Anybody built a pulse magnetiser?

Greetings Dan, You are correct about the pins. I will be using probably 4340 steel because I can get it in the heat treated condition so that it is already pretty hard and tough. I only need two poles so that's no big deal. I think I need to just build a C shaped magnetiser out of some steel rod, wind some wire around it, and try discharging a cap through it. Maybe use an old flash unit from a disposable camera since I have a few of them in a drawer somewhere. Eric

I'd like to hear some discussion on how this might be done.

If you connect a charged cap to an inductor, you're gonna get a damped sinusoid determined by R, L and C of the series circuit. Isn't that exactly what happens with a demagnetizer as you move the piece being demagnetized away?

If magnetization is a mechanical process that takes time to perform, there should be some interaction between that process time and the frequency of the damped oscillation??

The more I think about this the more questions I have. Seems like you need to maintain current for some minimal time to allow the magnetic domains to rearrange, then interrupt the current in a manner that does not allow the inductor current to reverse?????

You know, I think you're right. It seems like the coil and cap would ring. I'll have to look again at some sites that mentioned discharging a cap into a coil to make a pulse magnetizer. I know that a lot of magnetizers work this way, dumping current into a coil. Some turn the coil on for a brief period using some sort of switch. Others use a charged capacitor for the power pulse. If a cap and a rectifier are used in series that would stop the ringing, right? Anyway, I'll check. Eric

My experience with a one microfarad foil cap charged to 2000 volts and dump ed into a 0.2 ohm low inductance load showed no ringing. The cap discharge d in a couple of microseconds with no ringing. Peak current was about 2000 amps. I think that electrolytic caps would have a higher equivalent seri es resistance and would also not ring. But I have not verified that.

Dan

You are right. Without inductance a cap can't ring. The ring is caused by the magnetic feild collapsing across the coil, inducing a voltage that recharges the cap, which then discharges into the inductor - nd it keeps repeating itself. No inductance - no ringing.

Thanks Dan. Some real world testing is what is really needed. I don't need a strong magnet, in fact I need a weak one. But I do need reliable and repeatable results. I also need magnetic material that will not lose its magnetism easily. Cheers, Eric

A gas tube like you find in a strobe light for a camera is one type of switch. But metal to metal contact also works. But that will pit the metal.

Your hard 4340 is probably a good choice.

Dan

A diode correctly oriented will dump the ringing to ground, but will allow the field to initially build. As this is a one shot a smaller diode may be adequate. If it explodes, use a bigger diode or several in parallel.