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i have a strong electro magnet (12V, 15watt) and like to turn it on and off really fast. how can i do this? Answered

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icengBest Answer (author)2012-01-08

As Steve Says "Why not just use a flyback transformer ?"  that is made for high voltage without destroying the wire insulation.

Whereas an electro magnet low voltage winding made to generate huge EMF ( Electro Magnetic Force ) with no concern to inductance or kickback.
Will easily short out those windings without the diode to prevent excessive voltage from arcing a carbonized track through the insulating materials.

Also voltage is not as much a function of frequency as it is the speed of turning the current off  -di/dt
The faster you can interrupt the coil current.  The greater the kickback voltage.

A

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manfred2766 (author)2012-01-10

sourced a flyback now and it has 10 solder connections and 3 wires. :
heat, video, ground, abl, 25v, 16.5, B+, 45v, ?, hp and grey(video), black, red positive out.
now most connections i wont need but what are the essential once? i like to run it from a 10 or 12 volt source.

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iceng (author)manfred27662012-01-10

Here is a pointer to a fly-back xfmr.
Hope it helps.

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manfred2766 (author)2012-01-08

i want to switch it on and off as fast as possible. the diode i want to avoid because the high volts is exactly what i am after. will i destroy it? this is the magnet: GTO80-0 5000 - 12VDC

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steveastrouk (author)manfred27662012-01-08

Why not just use a flyback transformer ?

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manfred2766 (author)steveastrouk2012-01-09

thanks steve your a champ. will use a flyback transformer now, its all about know-how. will read up on them now, its exactly what im after.
many thanks

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steveastrouk (author)manfred27662012-01-09

I know everyone says find a flyback in an old TV, but I have just found a source in old photocopiers and laser printers.

Steve

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user

Old computer monitors are also good (CRTs). Make sure you discharge the capacitor first, though. Its built into it.

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steveastrouk (author)2012-01-08

As LMB says, it depends on the inductance. If its REALLY fast, you need to whack the coil with a lot more voltage than you would expect, and use a constant current driver. Ultimately, your coil voltage might need to be near the breakdown voltage of the winding !

And don't forget a SERIOUSLY big diode across it.

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aelias36 (author)2012-01-08

Control it with a 555 ic running in astable mode as a timer, connected to a transistor to handle the current. Don't forget to add a reverse-biased diode to protect the circuit!

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LargeMouthBass (author)2012-01-08

It depends on what you mean by "really fast". If that means a few times a second, you should be able to do it by using a transistor to complete the circuit, with the transistor being turned on and off by another circuit.

Exactly how fast you can turn it on and off will depend on the coils inductance, which will be relatively high. If you turn it on and off too fast, the inductance will prevent the current from reaching its maximum, and the field strenght will be reduced.

You will also need to keep in mind the high voltage produced across the coil when the current is abruptly shut off. This is commonly taken care of by a diode across the coil that only conducts when the power is removed, allowing the current in the coil to recirculate through the inductor until it is reduced to zero.

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