# how to prevent simple AA battery electromagnet short circuit/overheating

#### shannon

Jan 5, 2017
7
hello ...

when I search youtube for "how to make electro magnet" I see the results as posted in the attached picture:

All the video thumbnails show the same basic thing: a battery with wire going from one end to the other ... the batteries are 1.5V or 9V ... the videos usually mention that the battery will get hot.

My Questions:

1) - is this a short circuit (ie a AA battery with a wire going from one end to the other)?
2) - would this simple experiment be Dangerous if using a much larger battery, say 10*9V=90V?
3) - if 1) and 2) are "yes", then how to protect circuit (and person) from danger?

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#### davenn

Moderator
Sep 5, 2009
14,011
1) - is this a short circuit?

close to .... how many turns of what gauge wire ??

2) - would this simple experiment be Dangerous if using a much larger battery, say 10*9V=90V?

would be worse MUCH worse

3) - if 1) and 2) are "yes", then how to protect circuit (and person) from danger?

you build something safer

for an electro magnet ................. many 100's of turns of 26 - 30 swg (awg) wire

#### shannon

Jan 5, 2017
7
close to .... how many turns of what gauge wire ??
suppose Scenario A: 0 turns
suppose Scenario B: 10,000 turns

#### davenn

Moderator
Sep 5, 2009
14,011
suppose Scenario A: 0 turns

I didn't want scenarios

You posted a electro-magnet project .... I wanted to know how many turns of what gauge wire was stated ?

#### davenn

Moderator
Sep 5, 2009
14,011
suppose Scenario A: 0 turns

the load a straight piece of wire puts across a PSU, is still determined by its length and resistance

suppose Scenario B: 10,000 turns

will give a good electromagnet, again depending on voltage and resistance

#### shannon

Jan 5, 2017
7
Davenn, you mentioned
you build something safer
...

I suppose what I am hoping for is a suggestion on some simple, common, basic electronic component that I can put in the circuit (whether it is a 9V DC or a 90V DC circuit, with 0 turns or more) and feel confident that the battery will not be improperly affected (such as overheating or blowing up).

Is there some component that I put into the circuit to know that it is a safe simple circuit?

thanks, Shannon

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#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Well, you could use a fuse.

The alternative is a resistor, but you will need to learn how to calculate an appropriate value. In addition this will pretty much render the the device useless as an electromagnet.

The "appropriate" resistor will vary with the resistance of your coil, the battery voltage, the maximum safe current through the wire, and the maximum safe current from the battery.

The general solution is to increase the number of turns and/or reduce the size of the wire to increase the resistance of the coil itself to make it appropriate to connect to a particular per source.

#### Audioguru

Sep 24, 2016
3,640
Instead of adding a component that tells you the circuit is safe, why not design it to be safe and use common sense?
Simply do not use a little AA cell or little 9V battery to drive the starter motor (it is an electromagnet) in your car.

#### BobK

Jan 5, 2010
7,682
You make it safe by determining the maximum safe current from the battery, determining the resistance that will result in that current, then making the wire long enough to have that resistance.

For an AA cell, that is about 1A at which the battery will last about 1 hour.

To get 1A you need a resistance of 1.5Ω (for a single 1.5V cell)

#28 wire is the smallest you would use to carry 1A. It has 64.9mΩ per meter, so 1500/64.9 = 23m

So, to make an electromagnet running off 1 AA cell without overheating the battery you would wind 23 meters of #28 wire.

Bob