Making a solenoid!

[Makaram]

Quick question, making my first solenoid and keep seeing things about how creating a short circuit will ruin my battery. Planning on using a 12V powertool battery and solenoid needs to be active for periods of 5 - 10 seconds. how do i prevent the solenoid from ruining the battery

 

[carbonzit]

Off the top of my head, you can either 1) make the electromagenet big enough so it doesn't draw too much current (lots and lots of turns of wire), or 2) control the solenoid with a device, like a transistor or SCR, that can be current-limited.

Just curious: why are you making a solenoid instead of buying one? What's the application? What's your design (# of turns, size, core, etc.)?

 

[Makaram]

thanks man
i'm making a solenoid actuator that acts as a drive shaft, as far as i can tell theres none of these readily available to buy, not in NZ anyway. i've got about 2m of 2mm wire.
Is it best to just do 1 layer or multiple layers of coiling????

 

[carbonzit]

Is it best to just do 1 layer or multiple layers of coiling????

One layer? You must be joking: you'd have practically a dead short across the battery, with not much solenoid action in the bargain.

I suggest you look at some real solenoids to see how they're constructed. Most of them have many, many turns of fine magnet wire. A heck of a lot more than 6 feet, that's for sure.

 

[MikeMl]

You need enough wire for hundreds to thousands of turns...

 

[Makaram]

Hmm ya i've melted a couple of wires using thin and long :S i just thought with the higher voltage..

 

[Makaram]

my problem is, if i use a long thin wire, i have problems with overheating considering the load time, as the longer the wire the higher the resistance. But with a thicker wire, needs to be shorter as less room and battery shorting...

 

[MikeMl]

The resistance R of a given gauge wire is directly proportional to length. The force generated by your solenoid is proportional to nI, where n is the number of turns, and I is the current in Amps. The current I = E/R, where E is your power supply voltage.

Your problem is to select a wire gauge (cross-sectional area) that will fit on the form your are using (total wire area) consistent with the wire length to make a resistance which will limit the current to prevent the wire or the power supply from burning up.

I say again: You need enough wire for hundreds to thousands of turns...

Try this calculator:

A multilayer solenoid of 672 turns wound with 185 ft of 28AWG wire, on a 1 inch form, two inches long would have a resistance of ~12Ω, which would draw 1A from a 12V power supply.

 

[JimB]

Have a look at a relay, the coil there has many turns.
As has been said already, you need hundreds of turns for this application.

JimB

 

[crutschow]

my problem is, if i use a long thin wire, i have problems with overheating considering the load time, as the longer the wire the higher the resistance. (

True. The longer the wire, the greater the resistance. So you select a wire length that gives enough resistance to limit the current to what the wire can safely carry for the voltage of your source. That's what everyone is trying to tell you.