Switch box   Back to Electrics
 
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Power from the turbine needs to be connected to the batteries, and also to the load. When working on the turbine, such as when putting it up, it is desirable to short out the coils so that it will not spin. So the first requirement is some kind of connection and switch box.

Of course, before shorting the turbine, the battery needs to be disconnected, so it is best to have a single switch that simultaneously disconnects the battery and the turbine, and also shorts out the turbine coils. This requires a DPDT switch.

However, shorting out the turbine when it is spinning fast can cause a lot of mechanical stress, especially if it uses powerful magnets. So it is best to have a two stage brake - the first puts a very low resistance load across the turbine (and also disconnects the battery from the turbine), and the second phase puts a dead short across the turbine. So that requires a second SPDT switch.

Its often useful to know how much current is coming from the turbine, and to make it easy to measure this, a 'divert' is useful. This allows an ammeter to be plugged into the box, and a switch which diverts the incoming current via the ammeter. This requires a SPST switch and two banana plug sockets.

Similarly, it can be useful to measure the current coming out of (or going into) the battery, so the same arrangement is needed to do that. That makes another SPST switch and two banana sockets.

Finally, it can be useful to measure or use the power, so a positive and negative banana socket are useful. I also add a DC power type socket which I use for charging my 24V electric scooter.


Here is the back of the front panel.

Its convenient to make the box so that the front panel screws off. That way its easy to work on the wiring.

The box itself is made from a meranti plank 95x12mm. Only crosscuts are required, and the pieces are just glued together with wood glue.

This is a 'left handed' box, where the wires will be connected on the left side. The box below is a 'right handed' one.

And here is the finished box. The labels for the front panel are printed on transparency which is then glued to the front after punching out holes as needed. Tip: print a reversed image, and then the ink will be protected by the transparency.

Here I have used ceramic connector blocks for the incoming and outgoing wires. The ceramic can take a lot of heat, but you could also use plastic connector block strips. Be carefuly however, as with 20 amps or more flowing they can get hot or even melt. Make sure the wires are screwed in tightly, as loose connections cause a lot more heat.



Here are some older switch boxes I made.

I experimented with printing the front panel on plain papers, and epoxying it into the plywood front panel. As you can see, the finish is not as good as the one above.

You might ask why I made the two boxes separately, and not all in one enclosure. Well... mainly because I made them over time. However, having them modular is really useful. For example, with the batteries still needing a bit of charge the dump load controller can be safely disconnected and worked on. Or the main battery connect box can be disconnected, leaving the dump controller to prevent turbine overspeed