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Author Topic: External Power (3Com AC Adapter)  (Read 1001 times)
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Hello,

I would like to use my Arduino Uno with my 3Com AC Adapter.
I'm not very familiar with it, so I need your opinion.

Can I use it without any risks for my Ardunio ?

Here are its specs:

OUTPUT: +12.0V      1.25A

Thanks !
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It may work. It will only provide power to the Arduino on the positive half-cycles of the AC waveform. During the negative half-cycles, the diode in series with the 2.1mm power jack will prevent current flow.

This means the capacitor at the input of the linear regulator (47uF is specified on the schematic) must supply power to the Arduino for the majority of the time while it is in operation. Assume the Arduino consumes 20mA (optimistic) and does not power anything else. The capacitor voltage changes by dV/dt = i/C = 0.02/47e-6 = 0.425V/ms. The negative half-cycle of a 60 Hz waveform lasts 8.33ms, so the capacitor voltage will drop by 3.55V in this time. It will also drop more during the positive half cycle until the voltage is high enough to both recharge the capacitor and power the Arduino. But since your AC voltage is so high, it might just work.

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It will only provide power to the Arduino on the positive half-cycles of the AC waveform.
I suspect jean may have meant "AC Adapter" as-in, it plugs into the wall/mains.  Not that the output of the adapter is AC...  We should probably clarify that.

I would like to use my Arduino Uno with my 3Com AC Adapter.
Here are its specs:
OUTPUT: +12.0V      1.25A
Does the Output state that it is AC or DC?  What did this adapter originally power?
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I do suspect that this is actually an AC-DC adapter, because the output voltage is +12, and there is no stated frequency.
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Yes sorry, I don't speak english very well, sorry for the confusion.

This is probably an AC-DC Adapter...

It was originally powering a 3Com Wifi Router.

This is written as this:

       
 INPUT: 200-240V ~ 50/60Hz 0.4A

                             ___________
 OUTPUT: +12.0V    - - - - - - - - -         1.25A
« Last Edit: October 10, 2011, 09:57:20 am by jeanvaljean » Logged

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Yes it should work fine with your Arduino.
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Thank's I wasn't sure about the voltage (12V is pretty high for the Arduino, isn't it ?) and the amperage.
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Thank's I wasn't sure about the voltage (12V is pretty high for the Arduino, isn't it ?) and the amperage.
Current rating is a capacity of the source.  Your source is capable of providing 1.25A.  (It does not mean 1.25A is always flowing.)

The Arduino's practical voltage limit is 12V.  The on-board regulator is linear.  It will run hotter the higher the voltage above 7V.  (Technically the regulator will run up to 20V, but the amount of heat generated will shut it down.)
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And isn't it bad for the Arduino to be powered at its voltage limit all the time ?
Is it better to find a 7V adapter ?

Edit: Ok, I tried a few minutes but my Arduino became pretty hot...
« Last Edit: October 10, 2011, 11:31:48 am by jeanvaljean » Logged

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And isn't it bad for the Arduino to be powered at its voltage limit all the time ?
Is it better to find a 7V adapter ?

Edit: Ok, I tried a few minutes but my Arduino became pretty hot...

It all depends on how much current flows through the regulator.  The higher input voltage, the lower the output current.  The closer the 7V you get, the cooler the board will run.
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Okay, thanks.

But I think I will not plug it... It scares me a little to feel my Arduino heating...
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