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Old 02-26-2011, 11:00 PM   #1
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How to make a magnetic coil, without the short circuit?


I'm thinking of making a magnetiser for my screw drivers. I've done them before but the problem is I go through a lot of transformers due to shorting them out. How do I make it so it only draws a specific amount of amps instead of infinity? From my understanding, certain transformers like the ones in microwaves are "current limited". I basically need to do the same, but how? This would have to be DC, of course. Do I just stick a load on there, like a light bulb? I don't need the high voltage of a microwave transformer, but just something like a 12VDC adapter, so I need to limit how much current my device draws.

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Old 02-26-2011, 11:11 PM   #2
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How to make a magnetic coil, without the short circuit?


Might be easier to find an old permanent magnet gearmotor and disassemble it. Keep the case (with magnets) and store the drivers in it overnight. I know it is very effective, by accident.

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Old 02-27-2011, 07:51 AM   #3
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How to make a magnetic coil, without the short circuit?


Current limited or impedance protected depends on the alternating current frequency. DC (or too low a frequency such as the antiquated 25 Hz) will still burn it out if you short the output.

A transformer on its proper power source draws a very small amount of current with no (secondary) load and the current draw increases as the load is increased (resistance across the secondary terminals is reduced).

Yes you can connect an incandescent lamp in series with the transformer primary coil (not across the secondary or load terminals) to limit the current; it will also limit the strength of the magnetizing.
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Old 02-27-2011, 10:54 AM   #4
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How to make a magnetic coil, without the short circuit?


They sell screw driver magnetizers for just a couple bucks at Home Depot and probably any hardware store. Why would you want to make one like that? Sounds like a fire hazard to me

Another way to temporarily magnetize a screw driver is to drive it into the ground at a 30 deg angle towards North. Push it in the ground about an inch or so at that angle and then smack it in to its handle with your plyers. Pull it out and tada... you magnetized it!

I know this sounds like malarky but don't knock it till you try it! It does work...not well but it will make your screwdriver slightly magnetized.
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Old 02-27-2011, 11:23 AM   #5
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How to make a magnetic coil, without the short circuit?


Put a resistor inline. E=IR I=E/R R=E/I You know you have a 12V source. Figure out how many amps you want and calculate.
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Old 02-27-2011, 11:54 AM   #6
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How to make a magnetic coil, without the short circuit?


If you apply power to a coil without an iron it will fry in no time. If you must use coils not intended for this purpose, always make sure there is something metal running through the coil. An empty coil, is a burned out coil in no time.
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Old 02-27-2011, 01:24 PM   #7
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How to make a magnetic coil, without the short circuit?


Quote:
Originally Posted by J. V. View Post
If you apply power to a coil without an iron it will fry in no time. If you must use coils not intended for this purpose, always make sure there is something metal running through the coil. An empty coil, is a burned out coil in no time.
Hmm good point, so by having something in metal it basically gives it a resistance right? So the act of transferring energy to the metal in form of magnetism creates a resistance?

I know I can buy premade ones, but I just want to build this for fun.

I also would not leave this overnight. One I built previously as a kid only needed to be on for like a minute. It smelled funny when it ran, but it worked really good! I still have some screw drivers that are magnetized from it but they are weaker now.
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Old 02-27-2011, 01:26 PM   #8
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How to make a magnetic coil, without the short circuit?


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Put a resistor inline. E=IR I=E/R R=E/I You know you have a 12V source. Figure out how many amps you want and calculate.

I was thinking this too, might try that, or just a load like a light bulb.

I'm thinking too, if I use thinner wire the wire itself might have a slight resistance, but probably not really significant.
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Old 02-27-2011, 01:33 PM   #9
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How to make a magnetic coil, without the short circuit?


Any coil that does not have a metallic object inserted in through the hole or square opening will burn out in a matter of minutes. Some people insert a screw driver, so they can troubleshoot systems without shutting off the power.

To build a coil you will need magnet wire for the best results.

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