Never count your chickens before they are hatched …February 11th, 2011. Post by Quinta do Vale
… or your alternators before they’re run in.
We purchased this alternator from Presto Wind in the USA on the basis of its advertised power curves and a couple of videos showing no evidence of cogging, which was the problem with the first generator we tried. As soon as it was installed, it was running well over its claimed threshold for generating usable power, so it was just a matter of waiting for the bearings and rotors to run in and then the batteries would be getting some much-needed juice 24/7. Or so we thought …
After emails going back and forth for well over a month now, we (that’s me and my neighbours, who are installing a wheel on their part of the stream, and Wayne, the systems’ engineer) have a decidedly unpleasant taste in our mouths from our dealings with Presto Wind.
Our M-24 units are not producing anything approaching their advertised power curve. To begin with, when we had more water volume (it hasn’t rained in well over a month), they were producing about 50% of what they should be. Now it’s not even 30%. They’re not even producing enough power to contribute to the batteries and because of the particular way the company have responded and dealt with this, I’m taking the step of writing about our experience in some detail so others can read and judge for themselves.
At first we thought we must have got something wrong, but checking and rechecking the wiring found no errors and all connections were tight. I reported the low output to Presto Wind. The company asked was I sure the tachometer I was using to measure the rpm was accurate, but if we weren’t getting the expected output then something may be wrong. So far so good. I then, over the course of many emails, supplied full details of my system (and relevant details of my neighbours’) with photographs of all wiring plus regular updates on the rpm of the units and the power they were generating, making clear on every occasion that this was being measured open circuit with no load, which is the same conditions under which they produce their power curves. And we weren’t using a tachometer. We were counting wheel revolutions over a timed minute and multiplying that by the gear ratio, so we knew the rpm of the M-24s (+/-5% depending on whether you calculated the ratio by gear wheel diameter or number of teeth).
I frequently had to hassle them into responding after supplying them with information and getting no reply, whereupon I would be asked questions I’d already answered. After repeating myself several times and resending photographs, I was beginning to wonder if they’d paid attention to anything I’d sent, but still didn’t think more of it than that.
Eventually the company responded by saying there was nothing more they could do to help, claiming the underperformance could all be explained by water flow, wheel size, and other system components which, together with 35% efficiency, would easily explain our results. It wasn’t their PMA. It was physics. The units were installed and we couldn’t return them. I pointed out, as I had several times already, that not only was the water flow data irrelevant since we knew the rpm of the PMA (which they were obviously aware of, having asked about our means of measuring it), the rest of the system was completely irrelevant too. We were measuring the power open circuit straight off the rectifiers. And while 35% efficiency might be relevant to wind power, it was not appropriate for hydro. 60% is more the norm.
To prove beyond doubt that it was nothing to do with the rest of the system, we disconnected it all from the rectifiers, measured the power at the rectifiers in exactly the same manner as their demonstration videos (and of course got the same readings we’d been getting all along), took photos of it all, and sent that off with a request that they respond within a week. No response.
I emailed again, saying we wanted to return the units under warranty for a full refund because they were not performing as advertised. This time their explanation for the units’ underperformance was that we must have ‘damaged’ them, despite the units being installed by a qualified engineer in exact accordance with their instructions and with them having seen photographs of the installation and being able to identify no error.
During the course of the exchange, I asked them at least 3 times to confirm the basis of the relationship between rpm and power output in their permanent magnet alternators, because to do this would focus the discussion on the precise nature of the problem and clarify whether there was a fault in the units or whether they were making false claims for their performance. They ducked the question every time. When I sent an email asking just this question, they answered a different question.
We are still trying to get our money back, but it looks very much as if we’ve been had.
Since this has happened, we’ve heard reports of other people using these units in wind applications and finding the same underperformance, including units that have been re-badged for another company. And there’s posts on forums (here and here) suggesting that the company’s advertised power curves are intentionally deceptive.
So we’re back to looking for the right generator again. Intensely frustrating, particularly since Wayne hasn’t had to use a generator all winter with his wheel. Even though it’s now producing only 100W with the river being so low, his batteries are still full every morning. Unfortunately the PMG on his installation is no longer in production. Wayne is beginning to think about building one himself …
(The bottle of Portuguese cava was very good though. That I can recommend.)