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Understanding Swept Area

A look at how the swept area,
and therefore the power, of a
turbine changes with diameter.
Chainsaw blades! Page 1 | 2 | 3 | 4 | 5

Back to part 2

Ok, Test results.

Here is a graph of rpm/watts. I have placed a line of best fit for the prop curve. TSR 6 was just far too much, TSR7 and the figures were impossible. TSR 6.5 closely fits the results, and the wind conditions on the day/s. According to the weather man, no gusts were recorded greater than 30kmh so TSR6 was not possible by a long way. It was a clam day by our standards. I think 20 mph would have been as good as it got. (32kph).

I was not good enough to read three meters at once, so had to use a camera to do it for me, and this had it's own problems. The other problem was the sheer amount of power going into the batteries when I started this. They were truck batteries(which I grabbed out of the grader and dozer just to have a 48v load.
They are 700cca batteries, so I thought they weren't sissies, and that they could stand a bit of a belting ....not so. After setting things up in a small trailer, and getting organised, the batteries went from 13v/batt to 17v/battery in no time with 20 or so amps pushing in....

So the first shot looks like this 68.3v@18A= 1230 watts, and the batts didn't like it much.

So I waited for the wind to die down a bit (didn't feel very strong at all anyway). Later in the afternoon, it was peaceful, and the readings looked more like this...still high voltage, but amps had calmed down a lot (batteries won't love me after this. Meter on left is rpm/10

Note the voltage is about the same, but the batteries are not taking much charge now and probably only registering electrolysis if the truth be known. Had to stop this pretty soon, but took a number of readings... hence the graph.

The blades have now got a few coats of epoxy paint on them now, and look like this:

The tail is temporary to get the right weight and size for furling.

All in all, these chainsawn blades work far better than I had expected for such a quick effort.

Here is a pic of the test setup including the three phase 3kw motor I used as an initial load, it went over 1440 I think, and created a lot of air flow with that fan. At one stage the mill was driving it full speed and putting 19A@70v into the batteries at the same time (1.3kw for batts plus another 3-400w for the induction motor.... )

For those wondering what the performance is at ground level with a mill, here is an example of a few minutes power recording every 20 seconds.

That should read time in seconds. The interval used was in 20 sec blocks...

Having way too much fun down here

Next Page - An update

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