# Number of turns in a electromagnet

#### DesoxyN

Joined Oct 4, 2021
6
Hey all, Im an electrical engineering intern in a company that builds magnetic - electromagnetic seperators. Recently Ive been tasked to find the number of turns on these 2 big coils which works as a electromagnet. I have the dimensions of the coil and the coil resistance. Any help would be appreciated.

Inner Iron core diameter: 274mm
Outer Winding diameter: 114mm
Height of the coil: 430mm
1 Coil resistance(both equal) : 16.5ohms

I need the optimal wire diameter and number of turns. No data on inductance. Please try to explain everything you mention down below.

Last edited:

#### Alec_t

Joined Sep 17, 2013
13,228
You know the overall winding dimensions, so you can calculate the number of turns that would fit in for a given wire gauge. From that you can calculate the wire length and hence its resistance (assuming you know the wire chemistry). Juggle the wire gauge until the calculated resistance matches the measured resistance.

#### DesoxyN

Joined Oct 4, 2021
6
You know the overall winding dimensions, so you can calculate the number of turns that would fit in for a given wire gauge. From that you can calculate the wire length and hence its resistance (assuming you know the wire chemistry). Juggle the wire gauge until the calculated resistance matches the measured resistance.
Im pretty new to this stuff. So you recommend calculating for every wire gauge on AWG. Is there any optimal range for me to use or I should calculate all and see if I get the given resistance. Also what you mean by wire chemistry?

#### Alec_t

Joined Sep 17, 2013
13,228
So you recommend calculating for every wire gauge on AWG
IIRC there are on-line calculators for wire lengths v coil turns for various wire gauges and simple cylindrical inductors (which yours appears to be). Start with a wire gauge in the 10-20 range (I'd guess) and go from there. It will need to be something capable of handling 7A without over-heating in a closed environment. Shouldn't take long to find a likely candidate.
Also what you mean by wire chemistry?
Copper, aluminium, copper-coated aluminium, .........

Edit:
Just curious: is this task to test you, or does your employer really need to know the answer?

#### DesoxyN

Joined Oct 4, 2021
6
Every single calculator I found requires either inductance or number of turns. I only have coil dimensions and a single coils ohmage. The windings should be Copper. Calculating by hand is not a problem for me but not knowing what and how I should calculate on the next step is. If you can do a little research for me, I would be very grateful as I don't know where else to look. Even if I have enough data to calculate the windings is unknown to me atm.

Edit: This is actually some kind of a R&D project for the firm. No one knows how to calculate the windings on the coil. I am the only electrical engineer around here so there are none else to ask around.

#### shortbus

Joined Sep 30, 2009
9,760
Unfortunately I dont have the wire diameter. What I do have tho these 2 coils works on 150 DC Voltage and draws 7A.
I have my doubts that they even use wire in those coils. Really big electromagnets like that use copper sheets not wire. A crane magnet in a scrap yard doesn't use wire and they are smaller than the size those look to be. My oldest grandson worked before getting an apprenticeship as an electrician for a company making crane magnets, Winkle Industries, and they only used copper sheet.

#### nsaspook

Joined Aug 27, 2009
10,679
I have my doubts that they even use wire in those coils. Really big electromagnets like that use copper sheets not wire. A crane magnet in a scrap yard doesn't use wire and they are smaller than the size those look to be. My oldest grandson worked before getting an apprenticeship as an electrician for a company making crane magnets, Winkle Industries, and they only used copper sheet.
Correct.

That said, the ones the OP has are not really big electromagnets.

#### DesoxyN

Joined Oct 4, 2021
6
Hey all again, I was able to get the product catalogue and got some more information about the machine. It actually is a Jones type wet high intensity magnetic seperator (WHIMS). The model is P40. I leave some details down on the pictures below. We were able to measure 15000 Gauss on the rotor and grooved plate boxes part with a Gaussmeter. What I need to understand now is that what if I want to expand the rotor diameter from 400mm to 1000-1200mm? How would that affect the coils on the machine? Will I need more windings causing the wiring diameter to be bigger? Just trying to make sense on the whole operation about magnetic seperators here. I also calculated the turns with the given calculators and here are the results; @Alec_t

Does these makes sense for the given magnetic ? All help would be appreciated.

#### eetech00

Joined Jun 8, 2013
3,418
This doc might help. See page 24

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