Please explaine 3 phase to dc, I'm lost

[Saltwater]

So I'm looking and reading about different turbines and it crosses me...  A 3 phase turbine is just that, 3 phase, not 12, 24 or 48 volt.  So I start doing a little research, very little I might add, but my interest is peaked. 

If a person has a 3 phase turbine and wants to connect it to a battery bank of say, 12, 24 or 48 volts, what needs to be done to make the voltage correct?  I know there are rectifiers, but really, is there a charge controller that can make it the voltage that a person wants? 

I've been seeing a lot of turbines from the same manufacturer advertizing a 12, 24, and 48 volt model with the same watts, but all the turbines are 3 phase.  Seems to me it is just the charge controller that changes the voltage to what one wants.  Am I correct here?

If it is the charge controller, or whatever, is there a way a person can take a 3 phase turbine and connect it directly to the batteries?  I realize there will have to be a rectifier and maybe some other things, but most turbines are connected directly to the batteries right?  Then a controller and dump load from the batteries.

I'm at a loss.  Trying to figure out the conversion and giving myself a headache.  AC to DC and visa versa, I need a beer.  Then I read where the conversion can be made with a delta or star or something like that.  My head hurts and thought I would ask.  Seems to me a 3 phase generator could be rectified to either a 12, 24, or 48 volt charger with simple electronics.  Any thoughts?

Jeff

[kurt]

OK first off with a 3 phase turbine you normally hook your 3 wires to a 3 phase bridge rectifier or a combination of single phase rectifiers or diodes that do the same thing then you wire the + and - from the bridge to the battery when the wind blows the turbine will free spin until the alternator voltage reaches battery voltage that is called cut in then the battery will begin to charge as the wind increases the battery will hold the voltage down to battery voltage but current will rise with wind speed and this will continue until the battery is fully charged were the battery voltage will need to be controlled to keep it from rising to the point that it damages the battery you do this with a diversion controller and a dump load a member here ghurd sells a kit for a simple controller or you can buy a more complex commercial one depending on the size of your system.


when you see a turbine listed as a 12v, 24v or 48v turbine that is a nominal rating and means they are suitable for charging that nominal voltage battery.

i hope that helps. 

[Saltwater]

Now my brain is scrambled.  So I can make a 3 phase generator either a 12, 24 or 48 charger with the correct rectifyer(sp)?  How?

Jeff

[Madscientist267]

Yes, you are correct.

The only difference between 3 phase and single phase is that there are 3 different, independent sources of power at the alternator.

The 3 phases are 120 degrees "away" from each other so that each one peaks at a different time during the rotation. The end result of this when combined and rectified to DC is a more constant power output, that is more efficient to transfer over the wiring that connects the load to the generator.

These phases are then usually wired together in a scheme that additionally reduces the number (or size) of conductors needed to carry the current away from the genny, although not always. The rectification can take place anywhere from right at the turbine, to right at the batteries, or somewhere in between. Sometimes it is desirable to take 6 thinner wires down the mast, rather than 2, 3, or 4 heavier gauge lines (depending on the topology of the coil connections, and where rectification takes place). It all depends on the intent of the design; the turbine's power output capabilities, the length of the run from turbine to battery, and so on.

Either way, there are typically only 3 ways that a 3 phase alternator's output is configured, before being changed into DC. They are:

Delta - Gets it's name from the shape of the greek letter it's named after. The 3 sets of coils are wired end to end in a triangle, with each of the 3 power taps taken from the points on the triangle. This is then fed (in this case) to a special 3 phase bridge rectifier composed of 6 diodes, 2 for each phase. The DC from these rectifiers is then combined to form a single, two conductor output that connects to the load (batteries).

Wye - The inverse of delta, once again named after the shape they take on a schematic, the coils are wired so that one end of each coil terminates at an output, with the other end terminating at a common point. This wiring scheme has 4 conductors carrying the power away from the genny, and are also connected to a special bridge rectifier designed for 3 phase use. There are a couple of ways to conjure the DC from the bridge at this point, but in the end, the result is the same - the final output is two conductors, one positive, one negative, heading for the load.

IRP - This stands for "Individually Rectified Phases", and means that each coil is completely independent on the AC side of the bridges, and they are each fed to a standard bridge rectifier (of the 4 diode variety), then the DC sides of each bridge are tied together to give (you guessed it!) a single pair of positive and negative, headed for the load.

There are reasons to go with each, as they all have pros and cons, some provide higher voltage while trading off current, some provide higher voltage at lower RPM, higher current at a lower voltage, etc etc...

The design of the windmill plays into this, as well as the typical wind conditions for the area it's erected in. EDIT - There are even schemes to change between these methods on the fly depending on what the most efficient way is for that particular moment...  

The nominal voltage of the system does not really have anything to do with how the phases are wired; the concepts are the same for any voltage range. The effects of using one method over another for arranging the coils electrically and how they are rectified is more about the turbine and it's associated wiring, not the batteries. These differences are also relatively subtle; the voltage range does not change significantly enough to switch between different nominal system voltages for example, but more to compensate/tweak for cut-in and the like.

Nominal voltage of the entire system is determined by several factors, but usually the most significant is cost vs. need. The inverter you intend to use with the system typically determines what you need the nominal voltage to be, then the batteries selected and wired for that range, and then the turbine's properties, and so on.

Hope that helps a bit...

Steve

[snake21]

in mono phase (current in your home),the voltage travels like a pure sine wave,right?in 3 phase,there are 3 sine wave but they are further apart. current which has sine wave/s are called AC

like this     : http://www.google.mu/imgres?q=3+phase+wave&hl=en&biw=1920&bih=965&tbm=isch&tbnid=HhiZl48S5djsRM:&imgrefurl=http://www.3phasepower.org/&docid=0wo0S_Y2YQtxfM&imgurl=http://www.3phasepower.org/images/3PhasePowerWaveF.png&w=300&h=193&ei=T5PhTrTtH4mIhQfuhpTrAQ&zoom=1

now to charge a battery,you will need dc current not ac ,coz ac are always alternating

to make any ac current a dc current, you should rectify it,the current from the turbine goes through a bridge rectifier and is rectified and that 3 phase current ends like this :   http://sub.allaboutcircuits.com/images/03269.png

the rectifier bring all the negative signal to positive which brings you to a dc current(not perfect one) but it wil charge a battery.

a rectifier is normally rated in high voltage, but limited amps,you will have to chose a rectifier which the amps is rated more that your turbine maximum amps it can deliver.there is no specific rectifier for a particular turbine.lets say you have a turbine rated 1000w which you can charge 12v or 24v or 48v battery banks

1000w at 12v gives you 83 amps,  1000w at 24 v will give about 42amps and 1000w at 48 v will be around 21 amps. now lets say you have a bridge rectifier which is rated at 500v and 100amps, you will be able to use it for all 3 voltages.

[Flux]

I really think your confusion is about how a wind turbine works.

For any battery voltage a wind turbine will need to produce enough volts to charge that battery at cut in wind speed. At any speed above cut in you will have more than enough volts and the voltage will be clamped to the battery volts. The power available will be limited so the charging current depends on how much the OPEN CIRCUIT volts of the turbine is above the battery volts and the internal resistance,

If you take a turbine designed for 12v operation it will reach cut in in a reasonable wind speed ( below 10 mph) and will be designed to give the best energy capture to a 12v battery at a normal wind site.

If you connect it to a 24v battery then it will not work in light winds but may still work fine ( or better) in high winds. You will not get power on most normal days. If you connect it to 48v then you will only see output in storms and on most days you get nothing.

Now if you go the other way round and take a 24v machine and connect it to a 12v battery, you will see a tiny amount of power on days when the 12v machine wouldn't work, but it will be tiny ( no energy in the wind). On all other days the machine will be held back and stalled because of the wrong battery choice.

So as you can see, the voltage rating is nominal and chosen to best suit a particular battery voltage on an average wind site,

In the early days wind turbines were fitted with dc generators and the same was true, you chose it to suit the battery voltage you want.

Today all turbines use ac generators ( alternators) that for small cheap ones can be single phase or for the larger ones 3 phase is chosen. All the rectifier does is convert the ac to dc for the battery ( I think you understand that)

When you choose your turbine you need to be looking at the nominal battery voltage is id designed to work with. The manufacturer will be telling you that if you choose one for battery charging.

If for some reason you are just looking at alternators for wind turbines then you won't have the information you need as a lot of this comes down to blade matching and that is part of the machine design.

Similarly turbines are sometimes supplied for use with specialised equipment such as mppt converters and grid tie inverters, in this case the turbine voltage doesn't matter much as long as it suits the maximum and minimum of the inverter, but this is specialised and I doubt that is what is confusing you.

The nominal voltage of a wind turbine is really nothing more than the voltage the alternator will produce on open circuit at cut in wind speed on a normal site when rectified with the appropriate rectifier.

There are special cases where the charge controller determines the battery voltage, but these are specials. For any normal wind turbine it is the alternator winding and the volts that it makes at cut in that determine its nominal battery voltage. Does this clear up the confusion?

Flux

[frackers]

So I'm looking and reading about different turbines and it crosses me...  A 3 phase turbine is just that, 3 phase, not 12, 24 or 48 volt.  So I start doing a little research, very little I might add, but my interest is peaked. 

I think you are confusing two separate terms here - the number of phases has nothing to do with voltage. In the UK and here in NZ, household 3 phase is 440volts (no clue as what it is in the US) so thats what the term "3 phase" means to a lot of people. My turbine is 3 phase 24 volts - it just happens to have three sets of coils in it, designed for a 24 volt battery system. Some designs have 5 sets of coils (5 phase) or more. Most small turbines (below about 8foot diameter)  will be single phase - for example motor conversions - still only running at the voltage its been designed (or modified) for.

[Madscientist267]

Not to swerve the thread, but for the record, US single phase is 110/120, and split phase is 220/240.

Looks like everything is doubled in yer parts of the world. I've never seen 3 phase into a house here, not saying it doesn't happen, but it's not standard. It is of course used in industrial, and arrives as 208/220/240/480, depending (on things that head into a grey area for me).

I have to say, I'm kinda surprised that 440 is available in any residential environment. Bet it keeps the respect level rather high, huh? 

But anyway... I now return you to your regularly scheduled post. 

Steve

[CaptainPatent]

Hey Jeff - have a read over here: http://www.play-hookey.com/ac_theory/ps_rectifiers.html

I think some of your confusion may be about what kind of electricity a wind turbine actually creates too.

The output of wind turbines varies a lot. With a 48v machine that's designed to run in 15mph winds, if you have smaller winds you'll have less voltage and the frequency will go down. Also, if you don't have furling and winds get higher than 15mph, the voltage will be above 48v and the frequency will be much higher.

Because it is very difficult to regulate power that flucuates that much, the easiest way to deal with it is to convert the power to DC and either store it in batteries or use this much more easily regulatable power supply to create AC to ship back to the grid.

The job of the rectifiers is to change the AC voltage from the wind turbine that fluctuates in voltage, amperage AND frequency into (near) DC current that only fluctuates in voltage and amperage.

The job of the controler itself is then to start when there is enough voltage for the system to charge and dump electricity when there is too much to handle.

[kevbo]

In my limited experience, 415V / 3 phase is pretty common where the normal domestic voltage is 230.  This is double the also pretty common 115/208 in the US for exactly the same reason...when star connected you get the domestic voltage line-neutral and yet the line-line voltage is high enough to allow usefully smaller wire on high powered loads, so you can often get by with no transformers other than the pole-pig(s).

If it helps the OP's understanding, the alternator in all modern cars is also a three phase machine, with the rectifier usually built into the rear of the case.  In that case the magnetic field (rotating) is varied to avoid overcharging the car battery.  A few wind gennys do that too, but the electromagnetic field winding uses power, so it is less efficient, especially in light winds.

[Saltwater]

Thanks for the help everyone.

I've been doing some reading about different turbines and pretty much confused myself. 

Most turbines I see now are 3 phase, go thru a charge controller and into the batteries.  I was sorta under the impression the turbine was connected directly to the batteries and a dump load controller connected to the batteries.

Then I see wind and solar controllers.  Connect both thru the controller and into the batteries.  They are usually rated fairly low so I thought maybe I could bypass "their" controller and rectify the 3 phase from the turbine to connect directly to the battiers.  Make any sense?  Bad idea?

Jeff

btw, I've been learning a lot about this with your help

[Flux]

Not sure what you have been reading, but with the exception of grid tie and the classic mppt controller you are right in that the turbine rectifier is normally connected to the battery and if you need a controller then it will be a dump connected to the battery.

I don't look at the commercial market and I have no idea what the Chinese are doing these days but normally series controllers are totally unsuited to wind. Those things that disconnect the turbine from the battery and connect it to a dump resistor are a disaster waiting to happen.

Normally a combined wind and solar controller will be a dump controller. It may for convenience have the wind and solar connected through it if it is sold with a complete scheme but as I say I have no up to date knowledge of commercial products.

I think you misled everyone with your original question, now we know what is confusing you perhaps others will be able to give more advice but your original ideas are right about connecting directly and using a dump controller.

Flux

[birdhouse]

saltwater-
this is a complex question, but i'll try to answer it simply.  with wind, you can have any sort of voltages coming in via the turbine, and if connected directly to the battery, the battery will "clamp" the voltage to what the battery wants to see.  it doesn't matter if it's three phase, five phase of seven phase.  the rectifier will turn it into single phase dc (what the battery wants to see). 

so lets say you've got a genny putting out 40V and your battery bank is at 13.3v (12v nom.) when you connect the mill to the battery, the volts of the output of the mill will drop to right around the battery bank voltage.  and amps will start flowing into the bank.  alright, we're doing good!

the way most folks use a charge controller for wind in an OFF GRID battery charging outfit is to connect the mill directly to the batterys (after rectification).  the charge controller is also connected to the batteries, and monitors the voltage of the bank.  when the voltage gets too high, the controller starts bleeding off juice into a dummy (dump) load to keep the bank from overcharging. this may sound kind of backwards, but it's the simplest way to keep the mill always connected (no freewheeling of the mill (destruction!)).   

as flux says, any cheap controller that is before the battery bank on the mills wire run, are probably a bad idea.   

i hope this clears your head to a degree. 

adam

[birdhouse]

look into a morningstar ts-60.  they do diversion, and aren't all that pricey.  WAY better than any ebay junk out there.  you just need to build/buy/design the dump load for it to work in diversion mode. 

[Saltwater]

Thank you,

Questions answered.  Sorry if ping from one idea to another.  I get an original thought going that kinda evolves into something else.

Jeff

[Madscientist267]

the controller starts bleeding off juice into a dummy (dump) load to keep the bank from overcharging. this may sound kind of backwards, but it's the simplest way to keep the mill always connected

Not to point out the obvious to some, and it doesn't apply exactly to the OP, but worthy of mention for you (or anyone else wondering the "why" in the dump load thing) - In addition to protecting the mill from freewheel and batteries from overcharge, the dump load on high power systems inherently has an additional benefit in certain climates/conditions. Among the higher power turbine owners in the clan (1kW or so and up), some are using the dump load as a heat source to help with "challenged" thermometer issues in their dwelling.

Of course, if you live by the equator, its better to get rid of the heat outside.

Steve