How much voltage can I draw on the 5 V pin?

I have got the adafruit motor shield. One of its features is that it has 3 pins on which you can connect a servo. The only trouble is it draws its power from the 5V pin. as long as the servo is not stalled, this is ok. As its only a small servo and it will not use more than the 800 mA which is the maximum power usage of the 5 V pin. If the servo however would stall for a short moment it would possibly use more than the 800 mA allowed. Would it damage the arduino if more than 800 mA would be drawn for maybe a second? What would happen? The risk that the servo is stalled exists but its not big...

You should use an external supply as described here at adafruit.

Thanks for your answer, but I already knew about this. I want to keep things simple and use the arduino to power the servo. The thing is, the servo is small, so it does not need a lot of power, so the average amount of Amps used will definitely be low enough, to just let the arduino itself power the servo. But it might happen that the servo stalls, in which case the Amps going to the servo will dramatically increase. This is why my question is:

What happens if I draw, lets say 1 Amp, from the 5V pin for a very short time?

If 800mA is the maximum that is supposed to be drawn, it would be pure speculation to say what would happen if it was overstepped even for a short moment. If someone says "don't worry it'll be fine for 5 seconds" then you blow your board in 4 seconds?

Manufacturers give limits for a reason: use an external supply.

Of course, it's up to you if you want to risk it. You're probably not going to permanently damage anything. If it fails, most likely the voltage regulator will shut-down (or partially shut-down) and your Arduino will reset, and the cycle will repeat when the regulator cools-down.

The actual current the regulator can supply depends on the applied voltage. The higher the applied voltage, the more voltage is "dropped" across the regulator and the hotter it gets (assuming constant current). It also depends on ambient temperature. The hotter the ambient temperature, the more likely the regulator will overheat.

I just had an Idea: What if I power the arduino over usb? If the current used by the servo is higher than 500 mA (i.e. the servo gets stalled), the usb protection fuse will go and the arduino is saved. The fuse should reset later, right?

Don't trust a fuse!
Power high current devices from external power supplies.

If you like to learn from experience do it your way :wink:

bestanamnetnogonsin:
How much voltage can I draw on the 5 V pin?

Exactly 5 volts. No more, no less. That is why it is a 5V supply.

Presumably you question was inteded to be : How much current... (or How many Amps...)

yeah I know, nitpicking. :wink: At least all those who answered understood it that way. 8)

I just had an Idea: What if I power the arduino over usb? If the current used by the servo is higher than 500 mA (i.e. the servo gets stalled)

USB should be much safer for the Arduino. But, since the 5V is running the Arduino and the servo, if the 5V USB supply gets overloaded and cuts-out, your Arduino will crash and reset. Is it a problem for your application if your Arduino resets/reboots and your sketch starts-over?

...the usb protection fuse will go and the arduino is saved. The fuse should reset later, right?

I'm not sure if USB ports are guaranteed to be over-current protected. You might want to research that... A blown USB port would be more costly than a blown Arduino! :wink:

The fuse should reset later, right?

Well it might but the characteristics of the fuse will change. These fuses are slow to blow and can take up to 24 hours to recover. They just protect against gross over current.