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Topic: PoE module current question (Read 768 times) previous topic - next topic

Mr Parp

If I have an official Arduino Ethernet shield with PoE module and using a proper.3af 48V injector, in theory I can feed 15W in.  Question: is this 15W actually drawable via the Arduino +ve and GND supply rails?  If not, what's the point and where can I draw it?

I think I read the PoE module will convert from (36-) 48V down to 12V, but I'm also aware of current limitations on the Arduinos DC socket and wondering if the Arduino is going to limit the power from the PoE in any way.

(Motivation - I have quite a few external modules to power and talk to from the Mega and wondering if the PoE is up to the job).

johnwasser


Question: is this 15W actually drawable via the Arduino +ve and GND supply rails?  If not, what's the point and where can I draw it?


http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=6&products_id=148

Note: "High efficiency DC/DC converter (75% typ)".  That means that only about 75% of your 15W will make it to the Arduino.
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Mr Parp

Thanks John, so say thats 10W approx.  Does the PoE module makes this available via the 5V and GND pins on the headers?  I'm trying to figure if its safe to pull about 2A@5V from them to power various modules.  Is there any additional on-board limits or current protection going to restrict what the PoE is feeding?

johnwasser

The Arduino store sells the 12V 12W (1A) model and the schematic shows that output goes to Vin.  You can get 12V 1A from the Vin pin and regulate it yourself or draw up to 1A from the 5V line (5W) and hope the regulator can dissipate the heat (the other 7W turns into heat).

POE module datasheet:
http://www.semiconductorstore.com/pages/asp/DownloadDirect.asp?sid=1353084202849

You can also get the POE module in a 5V 9W (1.8A) model.  You'd have to route the output to the 5V line since the regulator on the Vin line needs more than 5V in to get 5V out.  Then you'd have 1.8A of 5V to play with... as long as the traces on the Arduino don't fry.
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Mr Parp

I was worried this wasn't going to be simple.  I have multiple modules to power (including the MEGA);  RS232, RS422 and the killer, the SM5100B cellular board which can burst up to 1.5A.  I know powering via USB is out of the question and even via the DC socket is not going to work reliably due to that cellular board, so I was hoping I could power everything neatly from the PoE.

What would you suggest in this situation?  It seems ugly but I suspect I need a PSU going into a new DC jack on my project box to power that cellular board and Arduino separately, and just forget about PoE.

Cheers

johnwasser

I'm no expert but maybe a "super capacitor" on the 5V line would take care of the 1.5A bursts from the GSM board?
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