I have a project in which I want a very small electromagnet to activate a very small lever for coupling/uncoupling NGauge model trains. I have wound a small coil (with 0.15mm enamelled wire) that is 6.5mm diameter and 9mm long. The power source is a small 80mAh LiPo cell (3.6v) - all controlled by an Attiny45.It almost works as I want it to but I have been unable to find any advice about the factors that improve or worsen the performance of the electromagnet (apart from the obvious ones like more turns or more amps - I don't have space for more turns or battery power for more amps).The problem is that it needs to move the lever a certain distance (about 3 to 4 mm) and the magnetic field is not quite strong enough to move the lever when it is 4mm away from the coil but works fine if it is only 2mm away (which is not enough). The lever is made from a piece of 16thou steel guitar string.The questions that are in my mind include ...I have a steel core (I will try to get a piece of iron later today - i.e. a nail). Is the magnetic force at the end of the steel/iron core affected by how far the core sticks out of the coil?Is the magnetic force increased or decreased if there is a "head" on the core - like the head of a nail, for example.I have taken a small relay apart and they seem to be designed so that the moving piece is magnetically connected to one end of the electromagnet and attracted to the other end. I don't think that would be practical for my project because my lever must be very lightweight.The websites that Google has turned up all seem to be about very basic electromagnetism demos using a nail or very advanced industrial stuff.I wonder if any forum reader has any practical advice or a link to anything useful?...R
I have taken a small relay apart and they seem to be designed so that the moving piece is magnetically connected to one end of the electromagnet and attracted to the other end. I don't think that would be practical for my project because my lever must be very lightweight.
@michinyon I am using a transistor to control the current. I think the resistance of the coil plus a 5R6 resistor is about 10 ohms and with 0.7v(?) drop in the transistor the coil current might be about (3.8-0.7)/10 or 300mA. I don't really want to draw more from the 80mAh battery in case it causes a brown-out for the Attiny. (By the way, the electromagnet is only activated for 1 second at a time).
it would be very heavy compared to 30mm of 16thou steel guitar string w