# Electromagnet Power Supply Connector Getting Hot

Joined Jul 6, 2019
10
Hi,
I'm creating an electromagnet for a project I'm working on. My problem is, if I connect the two ends of the coil to the positive and negative terminals of the power supply for more than 2-3 seconds, the power supply connector literally gets smoaking hot.

Parts:
For the core, I'm using an iron core that I salvaged from a weather station. Dimensions: 50.0mm x 2.0mm x 7.0mm
For the wire, I'm using this
For the power supply, I'm using this

I appreciate all responses.

Kind regards,

#### AlbertHall

Joined Jun 4, 2014
12,187
Your coil is drawing too much current - it doesn't have enough turns for use with that battery.
Can you measure the resistance of the coil?

Joined Jul 6, 2019
10
Thank you for your very quick response. Is it possible to calculate the resistance of the wire without an ohmmeter/multimeter?

#### AlbertHall

Joined Jun 4, 2014
12,187
Do you know how many turns of wire you used?

Joined Jul 6, 2019
10
Yes, I used 103 turns ± 2.

#### AlbertHall

Joined Jun 4, 2014
12,187
What is the length of each turn of wire (L in metres)?
30AWG copper wire is 0.339 Ω/m
The resistance of the finished coil will be R = 103 x L x 0.339 Ω
The current at 9V will be 9 / R.

Joined Jul 6, 2019
10
Ok, so the resistance is 0.314
And the current that it's drawing is 28.66... amps? That doesn't make sense, does it?

#### AlbertHall

Joined Jun 4, 2014
12,187
Ok, so the resistance is 0.314
And the current that it's drawing is 28.66... amps? That doesn't make sense, does it?
It won't actually be drawing that much current because the batteries can't do it but it will be drawing a LOT of current - essentially you are short-circuiting the batteries.

How powerful does this magnet need to be?
If we say that a sensible maximum, short term current for an AA battery is 1A and you are using 6 of them in series then you need around 2700 turns of that wire on that former.

Joined Jul 6, 2019
10
Oh, that makes more sense.

To be honest, I don't really know yet. Right now I'm sort of just seeing if it's feasible
Wow, that's a lot of turns! Is there any other way to reduce the heat?

#### AlbertHall

Joined Jun 4, 2014
12,187
You could try it with just one AA. That might give you about 4A.
Incidentally, you can get an idea of the strength of the field by multiplying current and turns to give you ampere turns.

Joined Jul 6, 2019
10
I have tried it with just one AA in the past. It could only pick up tiny screws and paperlips
Okay, I'll bear that in mind.

So there's no other way to reduce the heat or stop it from trying to draw so much current?

#### BobTPH

Joined Jun 5, 2013
6,078
The magnetic force is proportional to the current.
Times the number of turns.

Bob

#### transconductance

Joined Jun 29, 2019
80
Consider your magnetic circuit. If you can bring both poles to the armature (whatever you are trying to attract) the same number of ampere-turns will give you more mechanical force than a single pole.

Also, since it is a DC magnet, you want a soft iron core. Any chance what you have is some kind of ferrite?

Joined Jul 6, 2019
10
Ok, I'll try adding more turns.

Alright, I'll have a look at that.