Electromagnet Current

[EmeraldW]

I find some material on this subject but nothing seems to directly answer my questions.

Is there a formula that can be used to determine how much current is needed for electromagnets? Or what a known setup will draw? What affects the current draw, wire size, turns, etc?

What affects the strength of the magnet? I know number of turns has a lot to do with it but what about voltage or current?

 

[geraldfryjr]

The magnetic field intensity is only directly related the the current in the wire ,Not the voltage.

jer

 

[kinarfi]

so 1000 turns and 1 amp is the same as 1 turn and 1000 amps, right?

 

[alec_t]

What affects the current draw, wire size, turns, etc?

For a DC electromagnet:
Current = applied coil voltage/wire resistance.
Wire resistance is proportional to wire length and inversely proportional to wire diameter.

What affects the strength of the magnet?

Current, number of turns, coil geometry, magnetic permeability.

so 1000 turns and 1 amp is the same as 1 turn and 1000 amps, right?

Yes, provided the coil geometry is the same (in theory you would need the 1000 turns to occupy the same space as the 1 turn).

 

[EmeraldW]

So would the field be much different with these two setups:

1000 turns of #22 wire using 5 volts/ 1amp

and

1000 turns of #22 wire using 24 volts / 1amp?

 

[misterT]

So would the field be much different with these two setups:

1000 turns of #22 wire using 5 volts/ 1amp

and

1000 turns of #22 wire using 24 volts / 1amp?

Same number of turns and same current. So the fields would be exactly same.

(By the way: It is impossible to increase the (dc) voltage of a coil without rising the current too.)

 

[geraldfryjr]

Yes,This is true, But you must keep in mind that only the current is directly proportional the the magnetic field and not the voltage it takes to setup the current due to the resistance of the wire.

jer

 

[EmeraldW]

So what limits the current that the coil draws? Or does it draw what is available? I'm looking to build a fairly strong magnet with as little current draw as possible.

 

[misterT]

So what limits the current that the coil draws? Or does it draw what is available?

The wire resistance. If you apply dc voltage to the coil, the current is I = V/R.

I'm looking to build a fairly strong magnet with as little current draw as possible.

Then use lots of turns and thin wire (but thick enough to handle the 'little current').

Use this table to calculate the resistance of the wire and to check how much current it can handle:
https://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes

 

[crutschow]

As misterT said, for a given magnetic field with minimum current, you need to use small wire with many turns. Generally you use as small a wire (enameled wire) as can be easily wound without breaking.

 

[EmeraldW]

Thank you everyone, this is the type of info I need.

When winding the coil and you reach the end of the core, do you wind in the opposite direction for the next layer or start back at the original location and keep the layers ending on the same side?

 

[alec_t]

You wind in the opposite direction (meaning left to right then right to left). You must have all layers in the same rotary direction (e.g. clockwise, as seen from one end of the core).