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Hi I'm new to Arduino and have a question. In my project I have a large 5 volt regulated power supply. I want to power the Arduino with this supply. Can I simply connect the 5V out of my power supply to the +5V pin on the power connector or will this cause problems with the on-board power circuitry?
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Yes you can.  Disconnect it when you want to program via the USB connector tho, that seems to interfere with programming. Wire it so when you remove the 5v, the USB power is not powering all your external circuits also.
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Hi I'm new to Arduino and have a question. In my project I have a large 5 volt regulated power supply. I want to power the Arduino with this supply. Can I simply connect the 5V out of my power supply to the +5V pin on the power connector or will this cause problems with the on-board power circuitry?

Many do it that way. I would only make sure that you remove the external voltage when you wish to be connected to the PC's USB port as I don't thinks it's a recommended practice to have to different +5volt sources wired together at the same time.

Lefty

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We hear a lot about the current sourcing capability of the USB interface, but not much about its ability to soak up power.  My experience indicates that loads on the USB bus take power from any opportune source.  Stands to reason, it is a piece of wire.  I have a control package that includes an arduino.  Automotive !2 volts comes to the shield to power some 4-20 ma devices and a couple of solenoids,  The shield has a heat sunk 3 tab 5.2 volt regulator to provide 5 volt power to the board.

If the system is connected to a USB cable while the battery is connected, the USB will pull a couple of amps.  This was a surprise the first time.  We could not figure out where the load was that drained the battery so fast.

« Last Edit: February 25, 2011, 06:01:32 am by jcarrr » Logged

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We could figure out where the load was the drained the battery so fast.

I would have to see a wiring drawing of the whole system to understand your symptom better. The USB +5vdc if routed first on an arduino board through a 500ma polyfuse so that sets the limit on how much current the usb connection can source. Not sure I've ever heard of being able to sink current into a USB port, I wouldn't think that is possible?

Lefty
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The power lead in a USB cable is a piece of wire that can take power either direction.  It is not really a problem or a symptom, it is just an interesting condition.  Now that USB supplies power to many devices, there is one more set of things to consider. 
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The power lead in a USB cable is a piece of wire that can take power either direction.  It is not really a problem or a symptom, it is just an interesting condition.  Now that USB supplies power to many devices, there is one more set of things to consider. 

Well my understanding of USB power is that it is derived from the PC's 5vdc power supply and usually has some kind of overcurrent detection/protection. I can't see any means where the USB power wire could 'sink' current. If you could link to such information that would be great, otherwise I will chalk it up to misunderstanding or misuse of terms.

Lefty
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I suspect that powr is consumed by other devices connected to the same 5 volt USB bus or other 5 volt loads inside the computer box.  If USB power really is derived from from the 5 volt computer power supply, there is a lot of load connected to the power bus.  Clearly the USB power lead is not diode isolated because 5 volts is available at the end of the USB cable.  The USB current limit is what?  half an amp?  but some things come with the cable that splits and use 2 ea half amp allocations.  I don't think polyfuses notice which way current travels.   If there is some sort of active current sense device metering power out to a USB port and protecting if it from over current, does it know what to do if the current reverses?

I guarantee you that an external 5.2 volt regulated power source will supply current to a USB port and it will be a design consideration for me in the future.

JC 
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I guess what I will do is remove the USB current limiting fuse so that the PC cannot source or sink current from the power supply in my project.
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