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# Is it possible to apply too much current to devices? Answered

Again, another silly question. A lot of my projects are going to need batteries (as they will be used in props). I have a decent understanding of how electricity works and all that, as I have done quite a few things with it from the ground up (that is, I didn't copy a pre-existing set of plans). But with all the stuff I'm planning to do, I'm having issues keeping up with it all, mainly due to the fact that I am a tad unsure on amperage draw and amperage supply.

For the sake of understanding for myself, lets say I try and run an arduino nano using a battery pack that spits out 12v/2a. Will the arduino only take what it needs, or will it try and take all of what it is given and 'burn' up.
Alterativly, if I were to use a 5v/1a peltier element, will it also only pull what it needs, or will it burn up?
I would assume the peltier would just burn, as it has no way to limit what it's pulling, while the arduino will regulate what it's getting.

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I think rickharris was trying to say Current = volatage / resistance. Devices will draw what they need. One thing to keep in mind If you have a motor controlled by an arduino and the motor stales it will draw a lot of current to try and get going. The motor might be fine but you could fry your arduino. So when you work with motors you need to look at their peak current and make sure your speed controller can handle it. Putting a fuse in can also help avoid smoking stuff. I think LED resistance is so low most people use resistors so you can figure out the current that will be going through.

for example if you have 12v and a 220 ohm resister you get .05amps.

12/220 = .05

Darn it - Yes I=E/R - blame the tablet keyboard or my fingers.

Although that did help clear up Ohm's law a bit for me, I'm still a touch confused. And sorry if I sound rude with this! Text tends to rid the human element from times...

Anyways, I understand that my house hold socket will push out 120v, and I can pull 15amps in one room total. Lets say that I have an LED that can handle 120v and a forward current of 30ma (I know, very unlikely that an LED like this exists, but for the sake of the question, lets go with it). I know LED's are kind of a dumb device, and thats why we need resistors with them. Now if I swap out the wall outlet for a battery, what would happen? Do I still need a current resistor on simple components like LEDs, or not? And do I also need those resistors on things like arduinos?

Yes, you need them on LEDs, no you don't need them on Arduinos. The resistance of LEDs is very low.

In you example, your LED would go boom, because the LED won't limit the current itself.

Alright, perfect.

Is there any why to tell what will need the current limited?

Not really - I guess a simple check would be to measure the resistance - If it is very low - a few ohms - then limiting will be required.

This isn't perfect some electrical things will seem low resistance but work fine. If your not electrically aware then this is quite hard to explain.

As a general thing - excluding LEDs most electrical mechanical things - motors etc will self regulate provide they are designed to work on the voltage your applying, Most electronics will self regulate if the voltage is correct. LEDs are a different beast though - When illuminated their resistance is very low almost a short circuit so they need a limiting resistor.

That makes perfect sense, actually. I had a mini-brain wave with ohms law a bit ago, and was able to understand the relation of limiting current to amperage supply/demand. I know that stuff is childs play when it comes to anyone with decent electrical knowledge.

As for the voltage application, that also makes sense. I've seen a few devices already (arduino boards being the main culprit) that give only a voltage range, and not a current range.

Thanks again for the help!

Electrical items DRAW current - That is they have a current demand and if the PSU can supply it they will take what they need.

SOME electronic items such as LEDs and resistors will have a very LOW resistance and so the potential to draw a lot of current - Ohms law tells you how much - Current = voltage / current