Looking for a DC/AC inverter

vomusvomus Solar Expert Posts: 31
Hi!
I am looking for a DC/AC inverter for my wind turbine (1000W vertical). It has to input in a range of about 20-60 VDC and output 220-230 VAC. It would also be VERY nice to have some kind of monitotring interface (Modbus is fine), so I could read whatever it is doing.

This output AC has to have a good sine for I will plug it into AC2 of my Xantrex 4548. I browsed a bit and found grid-tied inverters that would meet my criteria but they are not what I need. Grid off inverters that I saw have a rather narrow input DC range and I would loose low winds.

Can anyone point me to the right direction? Thanks a lot in advance,

Comments

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Looking for a DC/AC inverter

    There is no way you could simply connect an inverter to a wind generator and expect a constant AC output.. wind is far to variable for that to happen anywhere on the planet. The generators output needs to be connected to a battery bank to even out the power available to the inverter.. All inverters are designed to operate over a narrow band.. its just way to hard to design and build them any other way at a cost you would be willing to pay..
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Looking for a DC/AC inverter

    No grid tie inverter would meet your demands.. wind comes ..wind stops. output is on .. output is off.. grid tie inverter gets confused gives up..
  • vomusvomus Solar Expert Posts: 31
    Re: Looking for a DC/AC inverter
    john p wrote: »
    There is no way you could simply connect an inverter to a wind generator and expect a constant AC output.. wind is far to variable for that to happen anywhere on the planet. The generators output needs to be connected to a battery bank to even out the power available to the inverter.. All inverters are designed to operate over a narrow band.. its just way to hard to design and build them any other way at a cost you would be willing to pay..

    I wanted to try to go AC route because Xantrex already has all that machinery and it will mix in the wind together with solar power. Do you have an example of such a wide range inverter so I could at least estimate what would go into this route. Otherwise I will go with DC.
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Looking for a DC/AC inverter

    If I understand your needs correctly... Yes, you may find a Grid Tied AC inverter (GT) that meets your needs (correct DC input voltage range and power requirements).

    Search the web/Ebay for a SWEA brand inverter (they seem to be everywhere). Not a personal recommendation (in fact, my personal recommendation is not to go this way unless you find a better quality inverter than SWEA--SMA used to make a small wind Gt inverter, but I think that is no more).

    Basically, you connect the GT inverter to the AC output of your XW inverter system. The GT inverter "syncs" to the AC output frequency/voltage and dumps energy into the XW's AC output. The GT inverter either helps power the load, or even can push power "backwards" through the XW and recharge the battery bank. Newer XW's (I think, you need to confirm) can be programed to vary the 50 Hz output voltage by +/- 1.0 Hz or so when the battery bank is full--This "knocks" the GT inverter off line until the battery needs to be recharged again.

    Of course, you need to ensure that your horizontal axis wind turbine does not "over speed" when the output load is removed.

    Better GT inverters and/or turbine combinations should have the ability the shut down the turbine when the loads are removed. Another option is to add a dump/diversion/shunt controller to the battery bank with a resistor load bank. When the battery is full, the diversion controller turns on the resistor bank and dumps excess charging current when needed.

    You can bypass the whole GT inverter thing and either direct connect the turbine to the battery bank, or use a MPPT type DC charge controller connected to the battery bank--With dump loads if needed too.

    Of course, your turbine has to have enough voltage to direct charge the 48 volt battery bank (probably ~70 VDC minimum output voltage).

    Your question of using a standard off grid AC inverter connected to the turbine and connecting the DC output to the AC input of the XW will not usually work. DC off grid inverters generally are not very happy with highly variable DC input voltage and available current.

    Can discuss in more detail if you need it... This is a complex subject and there are many ways to try and address your needs. But--In general, wind is a difficult energy source to master (cost effectively and reliably).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vomusvomus Solar Expert Posts: 31
    Re: Looking for a DC/AC inverter
    BB. wrote: »
    If I understand your needs correctly... Yes, you may find a Grid Tied AC inverter (GT) that meets your needs (correct DC input voltage range and power requirements).

    Search the web/Ebay for a SWEA brand inverter (they seem to be everywhere). Not a personal recommendation (in fact, my personal recommendation is not to go this way unless you find a better quality inverter than SWEA--SMA used to make a small wind Gt inverter, but I think that is no more).

    Basically, you connect the GT inverter to the AC output of your XW inverter system. The GT inverter "syncs" to the AC output frequency/voltage and dumps energy into the XW's AC output. The GT inverter either helps power the load, or even can push power "backwards" through the XW and recharge the battery bank. Newer XW's (I think, you need to confirm) can be programed to vary the 50 Hz output voltage by +/- 1.0 Hz or so when the battery bank is full--This "knocks" the GT inverter off line until the battery needs to be recharged again.

    Of course, you need to ensure that your horizontal axis wind turbine does not "over speed" when the output load is removed.

    Better GT inverters and/or turbine combinations should have the ability the shut down the turbine when the loads are removed. Another option is to add a dump/diversion/shunt controller to the battery bank with a resistor load bank. When the battery is full, the diversion controller turns on the resistor bank and dumps excess charging current when needed.

    You can bypass the whole GT inverter thing and either direct connect the turbine to the battery bank, or use a MPPT type DC charge controller connected to the battery bank--With dump loads if needed too.

    Of course, your turbine has to have enough voltage to direct charge the 48 volt battery bank (probably ~70 VDC minimum output voltage).

    Your question of using a standard off grid AC inverter connected to the turbine and connecting the DC output to the AC input of the XW will not usually work. DC off grid inverters generally are not very happy with highly variable DC input voltage and available current.

    Can discuss in more detail if you need it... This is a complex subject and there are many ways to try and address your needs. But--In general, wind is a difficult energy source to master (cost effectively and reliably).

    -Bill

    Thanks, Bill.
    See, the original thought was twofold. I have a wind DC controller that came with the turbine but it waits too long to close the circuit, so I loose low winds at about 5 m/s. The voltage that comes out of turbine at low winds is about 20 V. I do not want to loose it. Of course the power coming from such winds is not great but why would you want to loose it anyway? I also wrote some C code that looks how much I generate and plugs different loads to the alternative sources. So if I get some juice, it is even better.

    Another thought that I have is my Xantrex. It has an AC2 (AC1 is my utility grid) input where fuel generator is usually plugged. Having a wind turbine there is very attractive because such a setup will use all the functionality of Xantrex to be able to set priorities in power sources, charging batteries, mixing, monitoring, etc. And Xantrex to my mind is rather good in dealing with batteries. The controller that came with turbine is dumb in such matters. I can not set any parameter there.

    So right now I have the turbine plugged to my batteries directly, well, through that dumb wind controller, of course, and artificially decrease GridSupport mode voltage in Xantrex, so it draws power from DC when the turbine works.

    My first approach to the problem was to get a Xantrex C40 and plug it, again through DC, with a dumb load getting rid of the bad wind controller and replacing it with three phase rectifier. As far as I understand, this will solve my first wish to reach lower winds. Speaking of the second one... I kind of browsed through Alibaba and saw some grid tied DC/AC inverters that have a 20-60 V input range, can produce 220V AC and be able to dump an excess load to a resistor. But... They are grid-tied :-) so when there is no utility power it will simply shut down and this is now what I need. I have to have it continue working! This is what off grid inverters do but they have a much narrower DC input range and I could not see them to be able to plug dump loads.

    Besides, there is still an issue of stopping the turbine when winds are very high. :-( I could do it myself simply shorting the turbine though a controlled relay...
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Looking for a DC/AC inverter
    vomus wrote: »
    Thanks, Bill.
    See, the original thought was twofold. I have a wind DC controller that came with the turbine but it waits too long to close the circuit, so I loose low winds at about 5 m/s. The voltage that comes out of turbine at low winds is about 20 V. I do not want to loose it. Of course the power coming from such winds is not great but why would you want to loose it anyway? I also wrote some C code that looks how much I generate and plugs different loads to the alternative sources. So if I get some juice, it is even better.

    Most wind turbines do not generate much power below 4-5 m/s (9-11 mph)... So going to a lot of extra effort to harvest that power is usually not worth it.
    Another thought that I have is my Xantrex. It has an AC2 (AC1 is my utility grid) input where fuel generator is usually plugged. Having a wind turbine there is very attractive because such a setup will use all the functionality of Xantrex to be able to set priorities in power sources, charging batteries, mixing, monitoring, etc. And Xantrex to my mind is rather good in dealing with batteries. The controller that came with turbine is dumb in such matters. I can not set any parameter there.

    Understand your desire--But Wind -> DC input of an off grid AC inverter--Just not going to be a very easy match to get useful power. The XW will draw current (even 1 amp @ 230 VAC is 230 Watts), and that will usually "collapse" the DC input from the turbine (assuming the turbine is producing less than 230 Watts).
    So right now I have the turbine plugged to my batteries directly, well, through that dumb wind controller, of course, and artificially decrease GridSupport mode voltage in Xantrex, so it draws power from DC when the turbine works.

    As long as you have Utiltiy/grid power, that is a perfectly OK way of doing it. The "grid" is your dump load. And the XW sell voltage allows you to set the battery float voltage (basically) once the batteries are full. The XW would not care if the excess power comes from Wind or Solar to the battery bank (if I understand your setup correctly).
    My first approach to the problem was to get a Xantrex C40 and plug it, again through DC, with a dumb load getting rid of the bad wind controller and replacing it with three phase rectifier. As far as I understand, this will solve my first wish to reach lower winds. Speaking of the second one... I kind of browsed through Alibaba and saw some grid tied DC/AC inverters that have a 20-60 V input range, can produce 220V AC and be able to dump an excess load to a resistor. But... They are grid-tied :-) so when there is no utility power it will simply shut down and this is now what I need. I have to have it continue working! This is what off grid inverters do but they have a much narrower DC input range and I could not see them to be able to plug dump loads.

    You don't even need the C40--It is not doing you any good, unless you connect the C40 as a dump controller with a load bank--Having a second method to deal with "excess charging current" from a wind turbine (C40+dump load bank) is actually a good thing. It is a "safety" requirement in the US to have redundant charge controllers for wind power dump systems. If one fails, a second independent "thing" deals with the excess power instead of overheating/boiling the battery bank.

    The XW will be the "utility power" for the GT inverters when the utility fails-The GT inverter(s) will not care. Actually works pretty well. The issue is how to prevent the battery bank from being over charged on windy days and with low loads (and you are not their to shut down the turbine).
    Besides, there is still an issue of stopping the turbine when winds are very high. :-( I could do it myself simply shorting the turbine though a controlled relay...

    Stopping turbines on windy days by shorting the output--Sometimes easier said than done. There have been more than a few turbines that have still ran away/cooked the stator windings in storm winds.

    Furling/braking/feathering/etc. -- Having at least 2 independent means of shutting down a turbine is not a bad idea. Of course, installing the turbine a bit of distance away from occupied buildings is a good idea too (falling blades, nacelle, tower collapse safety zone). They are mechanical devices mounted in very difficult weather conditions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vomusvomus Solar Expert Posts: 31
    Re: Looking for a DC/AC inverter
    BB. wrote: »
    Most wind turbines do not generate much power below 4-5 m/s (9-11 mph)... So going to a lot of extra effort to harvest that power is usually not worth it.

    Understand your desire--But Wind -> DC input of an off grid AC inverter--Just not going to be a very easy match to get useful power. The XW will draw current (even 1 amp @ 230 VAC is 230 Watts), and that will usually "collapse" the DC input from the turbine (assuming the turbine is producing less than 230 Watts).

    What do you mean by "collapse"?
    As long as you have Utiltiy/grid power, that is a perfectly OK way of doing it. The "grid" is your dump load. And the XW sell voltage allows you to set the battery float voltage (basically) once the batteries are full. The XW would not care if the excess power comes from Wind or Solar to the battery bank (if I understand your setup correctly).

    Well, I can not just "sell" to grid because of two things. First, local regulations are murky on the subject but I could go by this as long as I produce less power than draw from the grid. I would only need to replace my utility power meter. However, there is another thing... I have a power stabilizer sitting between my Xantrex and the grid (power in the grid might fluctuate somewhat). So getting a power back to the grid through stabilizer seems to be impossible. So, I would rather dump the excess to heat and later will heat the water.
    You don't even need the C40--It is not doing you any good, unless you connect the C40 as a dump controller with a load bank--Having a second method to deal with "excess charging current" from a wind turbine (C40+dump load bank) is actually a good thing. It is a "safety" requirement in the US to have redundant charge controllers for wind power dump systems. If one fails, a second independent "thing" deals with the excess power instead of overheating/boiling the battery bank.
    Yes, this was my plan - to plug C40 as a dump controller, so the setup would look like Turbine->3phase rectifier->C40 with dump load->Batteries.
    The XW will be the "utility power" for the GT inverters when the utility fails-The GT inverter(s) will not care. Actually works pretty well. The issue is how to prevent the battery bank from being over charged on windy days and with low loads (and you are not their to shut down the turbine).

    Stopping turbines on windy days by shorting the output--Sometimes easier said than done. There have been more than a few turbines that have still ran away/cooked the stator windings in storm winds.
    Here is the question... How will the GT know that there is a power (either coming from the grid on AC1 or from inverting when there is no utility)? I presume this setup would mean plugging AC output of a GT to AC2 of Xantrex.

    Speaking of stopping the turbine... I have seen GTs that have dump loads with them. There are only two questions:
    (1) Can I trust those makers?
    (2) Is this going to be enough? I might get a higher value resistor...
    But going to actually stopping the turbine... I tried to shorten mine many times and it seems to work well. So I could measure voltage that comes out of the turbine and shorten it with some chip Arduino controller when it is. Or may be it would be better to measure the current that comes to dump load.
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Looking for a DC/AC inverter
    vomus wrote: »
    What do you mean by "collapse"?

    An Off Grid AC inverter is designed to be connected to a (more or less) stable voltage source--Such as a battery bank. The output power is defined by the AC load. I.e., a 100 Watt light pulls 100 Watts (or a bit less than 0.4 amps at 230 volts).

    If you attach it to the wind turbine, the off grid inverter has no idea how much energy is available from the turbine. If the AC load is less than the turbine's output power, the OG inverter will simply draw the needed current to support the load. If the AC load is greater than what the turbine can produce, the OG inverter will pull more current than the turbine can produce, and the output voltage will "collapse" and the OG inverter will turn off (hit low voltage cut off).

    There are some other issues in that the output voltage of a wind turbine alternator is probably not stable enough for an OG Inverter's limited input voltage range requirement (like 21 to 30 volts for a 24 volt inverter, or 42 to 60 volts for a typical 48 volt input inverter).

    A grid tied inverter is designed to work over a larger input voltage range (usually) and is designed to reduce the output current if the input voltage/current is less than rated value--So it is a better match to your needs.
    Well, I can not just "sell" to grid because of two things. First, local regulations are murky on the subject but I could go by this as long as I produce less power than draw from the grid. I would only need to replace my utility power meter. However, there is another thing... I have a power stabilizer sitting between my Xantrex and the grid (power in the grid might fluctuate somewhat). So getting a power back to the grid through stabilizer seems to be impossible. So, I would rather dump the excess to heat and later will heat the water.

    Always an issue with Grid Tied inverters... Local regulations prevent legal connections. And if the AC power is unstable, the GT inverters may not always sync with the AC grid (voltage/frequency out of range).
    Yes, this was my plan - to plug C40 as a dump controller, so the setup would look like Turbine->3phase rectifier->C40 with dump load->Batteries.

    Technically it would be:

    Turbine->3phase rectifier->Battery Bank
    Battery Bank->C40

    The rectifier and C40 are both connected to the battery bank in parallel.
    Here is the question... How will the GT know that there is a power (either coming from the grid on AC1 or from inverting when there is no utility)? I presume this setup would mean plugging AC output of a GT to AC2 of Xantrex.

    If you want "Grid Tied" inverter power even when the grid is down, you would connect the GT inverter to the AC Output of the XW. Within reason (i.e., the GT inverter is smaller than the XW inverter's AC power rating), the XW simply looks like the utility grid to the GT inverter. And it works the same.

    The XW inverter sets the voltage to 230 VAC and 50 Hz for your loads. If the loads are greater than the GT inverter output, both the XW and the GT inverter supply Watts to the AC load.

    IF the AC loads are less Watts than the GT inverter output, the rest of the power goes "backwards" through the XW inverter and the extra Watts goes to recharging the Battery Bank. When the battery bank is full, the XW goes to 51 or 49 Hz and the GT inverter tuns off because the XW AC frequency is out of range.

    The AC 2 output is for a generator, and would not feed back power from the GT inverter/XW inverter (would not do Grid Tied). AC generators are not designed to receive power from a GT inverter.

    And for AC 1, the XW is not designed to feed voltage/energy back to the AC 1 connection. The XW would expect to see 230 VAC and 50 Hz stable before it made a "connection" to the AC grid.

    A typical GT inverter is not designed to output "stable" 230 VAC 50 Hz by itself. Only an Off Grid AC inverter can do that (or a generator, or the utility grid).
    Speaking of stopping the turbine... I have seen GTs that have dump loads with them. There are only two questions:
    (1) Can I trust those makers?
    (2) Is this going to be enough? I might get a higher value resistor...
    But going to actually stopping the turbine... I tried to shorten mine many times and it seems to work well. So I could measure voltage that comes out of the turbine and shorten it with some chip Arduino controller when it is. Or may be it would be better to measure the current that comes to dump load.

    I don't know if you can trust a manufacturer or not. There are certainly mfg. with good reputations, and there are those with poor reputations.

    However, these are real physical devices and, as such, are not perfect. Things happen/go wrong. And the system should be designed such that if something goes wrong, it will (somehow) default into shutting down the turbine.

    A robust turbine system would generally have two different methods to shut down (i.e., shunting the output, feathering the blades) to lessen the chances of catastrophic failure. And in any case, the turbine should not be installed right next to a home if the shedding of blades or a nacelle fell off the tower, would not hit a home/school/office.

    Remember that the power in wind goes with the cube (to the 3rd power) of the velocity. For example, if your turbine outputs 1,000 Watts at 9 m/s (20 mph), at 18 m/s (40 mph), the turbine would need to manage 2*2*2 or 8x or 8,000 Watts to shut down. At 37 m/s (60 MPH) the stator/shutdown switch/cabling would need to manage 3*3*3 or 27,000 Watts of energy until the torque slowed the rotation to near zero RPM and the blades stalled.

    So while sorting the turbine alternator may work at 9 m/s, it may not shutdown in a heavy wind storm... I don't know anything about your turbine design/electrical wiring to know if your would shutdown properly or not. But, in any case, having a second method to shutdown is a good idea (large turbine mfg. usually have at least two independent methods to shut down in case of mechanical/electrical failure in the primary control system).

    Some folks have used a large resistor (load bank) to shunt the output of their wind turbine to limit current through the windings (provide enough current/torque to stop the spinning, but not a dead short so as to limit the output current and self heating/destruction of the stator/wiring). If that would work for you or not, I do not know.

    I personally do not trust using shunting of the AC Turbine output to be the only shutdown method of a wind turbine. Furling (turning the blades 90 degrees to the wind) and/or feathering the blades (adjustable blade pitch--turn the blades 90 degrees so that they don't turn in the wind) are both more reliable methods of shutdown in heavy winds.

    If you do not get "heavy" winds (hurricanes, typhoons, etc.), then you may be OK with just shunting the alternator output. Or, your installation will still be relatively safe if the turbine over-speeds/fails in a wind storm (small turbine, far enough from occupied structures) and you only have to repair the turbine after the storm blows through. I am not at your place--So I do not know.

    Treat the wind+turbine with great respect. These things can bite.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bpolitobpolito Registered Users Posts: 6
    Re: Looking for a DC/AC inverter

    It is challenging but by no means impossible to build an inverter that can deal with the dynamic input from a wind turbine - basically every grid-tie turbine has one. The difficult part is to build an input stage that can feed power smoothly into the inverter's DC link while performing the turbine management functions that are typically needed - e.g. optimally managing rotor speed in region 2 (between cut-in and rated power), keeping things safe in region 3 (above rated power), dealing gracefully with fault conditions, etc. This is tractable where the electronics designer has a solid understanding of the aero/electro/magnetic plant (e.g. the same team is designing both), but really difficult for one-of-a-kind homebuilt systems. Because every homebrew machine is different, we don't currently offer a generic WT input module for our X3001 inverter - as much as we'd like to.

    As a result, I think most home-builders are better off DC-coupling the turbine to the battery bank, and re-winding the generator if necessary to get a decent match between the rectified output and the battery bank - I believe the Otherpower guys and other Piggott-style builders have extensive discussion of this in their printed and online materials.

    Ben
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Looking for a DC/AC inverter

    To add some links to Ben's discussions:

    www.otherpower.com (good forum for DIY Wind Power)
    Hugh Piggott - Scoraig Wind Electric site for tons of info (from mike90045)
    Scoraig Wind "Recipe Book" for DYI Turbines
    www.greenpowertalk.org (added from "russ"--Like here but more wind/less solar)

    Midnite makes a very nice MPPT based charge controller + dump load for wind turbines. Can increase turbine output by 2-3x over a direct connect to battery bank type system. However, it ain't cheap (Clipper system):

    http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco.html

    If your distance from the wind turbine to battery bank is large--Then a GT Inverter type system or possibly a MPPT type controller is going to have an advantage because you can run the power at a higher voltage (and lower current) from the tower to the battery bank/shed/home. Can save lots of money in copper wire costs over running a low voltage DC direct connection to battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vomusvomus Solar Expert Posts: 31
    Re: Looking for a DC/AC inverter
    BB. wrote: »
    If you want "Grid Tied" inverter power even when the grid is down, you would connect the GT inverter to the AC Output of the XW. Within reason (i.e., the GT inverter is smaller than the XW inverter's AC power rating), the XW simply looks like the utility grid to the GT inverter. And it works the same.

    The XW inverter sets the voltage to 230 VAC and 50 Hz for your loads. If the loads are greater than the GT inverter output, both the XW and the GT inverter supply Watts to the AC load.

    IF the AC loads are less Watts than the GT inverter output, the rest of the power goes "backwards" through the XW inverter and the extra Watts goes to recharging the Battery Bank. When the battery bank is full, the XW goes to 51 or 49 Hz and the GT inverter tuns off because the XW AC frequency is out of range.

    The AC 2 output is for a generator, and would not feed back power from the GT inverter/XW inverter (would not do Grid Tied). AC generators are not designed to receive power from a GT inverter.

    And for AC 1, the XW is not designed to feed voltage/energy back to the AC 1 connection. The XW would expect to see 230 VAC and 50 Hz stable before it made a "connection" to the AC grid.

    A typical GT inverter is not designed to output "stable" 230 VAC 50 Hz by itself. Only an Off Grid AC inverter can do that (or a generator, or the utility grid).

    Plugging to the Output..Do you mean that the XW will change the frequency in its output? Hummm. In terms of the monitoring such a setup will not differ much from whst I have now. Now the DC from the wind simply appears on the batteries. In this case wind AC will appear on XW's output.

    But there is something I do not understand. If I plug the GT to AC2 of XW, why would XW want to put the power back. The GT will produce whatever the wind makes and throw the rest to its dump load. Do you mean that there not going to be anything on AC2 for GT to sync with? So it is not an issue of putting a power back but an issue of a "sync signal" that makes a GT work.

    A robust turbine system would generally have two different methods to shut down (i.e., shunting the output, feathering the blades) to lessen the chances of catastrophic failure. And in any case, the turbine should not be installed right next to a home if the shedding of blades or a nacelle fell off the tower, would not hit a home/school/office.

    Remember that the power in wind goes with the cube (to the 3rd power) of the velocity. For example, if your turbine outputs 1,000 Watts at 9 m/s (20 mph), at 18 m/s (40 mph), the turbine would need to manage 2*2*2 or 8x or 8,000 Watts to shut down. At 37 m/s (60 MPH) the stator/shutdown switch/cabling would need to manage 3*3*3 or 27,000 Watts of energy until the torque slowed the rotation to near zero RPM and the blades stalled.

    So while sorting the turbine alternator may work at 9 m/s, it may not shutdown in a heavy wind storm... I don't know anything about your turbine design/electrical wiring to know if your would shutdown properly or not. But, in any case, having a second method to shutdown is a good idea (large turbine mfg. usually have at least two independent methods to shut down in case of mechanical/electrical failure in the primary control system).

    Some folks have used a large resistor (load bank) to shunt the output of their wind turbine to limit current through the windings (provide enough current/torque to stop the spinning, but not a dead short so as to limit the output current and self heating/destruction of the stator/wiring). If that would work for you or not, I do not know.

    I personally do not trust using shunting of the AC Turbine output to be the only shutdown method of a wind turbine. Furling (turning the blades 90 degrees to the wind) and/or feathering the blades (adjustable blade pitch--turn the blades 90 degrees so that they don't turn in the wind) are both more reliable methods of shutdown in heavy winds.

    Well, I can not turn blades because my turbine is vertical Savonius (those semibarrels). In my area we do not usually get winds more than about 20 m/s. Last september we had 37 m/s which was historical record. The turbine was shortened at the time and survived the wind quite well. But of course, always watch out.
  • BB.BB. Super Moderators, Administrators Posts: 32,648 admin
    Re: Looking for a DC/AC inverter
    vomus wrote: »
    Plugging to the Output..Do you mean that the XW will change the frequency in its output? Hummm. In terms of the monitoring such a setup will not differ much from whst I have now. Now the DC from the wind simply appears on the batteries. In this case wind AC will appear on XW's output.

    Yes--When the batteries are full, the XW will (as I understand) will change its output to +/- ~1.0 Hz or so... That is just enough for the GT inverter to behave as if the power is going bad and disconnect from the "local grid" (5 minute timeout to re-qualify the AC power). SMA Sunny Islands will vary the frequency and their GT inverters will "throttle" rather than On/Off of the standard GT inverter. SMA (and perhaps XW and others) vary the frquency +/- ~1.0 Hz, so that clocks will keep accurate time (on average).
    But there is something I do not understand. If I plug the GT to AC2 of XW, why would XW want to put the power back. The GT will produce whatever the wind makes and throw the rest to its dump load. Do you mean that there not going to be anything on AC2 for GT to sync with? So it is not an issue of putting a power back but an issue of a "sync signal" that makes a GT work.

    Yes... The modern GT inverter does not make its own 120/240 VAC 50/60 Hz power--It simply "follows" the voltage (sine wave) already there. The XW expects AC Sine Waves as inputs to its AC 1/2 -- It does not "turn on" the AC 1/2 and feed back power to an otherwise dead circuit--It could not do this because if there was a real Grid or AC Generator power there--The two would not play well together (like connecting a pair of batteries with the wrong voltage/polarities together--Lots of current, popped breakers, and possible smoke.

    Technically, an Off Grid Inverter (and utility power/Genset power) are voltage sources (sort of like an AC battery). You can put loads on them that draw current as needed.

    Typical/modern GT Inverters are "current sources". They simply inject current based on instantaneous voltage of the sine wave.

    It is very much like the AC equivalent of your DC power system in your car... The Battery actually does the voltage regulation (12-14 volts), supplying/receiving current as need to keep the voltage stable. The car's alternator is (more or less) a current source (i.e., 50+ amp output when the engine first starts and quick recharge of the battery and then drops back to 10 amps or less as the battery gets charged and to supply power for the engine electronics/car radio/lights/etc. The alternator's regulator adjusts the current output based on the long term average voltage at the battery (around 13.8 to 14.2 volts or so). If you disconnect the battery, the alternator can over-voltage and destroy your electronics/blow your lights in the car).

    Most people have a good "feeling" for what voltage sources (Batteries, AC wall outlets, etc.) are. Current sources are an entirely different animal and not very easy to understand the details at first blush.

    Current sources are very handy and quite common in electronics/circuits. Quite a study in itself.
    Well, I can not turn blades because my turbine is vertical Savonius (those semibarrels). In my area we do not usually get winds more than about 20 m/s. Last September we had 37 m/s which was historical record. The turbine was shortened at the time and survived the wind quite well. But of course, always watch out.

    In general, vertical axis wind turbines will not over-speed if "unloaded". So, technically, you can just "turn off" the circuit and let the turbine freewheel (as I understand--I am not big into wind turbines). You don't "need" dump loads for VAWT (stopping them from turning in high winds may save wear and tear).

    Horizontal axis wind turbine can easily over-speed and self destruct if there is no load on the alternator. Hence a dump load/some sort of over-speed control is needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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