Electromagnetisim/Electronics Help

[cheesehead]

I'm currently working on a rather nifty project in my spare time, and it requires an electromagnet that will push on another magnet very, very hard for a very short period of time. I hope to run the thing off of a 9.6v 500mah Ni-cad battery pack, so the current draw should'nt be above about 40 watts or so. I was thinking about wiring a few VERY large capacitors in paralell with the battery. When the whole thing is connected with the electromagnet, it will recieve a large amount of current for a very short amount of time. Where can I find a suitable electromagnet (cylindrical, 1"-3/4" in diamter) and how should I wire it up? (It's going to be in an electromagnetic piston with a large neodiyum magnet, if you want to know.)

 

[bobsmith1492]

Wind it yourself would be the best bet. Get some heavier gauge magnet wire and a piece of steel or soft iron and wind it up! Plus, that way you can build it whatever size you need.

Also, to cut down on the massive current (which would be required for a large force) I'd try a higher voltage. Try line voltage with a bridge rectifier (120 V). That would cut your current draw and required wire size into 1/12 of that required at 10V for the same power output.

Oh yeah; what's the project?

 

[cheesehead]

I was hoping to try using it for an airsoft gun instead of a spring/motor assembly. For this reason, the battery pack needs to be pretty small, and the electromagnet needs to have a roughly 2-4 lb. push on the magnet. I can solder well enough, but I'm a little hazy on some of the more advanced areas of electronics, so I was hoping someone could give me a hand. Perhaps a transformer or similar device could be used to convert the 9.6v. to 60 volts or above?

 

[CrispyFried]

You would probably loose to much using a xformer, they are not 100% efficient. You can always double up the nicad packs if wire size gets to big for what you want.

 

[cheesehead]

A transformer might be inefficient, but there are ways of generating high voltages. By using one of these several large high-voltage capacitors, I hope to reduce the current draw on the battery. I heard of something called a flyback transformer that might work; although it would require quite a few diodes to get to over 100 volts, a voltage multiplier like this one might work. (http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/voldoub.html#c3).

 

[bobsmith1492]

You can't use a transformer; you need AC, but the battery is DC. You can generate AC but it would take some circuitry.

A flyback transformer would make way too high of a voltage at way too low of a current to be of any use.

Your best bet would be to make (or buy) an inverter (DC to AC), hook it up to a transformer, change that back into DC to charge caps, then fire it off through a homemade coil.

Sounds like a lot of work to me... and it definately will be too big for an airsoft gun.

 

[cheesehead]

That's actually not a bad idea. However, I don't have a 12-volt battery or appropriate charger, and don't feel like buying one. Perhaps the "Voltage Multiplier" shown above might be used to charge some large capacitors instead?

 

[bobsmith1492]

Again, you need AC to run that doubler which calls for an inverter (sine wave generator).

 

[FrankSchwab]

There are plenty of solutions to generate high voltage from a low-voltage DC source. You can build them, or you can buy them. For example, This or
this.

Nearly all are going to have a low output current; p=IV kinda demands it. You might want to consider the photoflash circuits; let'em charge a bank of half-a-dozen or so photoflash caps @ 300V, then figure out a way to trigger a discharge of the caps through the coil.

Not a project for the faint of heart.

/frank

 

[cheesehead]

Instead of using one gargantuan coil in conjunction with high voltage, perhaps it would make more sense to use numerous smaller coils in paralell. Twelve 1-ohm coils in paralell would leave me with a 115 watt draw on 9.6v; a few jumbo-sized capacitors (a few Farad's worth) should support the draw for the minute amount of time needed to fire the airsoft gun.
I've also seen some electromagnets used for physics demonstrations that can lift nearly a hundred pounds on 2 "D" batteries. Anyone know why they're so powerful?