Electromagnetic chuck on a Boyar-Schultz 612 grinder

As part of a scrap deal, I purchased a nonworking Anca Fastgrind CNC tool and cutter grinder, a coolant tank with numerous pumps and
motorized screen, and a Boyar Schultz 612 Deluxe surface grinder with a dust collector and an electromagnetic chuck. The total cost was $150 for everything, I had to remove.
Anyway, supposedly, the only thing wrong with the Boyar-Schultz grinder is that "the EM chuck does not work". I tried to diagnose it a bit today. I found out that the chuck itself works, if I apply DC current to it from a power supply, it becomes magnetic. So, my thinking goes, the power supply is bad. If so, what alternatives do I have? Would any 90v DC power supply work, if it can provide enough current? Is there anything special about the magnet's power supply?
i
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On Tue, 24 Sep 2013 22:05:25 -0500, Ignoramus20545

They typically use a standard bridge rectifier..available at Radio Shack (or use to be) for about $5.
Its a very simply 110vt input...through a bridge rectifier and out to the magnet. Some..some have a transformer inside to bring 220/440 down to the proper voltage.
Mine has an additional transformer...or rather a different transformer with voltage taps that are selectible through a rotary switch. Switch Pos 1= 25 volts, 3 is 50 volts and so on.
Some..some have a second switch or switch position..it shoots 90-110 AC through the magnet to demagnitize the part AND the magnet.
These fancier mag power supplies typically have a 90 vot power supply that provides clean DC, rather than 60 hz half wave DC.
Most of the standard version..are very very simple inside. Simply check if you are getting power in, power to the rectifier, and DC out of the rectifier and power to the output of the power supply. Some use a relay instead of switching the entire power supply off and on.. So check to make sure power is going to the relay, power off/on to the relay coil (from external switch) and 90vts dc coming out of the relay.
Ive fixed a shitload of them over the years and its typically a bad wire, a bad switch..then a bad rectifier..and then a bad relay.
If your power supply is old..and it has a selenium rectifier..and its bad...and it is likely to be..simply replace it with the Rat Shack bridge rectifier.
Gunner
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OK, great, seems like an easy enough job for me! Thanks a lot!
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On Wed, 25 Sep 2013 07:57:30 -0500, Ignoramus4074

Jervelcom!
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Yes, unless it does not have any provisions for demagnetization which I kind of doubt.
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Nothing special. Does the switch to the chuck also have a de-magnatize position? If it does that position provides AC to the chuck to de-magnatize the part being held. Just keep track of the wiring and you should be ok.
Best Regards Tom.
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OK, that's good to know, I will check it out.
Thanks
i
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    Another steal. :-)

    Well ... mine uses a bit more voltage (it originally had a very simple power supply consisting of:
1    Selenium rectifier fed from the 120 VAC input line.
2)    Surge current limiting resistor (perhaps 10 Ohms wirewound).
3)    Electrolytic capacitor marked as something like 8 uF, and     actually *measuring* something like 0.03 uF.
    And -- switching set up to feed either that DC to the chuck, or nothing, or AC (to degauss what was held as you remove it).
    I rebuilt that part (lives in the base of the benchtop Sanford grinder I have) using a silicon bridge rectifier, the same surge limiting resistor and something like a 2000 uF electrolytic.
    But -- the manual for that warns to not use coolant when using the electro-mag chuck. (Since there was no transformer, get it wet and you are likely to get a shock. :-) So I normally use a permanent magnet chuck for that.
    Anyway -- make a DC power supply for whatever voltage it likes, and provide for feeding it AC to degauss the workpiece and that is all there is to it.
    Enjoy,         DoN.
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