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Forum Index : Windmills : AC Servo Motor Generator
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| SimonP Newbie  Joined: 03/07/2014 Location: AustraliaPosts: 5 |
Hi all, Thanks for a great website and forum! I'm new to wind/solar off grid power. But want to start buying and making bits for a 48V off grid system for future use. I have wanted to make a wind turbine since I made a model for a year 10 science project MANY years ago! I may have jumped the gun slightly and bought a large AC servo motor to use as the generator. I have done some initial output testing with a friend. We connected it to a 24v battery bank and powered it with a 1Hp electric motor. Results were: 185RPM 0.5A 25.5V 13watts 210RPM 8.2A 25.5V 210watts 375RPM 21.A 26.5V 556watts 436RPM 26.A 28.V 728watts I couldn't test it any higher than this as the 1 HP drive motor was overloading. It looks like I will have to gear it up to nearly 4:1 to get the output I want at 48V The Servo motor specs are: 600v,30A,3800RPM and 7.9Kw As you can see, I am at the very beginning of this project, and will have plenty of questions as I progress. Thanks again for this great resource, Simon |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Simon Looks like the motor would be perfect for a 24v system, the RPM range is good and its making nice power. For a 48 volt system, it would probably work as it, but cut in would be around 350 rpm which is a bit on the high side. So you could gear it up, 2:1 or 3:1 would be OK. Or you could use a cap multiplier circuit, which means less mechanical parts, but more electronic bits. I'm currently running a OEM derived windmill, which was based on a electric bike hub motor. It was ideally suited to 12 or 24volt systems, but I run it on a 48 volt system thanks to a cap doubler circuit. I think it would have a similar RPM range verses power as your servo motor. The only "if" regarding a cap multiplier would be the AC frequency of your servo motor. Motors like the F&P Smartdrive or OEM hub motors have a high pole count and generate a higher AC frequency than most AC generators, possibly including your servo motor. Lower frequency means you will need much bigger capacitors in a cap multiplier type of circuit. Higher frequency means smaller caps. Phill might chime in here, he's got more experience with cap muultipliers. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| SimonP Newbie Joined: 03/07/2014 Location: AustraliaPosts: 5 |
Thanks Glen, I'm not sure of the no. of poles, but measured the resistance between the phases. Its .28ohms. I don't know if this sheds any more light on it. BTW the voltage is 460 not 600 as I posted earlier. I'm fairly ok with mechanical engineering/fabrication but not too flash with the electrical side of things. I'll do some research on cap multipliers. I wonder how efficient they are compared to mechanical gearing. I believe these motors when run as generators can run at 3 times there rated amperage. Going to 48v would give me a higher potential output without the risk of overheating the unit. I'm more than happy to build a 2:1+ overdrive for it if the cap multiplier wont work or be as good. Simon |
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fillm Guru  Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi Simon , Firstly welcome to the forum , as you have also contacted me WRT blades and questions about this project I will throw my 2 cents in here to. You have a few options that Glenn has outlined and one being the " Cap Doubler " which had its origins here a few years back and I will keep it named as intended here. They do work well but work better on a higher frequency. I have successfully used them with my AX FX designs, they are low frequency but need increased capacitance to compensate. There is the downside to the Cap Doubler, it does affect the Max Power Output. There are other options as well with using DC DC boost modules as well . As you are thinking of over driving 2:1 ~ 3:1 or with whatever gearing you choose with a large Dia set of blades to achieve 48V/ 2kw It is probably not a bad option in this case and to also experiment with the use electrical gearing as well when its all up and flying . The best direction is simplicity first and to keep blade rpm down at controllable levels and then you will not be building MK2. However, if you do intend to use a large blade set as you have mentioned in your email I would highly recommend to fit manual furling or a brake system to shut down when required, the GOE222 develop massive power in high wind . PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Phill I referred to the cap multiplier circuit as a cap multiplier because Simon's situation may need a tripler or quadrupler to get to get the best results. No point calling it a Cap Doubler if its a tripler, just creates confusion. For Simons low frequency servo motor, a tripler may be better suited, as it will reach charging voltage earlier than a doubler. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| SimonP Newbie Joined: 03/07/2014 Location: AustraliaPosts: 5 |
Thanks Phill, I have read that once this blade profile gets up to a certain speed, it takes a lot of slowing and even furling doesn't work that well? As you say, I don't want to be building Mk2 too soon! Do you have any data on the blades in use? Shaft torque at a given diameter & speed, or similar? What would you call controllable speeds for this blade? I have drawn it with a disc brake and caliper, but only wanted to use this to shut it down. I was hoping the reserve in the generator would be able to control the speed most of the time. |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Simon, That's a good move to add in a disc brake but can be complicated with control . If you are going to cable operate then slip rings are a must, otherwise the brake cable and 3 phase wiring will get twisted together unless you have the cable in a condute to separate the friction and tangling, but all that can get messy and its best with slip rings . Do not have any torque specs. but from experience 3.6m can give 4+ kW in strong wind , and the 3.2m set I am running at present easily gives 2kW @ 500rpm in 10~12 m/s .. Glenn, going from a doubler to tripler to Quaddrupler we are only talking milliAmps better than a doubler, but what does rise greatly is the cost of suitable caps. If you look at the pricing on higher voltage 250V + in the 1000uF~2000uF range they become expensive when you have to buy 24 to get 100~500mA. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| SimonP Newbie Joined: 03/07/2014 Location: AustraliaPosts: 5 |
Sorry about the slow reply. I've had to focus on another for project for a couple of days. Yeah, happy to make some slip rings. With the blades, do they have trouble furling because of the high blade speeds without the high axial loads to activate the furling? I have a couple of theories. If I was to run a 5 blade turbine, would this slow the turbine and increase axial load to help with furling? Would increasing the pitch help to make the blade less efficient at high speed, helping to prevent over speed? I don't mind gearing it to be a low speed grunter! Thanks again |
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| fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Simon , Yea, at high speed (450+) all blades have trouble furling because of the gyroscopic forces , its like trying to rapidly change direction and rotate a 9"grinder or spinning bike wheel. Most rapid furling happens with gusts so response time is slow at high Rpms which then compounds the power in the wind gust . Trying to keep the RPMs below the 350 @ full load helps with control, of course this is in the "perfect world" so other methods need to be adopted in conjuction with engineering design. Sometimes its just better to shut down and ride out the big wind / storm front and then start up after, you might miss out on a few A/hrs but if you are down for 1~2mths + $ ..... Well that decision is yours . The 5 blade will develop a lot more torque for a smaller Dia , but increasing the pitch will do nothing but give overall poor performance , unless it is done with a pitch control system and then you are talking " top of the line " RPM regulation. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| SimonP Newbie Joined: 03/07/2014 Location: AustraliaPosts: 5 |
Great info, ta. Going on that info, Ive sketched up an idea for a quick reaction, high torque, 4 way adjustable, low tech, unbelievably awesome furling system. (best I patent it now LOL) I should post a pic. It might get a few laughs but I believe it has some merit. It allows for adjustments on furl start speed, rate, furl torque and damping rates. That also makes sense re the sudden increase of blade speed in gusts being too much for a furling system. On first thoughts, adding inertia to the turbine might give the furling system a chance to keep up with the wind gusts? |
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| flowerpetal Newbie Joined: 26/08/2014 Location: AustraliaPosts: 5 |
I did some preliminary testing on fisher and pykel washing machine motors a few years ago and found if you did some minor rewiring you could change it from 3 phase to single phase and when it was run at the right speed to get 60hz it produced 120volts rms.Just by attaching a 2 to 1 step up tranformer it is possible to run 240v in real time |
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