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Connecting two turbines

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I have two identical 300Watt 48volt turbines that I want to connect together electrically so I don't have to use/buy two charge controllers. A single charge controller can handle the combined current.

They are wired in three phase star configuration.

Can I simply connect the + and - wires after the rectifiers? or would there be nasty feedback if say one of the turbines was not running??

Would connecting the centre tap of each turbine to each other help?

Wind turbines? In the same wind?

Electrically I don't see a problem. If one of them is not running, the diodes would disconnect it. If the controller is a maximum power point type, it might get a little confused; in particular if one of them is getting less wind, some of its available output may be lost.
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If the turbines output wild AC then you can't connect them in series as trying to synchronize the phases will be near impoosible. the only way is the put the rectifiers at the base of each tower and transmit DC volts. Then you can connect as many turbines as you want.

Cheers Bryan
It appears that my answer was confusing to some. I assume that you are connecting the DC outputs together
connect the + and - wires after the rectifiers
as you said in your original post.
yes (and to lengthen the answer to meet minimum forum requirements I put this in brackets)

Yes the DC will be connected in parallel
Well I tried connecting DC outputs together (with a lot of fuses to protect everything just in case) and no luck. The inverter (grid tie) has MPPT so as mneary said this might be the problem. I put a multimeter between the "bolted on" turbine and the primary turbine and it got to half an amp at times (not a lot of wind) but the total input into the grid did not change much from a single turbine. ie I was able to break the connection between the two by disconnecting the multimeter.

Would connecting the centre points of the two turbines (in star config) help? ie it provide a common reference point between the two turbines.

Out of ideas

You should be fine. Assuming the wind gen's are permanent magnet type their voltage will rise or fall based on current load for a given RPM.

Tieing them together after the rectifiers should be fine. You cannot push current from one into the other because of the rectifier diodes.

The MPP controller will load the pair to maximize the V*I. If one is rotating slower it just won't contribute as much current. I haven't thought about it too much but on rough guess I would say a wind MPP controller probably needs to react faster then a solar MPP controller to changes in output.

Even if MPP controller is slow to react, if one turbine speeds up the other one will also speed up as the electrical load is lightened on it by the turbine pushed by higher wind.

I would not rely on a multimeter to measure the current as the resistance may be too high for an accurate measurement. Try to use a shunt with millivolt meter. The inexpensive 200 mV LCD modules work good with shunts.
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Try disconnecting the "primary" generator and see how much power you get from the "bolt on" unit alone. Hopefully it's about the same. These are separate windmills, not on the same shaft, correct? As RCinFLA said, in the wind they should equalize naturally.
I think the only way you may be able to get the lower power ones energy out is by having to treat it separately. As mentioned before the stronger one will have the greater voltage and put its power out first. The lower voltage one will basically do nothing until its output voltage is equal to the other one.
Anytime one gets more wind its going to become the power producer while the other one will be unloaded.

Have you tried putting them in series?
By doing that they will share a common amperage in regards to their combined outputs and being rectified AC the lower powered one will just let the current pass through if it cant keep up.
When it does spin it will add a small amount of voltage at low speeds still and that should keep its load under control within reason.
However the total combined output voltage may cause problems at high wind conditions with the regulation system or what ever your dumping the power into. Maybe.
Its worth a try just to satisfy curiosity's sake if nothing else.;)
Thanks tcmtech,

"Anytime one gets more wind its going to become the power producer while the other one will be unloaded"

This should work well then if they are in the same wind. One will unload, speed up, generate more, unload the other and the cycle continues with the average output improving but I suspect not twice the expected output.

"Have you tried putting them in series?"
Yes I have. My concern has been the extra current flow may be too much for the turbines. The voltage I can handle with a brake.

The best outcome and most power will be gotten by having a separate controller for each wind turbine, that is, if you're gonna use a wind MPPT controller.

Otherwise, just tie them in parallel on the DC side to the one battery bank and use the one diversion controller.

well I have had to give up. There seemed to be no improvement AT ALL having the two turbines in parallel. It simply gave the same output as having the one unit there. I currently run each turbine into individual grid tie inverters. In a steady 10-12 KM/H wind I get about 60 to 65 Watts AC out of each inverter. When I parallel the turbines I get pretty well the same output from the one inverter. There may be a 4-5 watt better output but certainly not enough to justify paralleing two units.
The MPPT unit is probably drawing current from the turbine that produces the higher voltage, and as both turbines are connected via diodes the lower voltage producing turbine can't forward-bias its diode so can't contribute much current at all.

The MPPT unit will be maximising the voltage at the turbine, ie it is keeping the turbine DC voltage high. It's like the effect of both turbines going through their diodes into a large cap, the cap will be charged to the voltage of the higher turbine, then the lower turbine will hardly contribute at all.

There's no easy way around this, the 2 turbines will probably always produce different voltages and different output power, you really need 2 MPPT units, or no MPPT units so the turbines are tied to a low voltage load.
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