Cobalt Magnetiser Info

[moregoo]

What a wonderful Bulletin board, thank you all !

For a few years I have been interested in constructing a Cobalt magnetiser. Now I have most of it built and working. It's a Capactive discharge unit with an SCR switch. Total voltage is 750 and it has 74,000 uf Capacitors....However it does not fully charge SmCo magnets yet although it does seem to take them to about 80 % of their full strength.

Now..I have wound coils which are about 3 ohms each which are wired in parallel to give 1.5 ohms. This is on two steel cores of 20 mm diameter..I think my problem is in the design of the actual magnetising fixture which I suspect contains too much steel and is too inductive limiting the rise in the magnetic field. This coil design gives peak currents in the realms of a few hundred amps. Some data I have read refers to magnetising currents in the area of 3 to 5 THOUSAND amps ! This is possible to do by rewinding the coils with much fewer turns of larger wire, at present I'm using 18 AWG.

I have heard people mention "air core" designs, however I just cant imagine how one of these would look like, never mind actually making one. Could anyone give me guidance as to how the actual magnetising head is designed on real life working SmCo slot magnet magnetisers..

Also the concept of a "radial magnetic" field is interesting and makes me think of using a pole piece of half the magnet height and zapping diagonally across the magnets, doing this twice to magnetise and orient the madnet material in a radial pattern.

Also, a word of warning the power supply I'm using creates lethal voltages so don't try this at home...PS..I'm an electrician in the elevator industry so am qualified to blow myself to smithereens !

Keith

[Tom Marsteller]

Sounds like you would like the site called Teslamaniacs. Your zapper sounds nice. I have seen one similiar to what you have described that zaps cobalts. The one I have seen fits into about a carry size toolbox.

Tom......

[RomanK]

Out of my area of expertise....how about BigDaddy, you out there?

[MSWISS]

You'll need to suspend your cobalt mags or setup in an air coil to zap them.
Save yourself a lot of time on your radial idea.It can't be done. A cobalt mag
will only take a zap/charge in the direction/orientation the "strands"of the magnet were originally layed during construction of it .
>>>>>> can be changed to <<<<<<<<(reversed)
>>>>>> CAN NOT be changed to ^^^^^^^
no matter how you place/fixture it in the coil.
If it held/fixtured loosely it will rotate to it's
original orientation/position.
If it's fixtured tightly either nothing will happen
or if it's hit with a strong enough charge it will
crumble the mag.

[BigDaddy]

Roman... It's ironic that we just talking about this at the NATS warmup.

I started racing slots about 2 years ago after a 25 year vacation and I haven't seen a magnetizer personally since I was a teenager so I am not up to date on the mechanics of the newest designs. I think I can add a little to the discussion based on theory ( I am an electrical engineer).

If you are looking for an air core design, you will need a non-ferrous material to wrap your coils around. I have seen this done with your basic PVC pipe. For all practical purposes, the PVC has the same effect on flux density as air. I am a little rusty on my magnetic theory but the strength of the magnetic field is dependant on the amout of current, the number of coil windings and the permeability rating of the core material among other things.

I have included a link to a great definition of the permeability of materials and it should provide some insight to the effect it has on the stregnth of your magnetizer.

http://whatis.techtarget.com/definition/0%2C%2Csid9_gci543303%2C00.html

In general, if you are trying to increase the field strength, find a material with a high magnetic permeability rating. This generally means ferrous materials (i.e. high iron content).

I agree with the statement about a radial magnetizer design. It certainly is not something anyone in the hobby field is going to design. The multiple magnet setup probably best approximates a radial magnet if the magnets are oriented properly. By that I mean like wedges similar to slices of pie with the field orientation of each slice pointed toward the axis of rotation of the armature.

Anyway, I hope this answers some of your questions. Just ask if I can help further!

[moregoo]

Thanks all for your answers so far. I have to build a couple of bodies and get some tires ready then jump on an airplane and fly to Sydney for the Aussie Nationals this weekend.

After that (trophy in hand :-)) I might have some more questions concerning the magnetiser or magnetiZer for those located in the USA !

[[email protected].]

Moregoo,

Thanks for the disclaimer, now I'm not afraid to add some details. Everyone else - DO NOT TRY THIS AT HOME!!!

Yes, the inductance of steel cores will not allow the current to rise far enough to do cobalts, so an air core is mandatory. For ceramics, a steel core unit works just fine, even at voltages obtainable from household current.

The coil is a single layer, I'm thinking 8 or 10 guage wire, and the most practical way to wind it is around a plastic motor box (as sold by Koford or Camen - you know, the ones with a bit of radius along the edges). Wind it loosely enough that you can slide the box in and out of the coil. Inside, use a firm foam rubber to locate the can & magnet assembly, and turn a plastic slug to keep the assembly from collapsing. If doing magnets alone, use the plastic slug and a few layers of tape to keep things stable. The field will be developed perpendicular to the windings, so the magnets need to be aligned so that the outside curved surfaces face each open end of the coil. Polarity will be via the 'right hand rule', I expect you've seen that in basic magnetic texts, but your first use of the machine will confirm direction.

The last time I saw one of these beasts in action, the machine had a voltmeter attached - and the thing fired at something like 2800 volts. I've never seen an SCR rated for that kind of voltage, never mind the extreme current, and switching that sort of power has been the reason I've never built a cobalt zapper. The unit I witnessed was actually quite noisy when it fired (as opposed to the absolute silence of my iron core units I build for ceramics), so I'm guessing that a mechanical contactor of some sort was being used.

You are using double the capacitance of my zappers, and my hats off to you for finding capacitors that can take even 750 V. From what I've seen in surplus stores, energy storage type caps rated in KV are of the oil filled can variety. This makes sense, as electrolytics are made with tightly coiled layers of foil and paper, and therefore do have noticeable inductive delays in discharge. In any case, the big multi KV caps are generally rated in joules, and actually have capacitance of under 100 mfd. I suspect that truly high capacitance is not important in this application, whereas almost instantaneous discharge is.

Good luck with the project, and if you can figure out the switching mechanism, let me know so I can build one too!

[moregoo]

Thanks Monty,

That was the kind of practical info I was looking for. I'll see what I can come up with, it certainly seems an easier thing to do than the steel designs I've fiddled with so far. Here is a link to some good info about magnetizers:

http://oersted.com/magnetics_articles.shtml

PS...I didnt get the trophy from the Aussie nats..for G7 the results were as follows:

1 Tim Tyler 843
2 Tony (Alpha) Pye 836
3 Brad Bennet 823
4 Peter (Koford) Dight 818
5 Tony Bagnall (alias Stumpy) 757
6 Keith Wade 750
7 John Favorito 717
8 Dave Fitzgerald (alias Cuzzo) 495


http://oersted.com/magnetics_articles.shtml

[BigDaddy]

Moregoo,

Are you sure about that link? I can't find that page.

[moregoo]

Yes, I'm sure, it works from my end, that link takes you to a page which links to a few PDF files about magnetizers and related material.

[BigDaddy]

Thanks. It worked this time. It must have been a temporary problem on their end.

[Slapshot]

Zapper gone wild!!!!

[Slapshot]

Another Zapper gone wild!!!!