R.K. Fromm

FORMULAE

Ohm's Law:

Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)

Power - A/C Circuits:

Efficiency = 746 x Output Horsepower
                  Input Watts

Three-Phase Kilowatts= Volts x Amperes x Power Factor x 1.732
                                          1000

Three-Phase Volt-Amperes = Volts x Amperes x 1.732

3-Phase Amperes =            746 x Horsepower
                  1.732 x Volts x Efficiency x Power Factor

3-Phase Efficiency =           746 x Horsepower
                      Volts x Amperes x Power Factor x 1.732

Three-Phase Power Factor =        Input Watts
                             Volts x Amperes x 1.732

Single-Phase Kilowatts = Volts x Amperes x Power Factor
                                      1000

Single-Phase Amperes =        746 x Horsepower
                       Volts x Efficiency x Power Factor

Single-Phase Efficiency =        746 x Horsepower
                          Volts x Amperes x Power Factor

Single-Phase Power Factor =   Input Watts
                            Volts x Amperes

                                Volts x Amperes x 
Horsepower (3-phase) =  1.732 x Efficiency x Power Factor
                                      746

Horsepower (1-phase) = Volts x Amperes x Efficiency x Power Factor
                                          746

Power - D-C Circuits:

Watts = Volts x Amperes (W = EI)

Amperes = Watts  (I = W/E)
               Volts

Horsepower = Volts x Amperes x Efficiency
                         746

Speed - A-C Machinery:

Synchronous RPM = Hertz x 120
                  Poles

Percent Slip = Synchronous RPM - Full-Load RPM  x 100
                          Synchronous RPM

Motor Application:

Torque (lb.-ft.) = Horsepower x 5250
                         RPM

Horsepower = Torque (lb.-ft.) x RPM
                     5250

Time for Motor to Reach Operating Speed (seconds):

Seconds =       WK2 x Speed Change
          308 x Avg. Accelerating Torque

WK2 = Inertia of Rotor + Inertia of Load (lb.-ft.2)

Average Accelerating Torque = [(FLT + BDT)/2] + BDT + LRT
                                           3

FLT = Full-Load Torque             BDT = Breakdown Torque

LRT = Locked Rotor Torque

Load WK2 (at motor shaft) = WK2 (Load) x Load RPM2
                                  Motor RPM2

Shaft Stress (P.S.I.) =   HP x 321,000
                        RPM x Shaft Diam.3

Centrifugal Applications: Affinity Laws for Centrifugal Applications

Flow1 = RPM1
Flow2   RPM2

Pres1 = (RPM1)2
Pres2   (RPM2)2

BHP1 = (RPM1)3
BHP2   (RPM2)3

For Pumps:

BHP = GPM x FT x Specific Gravity
       3960 x Efficiency of Pump

BHP = GPM x PSI x Specific Gravity
       1713 x Efficiency of Pump

Head in Feet = 2.31 PSIG

For Fans and Blowers:

BHP =          CFM x PSF
       33000 x Efficiency of Fan

BHP =          CFM x PSW
       6344 x Efficiency of Fan

BHP =          CFM x PSI
       229 x Efficiency of Fan

Where:
BHP  = Brake Horsepower
CFM  = Cubic Feet per Minute
FT   = Feet
GPM  = Gallons per minute
PSI  = Pounds per square inch
PSIG = Pounds per square inch gravity
PSF  = Pounds per square foot
PIW  = Inches of water gauge
Specific Gravity of Water = 1.0

INDUSTRY ABBREVIATIONS

cm = centimeter
cu. = cubic
ft. = foot
gl. = gallon (US)
gr. = gram
Imp. = Imperial
in. = inch
kg. = kilogram
km. = kilometer

l. = liter
lb. = pound
m. = meter
mi. = mile
oz. = ounce
qt. = quart
std. = standard
US = United States
yd. = yard


LENGTH MEASUREMENTS

Common Usage
1 ft. = 12 in..
1 yd. = 3 ft.
1 rod = 5.5000 yd.
1 furlong = 40 rods
1 mile = 8 furlongs
1 mi. = 5,280 ft.
1 mi. = 1,760 yd.
1 fathom = 6 ft.
120 fathoms = 1 cable
1 league = 3 mi.
1 nautical mi. = 6076.11 ft.
1 hand = 5 in. (equestrian)

Reciprocal Value
1 in. = 0.0833 ft.
1 ft. = 0.3333 yd.
1 yd. = 0.1818 rods
1 rod = 0.0250 furlongs
1 furlong = 0.1250 mi.
1 ft. = 0.000189 mi.
1 yd. = 0.000568 mi.
1 ft. = 0.1667 fathom
1 cable = 0.00833 fathoms
1 mi. = 0.3333 leagues
1 ft. = 0.000165 natical mi.
1 in. = 0.2000 hands

METRIC
1 in. = 2.54 cm.
1 ft. = 30.48 cm.
1 m. = 3.2808 ft.
1 m. = 39.37 in.
1 m. = 1.0936 yd.
1 rod = 5.029 m.
1 km = 1000 m.
1 km = 0.621 mi.


1 cm. = 0.3937 in.
1 cm. = 0.0328 ft.
1 ft. = 0.3048 m.
1 in. = 0.0254 m.
1 yd. = 0.9144 m.
1 m. = 0.1988 rod
1 m. = 0.001 km.
1 mi. = 1.6103 km.


SQUARE MEASURES

Common Usage
1 sq. ft. = 144 sq. in.
1 sq. yd. = 9 sq. ft.
1 sq. rod = 30.25 sq. yd.
1 sq. mi. = 640 acres

Reciprocal Value
1 sq. in = 0.0069 sq. in.
1 sq. ft. = 0.1111 sq. yd.
1 sq. yd. = 0.0331 sq. rods
1 acre = 0.0016 sq. mi.

METRIC
1 sq. cm. = 0.1550 sq. in.
1 sq. ft. = 0.0929 sq. m.
1 sq. m. = 1.196 sq. yd.
1 hectare = 2.47 acres
1 sq. km. = 0.386 sq. mi.



1 sq. in. = 6.452 sq. cm.
1 sq. m. = 10.7643 sq. ft.
1 sq. yd. = 0.8361 sq. m.
1 acre = 0.4049 hectares
1 sq. mi. = 2.59 sq. km.