Anybody built a pulse magnetiser?

All, I have been looking online and have found lots of info but I would also like to hear from anyone here who has actually done what I want
to do. The goal is to magnetise a heat treated to 40 Rc steel rod that is .200 in diameter in the radial direction. The area to be magnetised needs to be about .350" from the end of the rod. The magnetism can be pretty weak, it only needs to hold a steel sleeve in place for a few seconds. But the end of the rod must have a very weak magnetic strength, weak enough that it won't even hold a straight pin. Thanks, Eric
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On Monday, March 23, 2015 at 3:01:02 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

Can you go a little bigger on the diameter? Ebay item 251422762446 is for 2 mm in dia by 1 mm thick magnets. 2 mm is bout .080 inch so drilli ng a 2 mm. hole thru the rod would not leave much.
I did build a pulse magnetizer way back when I was in college. I used a bu nch of electrolytic caps. Charged them up to a couple hundred volts and di scharged them thru a coil.
Magnetising in the length wise direction is easy. Radial is harder. I woul d try having two pole pieces of soft iron maybe 3/4 inch in dia and with a taper to .2 inch with the end contoured to fit the .2 dia rod. And wind a coil on each pole , connect the poles in series. and then connect them to the charged cap bank.
Dan
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Do you have a demagnetizer to erase mistakes?
-jsw
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Use a brass pin.
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snipped-for-privacy@whidbey.com fired this volley in

Yup... have done. I built a simple heavy coil, good for about 50A at 110VAC. (yes, AC).
"Fuse" it with a strip of foil -- you'll have to test to get the current to interrupt at the peak of one half-cycle of the incoming AC.
When it blows - violently - the coil will have been conducting huge current, and it will be interrupted instantly, with an arc that lasts through the collapse time of the field in the coil.
Works good! Lloyd
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On Mon, 23 Mar 2015 16:54:51 -0500, "Lloyd E. Sponenburgh"

I didn't build it or use it, but the magnets on a couple printed circuit axial field motors I have hanging around were pulse magnetized to peak plux at the factory - there is a strand of #14 insulated wire wrapped around all the magnets and the two ends are brought out of the case. When the motor was assembled, a large pulse from a capacitor discharge was applied to the winding to top it up. I'm told the current used is in the thousand amp range for about a millisecond - for a resulting 1000 amp turns magnetizing force on each magnet to "top up" the magnets.
If the motors are dissassembled the magnets loose strength and need to be "re-pulsed" to acheive dull design power again. Oviously they are not neomydium magnets - possibly Alnico, but I suspect they are Ceramic or Ferrite.
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On Mon, 23 Mar 2015 12:06:46 -0700, snipped-for-privacy@whidbey.com wrote:

===============I've never built one, but here is someone that did http://tinyurl.com/le7pnws
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Oh, I built one of those. I don't quite get the OP's question so maybe that isn't applicable to his needs. But it does work as advertized in the Gingery booklet.
--
Mike Spencer Nova Scotia, Canada

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Just use a Weller type soldering gun, the kind with the heavy copper tip th at is made from a piece of about 9 or 10 gage copper wire. Hold the part in between the legs of the coil and pull the trigger. Let go of the trigge r. If you stopped current flow at the peak of the sine wave you get a lot of magnetism; if closer to zero, you get less. Just try it until you get t he amount you want.
example of gun: http://www.testequipmentdepot.com/weller/solderandheatguns/8200.htm
Also works for demagnetizing stuff. Pull trigger, put part in, then slowly pull part away, until part is about 2 or 3 feet away before releasing trig ger.
Pete Stanaitis --------------
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On 3/23/2015 9:13 PM, snipped-for-privacy@baldwin-telecom.net wrote:

What happens if you put a diode in series with the magnetizing loop? Probably need another diode passing current outside the loop on the opposite half-cycle to keep the transformer happy.

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On Mon, 23 Mar 2015 21:13:54 -0700 (PDT), snipped-for-privacy@baldwin-telecom.net wrote:

Greetings Pete, I have a couple of these type of soldering guns. I need to have a repeatable process because I want to make lots of parts. So what if I use one of these guns with a diode in series? If the diode can take the current, that is. Eric
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Measure the voltage on your soldering gun's terminals. Mine shows 0.38VAC operating, 0.59VAC without the element. You'll have to do some research to find a Schottky diode with a sufficiently low forward drop at whatever high current you need. http://www.onsemi.com/PowerSolutions/parametrics.do
If you don't use a fairly predictable capacitor bank, do you have the equipment to measure single high current pulses rather than guessing?
-jsw
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On Wednesday, March 25, 2015 at 8:57:04 AM UTC-7, snipped-for-privacy@whidbey.com wrote:

Don't do that. The low resistance of the tip is the reason the transformer type gun gets away with a small core, and if you raise the resistance (or put a diode in) it'll just saturate and blow a fuse.
The diode would not likely pass the 200A or so of current that the gun tip operates with.
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wrote:

A long time ago, I fooled with lasers and their power supplies because they were the future. Until I melted a penny in the fuse box at Dad's.
Diodes able to handle the abuse I was giving were very expensive. Finally, a guy wrote an article (~1965-66-67)on holograms in Scientific American. He made a power supply that had a synchronous motor twirling a rotary switch to(full wave)rectify the AC from a center tapped neon sign transformer. I made one from his discussion and it worked great. No core saturation anymore because the switching time was so fast - I think about 3600 rpm. I just now went to the basement to dig in the archives (never throw anything away) to see if I could find the copy of the magazine. I know I have it. But where? Probably at Mom's. The power supply might be there too. If you're interested, I'll keep looking.
Steve
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On Wed, 25 Mar 2015 16:23:50 -0500
<snip>

Is this what you're looking for?
http://jesseenterprises.net/amsci/1967/02/1967-02-fs.html
"How to Make Holograms and Experiment with Them or Ready-Made Holograms by C. L. Stong February, 1967"
--
Leon Fisk
Grand Rapids MI/Zone 5b
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wrote:

Yepper! That's it. I still haven't found anything. Mom's house is 150 miles away, and I won't be there til Easter. SWMBO does not subscribe to "never throw anything away" so it might be gone.
Steve
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On Wednesday, March 25, 2015 at 11:57:04 AM UTC-4, snipped-for-privacy@whidbey.com wrote:

If I were doing it, I would use capacitors charged from DC supply and conn ected to a coil with an air core by a knife switch. The amount of magnitiz ing current easily adjusted by adding or removing caps and changing the DC voltage. That would be consistent. No guessing about how many cycles of A C used. The drawback is you might not have a large collection of scrap par ts to use in making it.
So you might try using your MIG welder as the supply and adjust the magneti zing coil to get the right amount of magnetising force. If you happened to have a mig welder with the optional timer used for spot welding, it would work really well.
Dan
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wrote:

If I were doing it, I would use capacitors charged from DC supply and connected to a coil with an air core by a knife switch. The amount of magnitizing current easily adjusted by adding or removing caps and changing the DC voltage. That would be consistent. No guessing about how many cycles of AC used. The drawback is you might not have a large collection of scrap parts to use in making it.
So you might try using your MIG welder as the supply and adjust the magnetizing coil to get the right amount of magnetising force. If you happened to have a mig welder with the optional timer used for spot welding, it would work really well.
Dan
================================I just tried magnetizing a 3/16" Allen wrench crosswise about 3/8" in from the end with a Neodymium button magnet. The whole end of the wrench is now magnetized pretty evenly.
I don't have an easy way to arrange two of them NS NS to concentrate the field.
-jsw
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    There are diodes which will take the current -- not exactly tiny ones, but some which will.
    However, I doubt that the voltage developed in the tip loop will be high enough to reach the forward conduction threshold of most diodes. :-)
    You could build a timer -- a 555 single-shot for example, which could be set to the time you want -- and have it control a SSR (Solid State Relay) to turn it on just long enough so you get a half cycle. Your single-shot would want to be set to something like 1/120th of a second (a half cycle of US AC current) so you you get a single short pulse through the gun. Perhaps add a standard silicon rectifier of appropriate current rating so you get only one half-cycle, not a full cycle . (Lots more complex circuits possible with counting timers and power MOSFETs controlling the current into the primary, and a sensor so the MOSFET is always turned on at the right point in the cycle.
    Enjoy,         DoN.
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On Monday, March 23, 2015 at 12:01:02 PM UTC-7, snipped-for-privacy@whidbey.com wrote:

A tape head demagnetizer (kind of a wand with a power cord) can demagnetize by slowly pulling away from the object. If, however, one switches it off instead of pulling away, it magnetizes any object near its tip.
So, for something this small, I'd get a tape head demagnetizer and put it onto a foot switch AC outlet.
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