Designing a drive belt
The simplest drive would be a belt drive running off the outside rim of the 2m wheel to a notched pulley, similar to a very large cam belt in a modern car. This pulley would have to be (2000/33.
59mm (say 60mm) in diameter - a good simple solution. To ensure the wheel runs true, the timber wheel edge can be machined in-situ with an electric planer. A concave surface will ensure that a timing belt (correctly tensioned) will run true on this machined surface. Buying a belt this long may be a problem as it may need to be 10m long. Also such a long belt may need support rollers to prevent oscillations of the belt in the straight sections between the 2 wheels.
If you search
https://www.aliexpress.com for “open ended timing belt W=30mm” you will get some hits. Look for 5mm pitch, polyurethane with steel core. These you can run at about 25N/mm, so for 30mm wide that is 750N of tension (76kg).
Power = torque x angular velocity
Torque = belt force x belt radius
= 750 x 0.060/2 = 22.5 Nm
Angular velocity = rpm x 2 x pi / 60
= 500 x 2 x 3.14 / 60
= 52.3 radians/second
www.powerspout.comEcoInnovation Smart Drive Applications Manual
© 2016 EcoInnovation Ltd (NZ) Page 35
This power belt can transmit = 22.5 x 52.3 = 1176W.
The mechanical power = electrical power / PMA efficiency = 500W/0.8 = 625W (less than 1176 W).
So such a solution is possible, but it only works for low power wheels that can use mass-produced timing belt material. Once set up it is a simple low cost solution.
Joining such a belt is tricky but can be done by sticking a 1m length over the join and then stitching them both together between each tooth. Clearly a join will not be as strong as the base material, so 625W would be a realistic rating for such a belt and should run for many years.
Another possible option is to attach such a belt to the outer rim of the wheel, teeth facing out and drive your 60mm pulley directly against this. The pulley will only have very limited tooth contact but with so many teeth on the large wheel it will still take a long time to get worn. Power rating will be less due to small tooth contact area, so it likely to be suited to 100-200W water wheels only.
The PMA is easy to select:
rpm = 500
Vmp= 28 VDC for 24V battery bank on charge and allowing for some cable loss let’s call this 30V
Vmp = V/rpm (from table) x rpm / 0.57
Hence V/rpm = Vmp / 0.57 / rpm = 30 / 0.57 / 500 = 0.105
From the table a 60R110-2s-6p-S would work well.
If we wanted to use a 150V MPPT controller then a PMA with a V/rpm almost twice as high would be suitable, but there is a danger of damage if the Voc gets too high in a runaway situation. Always check after the Smart Drive PMA has been installed and prior to connecting the MPPT controller that the runaway voltage (with full water flow onto the wheel) is under 140 VDC.
You can still use our online calculation tool to do cable loss calculations. Just select the PLT tool and enter data to get the same generation Watts (500W in this example). You can then enter your cable length and locate a suitably sized cable and see the % power lost in the cable selected.
For larger wheels, a mechanical multi-stage gearbox will be required, as can be seen in the picture opposite. This gearbox was located at a scrap yard and ran for over 10 years powered by a 4m water wheel that we made and installed about 20 years ago.
Below are some waterwheels we have made over the years. This was prior to us making the PowerSpout LH range of turbines