Maximum Power a Project can draw from PoE

The EtherTen combines an Uno-equivalent Arduino-compatible board and Wiznet-based Ethernet support, along with a microSD card slot and Power-over-Ethernet support. [Product page]
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liveitnerd
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Joined:Sat Mar 10, 2012 9:36 am
Maximum Power a Project can draw from PoE

Post by liveitnerd » Sat Mar 10, 2012 9:38 am

Hi,

I'd like to build a project which is completely powered off PoE but I want to power 2 or more LED Matrix Displays. What is the maximum amount of current I can draw from the +5Volt pins on the Arduino? Is there another way with PoE to get more juice without using custom injectors?


Thanks,
Peter

jebz
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Joined:Sun Feb 12, 2012 10:58 pm

Re: Maximum Power a Project can draw from PoE

Post by jebz » Sat Mar 10, 2012 9:31 pm

liveitnerd wrote:Is there another way with PoE to get more juice without using custom injectors?
You could take the supply from the POE feed prior to the regulator and regulate the supply to the LED displays on the display board.

liveitnerd
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Joined:Sat Mar 10, 2012 9:36 am

Re: Maximum Power a Project can draw from PoE

Post by liveitnerd » Thu Jul 12, 2012 2:09 am

Excellent idea. Thanks for the tip!

cef
Freetronics Staff
Freetronics Staff
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Re: Maximum Power a Project can draw from PoE

Post by cef » Thu Jul 12, 2012 6:21 am

I've seen note elsewhere (by Jon) that you should get ~2 Amps out of the 802.3af switchmode regulator, but that keeping it cool might be an issue.

Note that this should be at about 7.5 Volts (the voltage out of the regulator that FreeTronics supplies for using 802.3af on the EtherTen), and that unless you're using another switchmode converter, you will not get more than 2A at 5 volts. I don't believe that the 5V regulator on the EtherTen will supply 2A though. If you do tap off the 7.5V out of the 802.3af regulator, make sure to leave enough spare current to power the EtherTen.

The input of an 802.3af converter (aka output from an 802.3af switch) is between 44 and 57 Volts (usually 48V) at about 350mA (~15.4 Watts), though you're not guaranteed to get more than about 37 Volts at the device (~12.95 Watts). This means you may encounter situations where even if the switchmode regulator was 100% efficient, you most likely couldn't draw more than 1.73A at 7.5V. If you hit this situation, the only thing I can suggest is to shorten your cable run and/or use better quality cable, to reduce voltage losses.

Good page to check out for PoE is http://en.wikipedia.org/wiki/Power_over_Ethernet

liveitnerd
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Joined:Sat Mar 10, 2012 9:36 am

Re: Maximum Power a Project can draw from PoE

Post by liveitnerd » Sun Jul 15, 2012 1:10 am

Wow... that's great news. I really don't think I'll need to use more than 1Amp and am trying to minimise the footprint of the project as much as possible. With any luck I'll be able to post back in a month or so with the prototype.

Thanks again for the information and help.

harryman01
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Joined:Tue May 08, 2012 11:33 am

Re: Maximum Power a Project can draw from PoE

Post by harryman01 » Wed Jul 18, 2012 11:09 am

thanks for the information, but how do I make the connections to which pins, is there any diagrams available

Thanks

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