DESIGN OF SMALL IRON-CORED CHOKES AND TRANSFORMERS 



experience one's guesses improve. From Table 1 find out the number of 

 turns for one milUhenry (this is our (K^OKjuK^K^) in Chapter 4 all worked 

 out for us), and thus compute the number of turns A'^ required, remembering 

 that L oc (turns)^: also from Table 1 find out the 'window area' of the pro- 

 posed core, through which the turns will pass and, for safety, take two-thirds 

 of it (this is to allow for imperfections in one's winding technique). From 

 Table 2 find out the thickest gauges of wire which will allow one to get the 



TABLE 2* 

 Copper Wire Information 



For w ire insulated with enamel alone, the turns per cm^ will be somewhat greater, particularly in the fine gauges. 

 * Derived from reference 1 . 



required number of turns into the space provided : by multiplying the number 

 of turns by the mean length of turn, estimate the total length of wire required. 

 From the resistance per yard for the gauge of wire in use, compute the resis- 

 tance of the proposed winding; if this is less than Rmax, all is well so far, 

 if it exceeds Rmax, try the whole thing again with a bigger core. Assuming 

 the resistance criterion is satisfied, it remains next to investigate the amount 

 of magnetization that will be produced. We had in Chapter 4 that the 

 instantaneous e.m.f. across a pure inductance = K^N {d(f)ldt). If this equals 

 Kcos (ot, then, integrating, {Vlco) sin cot = K^N . 



V 

 or = K^Ncf)i 



COj 



-"max 



The maximum flux density, Bmax determines the degree of magnetization 



produced. 



^max ^ 



-Omax 



COr 



Cross-sectional area of magnetic circuit 



We are interested in the R.M.S. value of coil voltage, V, so 



(2)1/2 p y 



.K^NA 



5, 



max 



(OrninK^NA {ly/^TTK^NAFn 



311 



