Maximum input Current??

Hello there

I have an Arduino Duemilanove board and as its mentioned in its website that the Input Voltage (recommended) is 7-12V and Input Voltage (limits) is 6-20V. I would be grateful if somebody could inform me about that is the maximum current can Arduino board operates without any issue from a rechargeable battery?

Thank You

On the Uno at least (and I assume the due is the same) there is a restriction of 40mA on any one pin and an overall limit of 200mA. Even 40mA is not recommended - if possible keep it to half that. Given that you've chosen the motors forum to ask this, I assume you're planning to drive one from the Arduino. For all but the tiniest of motors, as you can see from the foregoing, the Arduino can't provide sufficient current and you will likely damage it if you try. You need separate power for the motors and a suitable transistor or H bridge to allow the Arduino to control it.

wildbill:

I would actually say, from reading the OP's message, that they are misunderstanding how current works (your explanation though is helpful): They seem to be in effect asking "I have a battery that supplies 'N' amps, can I use it to power the Arduino without blowing it up? How much current can I supply the Arduino?"

This question, though, is wrong.

You don't supply current - you draw it. A battery (or a generator, or etc) -sources- current; devices you connect to it -sink- current. Those devices will only sink a certain amount; you need to ensure that the battery can -source- that amount.

For instance, let's say at max the Arduino -sinks- 1 amp of current, and you have a battery that can source 200 amps (perhaps a car battery); you won't blow up the Arduino with that battery (although the voltage regulator is gonna get mighty warm!) - it will only ever draw that maximum 1 amp.

Now - let's say you had something, like a motor, that could sink 1 amp of current, and you hooked it up to the Arduino directly (don't do this!); in this case, the Arduino is -now- the current -source-; since an individual pin can only supply about 40 mA of current (and really, you should keep it much lower than this) - that pin will blow, because you are trying to draw 25 times that amount from it!

This can happen to batteries and other components too (often with a loud explosion and/or fire taking place); for instance, a direct short across a D-sized alkaline cell can cause many amps to try to flow - and the battery will likely explode or rupture in fairly short time (if it doesn't vent properly first).

I prefer to think of it in a more fundamentally accurate and perhaps more easily understood way.

The voltage of the power source and the resistance of the circuit correspond with how much current moves through the circuit. Adding more stuff onto the circuit in a way that reduces the total resistance at a given voltage allows more current through it which, if too much, can damage the circuit and/or the power source.

The power source (in this case a battery pack?) doesn't determine the total resistance of the circuit and therefor doesn't determine how much current moves through it. (Battery packs also have internal resistance which can limit how much current can potentially move through the circuit, but, when properly used, this is typically a lot lower than the total resistance in the circuit.)

The current ratings of battery packs are to show how much current they can safely produce for their own "health," (but not necessarily the "health" of the rest of the circuit and its components) and they aren't a measurement of how much current they actually will produce. It is also possible to "drain" more current from battery packs than is "healthy" for them.

Anyway, to make a long story short: Yes, you don't want too much current going through your Arduino, and you should be careful to prevent that from happening, but the power source (given that it's at an appropriate voltage level) won't "push" more current through the circuit just because it might be potentially capable of supplying/producing more current than another power source.

For most motors you'll want to use a relay of some sort, or a similar solution to prevent too much current from moving through the Arduino.

RoboM:
I have an Arduino Duemilanove board and as its mentioned in its website that the Input Voltage (recommended) is 7-12V and Input Voltage (limits) is 6-20V. I would be grateful if somebody could inform me about that is the maximum current can Arduino board operates without any issue from a rechargeable battery?

Volts measure voltage not current. Current is measured in Amperes, and is something that is drawn by the load, not pushed by the battery.

If your rechargable batter provides any voltage between 7V and 12V, it will be great for powering the Duemilanove through the DC-in jack. If it provides any voltage between 12V and 20V, it will still work, it just won't be the best source for the job. Trying to go below 7V may result in flaky behavior -- some people say 6V works fine, others find it doesn't.

...Current is measured in Amperes, and is something that is drawn by the load, not pushed by the battery...

I know that this is how it is commonly explained, though I'm not entirely sure why. (Perhaps to make it easier for people to predict how motors and other similarly less easily understood components with varying resistances will function in a circuit.)

At the more fundamental level, the voltage of the battery pack is what pushes/pulls the current through the circuit. Without voltage there is no current, regardless of whatever the "load" is. How much current there is depends on the resistance of the circuit and the voltage of the power source.

This is essentially the relationship that Ohm's law represents.

Let's put it this way: With no load, there is still a voltage, but no current. There will never be more current flowing than what the load draws.

If we want to be specific, then voltage sag from internal resistance in the power source comes into it, too; that, and thermal protection circuits, are the reasons why power sources cannot provide infinite current when shorted. Even though they may try, and burn themselves out doing it :slight_smile:

This is essentially the relationship that Ohm's law represents.

I agree and the three simple formulas, I=E/R R=E/I and E=IxR is all one needs to know to understand the relationship. And until they really understand Ohm's law (and to 'think' in ohms law) they will continue to have trouble progressing in learning electronics. There is a reason almost all electronics fundmentals course start with DC electronics and Ohm's law and only then progress further.

jwatte:
...There will never be more current flowing than what the load draws...

In a simple circuit, if the supplied voltage is increased or decreased, the current through the circuit will likewise increase or decrease, and increasing or decreasing the resistance of a circuit will inversely increase or decrease the current through that circuit. There are of course additional characteristics of specific components that determine how a circuit behaves. I'm just addressing these fundamentals.