Electromagnet with 30mA

[ismo100]

Hi,

I'm a kind of "crazy inventor", and have now certain kind of "break through" invention on my mind .

I have surfed hours on the web, finding answer what one can get for electromagnet with 30mA and 50-100 turns coil if you can freely select the core material and the shape of core. I have not found the answer. Because the answer is easy to be given for a prfessional, I hope some of you could give it!

"what one can get" equals, more or less to, how big force can be gotten!

Thanks!

Tapio

 

[UKpete]

First of all it depends on the required characteristics of the force. A simple solenoid type electromagnet (just copper and iron) will give a force non-linear with airgap between electromagnet and target - very low force at large airgap increasing sharply as the airgap closes, and high holding force when closed. Alternatively, a linear actuator (copper, iron and a permanent magnet) can give a higher average force and one that is linear with displacement.

 

[ismo100]

I would need about 1-2mm movement and linear force!

 

[UKpete]

There have been some similar threads regarding flux density and force calculations on this site recently, e.g.
thread340-141078
thread340-132216
If you are looking for the equation for force across an airgap:

Force (in Newtons) F = B²*A/(2*?₀)
where B is the flux density in the airgap (Tesla)
A = area of pole face (or area of airgap in direction perpendicular to flux) (m²)
?₀ = permeability of free space (=4*pi*10-7)
i.e. all in SI units

If you assume a typical flux density in the airgap of 1.0T, you can rewrite this equation as:
force/area = 0.4N/mm²
BUT - to get a flux density of 1.0T for an airgap of 1.0mm, rearranging the equation for reluctance of an airgap (given in one of the above threads) to give ampere-turns:
NI = B*g/?₀ where g is the airgap (in meters)
= 800 Ampere-turns
Multiply that by 2 (say) to account for reluctance in the rest of the magnetic circuit (>2 if you have another airgap elsewhere) gives 1600Ampere-turns.

I'm afraid you only have 1.5 to 3 A-t from you initial post, so the force you can expect is going to be tiny,
something like less than 1microNewton per mm².

 

[ismo100]

Let's continue this threat.

How about if I'll use a permanent magnet as an anchor? So the actual force cames from permanent magnet, and the electromagnet is only used as a controller?

Is there any, even hypothetical, way to increase the 1microNewton per mm2 with that kind of construction?

Thanks for your previous answers!!!!!

 

[UKpete]

Yes, this is where it gets a bit difficult, for me anyway. Certainly a suitable permanent magnet can provide very high forces, but how do you control that with such a low electrical input (I assume you have a limitation on the available electrical power). A limited motion PM actuator such as a voice-coil actuator - you could cut one out of an old loudspeaker - might be worth considering but designing it would be complicated, as would calculating the force characteristic. Possibly you might find some info on-line by "yahooing" on "voice coil actuator", such as:

http://www.beikimco.com/appguides/actuators.php

Perhaps as you require only a very small displacement, you could employ a step-down geared system.

 

[nbucska]

As a fellow inventor I understand your frunstration but
try to describe the problem well enough to help finding
a solution.


Plesae read FAQ240-1032
<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS