For a seemingly simple setup, the wind turbine certainly involves a lot more that I ever thought it would. A lot of folk with ‘big’ turbines certainly view the small, chinese made end of the market as very suspect, but my view has always been that at least if the design is fairly simple, then I could repair it myself.
Just as well really, as that is exactly what I’ve had to do. The actual AC generator bit of the turbine is grand, but the weak spot seems to be the brushes and slip rings that allow the head to turn freely on the mast (we’re waiting for the second replacements to arrive).
I got so fed up waiting for them to arrive, in fact, that I’ve simply bypassed the slip rings altogether and now the cable runs direct from the head down the pole. The upside to this is that it seems a fair bit of power was being lost in the slip rings and now makes its way to the batteries. The only downside is that occasionally the whole turbine needs poked round with a very long stick if the wires get a bit twisted up.

Another modification I made is to add a dedicated steel line to pull the turbine up and lower it down on, as I’ve always worried about the strain that gets put on the stay line when we winch it up and lower it. Just in case….

The second problem we’ve had (about 3 times now) is the electronic controllers failing. To be fair to the suppliers, they have been very patient, and replaced units, until the latest failure, when it was explained in great detail to me how exactly to test the system to ensure that everything is sized and functioning properly.

There followed one of those ‘ah’ moments, when it dawned on me that the Extremely Vital dump load wasn’t big enough. In theory it was just about, and I assumed that it would do, but this turns out not to be the case.

So….now we’ve got controller number four, which is basic but does the job, and a variety of dump load resistors to absorb any excess power that comes from the wind turbine.

What have I learned? Firstly that some basic rules are immutable and need to be observed.

Your dump load really does need to be bigger than the turbine can produce. This is worked out as follows –

Amps  = Watts / Volts, so for a 400W 12volt turbine (with batteries at 14.2v), Amps = 400/14.2 = 28, and that is a peak figure for our turbine which is 300W but can put out 400W if the wind is really howling.

So to be able to absorb that ampeage, we need  a suitable resistive load.  As the amps = volts / resistance, then resistance required = volts/amps. Hence we needed a resistor of 14.2volts / 28 amps = 0.5ohm and that needs to be able to cope with 400W.

Having seen lots of dump load resistors with enclosures for lots of money, I found a link to Hugh Piggot’s page on wind turbines with a link to 1ohm 200W wire wound resistors on the RS components site. Connecting 2 of these in parallel should give you a 0.5 ohm resistor that can cope with 400w, (although I’ve added one other just in case). Hugh’s site also gives a much better explanation of the necessary workings out for dump loads than I can offer here.

Of course, since fitting the new controller and dump loads, we have been totally becalmed, so I wait with interest to see what happens when things get breezy.


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