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Forum Index : Windmills : A/C vs D/C for transmision
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readyakira Senior Member  Joined: 17/07/2008 Location: United StatesPosts: 114 |
Was wondering why rectify the output on our mills at the mill instead of at the charge controller near the battery bank. I thought A/C was made to make up for the power losses that D/C suffers over distances? D/C was the more efficient use to drive your equipment, but A/C travels further distance without loss. So My only assumption is to reduce the number of lines running to the charging station? Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Yes, lines from the platform are the big concern --only yesterday did I start installing a 8 wire feed , I'm running 2 X 3 phase stators off the same shaft ,but would like to have the rectifiers down at my control cabinet,,so 2x3 wires plus a couple spares,,because the cables are 4 wire bundled type. Bruce Bushboy |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
AC has the big advantage that it is fairly easy to use a transformer to change the voltage. Higher voltages are better for longer distances as the resistance losses are less for the same power, but at a cost of better insulation and safety issues. However a particular transformer is only efficient at one frequency and unfortunately a wind turbine does not produce nice 50Hz or 60Hz AC. AC is also good for driving motors otherwise brushes and commutators or electronic switching is needed. There is a potential problem with DC causing electroylisis and corrosion at joints exposed to weather. Personally, I think there is a place for AC and transformers in our home made systems but I think I am nearly alone in the Back Shed with this opinion.  |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Kiwijohn, Your not alone in the wilderness with this. Transformers are very useful with high pole count machines like the F&P. The AWP over here shows just how good they are. The untransformed 3.6AWP (48v windings) puts out less than 1kw, the same machine with hv windings (240v) and transformers puts out 1.2kw and more (even in furl). The AWP has 30 poles, the F&P more.... more the merrier. .............oztules Village idiot...or... just another hack out of his depth |
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| matt down south Regular Member  Joined: 20/10/2007 Location: AustraliaPosts: 50 |
what type of transformers are you using oztules? matt |
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| readyakira Senior Member Joined: 17/07/2008 Location: United StatesPosts: 114 |
thats kind of what I was thinking. Insulation in ranges up to about 400v are not that bad, and by having a higher V from stator the current can be lower thereby keeing things cooler, making it possible for more power b4 a meltdown and allowing for further transmission distances with less loss. Then a xformer with a rectifier circuit to bring this to a lower battery chargning range. But where I get lost is in what way to make this work. I have pondered leaving the stator/rotor as is, with maybe just the old fashioned grind cores from flat to roundish. BUt that would also lower efficiency? So I have 2 of the older style rotor/stators lying here with no idea which way I want to approach this. If you use a voltage regulator circuit once you have a lower working voltage, Does it increase the current in orgder to keep voltage down? Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
The AWP (African Wind Power) 3.6m has a single three phase transformer that looks like this (in fact is this) 
It is nominally 350v input. You can use three single phase transformers instead of a dedicated one. At 240v input it puts out around the 55v mark up to 30 amps. The mill runs around the 240v range, but unloaded goes 600+ readyakira I can't comment on the F@P cogging etc, as I don't have one, but plenty of info here to decide. Your frequency is higher than the AWP, so your transformer can be considerably lighter than the AWP one I suspect. Rewinding ones from microwaves is a simple and dirt cheap way of getting the tranny's. It is most helpful to split the laminates completely and lacquer them if you want good efficiency. They are designed as a ferro-resonant transformer, so they don't care too much about core losses as they drive them deep into saturation anyway. You don't want to do that or you waste too much as heat. Even the primaries are probably only really 160v even though they run 240.... that's how they saturate them, but a 160v 50hz primary may be ok for the f@p as the freq is probably higher when you get going. The AWP is only 30 poles so it's freq range is lower. The batteries (and rectifier) will be the voltage regulator. It will depend how much leakage you build in as to how tight the coupling will be. If your cunning this can be used a little like resistors in the line to raise/ follow the tsr a bit. There appears to be some advantage to using the transformers on high leakage machines like the F&P. This appears to be why the AWP transformer version does so much better than the 48v version... (so flux thinks, and I tend to agree with him) ..........oztules (one feels a can of worms opening here) Village idiot...or... just another hack out of his depth |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Reading this I couldn't help but think 'Saturable Core Reactors!'; till I realized I had already offered that idea up for criticism and it had been shot down... http://www.fieldlines.com/story/2008/3/10/174916/035 KiwiJohn, you're definitely not alone in your opinion about transformers. There are a lot of advantages to a high-voltage generator; efficiency in generation and transportation are but two. With some electronics to convert to your desired end-voltage (12 or 24 or 48 or... whatever you desire). Using a PC PSU as small powerconverter was another one of those silly brainstorm ideas. Imagine, never having to rewind a stator for your particular system voltage ever again... Oztules, I've been thinking on and off about a very high pole-count machine by using a small slice (50-100mm thick ?) of a *very* large (100kW?) induction-motor stator. Another one of those silly ideas I hope to put into execution somewhere between now and my retirement  .
You may want to ask Ron to show you his stator some time too  . If that one doesn't make you drool I don't know what will....
Peter. |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Do you mean something like this? (only weighs a ton or so) 
I've seen Rons little stator. It is slightly bigger than the AWP stator. Same design. .........oztules Village idiot...or... just another hack out of his depth |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
What a coincidence: my hoist is rated for 1 ton. As if it was meant to be... I hadn't thought about that 500kW genny of yours yet... I count 60 stator teeth. So a 20 pole generator would be an option. Peter walks off to find his calculator... wonders how many 2x1x.5" magnets it would take... and what size blade... Peter. |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Thinking for those who are at the very basic stages of this activity and at the risk of revealing just how little I know of the subject how about using 12V mains transformers that we can find in hobby shops, junk shops in old battery chargers and some electric blanket power supplies? Use three of these with a unmodified F&P. Three HV lines from the mill down to the trannies that would be near the batteries. I know transformer efficiency drops off quickly when the frequency is below what they were designed for but what about higher frequencies? |
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Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
John, I think for higher frequency such as the F&P, a toroidal transformer will have better efficiency. Oz, That would seem probable from my thinking too as an inductive load will better match the impedance of the the generator. Same reason as why I see caps working. No can of worms here. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574 |
Oztules As you said something about transformer get hot and myself and other workmate we are building project F&P windmill and thinking about using 3 single phase 230 volts transformer by place into metal box fill up by using castrol oil TQ-95 that use on ford with electronic auto transmission as l prevous have using 2 bridge rectitifier in old stove pot of oil to keep the diodes cool without useing heatsink to charge the battery bank over 3 days and still use to top up the batteries when it need and work well so there is no need for a fan. So is any better ideas you have about place transformer in the oil ??  or 
dwyer the bushman |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dwyer, The oil bath should do fine, if it has good surface area exposed to cool air... bit messy but. It will depend on how bigger transformer you use. It will likely be operating at 100hz or more when it is putting out decent power, so your effective turns/volt will be near double..... ie your power handling should be much better than at 50hz. Your duty cycle will not be 100% either. Providing your transformers are say 300w each, I don't think you will require extra cooling for the F@P. If you use smaller, and they warm up excessively, then the bath should help. But in the finish, it will mostly depend what voltage you wind the secondary for, as to how it will load the mill. I don't know what cut in rpm you want, and what voltage is available at that rpm. This will determine if you need 12v or 18v or 24v secondaries. Village idiot...or... just another hack out of his depth |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gill, I do not follow this reasoning. A transformer will attempt to reject energy as the frequency increases. The windmill will be unloaded more as the frequency/rpm increases. This pushes the windmill loading further from the wind power curve. The capacitors on the other hand work hand in hand with the inductance and load the alternator more as the frequency increases, which keeps the loading closer to the wind energy curve. I think also that the problems with the alternator inductor directly driving the rectifier is just moved from the alternator to the transformer output winding. There may be a lower leakage inductance in this arrangement though. I would not use transformers designed for 50Hz on a F&P mill, where operating frequency is around 200Hz at a rotor speed of 400rpm. As oztules has said, remaking some transformers from a microwave may be a good option. Gordon. become more energy aware |
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| readyakira Senior Member Joined: 17/07/2008 Location: United StatesPosts: 114 |
well I have 3 transformers at my disposal that I planned to try... here is a pic... http://www.cardomain.com/ride/2327820/4 at the very bottom is the transormer. I was using it to drive me HHO project, but that is on the shelf till I find a few custom parts I want for it. The transformers are from small UPS's for home PC's. The batteries on those had died, so I pulled the Xformer and rectifiers from it. I plan to use the a VAWT turbine so rpms should be slower right? My hopes is to keep volts out of the stator to around 150-280v I don't know how frequency affects a transformer, but if 110v puts out 14.4v rectified, then 280v should be about 28-32v? But again I do not know how frequency affects a transformer although I would assume since it needs to be AC then the higher the frequency the more the xformer should xfer power from primary to secondary? I think I am going to try the file decogging on the first F&P and the stator twisting on the second to see if one outperforms the other. As for the battery becoming the voltage regulator, doesn't there become a point where too much voltage available to a battery is bad for it? Or will that not be a problem because the possible output from the mill is not enough to cause a problem? Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Gordon, If we could just focus on the topic of this thread first. This means putting aside other considerations such as wind power curve for the moment. For maximum power transfer the impedance of the load needs to match the impedance of the generator. The generators output is inductive(voltage leading, current lagging), we correct this by adding a series capacitor. Being opposite to inductance, this capacitance corrects the power factor until, at resonance, we have a pure resistive output with no reactive component. If on the other hand, the load is inductive(transformer), it will be best fed by a leading voltage lagging current supply. And this is exactly what our generator puts out, no caps needed for power factor correction. Well, rough enough because the perfect load would be another F&P where the impedance is an exact match at all frequencies. Perfect with the highest possible efficiency for power transmission over long distance. Would an electro/mechanical F&P to F&P step down at the battery be better than an electro/magnetic 3 phase transformer??? Don't know. Nobody has tried it. Perhaps the better long distance efficiency of a perfect impedance match may offset what I think would be a lower mechanical conversion efficiency. Or would a slightly lower transfer efficiency of the transformer load be offset by a better conversion efficiency of the transformer?? Who can say. It hasn't been tried. Anyone care to guess?? As for the caps ability to add greater load as fq increases for the purpose of better wind to generator power matching (fixed pitch), one of the other available methods could be employed for this purpose. Alternatively the caps could be placed after the voltage conversion (transformer or F&P to F&P) but still before the rectifier close to the battery. I think that should still load the wind generator to compensate for your lack of pitch control but would need testing to confirm this speculation. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gill, I fully agree. I do not have power transmission issues with my mills. In my situation I have both AC and DC power transmission cabling. I have discussed a Motor/alternator F&P dual system with bryan, like you have mentioned, so he can locate his mill at a better location on his property. He is still working on this. A normal transformer has a fixed turns ratio. This is optimised for a particular operating Hz. The output emf of a windmill with fixed pitch blades should increase linearly with windspeed. A transformer coupling with fixed turns ratio will convert this linearly up to the point where the upper operating Hz starts to limit. The battery cutin and matching is moved to the transformer output winding. A transformer coupling can reduce transmission losses, within limitations of the transformer operating Hz. I suspect that with long transmission distances, the losses with the transformer will be more than compensated for with savings on conductors. The problem with a windmill is that the generator requires a changing loading impedance, and the loading impedance needs to be decreasing with increasing frequency, for a fixed pitch mill. The problem of loading to the wind energy curve is moved from the windmill to the transformer. I agree that the series capacitor aspect with loading is not really applicable to the power transmission jist of this thread. Gordon. become more energy aware |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
I am not sure this is a problem. Remember, as we double the rpm, we double the freq and we double the volts... but the turns ratio stays the same.... this turns out to be good for us. The upper hz for the average transformer is way up compared to the max hz the F@P will deliver. Remember, very average transformers were used in valve power transformers up to 15khz. Good ones had sexy steel, the cheapies didn't... but the difference wasn't huge, so I don't think the hz ceiling is appropriate in this case, 200hz is small beans. The thing that works is that as the voltage doubles, and the turns of wire are fixed, we really need something else to happen or the transformer would burn up..not from the freq so much as the new EMF. Instead, the turns per volt is changed as well. At double the freq, we get the happy situation where the turns per volts comes down..... and we match again  ... and it just keeps going as the freq and voltage rise. Our power handling actually goes up in lock step with the freq and voltage.
So it is a good match to the increasing power curve of the alternator. Looking at it another way: Lets assume dI/dt is 5 amps/1 sec for a value of 5 . If we double the frequency the time will halve to 1/2 sec so that dI/dt = 5/.5 =10 . looking good so far..... But, doubling the frequency also doubles the inductive reactance ...(cursed thing).. so that will halve the current in this instance ...dI/dt = 2.5/.5= 5 , so we end up with the same as we started with at half the frequency. I wouldn't expect frequency/core issues to surface until well after 1khz. In the above example, current remains constant, but our voltage will double with a mill, so power increases at Esq x R, so power transfer will be a square function, just as the alt is. The turns per volt will follow it as well, so the transformer will not be driven into saturation because of the doubling of voltage. So that is why I think it works so well.... 
............oztules Village idiot...or... just another hack out of his depth |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
[Quote]The upper hz for the average transformer is way up compared to the max hz the F@P will deliver. Remember, very average transformers were used in valve power transformers up to 15khz. Good ones had sexy steel, the cheapies didn't... but the difference wasn't huge, so I don't think the hz ceiling is appropriate in this case, 200hz is small beans. I think you are referring to valve audio transformers working to 15kHz, not power transformers. I would need to check my facts but I think even a 60Hz transformer is not as efficient when run on 50Hz. What the difference is at 200Hz would need to be determined on a case-by-case basis. |
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