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Author Topic: Multible Wind turbines  (Read 2560 times)
Terryp
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« on: August 08, 2006, 12:48:59 PM »

I have a 24 volt battery system, but I require a 1KW turbine.  Can I connect 2 x 500w turbines and if so how is the best way of doing it.

Terry
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Ian
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« Reply #1 on: August 08, 2006, 10:59:08 PM »

Terry - Yes you can.

Connect them in parallel (join both positives together and both negatives)- AFTER the controllers. You now effectively have a single feed into the batteries (via a diversion load controller I hope).

I hope this helps.

Regards,
Ian
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Terryp
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« Reply #2 on: August 09, 2006, 11:14:07 AM »

Dear Ian,

As you can guess I am a new at this.  Am I right that the Navitron  500w 24v turbine Kit produces 24v AC and the Navitron kit supplied Rectifier/controller changes this charge to 24v DC.  I then have to feed both loads from the rectifiers to a a single diversion load controller which feeds it to the batteries.

Regards

Terry
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Ian
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« Reply #3 on: August 09, 2006, 07:49:40 PM »

Terry - spot on.

The Navitron wind turbines are PMAs (permanent magnet alternators). The name gives it away - it produces AC. The actual voltage and the frequency developed is directly proportional to the speed of the turbine. When the turbine just starts to turn, maybe a couple of volts are generated. When it starts to turn at a reasonable speed, maybe 20 volts are generated and when going absolutely flat out all sorts of high voltages could be generated - maybe up to 100 volts (yes from a 24 volt turbine) if open circuit.

A generator tries to shift electrons. If there are no electrons moving, there is no effort required, so the effort going into turning the generator is turned into a greater oomph (voltage) trying to shift them. So the voltage climbs. When electrons start to flow (current) - this requires work so some of the energy used to turn the generator is now diverted away from the oomph and goes into keeping the supply of electrons going. So as the current (amps) increases the voltage decreases.

The controller takes the AC coming out of the generator and rectifies it to DC. This is a very simple process using diodes and explains why some bits of the controller get a little warm when the generator is doing its thing. If you measure the AC voltage coming out of the generator and the DC voltage coming out of the controller, you will see that the DC voltage is about 1.41 times more than the AC input. So if the geenrator is pumping out, say, 20 volts ACrms, then the controller will convert it to about 28 volts DC.

Now, a 24 volt battery will not actually be 24 volts! It will usually be made up of individual batteries that themselves are comprised of 6 individual cells within the battery case. Each cell when fully charged will produce about 2.1 volts DC. Six of them together will produce a "12 volt" battery of 12.6 volts or so. Two of these batteries connected in series to give "24 volts" will actually measure 25.2 volts or so.

To charge a "12 volt" battery you need more than 12.6 volts. Usually 13.8 volts is given as the voltage to fully charge a battery. (There are a few complications here as different battery variants have different fully charged voltages and the end of charge voltage for them can be a little different but none of them go over 15 volts charge voltage at full charge.)

So a 24 volt battery set will require at least around 27 - 28 volts to charge the set fully, not 24 volts.

Back to the generator. Even though the generator can provide a higher voltage, we have seen that the voltage is (sort of inversly) proportional to the current provided. So if you connect the generator (via the controller) to a battery set - the generator will try to shift electrons as current (amps). No current will flow until at least the actual voltage of the battery is achieved. At this point, current will start to flow. If the generator is turning slowly, then the current will be low. If the generator is truning fast, the current will be higher. The voltage will only be as high as is required in order to maintain that current flow.

So, a Navitron (or any other) "24" volt turbine will not send out a fixed 24 volts. It just provides at least this voltage at its rated output current at its rated performance criteria. The windings in the generator (number of turns and thickness of wire) have been designed to do this.

As you can see from the above, once the battery set has reached its fully charged state (lets say it is 26 volts just to keep a little trickle charge going) in order to protect the battery set from overcharging we need to stop pumping current in. However, the generator will just keep upping the voltage becasue all it wants to do is move electrons around. There is a conflict here. This is why we use a diversion laod controller.

The dversion load controller makes sure that the battery set does not get boiled dry. It does this by diverting power from the battery set to something else. This keeps the batteries happy and it also keeps the generator happy.

I hope this helps explain a little more. Sorry if it tries to teach you to suck eggs!

Regards,
Ian
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mtimm
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« Reply #4 on: August 09, 2006, 09:43:49 PM »

A very good and comprehensive reply from Ian as usual,
Just to add that the turbine generating ac rectified to dc to charge batteries is exactly the same principle used in every car charging system today. The only difference is that car alternators have the rectifiers/ regulators built into them
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