Electronics > Beginners
Couple of Questions about a DC electromagnet & cap
THATguy:
Right so I should get a lot of my smaller capacitors then.
CatalinaWOW:
Some calculations will save you a lot of work. Simple stuff like ampere turns and impedance.
THATguy:
I've tried using inductance calculations in the past to build metal detecting coils, but found the explanations of width & such to be confusing (before I had these forums).
I'll be doing a lot of testing of prototype coil designs with small caps first.
Inadvertently it seems I'm creating a EMP blaster!
Just found out the large microwave caps have a built in discharge resistor, now thats annoying! Hope I can dig it out.
CatalinaWOW:
Coil equations can be very confusing. Not least because they are approximations. But even misapplied they should get you close enough to tell if you are getting in the ballpark you wish. Amp turns will tell you the magnetic field in air. If you have a core the B=mu H equation finishes that. Knowing how many hundred or thousand amps you need to get the field you want then lets you test feasibility using the resistance and voltage. At these levels you can't ignore wires or the internal resistance of your capacitors. On your first pass you probably won't like your answers and you can start playing with number of turns. But as turns go up size gets out of hand and you want to reduce wire size, increasing resistance. Inductance also goes up limiting how rapidly current can rise. If you look at all of the possible equations you might use for inductance (at least in the air core versions), you will find there isn't an order of magnitude difference in the answers. Which is all the closer you need to be at this step in the process. It is a race between whether current can get to the level you want before your capacitors drop voltage too much to drive that current.
A few simple equations in a spreadsheet can let you do a lot of experimenting before you get your hands dirty.
Brumby:
I wish you well in your experiments - but I, too, have some concerns.
Let me just say that, before you get up into some really high energy territory that you can wrangle some maths and understand the physical implications of that math in something you want to test.
There are two reasons for this. The first would be for your safety (sorry if this is sounding like a broken record - but I'm sure you know where I'm coming from). The second is for optimising your experimental efforts. If the math doesn't point to a particular experiment as being worthwhile, then why spend the time building it and running a series of tests? It's like trying to head-butt your way through a wall instead of taking the time to find the doorway.
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