I have a question regarding the construction of an electromagent. Is there a point at which the number of coils has diminishing returns on the strength of the magnet.
For my construction I'm wondering based on the following:
My first build used these specs and wound approximately 161.61m of wire with an end resistance of 38ohm resulting in .316 amps.
Because of the number of wraps involved, being very time consuming by hand, I'm hoping to find out if less wraps resulting in lower resistance and higher current will increase the strength of the electromagent. My understanding is that once the core is saturated that maximum strength is reached? If that is the case would decreasing the number of wraps but increasing core diameter have an effect on strength?
I'm pretty new to all this and have tried to research but the maths are a bit over my head.
Words into my internet search engine produce numerous results like the following:
To increase the strength of an electromagnet, you can increase the strength current, and there are several ways to do that. You can also increase the number of windings, lower the ambient temperature or replace your non-magnetic core with a ferro-magnetic material. How to Increase the Strength of an Electromagnet | Sciencing
Yes I understand the basic principal. I'm asking if there is a point at which windings have a diminishing return. I'd like to keep the materials and voltage specs the same as I have mentioned, with the possible exception of core diameter.
I'm hoping to optimize magent strength without using an excess of wire.
The basic principles are very well understood, and you can vary as you like, keeping the following in mind (not taking into account saturation of core material):
The field strength is proportional to the number of turns times the coil current.
The steady state coil current is power supply voltage divided by the wire resistance, which is proportional to total wire length.
Number of wire turns in a given volume and wire resistance depend inversely on wire diameter.
Coil power dissipation is proportional to the coil current times the power supply voltage, and you will want to avoid burning up the coil.
When you wrote this: "Yes I understand the basic principal. I'm asking if there is a point at which windings have a diminishing return. ". Then you really confused me. The ONLY way you can get diminishing returns is if you reversed the direction of winding the coils. Is this what you mean?
No. I guess I have multiple questions regarding that.
One being once the core becomes saturated can the magnet still grow stronger or are additional windings only serving to increase resistance and therefore reduce current. Since the basic principal is that the number of wraps increases the strength of the magnet but lowers the current (higher current results in a stronger magnet), is there a point at which one outweighs the other? Is there a point at which the total resistance of the wire hampers the current so much that it is too low to produce a strong magnetic field? Or do the number of wraps always continue to increase the strength of the magnet and the lower current just results in a lower wattage system?
For an air core coil, adding one turn increases the coil resistance as well as the field strength, but the added resistance depends on the coil diameter.
At some coil diameter, per added turn, you lose rather than gain field strength.
If the iron core is saturated, that is basically all you get.
jremington:
Adding one turn increases the coil resistance as well as the field strength, but that depends on the coil diameter.
At some coil diameter, per added turn you lose rather than gain field strength.
This is exactly what I'm asking about Is there a way for me to determine that point? I'd like to find out if I've exceeded this in my project and if reducing the amount of wraps will result in a stronger electromagnet.
So with an iron core your saying the strength of the field isn't lost with more wraps after saturation but rather I will just reach it's maximum?
Unless you know the magnetic susceptibility and saturation characteristics of the iron core, you need to measure the field in order to optimize the winding parameters.
You might post on Dave Jones EEVblog, where a bunch of electrical engineers hang out.
jremington:
Unless you know the magnetic susceptibility and saturation characteristics of the iron core, you need to measure the field in order to optimize the winding parameters.
You might post on Dave Jones EEVblog, where a bunch of electrical engineers hang out.
Thank you very much. I was afraid of having to take measurements as the winding takes awhile. I will check it that blog site. Thanks again for the info!
Once the iron core saturates extra amp-turns will still increase the flux density, but at a MUCH slower rate as its effectively become air-cored from that point up.
Magneto-motive force is measured in amp-turns per metre. A long core will definitely hinder attempts to produce a strong field.
You need be very careful to figure out what "magnet strength" means to you. Total field? Maximum Field? Maximum lifting force? They are all different. Lifting force depends strongly on the flatness of the magnet and load, for instance.
