How much current is OK from the voltage regulator?

Hi,

I couldn't find the answer to this question. If i power my arduino uno/mega with 12 volts, how much current is OK to draw from the VIN pin and the 5V pin. I was only able to find how much current the microprossesor could handle.

Thanks for any help!

Regards

Hello Carl, Kindly give a bit more detail like what components you want to use, so it would be easier to illustrate. Greetings.

Hi!

I want to power a lot of electronics from the VIN pin, but for example, would it be possible to plug in 12V in the power jack on the arduino, and drive 2 motors (total maybe 5 amps) from the VIN pin?

Regards

NO!

Barrel jack is followed by 1A rated reverse polarity diode. 5V regulator is only good for 800mA. If you try and put 12V, 800mA thru the regulator it will either go up in smoke, or, if you're lucky, merely go into thermal shutdown. Better to power your other devices in parallel with the board and not try to put all the current thru the board.

That being said, I've been running about 150mA through the regulator with no issue (12 LEDs plus a few other things). It depends on the application, but I would try to power as much as you can from an external source in parallel and minimize what runs off the 5V regulator.

I had a Duemilanove driving 4 MAX7219s driving 4 8x8 matrices. With 12V source, it would run for a bit and reset. With 9V source, was not a problem. So the amount of current being used and the source voltage is definitely a factor that has to be considered.

Ca_rL:
drive 2 motors (total maybe 5 amps) from the VIN pin?

That will certainly need an external motor drive circuit - the Arduino would control it but not power it. It would be reasonable to power the drive circuit from the same 12V source as the Arduino, but motor power would not go through the Arduino.

Thank you all for answering! So to summerize, if I run 12V into the barrel jack I can take 1 amp from the VIN pin and 800 mAh from the 5V pin.

Regards!

Ca_rL: Thank you all for answering! So to summerize, if I run 12V into the barrel jack I can take 1 amp from the VIN pin and 800 mAh from the 5V pin.

Regards!

For a very limited period of time. You are hitting the edge of the engineering tolerances, and while it will probably technically work, it is not a good solution. CrossRoads brings up the very good point that the more voltage you drop across the linear regulator, the faster it heats up. It 'eliminates' the extra voltage by literally burning it off as heat. So regulator needs to burn off (VIn-5)*(Current) Watts, which can quickly heat it up. So while it works, it is not a good idea for personal safety and lifetime of your circuit. And while it claims 800mA, I honestly doubt it can sustain that for long. Finally, if you are doing anything with a battery, you are basically wasting power heating something up.

Summary: Minimize large current applications drawing off of the Arduino board. My preference is about max 200mA, but I cannot give any concrete justification for that particular number. I would, if at all possible, have the Arduino board power as little as possible.

Ca_rL: if I run 12V into the barrel jack I can take 1 amp from the VIN pin and 800 mAh from the 5V pin.

I don't think that's safe at all. The 5V regulator has to run the Arduino as well as whatever you drive from it, so even in the best case you wouldn't have the full 800 mA available for your external circuit. 12V is right on the limit of the supported voltage range and the 5V regulator will have minimal spare current capacity at that voltage. It would make more sense to provide an additional 5V regulator with enough current capacity and heat dissipation to supply the Arduino and whatever else you have that needs 5V, without being thermally stressed.

OK, so this won't work: 12V to barrel jack of arduino. The internal voltage regulator support the arduino board and on my shield I place another voltage regulator and support that from the VIN pin. My external electronics operates at both 12V directly from VIN and 5V from the voltage regulator on my shield. This doesn't work becouse of:

Barrel jack is followed by 1A rated reverse polarity diode.

So the solution is: Another barrel jack on my shield, 12V to that and then to a voltage regulator and then to VIN pin of arduino. (Now the shield powers the ardino through the VIN pin instead of the opposite)

Thanks for your patient

Ca_rL: OK, so this won't work: 12V to barrel jack of arduino. The internal voltage regulator support the arduino board and on my shield I place another voltage regulator and support that from the VIN pin. My external electronics operates at both 12V directly from VIN and 5V from the voltage regulator on my shield. This doesn't work becouse of:

Barrel jack is followed by 1A rated reverse polarity diode.

So the solution is: Another barrel jack on my shield, 12V to that and then to a voltage regulator and then to VIN pin of arduino. (Now the shield powers the ardino through the VIN pin instead of the opposite)

Thanks for your patient

What you need is to make sure you have a connector (Barrel jack if you wish, or something else may work better) that can handle at least twice the current you expect to be running (Twice the voltage too, but that's likely to be automatically available). This will connect to your power input. After this, you just split off from this input into the arduino, any higher current regulators (by the way, look up switching regulators if you need to do high current applications with a regulator) , and anything that will run straight off the input. You want to run them all in parallel and not daisy chain them. Daisy chaining them will result in you double up on some of your inefficiencies.