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How to control heat in a winding of a micro wave transformer I use for a electro magnet on my milling M/C . I am using 240v

ClydeCrashKop

Well-Known Member
Most Helpful Member
Can you run coolant through it or in copper tubing against the sides?
 

shortbus=

Well-Known Member
That's why using windings from a transformer that wasn't made to be an electromagnet in the first place doesn't work so good. Electromagnets do get hot in use, but when made with the correct guage wire in the first place they don't get as hot. Are you using DC to power it? DC on and AC coil is also a problem, again mostly to the wire gauge. Take a AC relay coil, it doesn't work so well when used on DC.
 

Gregory

Member
I have tried Dc and 240 v AC they both get very hot.
The winding is AC from a microwave .
I would like to make a electro magnet for my miller.
What size wires would I use and what would be the layout of the fielders .
I require a magnet about 300 mm long and 150 wide.
Can you help me with the electrical setup.
Thank you
 

BobW

Active Member
Microwave oven transformers tend to operate on the border of saturation, which makes them run hot. If you can lower the supply voltage by just a few volts (maybe 10V) it will likely operate much cooler.
 

shortbus=

Well-Known Member
Gregory , are you aware of the pit falls of using a magnetic work holder in a milling machine? It will cause you problems especially with small diameter cutters and a low powered spindle. The chips will stick to both the work and the cutter and could break the cutter and give a very poor finish to the cut.
 

MaxHeadRoom78

Well-Known Member
Using an AC device as an electromagnet is inefficient, not a good idea.
Industrial lift magnets etc all use DC, the coil current is dependent simply on the resistance of the coil.
I have made controllers for scrap yard lift magnets and these use 100amps at 240vdc.
A shot of reverse current is usually required to avoid residual attaraction of the lift material.
These often get very hot, especially when working in hot environments, and lose their lift efficiency as the temperature rises, a water dip tank is often used to cool these off.
Smaller lift magnet applications do not usually suffer quite so much from this.
Obviously using DC on a AC transformer is going to produce a great deal of heat due to the lack of inductive reactance.
Max.
 

dr pepper

Well-Known Member
Most Helpful Member
I've used magnetic vices of the non electric kind on surface grinders, never seen one on a mill.
So long as the work is thick enough might work, and remanence shouldnt be a problem.
 

crutschow

Well-Known Member
Most Helpful Member
You could reduce the voltage to the transformer by feeding it from a lower voltage transformer or variac, or adding a large AC motor capacitor in series.
 

shortbus=

Well-Known Member
adding a large AC motor capacitor in series.
If doing that it would need to be a run capacitor, not a start cap. Start caps are only meant to be in the circuit for a short time. Most magnet 'chucks' the term for a magnetic work holding device are DC not AC.
 

crutschow

Well-Known Member
Most Helpful Member
If doing that it would need to be a run capacitor, not a start cap. Start caps are only meant to be in the circuit for a short time. Most magnet 'chucks' the term for a magnetic work holding device are DC not AC.
You could put the capacitor in the AC line powering a bridge rectifier to limit the DC load voltage.
 

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