Shorting Power Supply

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Hooligan383

New Member

• Jun 1, 2011

• #1

Hello,
I am having a small problem with a project i am working on. I am creating an electromagnet by using a 12vdc power supply to provide current through 20 gauge insulated copper wiring (which is wrapped in a coil around an iron nail), this in theory, would allow for the nail to attract other ferrous materials (making it magnetic). My problem is that when i hook up the wiring to the power supply it shorts the power supply. Why is that? How can i fix it?

for any questions about what i am trying to accomplish reference:
https://education.jlab.org/qa/electromagnet.html

Thank you for your time

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Jun 1, 2011

• #2

You need a LOT more wire.

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jun 1, 2011

• #3

I remember doing that experiment as kid. A lot more wire or use a current reguator, not voltage. It's easy to build one out of an LM317 (Radio shack Part) and heatsink up to 1.5 AMPs, but you'll loose 3 volts

 

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Hooligan383

New Member

• Jun 1, 2011

• #4

how much is a lot? in ft?
Thank you

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Jun 1, 2011

• #5

Add wire until it doesn't short the supply anymore.

You could also use thinner wire, so you can get more turns in a smaller area.

 

Last edited: Jun 1, 2011

crutschow

Well-Known Member

Most Helpful Member

• Jun 1, 2011

• #6

20Ga copper wire has a resistance of about .01 ohms/ft. Thus, for example, to limit the current to 1A with a 12V supply you would need 12 ohms or 1200 feet of 20Ga wire.

That's likely not practical so here are two choices:

One is to use much smaller wire to increase the resistance. For example 32Ga wire has a resistance of about 0.16 ohms/ft.

Alternately you could add a power resistor in series with the coil to limit the current.

 

Last edited: Jun 1, 2011

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Hooligan383

New Member

• Jun 1, 2011

• #7

in reference to crutschow post. i bought 28,29 and 31 gauge enameled coated magnet wire. what do you suggest would produce the best results..i am guessing the 31 gauge. Where did you get the information on gauge resistances and the limit of current needed for my 12V supply to not short. Also how did you derive 1200ft? Sorry for all the questions.. thank you

 

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cowana

New Member

• Jun 1, 2011

• #8

https://en.wikipedia.org/wiki/American_wire_gauge

31 gauge = 130 ohms for 1000 feet

You want about 12 ohms, so that's about 92 feet of 31 gauge wire.

Better than 1200 feet for 20Ga, but still a lot!

 

crutschow

Well-Known Member

Most Helpful Member

• Jun 1, 2011

• #9

Hooligan383 said:

in reference to crutschow post. i bought 28,29 and 31 gauge enameled coated magnet wire. what do you suggest would produce the best results..i am guessing the 31 gauge. Where did you get the information on gauge resistances and the limit of current needed for my 12V supply to not short. Also how did you derive 1200ft? Sorry for all the questions.. thank you

Click to expand...

I'm not sure what's the best, but the 31Ga wire would require the shortest length for the desired resistance.

If you google "wire resistance" you'll get many hits on determining wire resistance.

I don't know how much current your 12V supply can deliver before it limits. You have to determine that from its specs. I was just using 1 amp as an example.

For 1A at 12V by Ohm's law you need 12V/1A = 12 ohms. For a wire resistance of 0.01 ohm/ft. you would need 12/.01 = 1200 ft.