asterisk users - Nov 2006 - Why Aastra uses 48V whereas other IP Phones use much less, i.e. 5-12V

Hi,

Why Aastra phones use more electricity, i.e. 48VDC whereas other phones use
much less, e.g. Grandstream and Linksys both use only 5VDC. I first thought
it was because of PoE, but the ones with 5VDC also run fine on PoE. What is
the difference in power consumption then?

-- 
Zeeshan A Zakaria
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On Tue, Nov 21, 2006 at 08:57:44PM -0500, Zeeshan Zakaria arranged a set of bits
into the following:
> Why Aastra phones use more electricity, i.e. 48VDC whereas other phones use
> much less, e.g. Grandstream and Linksys both use only 5VDC. I first thought
it
> was because of PoE, but the ones with 5VDC also run fine on PoE. What is
the
> difference in power consumption then?
The difference due to the different voltages would be < 1w. Many of the
commercial phones (Aastra, Polycom, Cisco) use 48 volt power supplies
as it lets them have a single power circuit for wall-warts and PoE
(Standard PoE is 48 volts).

Basic electrical theory (for DC) is that power == Watts, and Watts Volts * Amps,
so the only real difference between a 5v input and a 48v
is that the 48v will use less current (although it might go through more
DC-DC convertors those are highly efficient these days)

Thanks,
Julien
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Also the 48v and higher systems can transmit the lower current further
than a low voltage with a higher current.



On 11/21/06, Julien Goodwin <asterisk-lists@studio442.com.au>
wrote:
> On Tue, Nov 21, 2006 at 08:57:44PM -0500, Zeeshan Zakaria arranged a set of
bits into the following:
> > Why Aastra phones use more electricity, i.e. 48VDC whereas other
phones use
> > much less, e.g. Grandstream and Linksys both use only 5VDC. I first
thought it
> > was because of PoE, but the ones with 5VDC also run fine on PoE. What
is the
> > difference in power consumption then?
> The difference due to the different voltages would be < 1w. Many of the
> commercial phones (Aastra, Polycom, Cisco) use 48 volt power supplies
> as it lets them have a single power circuit for wall-warts and PoE
> (Standard PoE is 48 volts).
>
> Basic electrical theory (for DC) is that power == Watts, and Watts >
Volts * Amps, so the only real difference between a 5v input and a 48v
> is that the 48v will use less current (although it might go through more
> DC-DC convertors those are highly efficient these days)
>
> Thanks,
> Julien
>
>
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-- 
---
Andrew Latham - AKA: LATHAMA (lay-th-ham-eh)
lathama@lathama.com - lathama@gmail.com
If any of the above are down we have bigger problems than my email!
Hind sight is most always 20/20 or better.
---

On 11/22/06, Zeeshan Zakaria <zishanov@gmail.com>
wrote:
>
> Hi,
>
> Why Aastra phones use more electricity, i.e. 48VDC whereas other phones
> use much less, e.g. Grandstream and Linksys both use only 5VDC. I first
> thought it was because of PoE, but the ones with 5VDC also run fine on PoE.
> What is the difference in power consumption then?
>
48V is also a sort of "standard" for telco devices.... if I remember
it
correctly...


-- 
Met vriendelijke groet / With kind regards,

H. van Wees
---
If UNIX isn't the solution, you've got the wrong problem.
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On Wed, 2006-11-22 at 12:01 -0700,
asterisk-users-request@lists.digium.com wrote:
> On 11/22/06, Zeeshan Zakaria <zishanov@gmail.com> wrote:
>         Hi,
>         
>         Why Aastra phones use more electricity, i.e. 48VDC whereas
>         other phones use much less, e.g. Grandstream and Linksys both
>         use only 5VDC. I first thought it was because of PoE, but the
>         ones with 5VDC also run fine on PoE. What is the difference in
>         power consumption then? 
> 48V is also a sort of "standard" for telco devices.... if I
remember
> it correctly...
> 
IIRC, It's not just that 48 is a popular source. Most POE taps will
regulate the voltage
down to whatever they need, which often is just 5V, or 12V. But we are
talking DC voltage here, and there are significant voltage drops due to
the [small, but not zero] resistance of copper. The longer the cable
from the injector to the tap, the bigger the resistance, and the more
the voltage drop. The amount of current figures in there, also. So, 48V
is a safer voltage in general to inject, as long lines will usually
still see hopefully more than 5V at the tap end.

If you are going to design networks with POE, you'd best pull out your
calculator, multimeter, and V=IR equations, and see if you'll get the
required voltage at the other
end of the wire, given the current the devices will use.

murf

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The amount of electricity used is constant. When run from 48v DC power they draw
less current (mA)...power (w) is constant. Devices run from 5 V DC likely draw
more current (mA). Power =
Voltage x Current.

Michael

--Original Message Text---
From: Zeeshan Zakaria
Date: Wed, 22 Nov 2006 21:29:46 -0500

Does it effect the performance/voice quality? Does this also mean that 48VDC is
using less electricity in an office than 5VDC IP Phones?



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