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Inexpensive power factor correction

Discussion in 'Home Power and Microgeneration' started by [email protected], Feb 3, 2007.

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  1. Guest

    A 12 uF recycled motor run cap on the same extension cord as a 61 W fan
    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
     
  2. You probably know but didn't mention that you must split the
    zip cord and wind each wire in opposite directions around
    the coat hanger so the magnetic fields add and you get an
    inductor.
     
  3. Guest

    I shoulda mentioned my plan to leave the cord unsplit, but reconnect
    the pair in series, with the end of one wire going to the beginning
    of the other.

    Mr. Clarke has another web site. He writes
    Nick
     
  4. Hmmm. Doesn't solve the problem, the current runs in opposite
    directions so the fields cancel. That's how you make a
    non-inductive resistor ;-)

    I make something similar out of zip cord extension cords,
    splitting the wire but not cutting it, wrapped in opposite
    directions around a piece of water pipe, to act as a
    blocking inductor for X-10 signals. Works but boy does it
    humm when set on something made of steel! :)
     
  5. Guest

    It does? :)

    Nick
     
  6. Maybe I'm not picturing it right. The current runs down the
    left half, through your splice, then up the right half?

    Like a twisted pair without the twist?

    Or waitaminute.. left wire, A and B ends, right wire, A and
    B ends. Are you connecting left-A to right-B? I was
    picturing left-A to right-A...
     
  7. Guest

    Yes. So current enters left B and exits left A,
    then enters right B and exits right A...

    Nick
     
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