I don't understand why powering a motor directly form arduino io pins would burn the arduino pin out? As I understand it as the resistance increases, the current decreases, so by powering a motor (with a large resistance) doesn't the current go down? Why doesn't powering an LED (something with much less resistance) burn out the arduino, as the current would be higher with something of a small resistance?
I know that my understanding is fundamentally flawed and I would appreciate if somebody could explain which if my assumptions are wrong and give an explanation of ohm's law. Every time I try to understand it, my brain just melts
Large isn't a mathematical quantity, so you can't use that with Ohm's law to calculate current draw.
Motors tend have very low electrical resistance. So I'm not sure why you mention a motor with a large resistance.
The Arduino I/O Pin (which is actually the ATmega328 I/O Pin) can only supply about 40mA before destroying the transistor on that pin. So if you have a load that draws more than 30mA, it causes damage. Most motors draw much more than 30mA.
Why doesn't powering an LED (something with much less resistance) burn out the arduino
LEDs turn into shorts when enough voltage is applied to them. (Their resistance actually becomes almost zero.) If you do not use a current limiting resistor with a LED on an I/O pin, it will burn that I/O pin out. (Usually not at first, but over time the transistor that is connected to that I/O pin gets destroyed.)
I think I might be confusing resistance to be something like current, as in, something that needs a lot of "power" has a high resistance. I have a lot to learn it seems :O.
Is it correct to say that current is the movement of charge? And charge is carried by electrons? So current is movement of electrons? How does resistance affect the flow of electrons?
Okay, thank you I wont keep asking you questions because that will just be a pain so I think I will spend the majority of tonight googling! Thanks for the help
The key is understanding what "Power", "Voltage", and "Current" are individually and how they are related. Once you start to understand their concept, it isn't a large leap to see how Ohm's law works.
There's the "water" analogy that holds up pretty well.
Electricity is like a flow of water. "Voltage" is like water pressure. "Current" is the flow rate. Resistance is like a narrowing of the pipe. The flow of water through the pipe (the current) will depend on the size of the pipe (its resistance) and the pressure that you push the water through (the voltage.)
westfw:
There's the "water" analogy that holds up pretty well.
Electricity is like a flow of water. "Voltage" is like water pressure. "Current" is the flow rate. Resistance is like a narrowing of the pipe. The flow of water through the pipe (the current) will depend on the size of the pipe (its resistance) and the pressure that you push the water through (the voltage.)
I was going to use the same analogy. To take it a little further:
Say you have a garden hose (wire hooked to a power supply) with nothing on the end and water running (wire shorting out the power supply). You have very low pressure (voltage) and very low resistance (resistance) this ends up with maximum flow (current.) As you block the end of the hose resistance goes up, and so does pressure (voltage) Flow (current) is reduced. Fully block the end ( or remove the wire) and resistance is infinite, Pressure (voltage) goes to what ever the house (power supply) can provide, and current (flow) goes to zero.
As you block the end of the hose resistance goes up, and so does pressure (voltage)
No the pressure remains the same in your water system no matter what you do.
The amount of push is governed by the water company and the geography of where you live. You are confusing this with the force that the reducing amount of water comes out of the hose, this is not water pressure as such. Think of pressure as the height you can get water to, through a hose. This is the same irrespective of the diameter of the hose.
As you block the end of the hose resistance goes up, and so does pressure (voltage)
No the pressure remains the same in your water system no matter what you do.
The amount of push is governed by the water company and the geography of where you live. You are confusing this with the force that the reducing amount of water comes out of the hose, this is not water pressure as such. Think of pressure as the height you can get water to, through a hose. This is the same irrespective of the diameter of the hose.
If you put a T with a pressure gauge at the end of the hose the pressure will read low when water is flowing completely free. If you block the end the pressure will go to the set point of the PRV if your house is equipped or to what ever the pressure capability of the incoming line is. It is no different from voltage drop in a wire or over taxed PSU.
No the pressure remains the same in your water system no matter what you do.
While technically true, the city water pressure is only regulated the water on the intake. Same as mains power. You only get 200 amps (typically) into your panel (100 per buss). But with stepdown xformers, you can take a 120v/20amp branch circuit and get 50 amps out of it @ the cost of voltage right? Or go the other way and install a fluorescent light fixture with will push a no load voltage of ~350 volts.
So with the hose, the "current" is increased with adding your thumb (resistor) to the end of the hose. The poor mans pressure washer
the "current" is increased with adding your thumb (resistor) to the end of the hose.
No. In this analogy the current is the flow of water and the voltage is the pressure. Putting your thumb over the end reduces the water flow because the resistance increases.
You might get the illusion that the pressure is increasing but it is not and anyway it is only an analogy it is not the real way electricity behaves. The point is that for a given voltage more resistance means less power. Not as was stated:-
as in, something that needs a lot of "power" has a high resistance.
This is the exact opposite of the truth. A 1KW heating element has twice the resistance as a 2KW heating element.
There are PLENTY of explanations online (Try googling OHM's Law)
However, you should also be comfortable asking for explanations on forums.
(God knows I've asked my share of questions that someone else could google but I wasn't quite finding answers.)
That being the case, why don't you go take a look at Lady Ada's tutorial on electronics. It's pretty decent.
Come up with some questions and come back here for more detailed answers.
But it doesn't, it is a constant irrespective of voltage.
You can get none linear resistances where the resistance is some function of voltage but that is more advanced stuff and ohms law doesn't work so well in those situations.
