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Efficiency of a Waterwheel

Overshot

85 to 90% Metal Waterwheel

70% for a Wooden Waterwheel

Undershot

60% Poncelet Waterwheel

30% River Wheel (Simple Paddles)

You need to determine how much power your site potentially might have.

For an Overshot Waterwheel

To do this you will need to know two things, the quantity of water and the height of the water fall. From this you can determine the Horsepower at the axle of the waterwheel.

One method to determine the quantity of water is to do a Weir Gate measurement. To use this method, click on the link for the Weir Gate Page.

** The height is the number of feet off the ground the water falls over the waterwheel.

** Weir gate numbers are in CuFt/Min. Remember to divide the number by 60 to get CuFt/sec. Then use the formula below to get your power number.

Horsepower = Constant x Quantity x Height x Efficiency

or

HP = Constant x (Cubic Ft / Sec of water) x (Height of Fall) x (Eff. of Wheel)

Waterwheel Horsepower @ Shaft 85% Eff Factor for the waterwheel

WaterWheel Diameter

Gallons Per Min 10 Feet 12 Feet 15 Feet 18 Feet 20 Feet

100 .215 .258 .322 .387 .430

200 .430 .515 .644 .773 .859

300 .644 .773 .966 1.160 1.289

400 .859 1.031 1.286 1.546 1.718

500 1.107 1.289 1.611 1.933 2.148

800 1.718 2.062 2.577 3.093 3.436

1000 2.148 2.577 3.222 3.866 4.295

1500 3.222 3.866 4.832 5.799 6.443

2000 4.295 5.155 6.443 7.732 8.591

3000 6.443 7.732 9.665 11.598 12.886

Example

Horsepower for 800 gal/min @ 15 Feet

*****

Horsepower = C* Q* H* E

*****

C= Constant (See Below)

Q= Quantity of water

(for cu/ft/sec multiply gal/min by 0.002228 )

H= Distance over Waterwheel

E= Efficiency of the Wheel

****************************************

Gallons/min to Cubic Feet/Sec

100 Gallons = .223 Cu/Ft/Sec.

200 Gallons = .446 Cu/Ft/Sec.

300 Gallons = .668 Cu/Ft/Sec.

400 Gallons = .891 Cu/Ft/Sec.

500 Gallons = 1.114 Cu/Ft/Sec.

800 Gallons = 1.783 Cu/Ft/Sec.

1000 Gallons = 2.228 Cu/Ft/Sec.

1500 Gallons = 3.342 Cu/Ft/Sec.

2000 Gallons = 4.456 Cu/Ft/Sec.

3000 Gallons = 6.680 Cu/Ft/Sec.

________________________________

Horsepower = .1135 * 1.783 * 15 * .85

Horsepower = 2.58

Where did the constant come from

Constant = (Water Weight lbs.) / (foot-lbs/sec)

Constant = (62.42 / 550.221)

Constant = 0.113491

1 Horsepower = 746 Watts

To get electricity out of a waterwheel you will have to gear the RPMs of the waterwheel (generally from 5-10 rpm”s up t0 500 - 1700 rpm’s) and then run it through a generator or a DC motor to charge a battery bank. This will generally cut your power at the axle HP by almost 1/3 to 1/2. A waterwheel is really designed to do mechanical work.

Most homes require 4000 to 7000 watts of power for simple operations.

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