# Thread: Help me understand inductors

1. ## Help me understand inductors

Here are some definitions of inductor:

"An inductor is a passive electrical device that stores energy in a magnetic field, typically by combining the effects of many loops of electric current."

"A coil onto which voltage is imposed by another coil."

After reading so many definitions I still don't understand why we use an inductor. I look at my old motherboard and see coils (inductors). If I was making a motherboard, why would I use a coil? To clear out bad frequencies? Why wouldn't I use a capacitor instead?

2. I've studied this in school but don't remember much beyond the basics, but perhaps another laymen's explanation may boost your understanding a bit more.

In the most general terms they are both electrical components that store energy. Capacitors store energy by separating positive and negative charges across plates in the device, thus setting up an electrical field, and subsequently a potential difference that can do work. Inductors store energy in coils via a magnetic field (the coils induce magnetic fields on adjacent coils).
Aside from minute internal resistance I do not believe inductors resist direct current, rather, they only resist *changes* in current (alternating current), while capacitors resist both direct and alternating current. I don't remember the specifics, but the current through and the voltage difference across capacitors and inductors differ (search for phasor diagrams to see what I am talking about).

3. So I would use a capacitor to resist large amounts of alternating and direct current. I would use an inductor to resist large amounts of alternating current. But why would there be alternating current inside of a computer? Isn't it all direct current, created by power supply?

4. One thing that is alternating current for sure is the clock of your comp, i guess.

5. A capacitor serves as a rechargeable battery of sorts. You charge it, it stores energy, connect it to something else, and it releases the energy. As the amount of energy stored increases, it becomes "more difficult" to store additional energy.

An inductor opposes any fluctuation in current. If there is a spike in current, the inductor will provide greater resistance decreasing the current that passes through the circuit. If there is a decline in current, the inductor will provide a positive voltage thereby increasing the current in the system.

6. Capacitors are also typically used in timers. Research monostable and astable 555 timers (the difference between them has to do with whether or not the input is external but I don't remember which is external input and which is internal input). You will find that the frequency and period entirely depends on the times it takes for the capacitor(s) to charge and discharge.

http://en.wikipedia.org/wiki/555_timer

I also started writing this to simulate a 555timer, but I'm kicking myself now for not finishing it (it was supposed to be for a neural network simulation where decisions are based on how hard each capacitor pushes back current, and the neural network is trained by adjusting values on the capacitors)

Code:
```/*

RS FLIP FLOP TRUTH TABLE

*/

struct	Timer555
{
Timer555()
{

}

BOOL	ThresholdComparator;
BOOL	TriggerComparator;
BOOL	RSFlipFlop;
BOOL	Output;

float	Voltage;

float	VoltRegion1;	//Potential between resistor 1 and 2, given by Voltage - (Voltage/3)
float	VoltRegion2;	//Potential between resistor 2 and 3, given by Voltage - (2/3)Voltage

float	Capacitance;	//In a real application this is usually in microfarads

//These will often be the same
float	ChargingResistance;
float	DischargingResistrance;
};```

7. Originally Posted by golfinguy4
An inductor opposes any fluctuation in current. If there is a spike in current, the inductor will provide greater resistance decreasing the current that passes through the circuit.
But don't capacitors prevent against spikes and brown outs too?

8. Originally Posted by Kleid-0
But don't capacitors prevent against spikes and brown outs too?
I dont know what you mean by brown outs but spikes yes.

Thats one of the reason why you use capacitors when building a Graetz circuit, because for Direct Current it will look as if it was a normal wire, but for Alternating Current it will work against the flow of the current, thus reducing the spikes and leveling the signal. The bigger the capacitor the flatter your signal will become ( because more current will flow in opposite direction).

9. So if I was building a motherboard, and I saw that DC and AC was going through at not very flat rates, then I would use capacitor. That would cause the DC & AC to not be as spiky.

Also golfinguy4 brought up the fact that a capacitor is like a battery, but that's not the part that matters, it's the fact that it flushes out current that is stable, for AC and DC.

If I just wanted DC current to go through and I had AC/DC on the line, then I would use an inductor/coil to stall the AC? Could we call the inductor/coil an ADC?

10. Also golfinguy4 brought up the fact that a capacitor is like a battery, but that's not the part that matters, it's the fact that it flushes out current that is stable, for AC and DC.
Actually the only thing a capacitor does is get an electric charge opposite to the change in current. Depending on how big the capacitor is it will be able to hold a larger current , elco´s typically can hold more current then a normal capacitor, although when using it you should be carefull because if you misplace it it could blow up in your face ( carefully respect the + and - ) , normal capacitors dont care how you place them.

You should also know that it is not instantly that when you turn on the power the capacitor will give an opposite current, first it will have to charge before it´s actually functioning.

I think a capacitor even reacts like a shortcutted wire on the moment the first current goes trough it, therefore when using them its a good thing to just have some resistor placed over them ( which you would normally have because it´d be strange to just have a capacitor without anything following after it )...

As for the part that it flushes out stable current for AC and DC , suppose you have a combined signal of DC and a AC current on top of that. The DC current will flow trough the capacitor without changing anything to the state of the capcitor, it is only the AC current that will cause the capacitor to react ( giving an opposite current -> leveling out the AC current depending on how much Fahrad your capacitor is ).

But if you really want to know everything about it i´d suggest following some electronics/ electricity classes or something...

11. Kleid-0

Speaking as a one-time electronics design engineer I can help you out here. But I've a poker game to go to this evening and I want to prepare a good answer for you.

I'll work out an explanation and post it tommorrow.

Popular pages Recent additions