I have designed and built a small solenoid and... it doesn't exert any force on the steel bolt I am using as a plunger. I could freely move the plunger back and forth without any resistance.
- I am using 0.2mm copper wire with a plastic coating.
- The coil cross-section is 15mm x 3mm (inside radius = 2.5mm, ouside radius = 5.5mm)
- I calculated that I could get about 1125 turns on the solenoid with a resistance of 14.7 Ohms. For the actual solenoid I measured 11.7 Ohms.
- The solenoid frame is made of plastic.
- The plunger has a 3mm diameter and the gap between the coil and the plunger is 1mm, of which 90% should be plastic and 10% air.
- The overall radius of the solenoid is 5.5mm.
- I applied 12V and the total current draw was 1.02A.
- The solenoid became hot after 20 or 30 seconds, as expected.
I put the values into this calculator: http://www.daycounter.com/Calculators/Magnets/Solenoid-Force-Calculator.phtml
- I = 1.02
- N = 1125
- A = 95 mm2 (PI x 5.5mm x 5.5mm)
- g = 1mm
and it give a force of 78.598 N.
Clearly I have done something fundamentally wrong, but what?
Could it be the steel bolt?
I've looked for an iron substitute but couldn't find anything except old nails with a large taper.
What would happen if I tried a 3mm diameter neodymium magnet?