Permaculturing in Portugal

One family's attempts to live in a more planet-friendly way

Hydro power commissioning

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.)

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  1. Andre May 11, 2011

    Hi guys!
    How are you getting on with the Presto Wind M-24?
    Wayne’s page has moved and your link is now pointing to the wrong page.
    Do you know the new page?
    I’m gonna have a look at the rest of your blog now.
    Keep us updated.

  2. Andre May 11, 2011

    I see I should have read “Never count your chickens before they are hatched …” before commenting.
    Sorry that it didn’t work as well as expected.
    I don’t understand anything about these systems but wouldn’t 12v be better for the flows you have or doesn’t the voltage make any difference??

  3. Quinta do Vale May 11, 2011

    Hey Andre!

    Ah! I see you found the next post! Yes, the Presto Wind M-24 was a complete waste of money. Apparently, according to the hydro power experts I’ve since talked to, this applies to all generators based on car alternators. We’re still working on it – have got another PMG installed now, and we’ve lengthened the chute to increase head and converted it to contain plastic guttering to minimise friction losses, but the rainfall has been so low this winter that water volumes have now fallen below the generating threshold. We’re getting there, but v e r y s l o w l y …

    And yes we could produce usable power for a 12V system but the idea is to integrate the hydro with our solar capacity. Our initial calculations showed that we ought to be able to produce enough power from the stream to charge batteries in a 24V system. We went for 24V and an inverter because we need to eventually supply power to 3 separate locations on the quinta and AC power travels so much better than DC. The cost of cabling for 12V DC would be prohibitive and separate systems for each location wouldn’t work because 2 of them get no sun in winter.

    Thanks for letting us know about Wayne’s site. It hasn’t moved, but perhaps they’ve forgotten to renew the domain/hosting. Will let them know.

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