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Hello,

2 quick questions :

1. If using a 12v battery, does it make any difference at all using the round 'centre-positive' jack input, or the Vin and ground pins ?

2. Will using an unregulated 12v lead acid battery, connected to the input power jack on a UNO be safe or not ?

Many Thanks
Twogan



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If I look at the schematic - http://arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf - the only difference is a diode (check the upper right part )

So as far as I understand it should just work.
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Either will work, but using the jack is better for 2 reasons:

1. The diode will protect the Arduino if you accidentally connect the battery the wrong way round;

2. The voltage regulator will dissipate a little less power (that power will be dissipated in the diode instead).
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3 reasons - much less likely to accidentally plug the jack into the wrong socket - whereas with the Vin header you could accidentally short the battery to ground by putting the wire in the wrong hole.

That would blow your fuse - you _do_ have a fuse don't you?  Large lead-acid batteries can source perhaps 1000A if shorted, a fuse is not a luxury.
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The 4 reasons Amongst the reasons (nobody expects the Spanish Inquisition etc.) for using the barrel jack are the above 3, and the fact that a loose pin with +12v on it may short against something whereas the +12v connection in the barrel jack is shrouded.
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And a fanatical devotion to the Pope

AND
it is just so dam convenient.
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