Solenoid

Hi Mutieerboy,

I agree with Del, better use a pre made article. there are plenty of solenoids around, depending on how much force is required, stroke length and voltage available. small units are found in domestic equipment. Stereos etc. Larger units on vehicles (Fuel solenoids, door locks)

I make the assumption that you are working with DC. You Will need to have enough wire on the coil so that the resistance limits the current enough to avoid that it burns out. You will need to use varnished wire, any other sort of insulation will mean that you will be unable to get enough turns on the bobbin. The varnish is much higher temperature than most insulants also.

Note that the force is not linear along the travel, magnetic attraction is a square law an so the shorter the stroke the more powerful the unit. If you get the pull you want and need to keep it connected you may find overheating problems. The usual solution to this is to add a normally closed switch which opens at the end of the stroke. This switch is across a ballast or economizer resistor so that when the contact opens the resistor is in series with the coil and reduces the current to a holding level, typically a tenth of the pull current. It can also be done with two coils but that would be much more difficult to set up for a one off job.

hope this helps

Chas

Hi capblanc

The current reduction resistance is a good idea in the case of robots as it will conserve critical battery power.

The poster can possibly jury rig the solenoid with a reasonable number of turns of extra heavy wire and with a large power supply maybe a welder if it requires a large operating current. Measure the amps required to operate the solenoid this will give the amp turns required. This can then be interpolated with the operating voltage wire size current capacity and resistance to arrive at the required turns,this can all be worked out from Clifftronics site formulae.

If you decide to make your own coil, you can find the way to calculate the force, wire size and turns on response #57 to "Quick Electromagnetic Question" posted 2/10/2009.

I'd like to add that unless you need/want to design a high volume custom solenoid, the advise of responses #1,2&5 should be strongly considered. As long as you have the space available, selecting a standard solenoid with their suggested parameters (force, distance, switching time, voltage, ambient temperature, etc.) and with an application engineer from the solenoid manufacturer is your best bet.

Mutineerboy,

We do appreciate that you wish to do the design work yourself, but there's a reason why EE students have a separate class on electromagnetics. It gets complicated very quickly.

The critical things you should be able to specify are your mechanical and magnetic design goals. Like how strong of a magnetic field is desired with the solenoid ON? How strong of a field is acceptable with the solenoid OFF? (Can you say hysteresis?) How quickly does the field need to be created? What will the solenoid be magnetizing? How much space is available for the solenoid? What voltage sources are available?