Arduino Uno 5V supply limit.

The Uno spec specifies that a maximum of 50mA can be drawn from the 3.3V supply socket.

How much can be drawn from the 5V socket?

Complicated question. It partially depends upon where the power is coming from, USB or external power.

If USB, the computer limits the current to 500mA, though some of that (~30mA) goes to the Arduino itself. So you can probably count on ~450mA or so for your own work.

If external power, current comes through a linear regulator that gets hotter with increasing current and difference input-output voltage. If it gets too hot, it shuts down. I generally suggest keeping linear regulator power dissipation below 1W, and if your output current is 500mA then input-output voltage difference should be no more than 2V, so something very close to 7V-8V is required...any higher and the regulator may overheat. There is some heatsinking on the PCB around this regulator so you may be able to push it above 1W, but we'll see....

If you need less current then you can tolerate higher input voltage (external voltage). For example, if you will draw 200mA then at 1W, the regulator power dissipation is (Vin-5V)*200mA=1W and Vin is as much as 10V.

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Thanks for the quick reply! :)

I am trying to control a RC car, I have stripped the circuit and I am building my own with an arduino and a Dual H-Bridge, I am unsure of the operating volatge of the motors tho, as they are embedded in the chasis and I do not wanna remove them. Thet were ariginally powered with 3.2V from 2 x AA batteries. I plan to power them with 5V tho.

I am using a 9V battery to power the Arduino and I would like to use the arduino's 5V supply to power the IC and the motors but I do not want to melt my Arduino.

If i make an estimate of 400mA @ 5V, as the demand for my system, this means that the limiter will need to dissapate 1.6W.... Which maybe an issue. But If I use 4/5 x AA, i might be ok?

Hmmm...not recommended for a couple of reasons. First, if your code is wrong and you turn the motors on at 100% duty cycle they will carry excessive current and can be damaged over time. Second, 400mA is actually probably a lowball estimate for these types of motors especially when they stall. Third, these motors are going to generate a lot of "back emf" noise which is going to couple into your Arduino board and could actually damage it if you're driving directly from 5V.

Why not hook the motors up to the 9V battery (which is probably a bit underpowered...AA's have more current capacity) directly? (through the motor driver of course). You can then use PWM (e.g., analogWrite()) to set a 33% duty cycle which is comparable to an effective voltage of ~3V, just like in the original car. The 9V battery (or whatever) powers the Arduino too, and since the Arduino only draws ~30mA the power dissipation of its regulator will be much lower.

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Good idea!

I never considered limiting the power to the motors with PWM! :)

Thanks very much! :)

Do you have any advice on the best battery option for powering an arduino and 2 x small dc motors + h bridge?

Can u power the board with a 5v usb power supply? If so how many volts come out of the digital pins?