# Short circuits

## Main Question or Discussion Point

so, i'm pretty bored and decided that i want to make a speaker. i've bought some thick copper wire, and twisted it in the form of a coil, then twisted some more with a larger radius so i can put the first one inside the second one and so on.. my motivation to buy the thick wire was to maximize the magnetic field produced, and that would need a lot of current, i.e. less resistance.
my question is this. how can i maximize the current through the coil without provoking a short circuit? i'm not sure on the reasons why a short circuit is produced, i just now that with very little resistance, you get one.. though, i dunno what it is that fails. any thoughts?

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Averagesupernova
Gold Member
I remember a high school student asked me something about "How low can somethings ohms can get before it shorts out?" A short circuit is when current in a circuit takes the short path instead of the intended path. Generally though, any time two conductors touch that are not supposed to be touching the condition is considered a short.
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So, in order to answer your question we need to know what type of amplifier you are using to drive the speaker. What sort of impedance is your amplifier able to drive? You can wind some wire and make a coil with a fraction of an ohm of impedance and if your amplifier is able to drive this impedance without harm (not likely), then you are ok. However, that is not to say that you have a satisfactory design.
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As for the thick wire, the wire needs to be thick enough to safely carry the current. The thickness has nothing to do with the field produced. The current is what determines the field. So shoot for a desired impedance, then determine how much wire you need to achieve this, how much space you have for winding, etc. and go from there.
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Or, if you want to do it the easy way just to demonstrate, put a resistor in series as to not damage the amplifier and listen. I tried this when I was a kid and although it made sound that was recognizable it was a stretch to call it a speaker.

hey, thanks. this speaker is medieval in every way anyways so it'll be, as you say, a long way from a speaker. but i what i don't have is an amplifier :S i don't want to plug it right into the wall because i'm afraid i'll take the power off the house. what i'm wondering is how much current can i pass through the plug so it won't flip off.. where i live, the voltage is ~220V. (imagine the field i'll produce with that voltage and no resistance! :P)

stop what you're doing before you start a fire or electrocute yourself

lol. i know :P (but that potential magnetic field stares at me very suggestively)

then keep your experimentation in a much lower voltage range. no more than 24V.

awww... well, i guess i really should buy a transformer.. i can't find any of that wire used for inductances. the one that has this thin coating.. right now i'm trying with regular wire and some candle wax. do you have any experience in building inductances? (now this thread starts to drift off)

Averagesupernova
Gold Member
Quantoshake11, I don't get the feeling you have a very good grasp of electricity in general. As proton said, stick with low voltages.
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As for this comment:
(imagine the field i'll produce with that voltage and no resistance! :P)
Pretty much demonstrates your lack of understanding. Any voltage with no resistance will cause infinite current to flow. Ohms law and all... No wire size you select will withstand this including the wire that leads to the outlet you would plug this contraption into. Lucky for you, the fuse will blow or breaker will trip in a split second assuming the wiring in your house is done correctly.

well, i think i have some understanding on electricity. when i said no resistance i was really saying very little. but even with no resistance, i would get a pretty huge (infinite) magnetic field and the statement prevails.. i'm just joking too much i guess. all i wanted to know is how much current can a regular 'house wiring' support before it shuts down (if everything is wired properly). or if there are any other things that might cause the house circuit to shut down.
edit: now that i think about it, with no resistance (supposing we are working in vacuum) the electrons wouldn't move within the wire, making them travel in other shaped paths instead of the intended one. But if we were in air! and the wire had no resistance, then maybe they would be trapped... anyways.... it was just an exageration

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you shouldn't assume a high current is inherently safe, even with a low voltage. let's say you took a 12V car battery and shorted the terminals with a wrench to get a few hundred or so amps of current. there's nothing safe about molten metal and exploding batteries.

just start small. go to Radio Shack. get some magnet wire, a nail, and a flashlight battery. measure the resistance of the wire on your spool and calculate how many ohms per foot you're looking at. and if you want more gauss out of your magnet, consider adding more turns to the coil instead of trying to push the current up to the fusing limit.

http://en.wikipedia.org/wiki/Inductor#Inductance_formulae