# Inexpensive power factor correction

N

#### [email protected]

Jan 1, 1970
0
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 A #### Andrew Burgess Jan 1, 1970 0 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.

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.

N

#### [email protected]

Jan 1, 1970
0
Andrew Burgess said:
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.

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
My ignorance of the magnetic properties of coathangers
is almost total

However, 200 sounds as good as any other value.

Working back from a 1.8" diameter core of 0.36" radius gives an
inductance of 0.398 mH and a flux density of 1.60 T, so it looks like
you're on the right lines.

As I remark at

trial and error ... sorry, iteration, is the way to go. You are in
a somewhat different position since you are able to choose arbitrary
dimensions for your core, but the nice BASIC program is as good an
approach as any...

Nick

A

#### Andrew Burgess

Jan 1, 1970
0
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.

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!

N

#### [email protected]

Jan 1, 1970
0
Andrew Burgess said:
Hmmm. Doesn't solve the problem, the current runs in opposite directions...

It does?

Nick

A

#### Andrew Burgess

Jan 1, 1970
0

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...

N

#### [email protected]

Jan 1, 1970
0
Andrew Burgess said:
... left wire, A and B ends, right wire, A and B ends. Are you connecting
left-A to right-B?

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

Nick

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