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_ Day 16
The changes were a great success, I may even add a 5th blade but I want to test it for a bit longer before making that call.
I also built a 5 Ohm dump load resistor today, nothing fancy & only a few hours work, getting the wire length, diameter, type & resistance was a lot more work.
The purpose of the dump load is when the turbine goes over speed or your batteries are fully charge you will want to stop the turbine from charging the batteries or creating to high a voltage. It would be easy to create a device to electrically disconnect the turbine but without an electrical load on the turbine it would accelerate in speed & can easily get out of control. So the idea here is to automatically disconnect the turbine in these conditions & automatically connect it to an electrical load that can handle the high power which will slow it down.
The main thing is to make a decision on where you want this extra power to go, it could power up a load of light bulbs although you would have these lighting up at strange times during the day & night plus the bulbs may blow. Actually adding or removing light bulbs until the turbine behaves the way you want it would be a good idea but I had another solution that I wanted to try.
One of the things I make & sell are hotwire cutters for cutting polystyrene, these cutters use Nichrome Wire (Nickel plus chrome) which is the same as any heating element wire. But because my hotwire cutters are 12 v I have a suitable range of different diameters that should work for a dump load. I say suitable because a toaster wire or heater element would normally have a larger diameter wire more suitable for mains power which would make it more difficult to use, although not impossible by wiring it up in parallel but a bit more precise & fiddly.
So when the wind was blowing I tested different gauge(diameter) wires & especially the lengths until I found a combination that would heat up enough during very strong winds to start to glow. This was a lot of trial & error until I got it right & the wind always seems to blow when it’s raining so I also got very wet.
The wire I ended up using is 5 ohms, 0.62mm & 1450mm bare Nichrome wire which I already sell by the metre. I coiled the wire around a strip of cement board & added a terminal post at each end as well as a fixing post at each end for securing to the back of a wall mounted box that I have yet to buy. You can use any none conductive strip that will not be affected by the heat but I had some of this cement board available & it is cheap. I bought the terminal posts for a few NZ dollars each but you could easily make something from some old bolts if necessary. I don’t think the dump load needs any further explanation, it’s fairly simple but depending on where you mount it you may want to think about how safe this is, the wire can get very hot. Mine will eventually be mounted inside a locked cabinet outside but I may still cover it just in case.