Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Electro magnet

Status
Not open for further replies.
Thanks Les. That has been in my "favorites" folder for a while now. Something to build 'someday', metal shaping is another hobby of mine, but will never get all my "want to build" stuff done in my lifetime.
 
this is a circuit digram for the magnabender.that I got on line.
The current would only be house hold current single fase 15 amp.240 Ac
Can you tell me what is the restance of the magnet field in this circuit.
I will attach a photo which has the web address of the bender image.jpgimage.jpgimage.jpgimage.jpgimage.jpg
 
After reading your posts I have decided to go with a microwave transformer winding and field as in the photo.
Having used the transformer as a magnet which was not to bad the leads connecting to the battery did not get hot and the transformer was cool.
The winding wirer is 1.1 mm in dia and the number of turns is 208 and the restance is 1.9 meg omes.
I would like to increase the magnetic field .
Can this be done removing 4 turns on the windings.
I am very great full for your support.

Hello,

There is a rule for electromagnets that is similar to the maximum power transfer rule in coupled circuits. The rule for max power transfer is that the max power gets transferred when the output impedance of the first stage matches the input impedance of the second stage. The rule for electromagnets is when the resistance of the wire matches that of the source voltage (like a battery) you get the maximum force that can ever be had from that source. There is an in depth calculation somewhere on this site i had posted quite a while back when someone else asked a question about electromagnets, if you can find it.
There is a catch however, and that is that the source must be capable of delivering the power required for that perfect match. Most users find this doesnt happen because the source resistance is very low. This means you only get what you get due to the higher resistance of the coil, and the only thing you can do it try raising or lowering the number of turns.
When you increase the number of turns the field strength would go up accordingly, but because the longer wire now increases the resistance the current goes down so you dont get the full effect.
When you decrease the number of turns the field strength would go down but because the shorter wire now decreases the resistance you get more current flow which also increases the field.
If you are operating near the max power point then a change in either direction will decrease the field. If you are operating on one side of that point then a change in one direction will increase the field strength.
Since the resistance of the wire is probably much more than the internal resistance of the source, increasing the turns probably increases the field strength (as well as the wire resistance a little) because the current only goes down proportional to the turns ratio (which is just a little) while the field strength would go up as the square of the turns ratio.
There is also a current saturation level that if reached prevents much more field strength. This happens when all of the so-called magnetic domains flip in the same direction. Once that point is reached it is hard to get any higher field strength out of the magnet. With the introduction of a gap this situation is relaxed, and for an electromagnet you have to have a gap somewhere anyway or else there is no face area to attract magnetically active objects. For a transformer core i would think the best bet would be to remove the "I" portion of the core so that you are left with only the "E" portion. This will limit the field strength but once something comes near the face it will be attracted and the attraction will grow stronger the closer it gets to the face.

As to the overheating wires, wires overheat when the current exceeds a certain limit. In transformers the heat can build up in one place though because the turns near the outside block some of the heat trying to escape from the turns near the inside of the coil. This means transformers have to have somewhat heavier wire than open air wires for the same current level. A rule of thumb here would be 300 circular mils per amp, but you might get away with more for short term use.

A construction like this with so little actually known about it is better off tested than calculated. You'd have to test with a different number of turns and see what happens.

In any case you really should remove the "I" if it is not removed already, as that will increase the ability for this thing to pick metal objects up and hold them.
 
Your power supply is in foldback current limiting. With just one of your magnets connected to 12 volts it would draw 9 amps. (You need to learn some basic electrical theory. Ohms law and power calculations.) To run 7 of your magnets from 12 volts would require 63 amps. (756 watts.) I had not heard of the "Magna bender" so I Googled it. I found out that it takes about 2.3KW I suspect the magnetic design is going to be far better than you or I could design so I would expect a DIY one to take more power. I do not think you will succeed with this project.

Les.
Having read your post the restance in the Magna bender is .0095 ohms is this correct
 
No. The resistance of the Magna bender would be about 24 ohms. (240 volts version.) (This is assuming that it takes the full 10 amps of it's current rating.)

Les,
 
image.jpg I have searched on the net and came up with this wirer size . Using the table the one that is highlited , would this do to wind a winding for the Electro magnet 900 mm long
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top