Vintage Demagnetizer Operation

[Tracy]

No wimpy ebay/made in China, blue plastic. $6 dollar watch demagnetizer here. I got me a badass demagnetizer—a 1902 Boettger & Wittig machine made in the U.S.A (Milwaukee WI). I did find it on ebay and bid $35 to win the auction. I didn’t care if it worked as I could make a steam-punk lamp out of it—If I could also use it to demagnetize watches/tools that would be a bonus. 

I finally got up the nerve to plug it in and after some trial and error I found that it does work. The tool is not UL listed (to say the least) and if the operator touches the terminals where the vintage lamp cord is connected, or the metal on the draw bar it presumably causes instant electrocution as these parts have 120 volts present. In 1902 electricity was still new and I am guessing that anyone that purchased one of these machines had enough education/common sense to not touch the metal parts with it plugged in. 

I had a question about its operation as the original instructions really don’t explain the finer points of how it works. The tools can be powered by either direct current (D.C.) or alternating current (A.C.) and both were available in 1902 for consumer use. At the time Westinghouse (A.C.) and Edison (D.C) were battling it out over which one was better—Westinghouse won.

I drew arrows to show the flow of current. 120 volts is connected to the screw terminals. The light bulb is in series in the circuit and adds resistance to lower the amount of current flowing to the coil. From the light bulb the wires are connected to a wiper that touches one side of the draw bar (pulled out part way at left—yellow arrows indicate 120v). The other 120v terminal connects to the other side of the drawbar. 

The coil has two wipers that touch each side of the draw bar. When the drawbar is pulled out the coil wipers alternate between each side of the drawbar (you can see the interlocking pattern of the metal on the drawbar) and thus the coil reverses magnetic polarity as the wiper arms touch the different sides of the drawbar. 

When plugged in the circuit is in one of three states depending on the position of the drawbar: 1) the light is bright and the coil is not receiving current, 2) the light dims indicating that the bulb is in series with the coil with is now an electro magnet, and 3) the coil 120v supply is reversed and swaps north and south magnetic poles.

With a screwdriver inside the coil If I pull the drawbar out so the light is dim (coil is on) and leave it for 4 seconds, then shut the tool off the screwdriver becomes magnetic. If I do the same thing but slowly remove the screwdriver from the coil about 2 ft. then shut the current off the screwdriver becomes demagnetized. 

The same thing happens when I slide the drawbar in/out but the light flickers as it is intermittent to the circuit. So my question is (finally got there) what advantage does sliding the drawbar out to either magnetize or demagnetize watches/tools have. The tool works the same either way—using the drawbar or just turning on the coil.

I included the instructions for reference. They are written in the formal language of 1902 and it is difficult to understand what they are trying to convey. 
 

 

[Geo]

I love it..............I want one.........just to look at!

[Watcher]

You need AC to demagnetize and so the drawbar converts DC to AC.

[robmack]

You have to withdraw the object from the coil while the electricity is applied and then switch off the electricity when the object is 1 foot or more away from the coil.

The reason the watch or tool comes out magnetized whether or not you slide the bar is because you  haven't varied the strength of the magnetic field during the process.  Withdrawing the object from the coil reduces the strength of the magnetic field, allowing the magnetic domains in the ferrous material to randomized and thus render the object demagnetized.

You probably could reduce the lethal potential of this tool by hooking it up to a 48 volt transformer. It will still work but 48 volts is that magical value at or below which electric shock remains only painful, not lethal.

[oli]

Sorry I can't help, but just wanted to say it really looks great!

[Tracy]

13 hours ago, robmack said:

You have to withdraw the object from the coil while the electricity is applied and then switch off the electricity when the object is 1 foot or more away from the coil.

The reason the watch or tool comes out magnetized whether or not you slide the bar is because you  haven't varied the strength of the magnetic field during the process.  Withdrawing the object from the coil reduces the strength of the magnetic field, allowing the magnetic domains in the ferrous material to randomized and thus render the object demagnetized.

You probably could reduce the lethal potential of this tool by hooking it up to a 48 volt transformer. It will still work but 48 volts is that magical value at or below which electric shock remains only painful, not lethal.

Yes, agree, It does work when I withdraw the object (screwdriver) slowly from the coil about 2 feet away then switch the coil off (not moving the drawbar). I just wondered if sliding out the drawbar with the tool connected to an AC voltage source would still reverse the polarity of the coil and if this offers any advantage to leaving the polarity in one direction. The instructions say slide the drawbar out while removing the watch from the coil. Would this offer any advantage over just removing the watch with the coil on (not sliding the drawbar out/reversing polarity)??

[robmack]

1 hour ago, Tracy said:

Yes, agree, It does work when I withdraw the object (screwdriver) slowly from the coil about 2 feet away then switch the coil off (not moving the drawbar). I just wondered if sliding out the drawbar with the tool connected to an AC voltage source would still reverse the polarity of the coil and if this offers any advantage to leaving the polarity in one direction. The instructions say slide the drawbar out while removing the watch from the coil. Would this offer any advantage over just removing the watch with the coil on (not sliding the drawbar out/reversing polarity)??

If you are applying DC voltage to the coil, then the draw bar will simulate a square waveform which reverses polarity on the coil each time the contact gets broken and then made.  The coil will only demagnetize the watch when you withdraw the watch at the same time as pulling out the bar.

If you apply AC voltage and attempt to draw out the bar, what you end up creating is pulses of 60Hz sine wave interleaved with huge spikes of voltage each time the contacts break and make.  That just worsens the situation, not make it better.  The voltage spikes will momentarily create a much stronger magnetic field that completely saturates the ferrous parts of the watch and magnetize them even more, unless you withdraw the watch at the same time you pull out the bar.

It's the act of withdrawing the watch from the magnetic effect of the coil that accomplishes the demagnetization.

Edited April 24, 2017 by robmack

[Tracy]

10 hours ago, robmack said:

If you are applying DC voltage to the coil, then the draw bar will simulate a square waveform which reverses polarity on the coil each time the contact gets broken and then made.  The coil will only demagnetize the watch when you withdraw the watch at the same time as pulling out the bar.

If you apply AC voltage and attempt to draw out the bar, what you end up creating is pulses of 60Hz sine wave interleaved with huge spikes of voltage each time the contacts break and make.  That just worsens the situation, not make it better.  The voltage spikes will momentarily create a much stronger magnetic field that completely saturates the ferrous parts of the watch and magnetize them even more, unless you withdraw the watch at the same time you pull out the bar.

It's the act of withdrawing the watch from the magnetic effect of the coil that accomplishes the demagnetization.

You're fight about the square wave vs. sine wave--I should have though of that I even own an o-scope. I guess the idea was pretty clever at the time to be able to use the DC input to reverse the coil's N/S poles--on wonder it was patented.

[Tracy]

Since I got such a good deal on the demagnetizer ($35) I couldn't resist and bought another on ebay. No drawbar--just 120 coil. It really work great--magnetized a 10" screwdriver--could pick up a hand full of nails--then demagnetized it. Haven't tried a watch yet??

 

[Wesley881]

Hi @Tracy, great finds!  Those are true pieces of history.  So I'm wondering if you or someone else could help me out.

I bought the blue cheapo and, well, I think it's because it was cheap but here's my issue:

Got a fairly large pocket watch movement up and running and wanted to demagnetize it to see if I could stop the hairspring from skittering (at 170+ years old it's gaining 6-8 min/day!).  Admirable, but not desirable.  I placed the movement onto the tool and pressed the button down and was prepared to slowly lift it away as advised but within two seconds the thing hummed, sparked and went *POOF*.  I saw plenty of response in the movement, so a field was present.  I feel like perhaps there was too much material for the tool to handle and the current required to induce a field was beyond the capability of the coil?

Help!

C

 

[Tracy]

I have the same tool. I think that yours just shorted out. The size/volume/weight of the object placed on the blue tool should not have caused this. I have found that my blue demagnetizer only works for small parts (works well on screws). I have not tried to demagnetize a wrist or pocket watch--seen others do this on Youtube--appears to work. If you are located anywhere near Maryland I would let you use my demagnetizer.

Also, if you search ebay for "Vintage watch demagnetizer" you will find other tools similar to the one I just posted for not too much money.

 

Edited April 24, 2017 by Tracy
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[Wesley881]

Thanks, that's very helpful.  I'll surf around on the bay and see what's happening.  Have to say I'm about 3 hours from Maryland otherwise I'd have been over with lunch by now!

Best,

C