How do you wind a toroidal inductor?

Thread Starter

noob_whale

Joined Dec 28, 2013
5
Hi, I'm just starting out with electronics, and recently, I've been attempting to make an electro-magnet out of a toroid wrapped with magnet wire. For whatever reason though, the toroid isn't producing a noticeable magnetic field. I've been able to make a simple electro-magnet from wrapping magnet wire around an iron bolt, but the toroid isn't working for me.
 

Dr.killjoy

Joined Apr 28, 2013
1,196
Hi, I'm just starting out with electronics, and recently, I've been attempting to make an electro-magnet out of a toroid wrapped with magnet wire. For whatever reason though, the toroid isn't producing a noticeable magnetic field. I've been able to make a simple electro-magnet from wrapping magnet wire around an iron bolt, but the toroid isn't working for me.
I could be wrong but what you are making is what we call a choke,coil, transformer .. ..

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/toroid.html
 

GopherT

Joined Nov 23, 2012
8,009
Wont the toroidal shape of the electromagnet cancel the poles out therefore yielding no result?
Yes, that is the whole point of a toroidal core. Think of wrapping wire around a nail to make an electromagnet - north at the head and South Pole at the point. Now, bend the nail into a circle (toroid) and North cancels South. The magnetic field should be perfectly inducted through the circumference of the toroid and no emi outside the toroid.

toroid cores are used in transformers for high-end audio to specifically prevent any signal cross-over from the transformer.

If you want to make an electromagnet, break/cut the toroid in half. If you score it and tap it, it should crack. If it is an iron powder core, you can cut it with a saw - the powder is held together with epoxy. Or, more simply, just use a nail.
 

wayneh

Joined Sep 9, 2010
17,495
Is there usually a noticeable magnetic field with components such as this?
Not outside of the toroid, ideally. There may be some small leakage but very little compared to the field contained within the toroid. Look up "gapped toroid" if you want to get a strong field using a toroid.
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
One reason why toroid transformers became so popular in audio equipment, the field is contained within the toroid, so minimum Hum pickup or transfer.
And also makes them more efficient than EI types.
Max.
 
Last edited:

ian field

Joined Oct 27, 2012
6,536
Hi, I'm just starting out with electronics, and recently, I've been attempting to make an electro-magnet out of a toroid wrapped with magnet wire. For whatever reason though, the toroid isn't producing a noticeable magnetic field. I've been able to make a simple electro-magnet from wrapping magnet wire around an iron bolt, but the toroid isn't working for me.
If you got loadsamoney you can get a toroid winding machine - otherwise it can be difficult and tedious.

If the winding wire isn't too long, you can sort of halve the difficulty by threading the wire through and hold the 2 ends letting the weight of the toroid fall to the middle - then wind the 2 ends on in opposite directions.

It simplifies things if you wind one end on, then deal with the other - you can tape the free end to an AA battery or other weight so it hangs without tangling and kinking while you wind on the first end.
 

WBahn

Joined Mar 31, 2012
29,932
Hi, I'm just starting out with electronics, and recently, I've been attempting to make an electro-magnet out of a toroid wrapped with magnet wire. For whatever reason though, the toroid isn't producing a noticeable magnetic field. I've been able to make a simple electro-magnet from wrapping magnet wire around an iron bolt, but the toroid isn't working for me.
Good. You are getting the results you want -- you just don't realize it. The primary purpose of using a toroidal form is that the magnetic flux is, ideally, completely trapped within the torroid. Thus, it isn't accessible for you to use a magnet outside of that. If you were to cut a slot in the torroid, you would get a good magnetic field in the gap.
 

#12

Joined Nov 30, 2010
18,224
Don't worry too much. I pulled a similar stupid a few weeks ago when I tried to wrap 100 turns around a wire and use that to measure current in the wire. Dummy! That shape of coil doesn't cut across any lines of the magnetic force. You have to remind your self to think about the 90 degree directional shifts between current and magnetism.
 

ian field

Joined Oct 27, 2012
6,536
Yes, that is the whole point of a toroidal core. Think of wrapping wire around a nail to make an electromagnet - north at the head and South Pole at the point. Now, bend the nail into a circle (toroid) and North cancels South. The magnetic field should be perfectly inducted through the circumference of the toroid and no emi outside the toroid.

toroid cores are used in transformers for high-end audio to specifically prevent any signal cross-over from the transformer.

If you want to make an electromagnet, break/cut the toroid in half. If you score it and tap it, it should crack. If it is an iron powder core, you can cut it with a saw - the powder is held together with epoxy. Or, more simply, just use a nail.
Ferrite isn't great for making electromagnets - as long as the OP is using DC to energise the coil, a nail (or bunch of nails) can't be beat.
 

Thread Starter

noob_whale

Joined Dec 28, 2013
5
Don't worry too much. I pulled a similar stupid a few weeks ago when I tried to wrap 100 turns around a wire and use that to measure current in the wire. Dummy! That shape of coil doesn't cut across any lines of the magnetic force. You have to remind your self to think about the 90 degree directional shifts between current and magnetism.
What do you mean about 90 degree directional shifts? Thanks.
 

Thread Starter

noob_whale

Joined Dec 28, 2013
5
Good. You are getting the results you want -- you just don't realize it. The primary purpose of using a toroidal form is that the magnetic flux is, ideally, completely trapped within the torroid. Thus, it isn't accessible for you to use a magnet outside of that. If you were to cut a slot in the torroid, you would get a good magnetic field in the gap.
So, if I were to use a gapped toroid, the magnetic field would only be at the two poles on each side of the gap? Is it possible to make a magnetic field only in the "hole" of a full toroid?
 
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