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Hi
I have a setup with a 12 volt battery a 5 volt power regulator and an Arduino with shields.
I have a powerplug going from the 12 volt to the Arduino. However when I use this plug the Arduino becomes hot (At the power conversion chip)
When I power the Arduino with USB from my PC there is no problem. When I power with a 9 Volt battery there is also no problem.

I tried powering the Arduino via the 5 volt pin before with weird behavior http://arduino.cc/forum/index.php/topic,87811.msg659399.html#msg659399 and now I see following line in nearly all Arduino board description "Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it." http://arduino.cc/en/Main/ArduinoBoardUno

I know for sure this comment wasn't there last time I  looked. The good thing is that now known that supplying 5 volt via the 5 volt pin is now officially not OK.

I had this idea to solve my powering problem. Why not take a usb cable and power 5V from my switching regulator and plug this USB cable in the Arduino.
I have never done something similar and my search didn't reveal any proof this has been done before.
What I need to know before I want to give this a try is:
Which wires do I need (never opened a UBS B connector -I'll look this one up).
What do I do with the other wires
Is there any reason to believe that Arduino will not work this way?

Best regards
Jantje

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The 5V on the USB cable simply connects to the 5V rail on the Arduino - its equivalent to directly powering the 5V pin.

There is nothing wrong in powered the Arduino via the 5V pin - but you _must_ ensure it is a regulated 5V which never ever goes above 5.5V or so...   If you have a cheap-and-cheerful "5V power supply" its up to you to verify it does actually put out a well-regulated 5V.  You need to measure it with a multimeter under no load and under load (not your Arduino!) to check the DC output is 5.0V +/- 0.1V and that the AC component is small (< 50mV is advised).

If you use a switch-mode 5V power supply it may be quite noisy - which can be fine except that analogRead() values pick up several LSB's of noise.

Beware any cheap power supply from ebay, you may be taking a gamble with quality (understatement).

Also some power-blobs are sold as 5V regulated and aren't regulated... beware.
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The good thing is that now known that supplying 5 volt via the 5 volt pin is now officially not OK.
I don't think you can come to that conclusion from those comments.
Powering an arduino with 5V through the 5V pin is fine, providing that is what you do. Powering the arduino from a bunch of batteries no matter what they say on the side can be a problem if the real voltage is greater than 5.5V.

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I have a powerplug going from the 12 volt to the Arduino. However when I use this plug the Arduino becomes hot (At the power conversion chip)
Yes it will it is burning off the excess power in the form of heat. With 9V there is not so much to burn.
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Markt
The 5V on the USB cable simply connects to the 5V rail on the Arduino - its equivalent to directly powering the 5V pin.
I'm an IT guy not a electronics guy; so I don't dare to say you are wrong but the info you provide is seem conflicting to me with other info available.
When looking at he schematics http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf I can not conclude Vin and USB power line are connected. I don't know what you mean with equivalent.
If the 5V and USB are connected I think I would have a problem when I connect my USB cable because then I would put my USB power in parallel to my switching regulator. In that case I would prefer to power my Arduino with a USB cable because I need to unplug it before plugging in a USB cable connected to my PC.
If they are not connected Arduino explicitly states that 5V does not go over the regulator so plugging in a USB must give problem when having power on 5V.
There is nothing wrong in powered the Arduino via the 5V pin - but you _must_ ensure it is a regulated 5V which never ever goes above 5.5V or so...   If you have a cheap-and-cheerful "5V power supply" its up to you to verify it does actually put out a well-regulated 5V.  You need to measure it with a multimeter under no load and under load (not your Arduino!) to check the DC output is 5.0V +/- 0.1V and that the AC component is small (< 50mV is advised).
These requirements seem tight to me. I don't think I can measure this with a multimeter. I guess you need a scope because you need to switch on and off devices to be sure there are no voltage drops and peaks.

Best regards
Jantje

PS I'm currently using a switching power regulator and a 100uf cap over it.

[Edit] Corrected the Vin pins to 5V pins
« Last Edit: April 29, 2012, 07:51:51 am by Jantje » Logged

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I'm an IT guy not a electronics guy; so I don't dare to say you are wrong but the info you provide is seem conflicting to me with other info available.
When looking at he schematics http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf I can not conclude Vin and USB power line are connected.

USB power feeds the +5v line via mosfet T1, initially through its body diode. If there is no supply attached to Vin then the output of U5A goes low, turning T1 on and providing a low-resistance connection between USB power and +5v.

If you power the Arduino with +5v from a regulated PSU and also connect the USB port to as PC, then the output of the PSU does get connected to USB power, which is not such a good idea, although the fuse provides some protection. Powering the Arduino from a higher voltage applied to Vin or the barrel jack is safer, because under these conditions T1 will not be turned on.
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I'm an IT guy not a electronics guy; so I don't dare to say you are wrong
Good because I am a hardware guy.

Quote
but the info you provide is seem conflicting to me with other info available.
This means you are not understanding the other information correctly.

Quote
I don't know what you mean with equivalent.
It means 'the same as'

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These requirements seem tight to me
They are not, remember you are not a 'electronics guy'

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Arduino explicitly states that Vin does not go over the regulator
No you are wrong, no such thing is stated, the current from the Vin flows through the regulator.
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My conclusion from the discussion
If I power 5V I can not connect a USB cable safely.
Knowing myself I prefer powering over  a USB cable. This way I'm sure I unpower before plugging in a USB cable (Call it idiot proof)
Remaining questions
What do I do with the other wires
Is there any reason to believe that Arduino will not work this way?

Best regards
Jantje
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I cut a USB A USB B cable
Connected black to negative
Red to 5V of a good switching regulator
made sure the other wires are properly isolated
And it works fine  smiley-cool

Best regards
Jantje
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