# Electromagnets and contactor relays

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1. Aug 16, 2015

### raymond621

I am supposed to make an electromagnet for a project.
how will i know what gauge of wire to use and how many turns do i need so that my electromagnet will only get 100mA of current from a 24V dc source?
Thank you!

2. Aug 16, 2015

### davenn

Hi Raymond
welcome to PF

do you know Ohms Law ?

if I said Resistance in Ohms = volts / current

can you plug in the values and come up with a value of resistance

then you will need to do some searching on values of resistance per metre (foot) of different gauges of wire
and determine how much wire you need

lets see how you go with the first part for a start

Dave

3. Aug 17, 2015

### raymond621

Thank you sir! Well I have solved it already. I got 2 different gauges of wire to be sure. I need to get less than 100mA of current so,
For the 31 awg wire, I need to have 500 m of wire.
For the 33 awg wire, I need to have 670 m of wire approximately.
My problem is now how many turns or how many times do i need to coil it around my steel core?
Actually I need this electromagnet to make a contactor relay. Is there any more things I need to consider in order to make the relay work for at least 10 minutes?

4. Aug 17, 2015

### davenn

That sounds the wrong way around

33awg is thinner than 31 awg so it's resistance would be higher and therefore a shorter length needed

I hope it is enamel insulated wire ? ( sometimes called magnet wire)

you need ALL of it wrapped around the core, except the fly leads off the end to go to the power supply

time isn't an issue with the small current you are drawing from the power supply

Dave

5. Aug 17, 2015

### raymond621

Yup, a magnetic wire! Thank you very much for your help Mr. Dave!

6. Aug 17, 2015

### davenn

you are welcome

post back in the thread at some stage a pic of your electromagnet
and keep us informed on how your experiment is going

7. Aug 18, 2015

### raymond621

Allright! Thanks again sir!

8. Sep 2, 2015

9. Sep 3, 2015

### davenn

looking good, have fun with your continued experiments