Can two or more turbines be connected in parallel after the rectifiers?

[makenzie71]

Assuming all turbines on the circuit are rectified to DC before being connected.

[JW]

Please explaine 3 phase to dc, I'm lost


https://www.fieldlines.com/index.php/topic,146199.msg998931.html#msg998931

[makenzie71]

I didn't see anything in Flux's post, or that thread, that really confirmed what I'm asking.  Closest I've be able to find to seeing it directly addressed here is Flux's post in this thread...but, if I'm reading that correctly, he's just saying it shouldn't be considered.  I'm just trying to learn why/why not.

[JW]

https://www.fieldlines.com/index.php/topic,146533.msg1003638.html#msg1003638

[boB]

Parallel should work OK.   

Series, no.  That would be crazy.

boB

[Adriaan Kragten]

Parallel connection is possible but both turbines must be designed for the same nominal battery voltage. Assume the nominal battery voltage is 24 V. The real charging voltage will vary in between about 24.5 V and 27.6 V depending on the charging state of the battery and the DC current of both wind turbines together. It is assumed that a battery charge controller is used which limits the maximum charging voltage up to 27.6 V.

Assume that one wind turbine is rotating and one is not. Assume that the one which is rotating is supplying a current that large that the charging voltage is 27.6 V. Assume the second wind turbine starts rotating. This one will only supply a current if the open rectified voltage is 27.6 V. So it needs to run at a little higher rpm than when it was running alone because when it is running alone, it starts charging if the open rectified voltage is 24.5 V.

It will be clear that the required battery capacity for two identical wind turbines must be double the capacity for one wind turbine. If you don't double the battery capacity, both wind turbines together will supply the current for which the maximum charging voltage is reached, already at a low wind speed. So at high wind speeds, a large part of the generated energy will be dissipated in the dump load of the battery charge controller if the battery capacity is too small. The dump load should also have the double capacity.

[TomT]

For me it depended on conditions and money.
I have (2) 12 Volt generators running thru two rectifiers to a Classic.
But I do  have winds from the same direction.
Most of the time.
So it took a while for me to make the curve.
But I did run it for a while directly to the 12 volt battery.
They do add the currents to the battery.
Just it was nearly half of what I get with the Classic.
also being I hardly have winds where I would need two Classics I was better with one.

[richhagen]

I have connected two tiny wind generators in parallel after the rectifiers before.  They will both be held to the battery voltage, meaning the RPM's will adjust to the voltage of the battery, with the allowance for the resistance in the lines to the genny.  As long as the generators are designed to run in the RPM range that they will find themselves, and you have a sufficient dump load for high wind conditions for both turbines,  it should not be a problem.  Just my two cents, Rich

[clockmanFRA]

I have 3off 12footers connected in parallel after each turbines rectifiers to my 48v 1300ah battery bank.

However, at 12 footer size, YOU MUST USE some sort of dump load system for those very windy gusting days.

Even with 1300ah battery bank its insufficient to clamp/control the voltage down to safe charging level for the batteries.  Empirical evidence.

I use Morning star Tristar 45 amp controllers that are set for diversion mode, as once the battery charging voltage is reached any excessive voltage above the set charging levels is then dumped by the controller in diversion mode.

For the dump load I use 2kW resistor air heaters on each controller.

As I have 3 wind turbines I have 3 controllers with 2kW heater dump loads for each.

My dump load heaters are up at the house a distance of about 150ft, cables are a minimum of 10mm/2 thick for each of the 6 cables.

The most I have seen being dumped to the heaters is about 8Kw just for a brief second during a very windy storm and even when the wind turbines were 'dancing', ie being pulled out of the wind by their tails .

Although each controller is set exactly the same, In reality each controller matches in and out at different times. When one is maxed out then the next steps in, and so on, but that can be allot of heat to dissipate.

Have a look at Hugh Piggott's site for further details on operational Dump Loads.

http://scoraigwind.co.uk/installing-and-configuring-a-tristar-controller-for-a-wind-system/


The below photo is my three. We are about half way up the side of a hill, so our wind is relatively consistent and from the same direction.   In the photo its a flat calm
 Yes it would be nice for them to be higher, but the French law allows me to put them up to 12meters, 40 ft high without planning or building permission consent. We are in a Low fly zone for military pilots training, so going higher might create more hassle.


 

[Adriaan Kragten]

I would not use a battery charge controller for each wind turbine but one big controller for two or for three wind turbines. I don't know how your battery charge controller works by I have described a 200 W, 27.6 V battery charge controller in a manual which can be found on my website www.kdwindturbines.nl at the bottom of the menu KD-reports. This battery charge controller has a voltage controller and a dump load.

The voltage controller can be adjusted at a certain voltage by a potmeter. The electronics of the voltage controller keep the voltage almost constant for a very large difference in current flowing to the dump load. So the voltage at low currents is about 27.6 V and at maximum current it is not higher than 27.7 V. So if you put two voltage controllers and two dump loads in parallel and if there is the slightest difference in starting voltage, only one dump load will take all the power. Two voltage controllers can only work in parallel if the voltage rises more than 0.1 V in between minimum and maximum current and still then, the starting voltage of both voltage controllers must be very accurately the same.

[electrondady1]

i had 5 single phase l vertical axis  windmills running in parallel after rectification  for several years. running an electrolytic cell the hydrogen didn't mind.

[clockmanFRA]

The 'Tristar' is a dedicated battery charge controller with the capability of diversion to a Dumpload. It can offer differeing charge rates for 12v, 24v, 36v, and 48v by selecting internal DIL mini switches.

Hugh Piggott advised me that 3 'Tristar' controllers individually connected to the battery bank would work well.

And I agree with Hugh, the 'Tristar' is excellent, fast operation, well built, robust and just does its job.

The wind turbines are connected to the battery bank, the battery bank clamps them down.

In a winter storm and a few days later and the battery bank is fully charged, then the 'Tristars' step in. At first just one of the 'Tristars' will start dumping to dumpload heaters when the battery shows it is full and the controller will not allow overcharging of the batteries.

So, No 1 'Tristar' max's out and is dumping 2kW, but No 2 'Tristar' now see's that the battery voltage is rising above the set battery charging rate, and it starts dumping 2kW. And this procedure is then carried into the No 3 'Tristar' controller, and so on, actually I have 4 'Tristars' but have never got to use 4off 'Tristar' 45's, but  it does mean that if there is a cable failure or controller failure, then No 4 is always ready.

The 'Tristar' is not expensive at about $170, it is bullet proof and continues when its maxed out at 45 amps. The LED screen option show data etc and in this photo shows ALARM, but hell it keeps on working.

Empirical evidence . ...... After a good 10 years of operation they are excellent and certainly more guaranteed reliable than just One BIG controller when we are dealing with 6kW to 8kW of Dumping to heaters. Every 3 years I check the controller connections.



This is 'Tristar' controller No 1, it does most of the work, as you can see its dumping 30amp and also it shows ALARM state so a few moments ago it exceeded its own 45amp rating, and therefore 'Tristar' Controller No 2 stepped in.

 

Here is Wind Turbine No2 control box, with the lids removed on the internal boxes/enclosures, each of my turbines has the same arrangement and its own Box.
DC MCB fuses, AC Short out switch, Amp meter, Rectifiers and heatsink, and yes that heatsink is just right,
and the 'Morningstar Tristar' 45 PWM Controller set for diversion mode.

[Adriaan Kragten]

These Tristar controllers can only work together if the voltage at which the dump loads of each controller starts taking power, can be adjusted very accurately. This isn't possible with a normal potmeter but they might have used another method and as this controller has a digital display, it is possible to see what voltage is adjusted for each controller. I can imagine that it works if one controller is adjusted at 27.6 V, the second at 27.7 V and the third at 27.8 V for a 24 V battery system. But this only works if you get a substantial rise of the voltage if the dump load has reached its maximum capacity.

I would not advise to do it this way for my controller. For my controller, Darlington transistor are used at the cooling plate and these transistors need only a very low base current. So several 200 W modules can be connected in parallel for one voltage controller. But if you can buy a good working controller for a rather low price, it is easier and may be even cheaper than building one yourself.

[clockmanFRA]

Installing a Tristar ......  Hugh Piggott explains......

http://scoraigwind.co.uk/installing-and-configuring-a-tristar-controller-for-a-wind-system/

I have attached a few images of Hugh's Blog and his explanations.  Thanks Hugh.

Remember each one of my 4off Tristar Controllers has a dedicated 2kW Dump Load each.

[kitestrings]

Looks like a time-proven approach to me.  ~ks

[Adriaan Kragten]

So if the Tristar is used in combination with a wind turbine, one has to use a set a resistors and a heat sink in which the surplus power is dissipated. I suppose that these resistors are not included in the price of the box which contains the electronics. Hugh writes that the system can't work without batteries as the voltage may become much to high. This is strange as the dump load must be able to dissipate the full power. My system can work without batteries.

[kitestrings]

I wonder if this is required to establish the base, source voltage?  The logic, in diversion mode, I assume is to divert above the preset voltage of the bank, so it would need that as a source reference I would think.

[clockmanFRA]

You set the Tristar's for the battery voltage that you are using.

For me that's a 48vDC system.

The Ttristar monitors the battery bank, and can Auto equalise the battery's if so selected, does a Absorb/bulk charge and then a float charge when the Tristar thinks the battery voltage has sufficiently charged the battery bank.

Depends on environmental heat conditions, as the Tristar modifies charge rates, but for my battery bank of 48vDC 1300ah SLA then its approx. 59.8v to 61.2v equalise, 58.4v to 59.2v for Bulk/absorb rate, and 54.4v to 56.3v for float rate.

The Tristar Manual also shows the battery charging algorithm and 8 switch settings for 8 differing battery types, which includes a custom setting.

Below photo shows 2 of my dump load resitors before installation. Also shown is a Solid State Relay.



Dump load resistors enclosed with a steel mesh cover, secured to a cradle that can be moved.
 


Please note these Resistors/heaters when they have the full 2kW get mighty HOT.

I have in the passed used Dump loads with Nichrome resistor heater wire at 4mm diameter, and wound in a coil to achieve a correct resistance.  But at 2kW dissipation each, its very hard to achieve a RIGID and SECURE cable connection to the Nichrome resistane wire it self, as it glows red hot. And after a couple of years in operation the connections would become loose.

So hence me converting totally to the green resistors as in my Photos and available here ......... 
https://uk.rs-online.com/web/p/panel-mount-fixed-resistors/7015850/

A 2kW 2.2 Ohm resistor is approximately $80, and in my opinion that's very good value.
 

[Adriaan Kragten]

In diversion mode, there must be a kind of reference voltage which limits the maximum charging voltage. If this reference voltage is reached, that much energy is guided to the dump load that the charging voltage is no longer rising. This function should also work if there is no battery.

I can imagine that the system can't work without a battery if it is used without a dump load and connected to only a solar panel. This is because for a solar panel, the batteries can be disconnected from the solar panel if the charging voltage becomes too high. The maximum voltage of an unloaded solar panel is much lower than that of an unloaded wind turbine. So the maximum voltage of a solar panel won't blow the electronics in the voltage controller but a wind turbine might do.

[clockmanFRA]

Please find below Hugh Piggott's explanations.

I think he is far better at explaining things than I am.

Thanks again Hugh!.



And using a SSR, solid state Relay, to divert AC from your Inverter that is running from your battery bank to a load, ie normal AC water heater.

[clockmanFRA]

The Tristar is deliberately set for diversion mode for our use, ie a Wnd Turbine.

Its diversion mode it is purely just a battery voltage monitor.

Once it sees that the battery voltage is rising above its internal settings, then it dissipates excess energy to its own personal connected dump load.

As I have already said, once the Tristar is maxed out and reached its maximum capabilities it just carries on at its maximum capabilities and starts showing ALARM on its LCD display. ITS IN OVERLOAD, and continues to work and function, it does not overheat it does not FRY it DOES NOT FAIL.

The battery voltage now being high now triggers my 2nd Tristar to function, and 3rd Tristar and so on.

The Tristar is bullet Proof well tested proven and well used, somewhere, Hugh Piggott states that he loves his Tristars.

For me personally controlling the power from my 3off 12footers/3.7m and my battery bank,  the Tristar and its dump load is Simple, Very Robust, and importantly very Cost Effective at $170 and $80.