Electromagnet: How to build the right one?

[deanEdinburgh]

Hi there! I hope someone can help me ... I'm trying to build an electromagnet to use in a system inspired by Bob Beck and electro-medicine.

I have a friend building me a circuit to generate a pulsed wave to drive an electromagnet. It's my job to build the electromagnet, but after several weeks of scratching my head on the maths for this, I still can't figure out how many times I should wrap the copper wire around the core? (and what materials I should use for the core and the copper wire).

I would like the magnet to be 10cm wide, with a maximum field strength of 6000 Gauss.

I understand using a iron core, with copper wire is best, but how many turns and of what thickness wire should I have? If the current is too high, thinner wire might burn out.

I understand Neodymium core magnets would be helpful in increasing the magnets strength and lowering the amount of turns of copper. However, cost is an issue for me, so I don't mind doing the extra work with an iron core if that can still reach the target field strength.

Also, how much current is required to reach the target field strength level, if the unit is being pulsed at 10hz?

I am a medical student and am building this magnet so that I can test the Bob Beck thesis out to see if pulsed electromagnetic fields can work to regenerate tissue and joint damage. Any help you can offer would be greatly appreciated!

[Chaz22]

I understand using a metal primary, with birdwatcher cable is best, but how many changes and of what width cable should I have? If the current is too high, slimmer cable might get rid of out.

Memphis Fitness Center

[vallentin]

Electromagnet

Bob Beck's march 7, 1998 lecture notes
First wind the applicator coil. Junk VHS videocassette reels are cheap, plentiful and adequate for this application. Remove 5 screws from shell, remove reels and discard tape. Be SURE alternative spools (if used) are non-conductive or system will not work. Avoid shorter length VHS tape reels which may have center hubs larger than 1" dia. and won't hold sufficient wire. Drill 1/4" holes through hub and through center of flange(s). Make two 4" discs from 1/4" thick plastic or fiberboard, drill 1/4" center holes and another 1/4" hole off-center so coil's inside lead wire can be pulled through. These "stiffeners" will sandwich reel's flanges so they won't warp or split as wire pressure builds up while winding progresses. A 2" (or longer) 1/4-20 machine nut and bolt with washers through centers will clamp flange stiffeners and reel and also provide a shaft to hold in a variable speed drill motor or similar winding device if used. Then remove bolt and stiffeners.

Specifications: Completely fill tape spool with #14 or 16 enameled copper magnet wire (130 to 160 turns) wound onto the 1" dia. hub and ~3-1/2" OD spool with a gap width for wire of 5/8". Scrape enamel insulation 1/2" from ends and tin. Pull inside end of magnet wire through hub and stiffener and to outside. ~130 turns should fill spool. Remove bolt, stiffeners, and finished coil. Now solder ends of 3 ft of heavy two-wire extension cord to each side of coil. Finished coil weighs ~1 LB 3 oz, has ~0.935 millihenry inductance, 0.34 Ohm resistance, and takes ~20 minutes to hand wind or ~3 minutes with drill motor. An excellent alternative is an AMS brand air-core crossover inductor for home audio, MCM Electronics, Centerville, OH 45459, (800) 543-4330 catalog # 50-940, #16 gauge, 0.58 Ohm, 2.5mH, 2-7/8" dia., $10.65.


Strobe modification consists simply of wiring the finished applicator coil with 4' ft. leads in series between either flash tube electrode. Be extremely cautious when working with case open because a strobe's capacitor can hold a residual high-voltage charge for a long time even when "off". Before modifying and to avoid shock, short out the capacitor by placing clip leads directly across the flash tube. Remember to remove this shunt later. To install coil, unsolder either wire from flash tube and connect one lead wire from coil to that side of tube. Connect the other lead from coil to the wire you just removed from tube. Insulate connections with tape. This places your coil in series with the flash tube and enables the tube to act as an ionized gas relay or "thyratron" that dumps most of capacitor's stored energy through coil when fired. Lamp will still flash but less brightly. Cover flash window with black paper. Replace case. You're done!