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Starting a windmill project | DC Motor Generator Section | Making Propellers out of SCH40 PVC | Making an Anemometer for the Windmill | Charging Some Batteries | Notes and Updates
Charging Some Batteries
Ok, now we are ready to start putting the output of the generator to some use, or atleast store it for use later on....
Before we can charge any batteries we need some other things first, such as a blocking diode and a type of controller to monitor the battery charge levels.
Diodes are basically like a faucet, but it only lets water run through it in one direction. This will allow your generator to supply power to charge the batteries, but prevent your batteries from powering your generator, since it is a DC motor, once you connect the leads to the battery, it will start spinning and kill the batteries! So we will need a diode in series with every source we are connecting to the batteries to prevent the source from draining the battery charge. The generator output would be tied to the lug on top of the diode, then the battery will connect to the threaded end of it. An appropriate sized heatsink needs to be used since this will heat up if your passing some high currents through it. Do not let the heatsink touch any other metal parts on the sytem since this will create a dead short.I used a 40 Amp, 600 Volt blocking diode I got off of Ebay....
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Now onto the charge controller/battery charge monitor circuit....
Most solar panels come with their own charge controller, which are not suitable for wind or hydro generators. Charge controllers intended for solar panels work by monitoring the battery voltage, and once it reaches full charge, the controller simply shorts the solar panel leads together. This doesn’t harm the panels, but it does waste any power they are generating, and this energy ends up heating up the transistors in the controller. This type of controller will not work for wind or hydro generators, since shorting the output of a windmill generator while it is spinning at high speeds will generate a huge spike, which could possibly damage the controller and the generator. Simply unhooking the windmills generator output will let it free spin and over speed and possibly self-destruct.
The ideal solution is to charge the batteries until they reach a full charge, then switch to an alternate load where the energy can be safely diverted. This diverted energy should be used for some useful purpose, such as supplementing a water heater, or powering a peltier junction refrigerator, or divert the power to another battery bank. Most people would just route the power to a bank of 12-volt lights or to a dummy load consisting of resistors or heater coils in a pinch.
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So I did more research, and dug through my spare parts boxes ( I have A LOT of boxes full of "parts" I really need to find time to sort thorugh all of it!) until I came up with a viable low cost solution....
The function of this controller is very simple, the incoming battery voltage is divided in half by a pair of resistors, so you can adjust the desired trip points to one-half of the desired voltage, the actual trip points would depend on your particular type of batteries. A good starting point is 14.5 volts for full charge and 11.8 volts for discharge, so the test points (pin 2 of comparator IC) should show 7.25 and (pin 5 of comparator IC) 5.9 volts. You will need to monitor your system through several charge/discharge cycles to determine the perfect trip points for your system. The 2 potentiometers gives you the ability to adjust these trip points to suit the system. This circuit is very similar to a lot of other ones out there on the web, so I don't claim to have invented it, just redesigned to suit what parts I had on hand and possibly improve on its design to make it more versatile.
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The outputs of the controller are latched, and drive a pair of IRF640 MOSFETs, which serve as relay drivers. If you use a SPDT (single pole, double throw) relay (Shown in the photo is an automotive type relay, rated at 40 amps), only one output is necessary since the relay can switch the incoming power between the battery bank and the alternate load. The secondary output can be used to switch on a small 12-volt DC fan to exhaust the hydrogen gas from the battery enclosure to prevent an explosion when charging the batteries (See diagram below). This is a PCB I ran on my homemade CNC Mill/Drill, this is the first "production" one after testing of first prototype was successfull.
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I mounted the first prototype built on a breadboard into a NEMA13 type enclosure to give it some weather proofing. I placed my alternate load (which is a couple of 5 ohm, 25 watt wirewound sandbar resistors) inside the box with everything else.
I mounted 2 switches, the 2 LED's along with a charge level meter onto the cover of the enclosure and sealed everything with some hot glue.
The 2 switches provide a way to manually toggle between outputs when the system is in the “null zone” between the set trip points. 2 LED’s also serve as indicators to visually indicate what state the controller is in, RED for charging and GREEN for charged and switched to alternate load.
With a push of another button I can visually see the batteries charge level, or view the output of the windmill if it is charging the batteries. There is also a 25A resetable breaker for the incoming power, and other fuses to protect the monitoring circuitry.
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The batteries I had on hand were some 7.2 Amp Hour 12v Sealed Lead Acid (SLA) batteries, which I wired together to retain the 12 volts but triple my current output, so this should give me atleast 21.6 amp hours, not much, but a good start for more testing.
considering if I ran a 60 watt light off of this, I might get around 3.5 hours or about 210 minutes run time! Boy that sucks!
(I used an online calculator to get these results, the results do not include what the inverter would consume or loses due to system wiring.)
But soon I will be adding some deep cycle batteries with larger amp hour capabilities, as soon as I find some somewhere or get some for free hopefully....
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Everything was placed inside a water tight container and connected to the windmill, when I first connected everything the batteries where only showing around 11.59 volts at around 6 pm that night, the next day early am, the battery charge was at around 12.9
Still doing some more real world tests and improving on the system.. It has been up and running for a few weeks now and everything seems to work as expected.. next a battery desulfator to help in reducing battery sulfation....
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