Magnets & Inductors

[AtomSoft]

Ok i always see this simple Wrap Wire around pencil to make inductor and wrap around iron to make a electromagnet. But they all seem to fry a battery. How is that useful?

My question would be How would you make a electromagnet that wont fry a battery but that is DC. And the same for a inductor.

What would be usefull applications for inductors. I understand somewhat how inductance works but the use of 2 coils which never touch but i think thats like a transformer. What exactly do you gain or loose from using inductors?

Yes there are measured in Henrys (i think thats how its spelled) but how do you use that HENRY to calculate voltage or Amperage change?

 

[ronsimpson]

“Fry a Battery”. If you put 5 inches of wire across a battery it will drain the battery! It does not matter if it is wound around a pencil or not.
To make a low current electromagnet use very small wire and many many turns.
“Applications for inductors?” Inductors pass DC like from a battery and block AC. One application is to filter out noise (AC) from power (DC).

 

[AtomSoft]

Ok but if i use thin wire like 30 AWG then wont it still cause a short?

 

[Nigel Goodwin]

You use a LOT of it, and winding it round a metal core increases the inductance considerably.

 

[arhi]

Ok but if i use thin wire like 30 AWG then wont it still cause a short?

many many many turns ... many many many meters of wire ... on top of that, when you wind it around the iron the inductivness or inductance or what ever is the right english term will be high enough not to act like "short circuit"

edit: nigel was faster

 

[AtomSoft]

The reason im asking is because i want to make a small electromagnet to open/close a small box. I was woundering because they only have tutorials on how to make one and the battery always get too hot and some even leaked. So you are telling me if i wind it enough it will stop this? also if the wire is thin. and possibly the core of it?

So does anyone have info on practical use/creation of electromagnets and inductors which are like cousins lol.

 

[ericgibbs]

Ok but if i use thin wire like 30 AWG then wont it still cause a short?

hi atom,
Look at these copper wire resistance calculations in order to work out the resistance of a inductor/coil.

Copper wire

 

[ronsimpson]

AtomSoft, Yes wire is a short but; a VERY LARGE AMOUNT of very small wire has high resistance. #30 wire has 0.1 ohms/foot so 150 feet is 15 ohms and using a 1.5 volt battery is 0.1 amp.
Using a metal core does not effect the resistance (at DC) where the battery is. Using the metal core does greatly effect the inductor at 10khz (AC).

 

[arhi]

So you are telling me if i wind it enough it will stop this? also if the wire is thin. and possibly the core of it?

You can always use some current limiting resistor, but it is better to use more wire (to achieve resistance you want to limit the current) as it will make the magnet stronger

Do not forget the back EMF protection diode

 

[AtomSoft]

so if i wrap 200ft of #30 wire and use a 5v battery that would be... 250mA.

But the question for that would be ... the 250mA would be the output current comming out of the coil? Or the current it uses?

Also whats the end voltage or is it the same?(voltage out of coil)
How would i change the current to voltage ratio?
Because i hear you can use a inductor to take 5 volts and make it like 50v but you lose some current OR you can take 5v @ 1A and change to 2A but lose voltage... How would this work? I know it has to be 2 coils i think.

Also if i wrap a piece of metal than can be magnetized with this wire and make a electromagnet would it work against other metals only or both other metal and magnets.

 

[arhi]

so if i wrap 200ft of #30 wire and use a 5v battery that would be... 250mA.

But the question for that would be ... the 250mA would be the output current comming out of the coil? Or the current it uses?

look at the coil as a simple resistor when it is used in DC circuit. So, if the 200ft of #30 wire is 20R then current flowing trough your coil is I = U/R = 5v/20R = 0.25A

If your whole circuit is battery and coil, then the current flowing trough the circuit is 250mA .. not sure what you mean by "coming out of the coil", the current is flowing trough the coil, going in on the one side and coming out on the other side ... while current is flowing the coil will generate magnetic field.

When you "stop" current from flowing, for example by using the switch, or disconnecting the battery, the coil will generate strong EMF pulse that can be few hundred volts (low current, short time) that can burn out any transistor or IC in the circuit, that is why you need the back EMF protection diode (just add reverse polarised signal diode parallel to the coil) so that EMF does not cause havoc in the circuit

Also whats the end voltage or is it the same?(voltage out of coil)

Voltage were? Voltage on the end of the coil will be the one you apply to it if that is the only element in the DC circuit (apart from the power supply).. As I said, consider that coil as regular resistor if the circuit is DC. If circuit is AC then it gets bit more complex

How would i change the current to voltage ratio?

I = U/R
U/I = R
R = U*I

What is the constant and what you can change ?
If your voltage is static (1.2V battery for example) you can increase current by reducing the resistance of the coil (less wire) or you can decrease current by increasing the resistance of the coil (more wire)...

Because i hear you can use a inductor to take 5 volts and make it like 50v but you lose some current OR you can take 5v @ 1A and change to 2A but lose voltage... How would this work? I know it has to be 2 coils i think.

You cannot make that using simple DC circuit you will have to make a "voltage pump" or whatever is the real name for it, or so called DC DC converter circuit.

here is a very good link with explanation, example circuits and graphs
**broken link removed**

Also if i wrap a piece of metal than can be magnetized with this wire and make a electromagnet would it work against other metals only or both other metal and magnets.

You need to wrap wire around the metal, not metal "with" wire to make it magnetised. The amount of "force" magnet will have towards other materials depends on their magnetic properties
Magnetic properties of materials
Magnetism - Wikipedia, the free encyclopedia

hope this helps

 

[ericgibbs]

so if i wrap 200ft of #30 wire and use a 5v battery that would be... 250mA.

But the question for that would be ... the 250mA would be the output current comming out of the coil? Or the current it uses?
Its current flowing thru the coil and battery loop.

Also whats the end voltage or is it the same?(voltage out of coil)
How would i change the current to voltage ratio?
Use Ohms Law: Current = voltage/resistance

Because i hear you can use a inductor to take 5 volts and make it like 50v but you lose some current OR you can take 5v @ 1A and change to 2A but lose voltage... How would this work? I know it has to be 2 coils i think.
This is Lenzs Law: refers to EMF = -L * di/dt
Thats Voltage = - Inductance * Rate of change of Current with respect to Time.


Also if i wrap a piece of metal than can be magnetized with this wire and make a electromagnet would it work against other metals only or both other metal and magnets.
Works with all Ferrous metals, magnets and electro magnetics

hi atom,
What are you trying to do,?

 

[audioguru]

There is no such thing as a 5V battery.
What is the battery voltage, its chemistry and size?

A little 9V alkaline battery gets pretty hot if you short it with a short piece of wire.
Then it will quickly be drained and will need to be replaced.

 

[AtomSoft]

Ok what i mean by coming out the coil is. If i have a 9v battert and connect a LED with a resistor then add a inductor parallel with a diode to this wouldnt the current going in 1 side of the coil be different than the other side? also would that affect the LED. Remember current travels in 1 direction i assume it does go back and forth.

Like from A--------->B so wouldnt A have different properties than B since A is the start before the coil.

audioguru: We all know there is no 5v battery but you know what i mean (5v regulator)


Ok so the main reason to use a Inductor is to clean up signals? So its kind of like a resistor and capacitor together?

So what are other uses for it besides cleaning signals? How would one use HENRYs to calculate this?



Ok now for the electromagnet. Ok so I wrap the core with this wire and then when current goes through the wire it creates a magnetic field and that magnetizes the core making it a electromagnet. I would have to wrap it as i would an inductor to create a resistance so as i dont short anything out. Also i would need to add a diode for the EMF protection.

Would that sum it up?

I have some (2) electromagnetic door openers both are 12v I will open it up to see exactly how it looks and stuff. I will also try to recreate it even if i cant 100%.

 

[arhi]

Ok what i mean by coming out the coil is. If i have a 9v battert and connect a LED with a resistor then add a inductor parallel with a diode to this wouldnt the current going in 1 side of the coil be different than the other side? also would that affect the LED. Remember current travels in 1 direction i assume it does go back and forth.

AC or DC ? Continuous or pulsed ?

If you run continuous current trough that circuit, the current will flow in one direction and the coil will behave like resistor and inductance of the coil will not play any part, when you stop the current the coil will produce back EMF. If you run AC or pulsed then inductance of the coil will play a part (check that link I gave you for DC DC conversion for some graphs, explanations, circuits).

Ok so the main reason to use a Inductor is to clean up signals? So its kind of like a resistor and capacitor together?

NO

In DC current, you can use inductor to clean up signal (as it's resistance is different for DC and for AC component of the signal), In that case you can look at it as resistor + capacitor but

in ---R---------- out
          |
          =
          |
         GND

that is not "exactly the same thing" just "similar" the inductor is inductor, capacitor is capacitor ... this is similar circuit if we talk about filtering but not "general case"

So what are other uses for it besides cleaning signals? How would one use HENRYs to calculate this?

The henry's come in use when AC or pulsed signal is going trough the coil.
The back EMF will be higher if more henry's

Ok now for the electromagnet. Ok so I wrap the core with this wire and then when current goes through the wire it creates a magnetic field and that magnetizes the core making it a electromagnet. I would have to wrap it as i would an inductor to create a resistance so as i dont short anything out. Also i would need to add a diode for the EMF protection.

Would that sum it up?

yup

I have some (2) electromagnetic door openers both are 12v I will open it up to see exactly how it looks and stuff. I will also try to recreate it even if i cant 100%.

It is fairly simple, you have SPRING that push the piston out and you have electro magnet that pull the piston in. When you apply 12V the magnet pull the piston releasing the mechanism and when you remove the 12V the magnet allow spring to push the piston back into place. On the control board (that is usually not inside the lock) there is usually small relay or transistor driving the lock with back EMF protection diode in some "better" locks, and "no diode" on some CNG models.

 

[arhi]

check out this link, it will give you some background on inductors (also pretty good about some other "basic" stuff")

 

[AtomSoft]

OMG thanks i lost my favorites a while ago and i know that site was in it. I guess i never got back to it. Thanks i read the first page 2 times and awesome info!

i now understand the EMF diode scenario.. discharging... i see why the diode is needed. And the formula on the next page should help me a lot also. Thanks