I find it intresting to see how this simple setup: a reed switch that needs to be triggered by an electro magnet where both components are next to each other, can have different opinions how to realize.
@Cachehiker:
OK now I get how you do the calcualtion, one more thing;
If I do a more correct calculation of the wirelength with the, on each layer, changing circumference I get this;
Turns PI 3/8" 36AWG inches
200 3,1415 0,375 0,005 238,75
200 3,1415 0,38 0,005 241,90
200 3,1415 0,385 0,005 245,04
200 3,1415 0,39 0,005 248,18
200 3,1415 0,395 0,005 251,32
200 3,1415 0,4 0,005 254,46
200 3,1415 0,405 0,005 257,60
200 3,1415 0,41 0,005 260,74
200 3,1415 0,415 0,005 263,89
200 3,1415 0,42 0,005 267,03
200 3,1415 0,425 0,005 270,17
200 3,1415 0,43 0,005 273,31
Total: 2799,08
While calculating it in 1 pass has an about 14.5% greater value for the total wire length.
2400 3,1415 0,375 0,06 3279,73
The manufactor of the ready made small electro magnet, Kuhse Gto 18 (1,4W 12VDC) says;
this application is not the standard application of these solenoids. Normally they are used to hold a plate our something else made of steel. That is why the magnetic filed goes not more than a few millimetres away from the holding surface. Especially this little type of holding solenoid has only 2-3 millimetres magnetic field.
detailed PDF specs:
https://www.kuhse.de/fileadmin/download/datenblatt_de/Katalog_Haftmagnete_de_uk06.pdf
So it still looks like a challenge to find a suitable electro magnet to trigger the reed.