Electromagnetic Chuck

[ddickey]

My little 3x5 chuck on my Sanford works fine but I'm thinking about replacing the antiquated electronics that provide power to the chuck.
Anyone know of an affordable way to rectify 120Vac into 400Vdc?

 

[markba633csi]

Are the electronics giving problems? Those things are usually pretty simple and reliable
-Mark
400 vdc? sounds high- 400 watts I would believe

 

[Reddinr]

What sort of current is needed? In round numbers, a rectifier (without a capacitor filter) that outputs 400 VDC peak voltage needs about 285V VAC RMS for its input. A rectifier that outputs 400 VDC AVERAGE voltage requires 450 VAC RMS for its input. Which do you require? How much current is needed?

In either case, the voltage can be had a number of ways:

Isolation transformer, step-up, followed by a 4 diode bridge rectifier.
Isolation transformer, center-tapped, step-up, followed by a 2 diode bridge rectifier.
Auto-transformer, boost type, followed by a bridge rectifier.
Switch-mode power supply, chosen for the DC voltage required.
For small currents, there are circuits called voltage multipliers that consist of diodes and capacitors. Typically for a handful of milli-amps.

All of these come with safety-related issues that have to be considered.

 

[rwm]

My little 3x5 chuck on my Sanford works fine but I'm thinking about replacing the antiquated electronics that provide power to the chuck.
Anyone know of an affordable way to rectify 120Vac into 400Vdc?

Does that sucker really run on 400vDC?
Robert

 

[Weldingrod1]

Also, you will need demagnetizing. The Magnabend design has a nice system for this.
I dont think most electromagnetic chuck power supplies are electrically isolated. The coil should be well insulated, and the housing grounded.
The one I built years ago used a variac and a three position switch. Forward polarity, off, reverse polarity. Pick a direction, turn on, ramp up voltage. Do work. Ramp down voltage part way, reverse polarity, ramp down more, reverse polarity, repeat once more. You need to have something to keep from arcing the snot out of the switch too...

Sent from my SM-G892A using Tapatalk

 

[benmychree]

Every electro mag chuck that I have ever seen runs on 100 VDC. The Chinese make a 100 V power supply that is not overly expensive, is compact, and has the automatic de mag feature like the USA Neutrofier, they feature variable magnetism and automatic de magnetizing with variable time cycle.

 

[ddickey]

I don't think this chuck had the demag. If it did I never knew it. I measured the output to the chuck and it was 400vdc. I agree it does seem very high. I also measured the resistance of the chuck, I think it was around 800ohm but should probably check again. Could also check the transformer.
Chuck works perfectly fine. I needed to take out the components and switches so I could easily work on the grinder. All the wire is in terrible shape, brittle and cracking in some spots.

 

[brino]

Depending on the current requirement, you might look at diode based voltage multipliers.
https://www.electronics-tutorials.ws/blog/voltage-multiplier-circuit.html
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/voltage-multipliers/

Please pay special attention to the warnings about line driven circuits.

-brino

 

[markba633csi]

Got any pictures? Sounds like an unusual beast
-M

 

[rwm]

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I think that is good for 5 amps, but if your coil is 800 ohm it would only draw 125 mA. Seems too low?
R