Vin pin, how much current can I draw for 12V LED strip?

The Vin pin, if I've understood correctly, is connected directly to the +Ve of the barrel connector and so by passes the regulator. Putting 12V on the barrel connector will give me 12V on the output Vin pin. Is that right?

I've seen some posts about the Vin pin, and one says that I could draw up to a max of 1A.

I've had a look at the PC tracks for the Vin pin on an "UNO" and they don't seem very thick, is the 1A max correct? (Assume that the PSU can supply the Arduino with 1A left over).

I intend to use 250mA, but I like to have a large margin of error.

On an UNO, there is a diode between the jack and the Vin pin.

Therefore, if the jack is 12v, Vin is 11.3v

250mA from the Vin pin is no problem.

Many thanks for the reply. The diode is shown as D1 top right of the schematic to anyone else following this.

If you have a 12v supply and you want to power something at 12v connect to it -there is no need to go via the Arduino

@hammy , but that pin is so convenient, physically. Otherwise I'd I have to add another connector. I think they put it there for that reason, no? Convenience.

The pin is really put there to be an alternative power input , not for supplying power to other devices . ( hence called “Vin” , not “Vout”. !) You can use it , For “accessing the voltage “, whatever that means, but I’d suggest not as a power supply ..

A read of the official documents , which should always be your reference ,says

“ The power pins are as follows:

  • Vin. The input voltage to the Arduino/Genuino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.”

So officially it can be used as an input or output. It would seem. From that phrase.

So officially it can be used as an input or output. It would seem. From that phrase.

Yes, but only if power is applied to the barrel connector upstream from it and in that case the Vout will be about 0.7 Volt less that the supplied voltage. See the schematic Larry D posted in post #2 above. On an Arduino UNO board laying here if I apply 12.00 VDC to the barrel connector I get a Vout on the Vin pin of right at 11.20 VDC. I just see no reason to do anything this way.

Ron

Convenience. For my project it is very convenient. I need roughly 12v 120ma to a strip of LEDS.

Then go for it. A little unconvential but if it works for you then use it.

Ron

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Everything is a bit prototypee at the moment, I'll see if it goes ok...

Aside from what is drawing current through the Vin pin, what else is on the 5V rail. Do you know that the current that the 5V regulator can supply is limited when supplied by the power jack (or Vin)?

The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. The amount of current depends on the voltage input to Vin or the power jack. The higher the voltage the less current can by supplied.

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Aha! now that is something I had not thought off. Hmmm. I may have to rejig things...

Actually, it is the very first consideration.

The "Vin" pin or in fact the "barrel jack" which is the same with a diode, was originally provided to demonstrate the Arduino. Once you start connecting things that draw current, and that includes connecting things to draw current from the "5V" pin, you are playing with fire - or not! This is even worse for the Mega as it has more pins to connect things to! :astonished:

The on-board regulator - unless you use a variant such as the "RoboRed" (it has a proper switchmode regulator) - has no heatsink of significance. It may theoretically have a rating of 1 A, but only when bonded to a substantial heatsink. You can barely see it on the Arduino board. You will not get 1 A at 5 V from the board with any "Vin" voltage for more than a second or two before the regulator overheats - and hopefully shuts down peacefully. You may be lucky to get 150 mA. :roll_eyes:

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I'm a slow learner but I think I got there in the end. Since I also have to power servos at 5V I decided to power the Arduino and the servos from the same 5V regulated power supply and put the 5V into the Arduino using the USB connector:

I used an old USB cable, but these days the 0V is black (not brown) and 5V is red (not white).

The 12V for the LEDs will no longer even touch the prototype board.

Thanks to you all for your advice and nudging me in the right direction...