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Author Topic: Powering off a 12VDC outlet  (Read 720 times)
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NSW, Austalia
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Hi i would like to power my Arduino UNO, Relay/Relay Sheild and a realy loud piezo siren using my boats 12v outlet,
I don't want the Arduino's voltage regulator to overheat from too much input voltage will the 12v supply be alright?

Also the Arduino has to be in a Rugged Case due to the fact its in a boat (authough it will be placed in a generaly dry part of the boat),
Any recomendations on a 12v outlet connector and case?

 Thanks in advance,
 Alex  smiley
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I'd get a cheap/used cellphone car charger with a Mini-USB or Micro-USB connector.  That should provide a reasonably regulated 5V 500 mA which you can connect right to Gnd and +5V on the Arduino (after cutting off the connector).  You can run the wire through a small hole in the case and seal it with silicone seal.
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I'd get a cheap/used cellphone car charger with a Mini-USB or Micro-USB connector.  That should provide a reasonably regulated 5V 500 mA which you can connect right to Gnd and +5V on the Arduino (after cutting off the connector).  You can run the wire through a small hole in the case and seal it with silicone seal.

Thanks for replying im just concerned about 500ma powering a relay and a large buzzer (110db atleast)?
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Too bad the 5V buzzers only go up to 90dB.  They only draw 30 mA so if you were using the relay to switch 12V to the buzzer, perhaps two or three 90 dB buzzers would be loud enough?
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Thanks for the advice it was very helpful im just going to use a couple of 5v buzzers
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After abit of thinking i realised that 90db wasnt enough as the siren needs to be heared 70ft down a ski rope over a V8 engine noise.
So I decided to go back to the drawing board and use a 12v siren and the seeed relay shield http://seeedstudio.com/wiki/Relay_Shield.

I also drew up a schematic https://docs.google.com/open?id=0B_MdMCK5b3yYV3NYS0VwWlE5LU0, as i am a complete noob to electronics and arduino (First Project),
If someone check over it and tell me if it will work it would be muchly apreciated
Alex smiley


* schematic.png (57.91 KB, 1256x668 - viewed 8 times.)
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There's no reason why you cannot power the arduino directly (through the coaxial power plug, naturally) from +12V.. the regulator drops the voltage down to +5V, and likewise the +3.3V regulator is powered off the +5V.. I might be wrong, but I think the +5V regulator should be able to handle up to +20V input  (can't find the Vin-Max listing from the MC33269D-5.0 datasheet.).  as long as you're not powering devices off the Vin pin of the board, you're okay. (I've done it, feeding a 7805 regulator for three servos, but the current draw was negligible.)    The 3.3V regulator is fed from both the +5V output of the regulator, and the USB +5V pin..BUT... you cannot power that much off the +5V from the USB port, without taxing the device. (and, possibly blowing the fuse on whatever is powering the USB)

I've been able to power a UNO, a Wiz-net shield, and a LG Wifi router off a single +12V gel cell, as well the 7805 regulator to the +V on 3x Futaba 3004's, for a robot design, without problems.  As long as the Relay shield is running the relays off some form of Darlington or transistor to switch the relay coils on/off, you should be fine. Directly driving the relays coils, could prove fatal to the Arduino.  Also, note the voltage of the relay coils, as not to burn them out either. (sniff-sniff.. Do I smell burning plastic?  OH-NO!!!)

Stephen (gelfling6)
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