <<a href="mailto:jvonau@shaw.ca">jvonau@shaw.ca</a>>,<br>
server-devel <<a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a>>, Tony Anderson<br>
<<a href="mailto:tony_anderson@usa.net">tony_anderson@usa.net</a>><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID:<br>
<<a href="mailto:CAFM0qr1sZg2HJQemRKNuu1SqSncZpdHnFchC9UWc7T%2BhpqJYcg@mail.gmail.com">CAFM0qr1sZg2HJQemRKNuu1SqSncZpdHnFchC9UWc7T+hpqJYcg@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="iso-8859-1"<br>
<br>
On Wed, May 29, 2013 at 5:26 PM, James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>> wrote:<br>
<br>
><br>
> If the AP was USB powered Wifi dongle, the problem goes away.<br>
><br>
><br>
Speaking of, and this would only be appropriate for extremely small<br>
deployments, but I started messing around on the XSCE with hostapd with a<br>
wifi dongle this very afternoon. It's been on my wishlist for a long time,<br>
but earlier kernels didn't have support and it is such a PITA to compile<br>
the XO kernel.<br>
<br>
Anna<br>
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<br>
Message: 5<br>
Date: Thu, 30 May 2013 00:05:48 -0400<br>
From: Adam Holt <<a href="mailto:holt@laptop.org">holt@laptop.org</a>><br>
To: <a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID:<br>
<<a href="mailto:CAHaBuGcuj_PHoPaZ9aFETq5CvbRGGXzhV4mjdMPqUswnRO1bkg@mail.gmail.com">CAHaBuGcuj_PHoPaZ9aFETq5CvbRGGXzhV4mjdMPqUswnRO1bkg@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="iso-8859-1"<br>
<br>
Just a reminder to include <a href="mailto:power@lists.laptop.org">power@lists.laptop.org</a> if this discussion<br>
advances, the tightly focused electrical/energy list run by Richard Smith<br>
for many years to come God willing =)<br>
<br>
<a href="http://lists.laptop.org/listinfo/power" target="_blank">http://lists.laptop.org/listinfo/power</a><br>
<br>
<br>
On Wed, May 29, 2013 at 8:46 PM, Anna <<a href="mailto:aschoolf@gmail.com">aschoolf@gmail.com</a>> wrote:<br>
<br>
> On Wed, May 29, 2013 at 5:26 PM, James Cameron <<a href="mailto:quozl@laptop.org">quozl@laptop.org</a>> wrote:<br>
><br>
>><br>
>> If the AP was USB powered Wifi dongle, the problem goes away.<br>
>><br>
>><br>
> Speaking of, and this would only be appropriate for extremely small<br>
> deployments, but I started messing around on the XSCE with hostapd with a<br>
> wifi dongle this very afternoon. It's been on my wishlist for a long time,<br>
> but earlier kernels didn't have support and it is such a PITA to compile<br>
> the XO kernel.<br>
><br>
> Anna<br>
><br>
> _______________________________________________<br>
> Server-devel mailing list<br>
> <a href="mailto:Server-devel@lists.laptop.org">Server-devel@lists.laptop.org</a><br>
> <a href="http://lists.laptop.org/listinfo/server-devel" target="_blank">http://lists.laptop.org/listinfo/server-devel</a><br>
><br>
><br>
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<br>
Message: 6<br>
Date: Thu, 30 May 2013 06:47:26 +0200<br>
From: Tony Anderson <<a href="mailto:tony_anderson@usa.net">tony_anderson@usa.net</a>><br>
To: Anna <<a href="mailto:aschoolf@gmail.com">aschoolf@gmail.com</a>><br>
Cc: server-devel <<a href="mailto:server-devel@lists.laptop.org">server-devel@lists.laptop.org</a>><br>
Subject: Re: [Server-devel] 12 Volt power system for School Servers.<br>
Message-ID: <<a href="mailto:51A6D9DE.6060804@usa.net">51A6D9DE.6060804@usa.net</a>><br>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed<br>
<br>
Hi,<br>
<br>
<br>
The setup at the Kokobe Primary school in Lesotho has a small solar<br>
panel (too small) which attempts to charge two car batteries (deep cycle<br>
would be better but not available).<br>
<br>
The router (Belkin) runs directly from the battery (we cut the cable).<br>
Linksys and other routers I have used all run on 12vdc at 1A.<br>
<br>
The MSI server does not run on 12vdc because of the design of it's power<br>
supply which requires a higher voltage (15vdc works). I purchased a<br>
Zotac which also uses an Atom processor but houses a 2.5in drive. It<br>
requires 19vdc.<br>
<br>
Most standard laptops require 19vdc at 3.2A (maximum) to charge the<br>
batteries. I suspect the MSI and Zotac simply use laptop hardware for<br>
the power supply even though no battery is involved.<br>
<br>
The router problem is that most home routers ($30 variety) can handle a<br>
limited number of connections (less than a classroom of XOs). OLE Nepal<br>
has found that a TP-Link router with DDWRT handles 25 connections (15<br>
with the delivered firmware). In any case, a school really should have a<br>
router per classroom to provide enough connections (not to increase<br>
signal strength). OLE Nepal powers all of the routers in a school from<br>
the same UPS that powers the server so that the network will continue to<br>
operate in a power failure. Since the routers are also connected by an<br>
ethernet cable, PoE would be quite useful.<br>
<br>
This discussion is relevant because 12vdc does not travel well over long<br>
distances. It may be necessary in a school with multiple classrooms to<br>
use an inverter to provide 110 or 220vac to the routers via PoE.<br>
<br>
So far in Lesotho, the laptops have been used in a single classroom next<br>
to the server and router so I don't have live experience in distributing<br>
routers. We will face that problem next year at the Nohana school which<br>
has two classroom buildings about 50m apart and where the teachers want<br>
to use the laptops in their own classroom.<br>
<br>
Tony<br>
<br>
<br>
<br>
------------------------------<br>
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End of Server-devel Digest, Vol 73, Issue 17<br>
********************************************<br>
</blockquote></div><br></div></div></div>