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Simple Windmill/Solar controller

Based on a TL084 op amp,
this is a easy to build controller
suitable for wind and
solar applications.

Build a encapsulated load resistor.

Page 1 | 2 | 3 | 4

Back to Page 2 This started as a 1Kw load resistor for around 29 volts.
Holes were punched in a sheet of stainless sheet
Better to punch the holes rather than drilling as it gives support to the resistors on the other side
A copper tube coil was made from 3/8 (10mm ) tube, and wound in a oval, around 2x pieces of 30mm steel tube clamped together. It is important to wind straight around and only cross over to the next coil at one end of each oval loop (easier said than done)
The cross over of coils will end up on the inside of the resistor hoops. For this reason the copper coils need to be made and located first, so the resistors can be inserted in over the copper pipe.
Here the electrical wiring is part way done. A male spade crimp terminal with the plastic bit removed, is crimped to the ends of each wire. It is important to ensure the nichrome wire is also crimped together with the copper securely. I would prefer a ceramic terminal block but they are expensive and hard to find. After fitting terminals Teflon tape is wrapped around the wire between terminal and resistor. The tape is also packed into the end or the resistor 4-6 mm where some of the mineral core material was removed. Teflon tape acts as a insulator for heat and electrical, and support for the wire. This is only built as a demo to show what can be done. The actual wiring method and configuration, is more so left to the end user to choose and construct.
MOUNTING For the heat exchanger to work it will need to be mounted in a vertical position with the cold water feed in connected to the bottom tube (inlet) The top tube being heated water out (outlet) If this was connected to a container full of water ( a water heater ), the heat exchanger inlet would be connected to an outlet located at the bottom of the container, and the heat exchanger outlet connected to an inlet in the container at a height not less than the height of the top coil. The water level in the container should be above the outlet side of the copper tube at all times ( higher than both copper tubes). Thermosiphon will then move the water from the container through the heated coils and back to the container. Some care should be taken not to get an air lock trapped in the copper coils. Should this system run dry of water than I can see no problems, other than the resistors running a little hotter due to less airflow around them, with the coils installed.

ELEMENT CHOICE

There is an endless selection in the choice of elements you might choose to modify, the best ones are what you have or get for free.

If I had a choice I would look for the longest in length with as little bends in it as possible. The longer elements with lower wattage ratings appear to have the heavier gauge in nichrome wire, being easier to work with. One element not tried but would think it to be a good source, is the element used in the Simpson clothes dryers and most likely other brands. They are a round ring of about 600mm dia, giving around 2mtrs of element. Worth a try if you have one!! ( I threw a heap out 6 months ago )

The elements used for the project was one I found in the shed from a dishwasher and the others purchased second hand for $2.00 each at a junk yard (oven elements). If removing the elements from a discarded stove then take a bunch of the wire used in the stove, as it has high temperature insulation and most times a female spade terminal on the end. Great for wiring the resistors up with ( and its low cost ).

Even if the elements were to be purchased new at a guess of $50.00 each, it would still be cost effective considering some of the other choices. I much prefer low cost or free, as there is nothing to loose and lots to gain.

The element above has 2 x 1200 watt (240v) elements in it, and would yield 6 x pre made hoops if cut on the line made by the rod resting on top. At a guess this would give 6 workable resistors of around 5 amp at 29 volts or about 150 watts each.

This resistor to the left was made from a submerged element water heater. The mounting end was removed from the original element and reattached with silver solder to a cut down section of element to show it is able to be done.

Please note :- This project was only constructed to show what can be done, and has only been tested in simulation from a transformer and not tested in a field application. I see no reason why it will not preform the same if used in a RE field situation. Watts of energy lost in resistors = heat, and no matter how the energy is dispersed the same amount of heat will be generated, weather it is over 1 resistor or spread across 10 resistors the combined heat will be the same.

For this reason care should be taken in the mounting and the location of the resistor bank with some protection of the resistors implemented as theses will run very hot (even glow red in some cases) whist under load. Remember they are a heating element in every form.

I welcome any input to this project and any feed back from someone who has used modified encapsulated elements before, or anyone who constructs one from information given above. hope it helps.

Happy Tinkering.

From Pete (Downwind).

Next Page - My own encapsulated resistor dump load