This maybe a very stupid question but, how much power is available via Vin pin? I am assuming it is 5 volts, but how much amps are provided?


I am trying to run a dc motor using ardumoto shield, AFAIK it gets power from vin, arduino is connected to a power source that provides 9v 2amps, so i am assuming say if i have x volts and y amps on the vin pin, i can get a motor according to this spec? in this question someone said ardumoto supports up to 50v and 2 amps, i am trying to figure out how pass more current to the driver shield to run a dc motor in a RC car.

  • \$\begingroup\$ According to the spec sheet, which I got from a link from the SparkFun Ardumoto site, the device can take 46V up to 2A per channel, 4A total, for close to 100W per channel or roughly 1/8 HP (.13). At 2A, 9V, you're looking at 18W or 1/40 hp, which might be too low. I've added a comment to post the motors you have used on the other question, and if you would be so kind, post the power supply, code, and any other customizations you have made as well. It sounds like you may need more power, but if you post this info we can certainly help you troubleshoot and make sure nothing else is going on. \$\endgroup\$
    – Lou
    Jan 22, 2010 at 19:33
  • \$\begingroup\$ Lou thanks, my power source is a generic adapter which provides 9v 2 amps as for the motors they don't have any make or model on them i'll check with the shop i bought them for the specs tomorrow it's 10pm here. \$\endgroup\$ Jan 22, 2010 at 20:09
  • \$\begingroup\$ No problem! We're here to help! You'll probably have a slew of stuff come in over your night as the Americas get off of work (just a few hours...). \$\endgroup\$
    – Lou
    Jan 22, 2010 at 20:19

2 Answers 2


Vin pin is connected directly to the external power supply you use (if you are not powering from USB). Voltage is therefore down to the the supply itself. Amps available is also down to the supply (less a bit for the Arduino consumption). In general I would not advise drawing more than 1 amp through the board - if you need that sort of power then you should be connecting directly to power supply.

If you are powering from USB then there is nothing on Vin.

If you (say) use a power adapter giving 9V and 2A then you will get 9V and a little under 2A, say 1.9A at the Vin pin.

  • 1
    \$\begingroup\$ Vin can also be used to supply power to the Arduino. It comes in, as expected, before the voltage regulator (That's why it can be used to tie in directly to the external power supply and why it has no potential when the board is powered over USB). \$\endgroup\$
    – Lou
    Jan 22, 2010 at 16:49
  • \$\begingroup\$ So does that mean, if i use a 9V 2amp adapter connected to the power plug on the arduino do i get 9v 2amp on the vin pin? \$\endgroup\$ Jan 22, 2010 at 17:48
  • \$\begingroup\$ You should consider editing the question above to add this. I'm a bit confused as to what you mean. Is the connector rated at 9V, 2A, or is your connector hooked up to a power supply that can yield 9V at 2A? If it's the former, no: Whatever you are using (say, a battery) will determine your specs, and if you go over the adapter's limits you risk causing permanent damage. If it's the latter, possibly, but remember the Arduino will need current to run as well. It sounds like you have a project in mind. Perhaps if you told us more about the project, we could give more helpful answers. \$\endgroup\$
    – Lou
    Jan 22, 2010 at 17:54
  • \$\begingroup\$ i have edited the question to include information about what i am trying to do. \$\endgroup\$ Jan 22, 2010 at 18:29

The Vin pin is NOT "DIRECTLY CONNECTED to the external power supply", or at least is NOT at the same voltage. This is obvious from direct experimentation with a wall wart with regulated (yes, regulated) voltage, this one at 1A capacity. Measuring the voltage from the wall wart open circuit on my newer model Fluke, it is almost a FULL ONE VOLT HIGHER than the voltage on the 'Vin' pin with the wall wart plugged directly into the Uno R3's coax power input jack. On the other hand, when I strip the wires on the end of the wall wart cable and plug them into Vin, the voltage then measured at Vin is within .01 volts of the OC voltage from the wall wart.

Quite obviously, there is some circuitry on the Uno (R3) that is loading down the supply when the coax jack is used, quite considerably in fact. Ergo, the 'Vin' pin is NOT cleanly connected to the supply. It is NOT THE SAME VOLTAGE AT ALL, or at least not dependably.

One must conclude that plugging in a wall wart to the coax jack, then attempting to draw real power (more than a few ma) from Vin is hazardous to the health of the Uno.

So much for the idea that they are the same point in the circuit.

  • \$\begingroup\$ I don't see how this answers the question. This looks like a reply to the other answer. If so, it should be a comment instead of an answer (you can comment everywhere once you have earned 50 reputation). Perhaps you could reword it so that it does answer the question. \$\endgroup\$
    – Null
    Nov 24, 2014 at 1:13
  • \$\begingroup\$ @jrc Please don't use all-capitals. If you need to emphasize something, you can use italics. Also, fyi, Arduino.stackexchange.com might be a better venue for Arduino conversations. \$\endgroup\$ Nov 24, 2014 at 1:51
  • \$\begingroup\$ There is a diode between the barrel jack and Vin, which is causing the voltage drop you are measuring - see forkrobotics.com/2011/11/powering-an-arduino. \$\endgroup\$
    – Andrew
    Feb 10, 2015 at 3:11

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