Im running an electromagnet straight to a power supply which is providing 12v, my electromagnet is gauge 0.8 and has 128 turns. For some reason when I power on the supply it’s powers for a few seconds until the fuse kicks in. Would I need a resistor? If so how many ohm’s?

 

hi JP,
Welcome to AAC.
Have you measured the resistance of the magnet coil.?
What is your power supply current rating at 12v.?
E

 

hi JP,
Welcome to AAC.
Have you measured the resistance of the magnet coil.?
What is your power supply current rating at 12v.?
E

In my electromagnet I have 2 wound up coils which I power in series, when I put the multimeter at 200 I got a total reading of 0.4 when both are in series.

I just did some research and apparently the power supply current is 5-6amps at 12v
Source:https://www.haines.com.au/index.php/power-supply-standard-2-12v-ac-dc-5a.html

 

hi,
With a 0.4R resistance at 12V thats 12v/0.4R = 30Amps!!!!
If you want the maximum current from your 5A supply thats a resistance of 2.4R, so you need a 2R resistor in series with the coil.
The rating of the 2R needs to be greater than 50Watts. == 5*5 * 2R = 50W.
For continuous use a 100W resistor would be advisable.
E

EDIT:
If you could pick up an old 12V vehicle headlamp bulb, rated at 50W that could be used as the resistor.
A lower bulb wattage would be OK, say 24Watt would reduce the load on your power supply, but it would reduce the coil magnetic strength..
BTW: the coil will get hot.!

 

Hello,

With a 0.4R resistance at 12V thats 12v/0.4R = 30Amps!!!!
If you want the maximum current from your 5A supply thats a resistance of 2.4R, so you need a 2R resistor in series with the coil.
The rating of the 2R needs to be greater than 50Watts. == 5*5 * 2R = 50W.
For continuous use a 100W resistor would be advisable.

Or put the powersupply at 2 Volts to stay at 5 A.

Bertus

 

If the measurement is performed with ordinary two wire instruments, the resistance in the coil is certainly far below the specified 0.4 Ω

 

Hi everyone,
Thanks for the great replies, i have just one more question...


https://www.jaycar.com.au/2-2-ohm-10-watt-wire-wound-resistor/p/RR3344
Say I get 10 of these resistors and then I connect them in parralel to create 100 watts (and use heatsink).
Would that work?
Also so that the coil doesn’t heat up could i use a 10r?

 

hi JP,
It is possible your power supply will not last long running near its current limit.
Give us more details of the power supply and your application.
E

 

I couldnt find a lot of information on the power supply as i dont have any manuals.
The site i listed previously is all i know about it.

 

OK, read that spec, why don't you do as bertus suggested, select the 2V output and use a smaller resistor.?

 

Hello,

The power supply seems to be rather crude, as this is the description going with it:


Power Supply, 2-12V AC/DC/5A
The IEC Power Supply is a compact, general purpose power supply to provide
switched AC and DC voltages at 2, 4, 6, 8, 10 and 12V.AC and DC at about 5 to 6A.
The DC output is full wave rectified but not filtered. Made in Australia

Bertus

 

If you designed the electro magnet, how did you arrive at the No. of turns? and what is its function?
Max.

 

It’s going to be used to make a solenoid motor, would it be easier to get a power plug rated at 12v and 1-2 amps rather than getting big resistors? The only reason I’m leaning against it is if the coil won’t be as strong.

 

The magnet field of a coil is determined by the ampere-turns (amps times turns).
So if you reduce the current and increase the number of turns with smaller wire, you can still end up with the same magnetic field.
That will save power.
So for example 5A @ 128 turns is the same as 0.5A @ 1280 turns.

 

Also I checked and 2v5amps is way too low for my circuit

 

The magnet field of a coil is determined by the ampere-turns (amps times turns).
So if you reduce the current and increase the number of turns with smaller wire, you can still end up with the same magnetic field.
That will save power.
So for example 5A @ 128 turns is the same as 0.5A @ 1280 turns.

Oh I didn’t know that thanks

 

Have you thought of using the coil assembly from a 12V relay? Just remove the armature and contacts then you will be left with a good coil.
Just out of interest, it looks like you are in Oz. I'm a couple of hours North of Melbourne.