Need Help!- Build Circuit for DEMAG TABLE

[parametric.ms]

Does anyone here know schematic for controlling DEMAG TABLE?

The specification on Table show 100V 0.85A

Thanks

[vger]

For demagnetizing you need an AC current that decreases over time. The easiest way I can think of to do this is with a VARIAC or adjustable autotransformer.
Here is a link to a photo of one...

https://id38.securedata.net/sweetmar...weetmarias.jpg

You may not need one that large for your table. There are about 100 of them on Ebay

Steve

[parametric.ms]

thanks steve,

I can't even figure out to using that transformer. Its so simple

Regards,
Andre

[vger]

Just take the output of the transformer and connect it to the DEMAG table. Set the transformer to lowest setting ( 0 V ) and turn it on. Turn the transformer up to 100 V and then turn it slowly down to 0 V again.

Steve

[parametric.ms]

the problem is I'm not really sure that my table using ac or dc voltage. I only see 100V 0.85A. what do you think? 0V for demagnetize and 100V for maximum magnetize, right?

[vger]

Originally Posted by parametric.ms the problem is I'm not really sure that my table using ac or dc voltage. I only see 100V 0.85A. what do you think? 0V for demagnetize and 100V for maximum magnetize, right?

Ok, to magnetize you would use DC. To demagnetize you would use AC. Using DC the magnetic feild would not reverse and the magnetic domains in the material will become alligned. Using AC the magnetic feild reverses every cycle of the AC (alternating current) causing the magnetic domains to flip back and forth, and if the alternating feild is reduced slowly, then the domains are left in a random alignment and the piece is demagnetized.

Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal. Vibration has been shown to increase the effect. Ferrous materials aligned with the earth's magnetic field and which are subject to vibration (e.g. frame of a conveyor) have been shown to acquire significant residual magnetism. A magnetic field much stronger than the earth's can be generated inside a solenoid by passing direct current through it.

Placing the magnet in an alternating magnetic field, such as that generated by a solenoid with an alternating current through it, and then either slowly drawing the magnet out or slowly decreasing the magnetic field to zero. This is the principle used in commercial demagnetizers to demagnetize tools and erase credit cards and hard disks, and degaussing coils used to demagnetize CRTs.

steve

[vger]

Hmmmm, are you talking about a magnetic table for holding parts and all you want to do is hold the part, or not hold the part?

[parametric.ms]

yes steve, its use on surface grinder table. I'm sorry if I didn't mention it.

so, what should I use steve? AC or DC? and what kind of circuit if I want to use DC Voltage 0 - 100V?

[vger]

It will be DC to hold the part(s). You could use the variac with the output going to a rectifier to change it to DC and perhaps a filter capacitor then to the table (chuck). You would only want to set the transformer to about 70 volts to limit the DC voltage to 100 V or so. If you wanted to be able to demagnetize the parts after grinding, you could add a DPDT switch to connect the table to the AC output of the variac, and then reduce the voltage to demagnetize the part(s).

[Al_The_Man]

Demagnetization can also be a shot in the reverse polarity, commercial units often take advantage of the collapsing EMF at turn off to demag.
Did you see the circuit I posted?
Al.

[parametric.ms]

@steve : I need a complete circuit for that. Electronics is my weakest part

@alan : yes al, I've seen your circuit, but I need more specification for toroidal transformer and Rectifier Bridge. What 18g mean? Is toroid same with noise filter? should I put a heatsink on triac or diac?

[vger]

OK, here is a rough schematic. I don't know what line voltage you have, 120 or 220? so that will make a difference in component selection. Generally you will want a bridge that has a PIV (PRV) at least 2 times the maximum applied AC voltage and Amp rating about 2 times the maximum current. The capacitor may be optional, but it's voltage rating should be at least 50% higher than the peak voltage of the applied power. 120 V AC has about a 170 V peak. The switch is a DPDT switch, and should have about 5 Amp rating.

******************
You will need to limit the maximum AC output from the variac to about 70 volts to keep the DC voltage going to the table below 100 V DC.
******************

If you have only 220 V AC available then everything changes....

(((( Al, does this one look acceptable to you? )))

Steve