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Coil design
The max. conduction theta in A can be derived from the fieldnumeric calculation; it results in turn in the determin of the concrete coil data with the connected voltage specified:
Example: A spreading magnet with poles and 3 coils
:: conduction theta = 2200 A for each solenoid
:: cross- sectional area of the coil space: 1200..²
first of all one single turn is assumed, so that 
| U' | = R * I = p * Lm / (A*FCu) *
I = 0.0175mm² * Ohm / m * 0.266m / (1200mm² * 0.55) * 2200A = 0.01566 V |
| FCu =
copper bulk factor, Lm =
mean turn length, p = specific resistance of Cu, A = cross section area |
|
chosen voltage = 30V, so the number ot turns is specified by:
N = U/U' = 30V/0.01566V = 1914 turns.
This results in the required wire cross section:
Ad = 1200mm² * 0.55/1914 = 0.345mm²
and then a wire diameter of:
The standard series offers a wire diameter of 0.67mm; fitting very well to the wire diameter calculated. The max. current through the wire is as follows:
Id = 2200A/1914 = 1.15A, with the density of current being
j = 1.15A/0.345mm² = 3.4/mm²
This density of current shows that the electrical spreader
may have an operating time of 50%, since otherwise the admissible
housing temperature of 75 °C would be exceeded. In case
of an operating time of 100 % the density of current should
not exceed 2.5 A/mm2 . As all 3 coils are to be connected
serially, the connected voltage is approx. 90 V in the cold
state. In order to have this current in the warm state as
well, the voltage would have to be approx. 40 % higher, since
the coils are heated up and the resistance is increased.
So if a constant magnetic field resp. a constant spreading
effect is required, a current regulator will have to be provided.
