No matter how much effort goes into the attempt to get it right first time, inevitably, and most especially with experimental technologies, there’s a teething problem or two …
With rainy days becoming more frequent now – so that finally, after a long dry summer, there’s more than 1 litre per second coming down the barroco – we’ve had the chance to finally commission our water wheel installation and see how much power it’s capable of generating.
So far, next to nothing.
With the stream in full spate, it was generating power, until a particularly heavy downpour sent a massive surge of mud and rocks down the barroco and washed away the temporary dam we’d built to direct water down the wheel chute.
After rebuilding a more robust and permanent dam and playing around with gear ratios for a bit, we finally had to recognise that the Miniwind 2200W-24V permanent magnet generator is not suitable for this site. It had looked perfect on paper, but in practice, it has too much resistance – cogging torque or ‘magnetic reluctance’ – to allow the wheel to reach effective generating speeds with our average water volumes.
With the stream in full spate, the water wheel was maxing out at 52rpm (though had been capable of 65rpm at only 2 litres per second before the PMG was hooked up and a maximum velocity of around 100rpm freewheeling). For a 24V system such as ours and with a 4:1 gear ratio, the water wheel needs to be turning at 50rpm (ie. 200rpm for this particular PMG) to start producing 24V power.
Consequently, this generator needs to be in a situation where the water wheel is continually running close to its maximum capacity, ie. where water volumes are very much greater. And unfortunately this particular model is wired internally in delta mode so can’t be switched over to star by altering the wiring configuration on the rectifiers (which would enable it to contribute at less than 24V).
After a lot of internet research, Wayne (the wheel’s engineer) has managed to source a permanent magnet alternator designed specifically for low wind (and consequently low water) situations. The Presto Wind M-24 claims to be capable of generating 24V power at only 80-100rpm. This particular generator is a dual output system: effectively 2 generators in one with 2 rotors and 2 stators, meaning that the magnetic reluctance is half that of a single generator. Since the water wheel in its present configuration is capable of 20rpm at flow rates of 2 litres per second, this PMA would generate power. And with half the resistance, at 2 litres per second, we should theoretically be getting somewhere nearer 40rpm out of the wheel.
It’s on order. Watch this space! (And the Miniwind PMG already has a new home lined up in a situation with much greater water volumes.)