N

#### [email protected]

- Jan 1, 1970

- 0

raised its power factor from 0.69 to 0.98, with an audible spark. A series

choke with 18/2 lamp cord ($31 for 250' at Home Depot) wound on a square

varnished steel coathanger core might limit the switch inrush current.

R. Clarke's nice web page on magnetism

http://www.ee.surrey.ac.uk/Workshop/advice/coils/terms.html#efarea

says magnetic flux Phi = IL/N = 0.04/N webers, and the max flux density

B = Phi/Ae = 1.6 teslas, to avoid saturating steel, so NAe = 0.04/1.6

= 0.025 = NPir^2, for a core cross section of radius r, and L = 0.004

= Mu0MurN^2r^2/Le henrys, where Le is the core perimeter in meters...

10 PI=4*ATN(1)'powfac

20 V=120'load voltage (rms)

30 P=61'load power (watts)

40 PF=.69'uncorrected power factor

50 XC=V^2*PF/(P*SQR(1-PF^2))'reactance (ohms)

60 C=1/(377*XC)'ideal PF correction capacitor (farads)

70 PRINT V,P,PF,1000000!*C

80 CS=12'standard cap value (microfarads)

90 C=CS/1000000!'standard cap value (farads)

100 IC=V*377*C'cap current (amps)

110 IMAX=20*P/V'peak cap current (amps)

120 DT=V*SQR(2)*C/IMAX'charging time (seconds)

130 L=V*SQR(2)*DT/IMAX'series inductance (henrys)

140 FRES=1/(2*PI*SQR(L*C))'resonant frequency (hertz)

150 PRINT CS,IMAX,L,FRES/60

170 MU0=PI*.0000004'free-space permeability

180 MUR=200'relative steel permeability

190 MU=MU0*MUR'absolute steel permeability

200 B=1.6'allowable max flux density (teslas)

210 NR2=IMAX*L/B/PI'Nr^2 constant

220 N2R2=4*L/MU/PI'n^2r^2 constant

230 WA=.1*.1/(39.37^2)'wire area (m^2)

240 NL=50'initial number of turns

250 R=SQR(NR2/NL)'core radius (m)

260 E=2*R+SQR(NL*WA)'square core edge (m)

270 N=N2R2/NR2*E'iterate

280 IF ABS(N-NL)>.1 THEN NL=N:GOTO 250

290 N=2*INT(N/2+.5)'round to even number

300 WIRELENGTH=3.281*PI*N*R'bifilar wirelength (feet)

310 PRINT N/2,WIRELENGTH

320 ECORE=39.37*E'core edge (inches)

330 RCORE=39.37*R'core radius (inches)

340 PRINT ECORE,RCORE

350 VCORE=4*ECORE*PI*RCORE^2'core volume (in^3)

360 LCOAT=36'coathanger length (inches)

370 DCOAT=.07'coathanger diameter (inches)

380 VCOAT=LCOAT*PI*DCOAT^2/4'coathanger volume (in^3)

390 NCOAT=INT(VCORE/VCOAT+.5)'number of coathangers

400 PRINT LCOAT,DCOAT,NCOAT

volts watts Power factor ideal PF cap (uF)

120 61 .69 11.78694

standard peak current inductance 60 Hz

PF cap (uF) (A) (H) harmonic

12 10.16667 3.343618E-03 13.2425

wire turns length

53 8.751237 feet

core edge radius

1.657399 in .3153355 in

coathanger

length diam number

36 in .07 in 15

Nick