Where to find a solenoid

  • #1
Albertgauss
Gold Member
236
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Hi everyone,

I am doing a project where I need a device with a strong magnetic field but low current. It also needs a simple relationship with the current. Solenoids and toriods are the best I can think of to use. However, because I want to keep the current low, I want to keep a high magnetic field with a lot of turns, as high a magnetic field (hopefully much more than a milli-Tesla) I could generate with less than an amp of current. I will power the solenoid/toroid with a 20 volts power supply DC current. It is pretty easy to get a solenoid with a few hundred turns, but what about say 10,000 turns?

Does anyone know where to obtain a 10,000 (or even 5,000 would be good) turn solenoid? Or is this simply impossible? It seems like it would just be a 1,000 turn solenoid wrapped around 10 times, but maybe its hard to make such a device or no one needs them and thus such high-turn solenoids are not made.

Some places I have looked: stereo loudspeakers, chokes and inductors in the context of general search of automotive parts, etc. transformers. The auto parts that came back in my general internet searches have returned parts that seem far too small and not capable of generating a high magnetic field---are there other car parts that could do the job? What about electric guitar coils---I've heard they (or devices used by them) have coils of 3,000 to 6,000 turns--would they count as a solenoid that I could use for my purpose? Does anyone know of any appliances or more specific car parts that use solenoids with thousands of turns? How much current do such devices typically take? If you know specific names of some of these parts, that would be helpful.

I don't need a magnet core in the middle of the solenoid, I prefer it to be hollow, but I can deal with a core if need be.

I can spend up to a few hundred dollars on a solenoid/toroid/coil if I need to.
 

Answers and Replies

  • #3
berkeman
Mentor
59,013
9,109
I don't need a magnet core in the middle of the solenoid, I prefer it to be hollow, but I can deal with a core if need be.
You will get a much stronger magnetic field by using a gapped magnetic toroidal core, with as small a gap as possible to support your free-air application.

You will get the most efficiency by matching the resistance of your solenoid coil (wrapped around the partial toroidal magnetic core form) with the internal resistance of your battery power source (that's how you get the best power transfer).

You will get the most Amp-Turns by using a smaller guage wire with more turns, but at some point, you will lose too much power in the IR losses in your coil. You should be able to write the equations for the number of Amp-Turns versus the wire guage and resistive losses to optimize the B-field generation. Let us know what you find!

BTW, is the battery life per charge in this system a consideration?
 
  • #4
Albertgauss
Gold Member
236
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I just read the reference listed above. I didn't realize the air-gap would have such an effect. Gapped magnetic torioid sounds like the best bet for me.

Does anyone have any experience with what brand/kind of small gauge wire is best for making magnets? I can order online if need be, if such special wire is available only over the internet.

I'd prefer to buy the magnet rather than make one, if possible. That's why I was looking for appliances and parts etc, to cannibalize. However, due to the air-gap in the previous post, I realize I must be open to making my own magnet. I will pursue both methods until I get something that works.

Battery is irrelevant, since I am using a power supply (20 volts DC, I could maybe obtain 50 volt power supply later).

I'll reread the previous link. I didn't understand how to get to 1 Tesla. That would be fantastic! But if I could get that high a B-field for ~10's of mA, that would be great!

I'll do the calculation today. I have to go to work now, but I will return this afternoon.
 
  • #5
berkeman
Mentor
59,013
9,109
Does anyone have any experience with what brand/kind of small gauge wire is best for making magnets?
"Magnet wire" is used to wind magnetic coils. It is special because it uses a special kind of insulation that is as thin as possible, so you can wind more turns into the same "window" size. For your low-voltage application, you can use "single build" insulation magnet wire, which has the thinnest insulation. If your application involved high voltages, you would go for "double build" or "triple build" magnet wire.

MWS is a common supplier of magnet wire: http://mwswire.com/

:smile:
 
  • #6
Tom.G
Science Advisor
3,695
2,384
How about cannibalizing an automotive ignition coil? The secondary has a generous number of turns, I've never counted them though.
 
  • #7
Albertgauss
Gold Member
236
20
I clicked on the link above for the insulated magnetic wire and got this error message:


Configuration Error
Your wp-config.php file has an empty database table prefix, which is not supported.

Then I went to the internet, with chrome an internet edge, and got the same problem. Is that company still in business? If so, can you provide me a link for them that will work?

For the calculation of B field in Tesla for wire and power supply values (N turns, DC power supply current and voltage output, type of AWG wire), I attached JPEGs of a powerpoint I used to do the calculations. Its easier for me that way since powerpoint still has an equation editor. Let me know if my calculations seem right, close, or even just a long way off. I admit I could not find any easy expression for the power (watts) at which a solenoind ramps up to its magnetic field.

The blue color fonts in the attached jpegs represent algebra changes as I move from one expression to the next.
 

Attachments

  • #9
jrmichler
Mentor
1,398
1,537
McMaster-Carr (mcmaster.com), Newark (newark.com), and Digikey (digikey.com) all list magnet wire in sizes down to 36 or 38 gauge as in stock. I have had good experiences with all three of these suppliers.
 
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  • #10
Albertgauss
Gold Member
236
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Ok, Excellent, I will check all that out. That is really helpful.
 

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