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Forum Index : Windmills : Are these Motors good for wind turbine?
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| Khalid Newbie  Joined: 23/07/2011 Location: PakistanPosts: 14 |
Dear All, I have purchased two PM DC motors and checked the Voltages, Amperage on Lathe. 1st Motor: RPM Voltage(V DC) Amperage (A) 200 4.45 5.4 300 6.68 8.4 400 9 11.75 500 11 14.5 600 13.35 17.5 700 15.8 19.7 800 17.65 (Meter Blown off) 2nd Motor: RPM Voltage(V DC) Amperage (A) 100 1.5 1.55 200 2.9 3.12 300 4.3 4.83 400 5.77 6.65 500 7.09 8.67 600 8 10.93 700 10 12.36 800 11.84 14.46 900 13.15 16.4 The Average wind speed at my location is 8MPH. Should i use gear to make the RPM down to 300 range? My Projects: www.my-woodcarving.blogspot.com www.free3dscan.blogspot.com |
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fillm Guru  Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Should be able to charge a couple of mobile phones with those .  PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
As-Salam Alaikum Khalid Yes, I think you would have to gear those motors to get a useful output from them. John New Zealand |
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| Khalid Newbie Joined: 23/07/2011 Location: PakistanPosts: 14 |
Couple of mobile phones  but on what basis?...I am planning to use 14ft diameter PVC blades. My Projects: www.my-woodcarving.blogspot.com www.free3dscan.blogspot.com |
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| Khalid Newbie Joined: 23/07/2011 Location: PakistanPosts: 14 |
Walaikum Assalam John, Thanks for the reply... I live in the coastal area of my country (Karachi). I shall install this turbine at the top of my 3 story building( No trees and other buildings). Surely, i shall gear down.. My Projects: www.my-woodcarving.blogspot.com www.free3dscan.blogspot.com |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hi Khalid I have visited Karachi several times and always enjoyed my time there and the people I met. Please post pictures as your project proceeds,  there are many people here with a lot of experience in wind turbines and they may be able to offer assistance if required.
Best regards John |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Khalid You may be able to use the first motor, but yes you will need to gear it up. 1:3 or better would be needed. You could use bicycle chains and sprockets, or a gearbox from a angle grinder. Dont expect too much, less than 100 watts on average, but it would still be a fun project. 13 foot is a bit on the big size for a first project, I would try something closer to 7 foot. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Khalid Newbie Joined: 23/07/2011 Location: PakistanPosts: 14 |
Hi Glenn, Thanks for the valuable response.. Their are certain reasons i am making the wind turbine although had no experience in past. 1- We have 12 Hours load shedding in Karachi i.e. 2 Hours electricity and next two hours load shedding. The problem arises when in night this alternate hours load shedding happen. Due to high humidity my family is unable to sleep. We have a Gasoline driven generator at the top of the roof. It is now difficult to start and stop the generator especially in night. Very bad conditions here. 2- A week back my father had Heart attack and luckily he survived. He is the one in my family who is very hard worker in this age (64 years). I am doing job in another city far away from my home. 3- I want to give relief to my family. Two pedestal fans and few energy savers from the Wind turbine is my expectations during the load shedding hours. I am not expecting KWatts from the wind turbine. Now, due to scarcity of time and money, and with the help of the great experienced guys in this forum, if these motors are not going to full fill, i can go toward making Axial Flux turbine... Glenn, now my questions: 1- Are you considering the wind speed as limiting factor for getting 100 watts or the Motor itself? Thanks for all of your help. Regards My Projects: www.my-woodcarving.blogspot.com www.free3dscan.blogspot.com |
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| daveames Newbie Joined: 19/09/2009 Location: United StatesPosts: 30 |
Hi Khalid Seeing your goal is to provide some relief during the rolling blackouts the very first thing to tackle might be to set up a UPS system (uninterupted power supply) charged during the on times from the grid then discharged during your turn at power sharing? Might be best to keep looking for a more suitable motor for the mill. Then use the mill to help keep the UPS system charged. UPS <- we are using that term loosley here and could be as simple as a charger, a few batteries and a DC fan?..or manualy turn on an inverter. kind regards, dave |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Good idea Dave. Why not use one of the motors as a 12v fan. Here's a fan I converted to 12v, and I used it when we lost power for a couple of days after a cyclone on 2010. http://www.thebackshed.com/Windmill/articles/12vFloorFan.asp A big old truck battery or two could power a couple of 12v fans for a few hours. Charge the batteries with a normal battery charger when you have grid power, and then use the battery power to run the fans and a light or two when the gid power is off. The limiting factor is the motor itself for the windmill. Chain drives and DC motors dont work very well. They do work a bit, but like I said you would be luckty to see much above 100 watts. If you have nothing else to use, then its fine, but there are better options. Glad to hear your father is OK. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Don B Senior Member  Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Khalid, Looking at the test figures given in your first post, you don't say how you measured the voltage and amperage. I assume that there was no external load other than the meters themselves, so, essentially you are showing the open and short circuit values. Taking the first motor at, say, 700 rpm, the 16V open circuit voltage and the 20A short circuit current suggests that the internal resistance of this motor is 16/20, or 0.8 of an Ohm. If you connected it via a diode to a 12V battery and tried to charge the battery to, say, 14V, then you would have 14V across the battery, 0.7V across the diode, and 1.3V available within the motor to drive current through its 0.8 ohm resistance. This says that the charging current would be 1.3V/0.8Ohm, or about 1.5A. This would be the current with the battery fully charged. When the battery was discharged to 12V, you would have 16V - 12V - 0.7V, or 3.3v to drive current through the 0.8 Ohm resistance in the motor, and this would give you an initial charging current of 3.3V/0.8 Ohm, or about 4 Amps. Note also that 4 Amps at 16V total output Volts gives an output from the motor of 64 Watts, of which 4A X 4A X 0.8 Ohm = 12 Watts are lost as heat in the motor, and 4A X 0.7V = 2.8 W are lost as heat in the diode. Note also that, for the motor to output 64 Watts of electrical power at 700 rpm, it would probably need around 80 to 90 Watts of mechanical input. The awkward thing about wind generators is that, while you can get more power out of larger diameter blades, they will turn more slowly. This is because the tip speed ratio (TSR) for any given set of blades is constant for most efficient operation. The tip speed ratio is the ratio of the speed of the blade tips, and hence the rotational speed, to the wind speed. The less number of blades you have, the higher the tip speed ratio that you can use, but there are limits to the TSR band that you can use for any given number of blades. In your case, your wind speed is 8 mph, and, for, say, a 2 blade turbine, you could maybe stretch the TSR to 8, or maybe a little more. This gives you a blade tip speed of around 64 mph. When you have settled on a blade diameter, you can back calculate the shaft speed from this. There are tables available that relate wind speed, and power for a given blade swept area that will tell you what diameter you will need to get, say 100 Watts of wind power. When you have the diameter that you need for your 100 Watts at 8 mph, you can determine the shaft speed from your tip speed ratio. I don’t have access to these tables at the moment, so I can’t give you any numbers. If you are lucky, you might be able to get 100W from a 2 blade turbine in 8 mph wind at 700 rpm but, if not, you will need to gear it up, which will involve further losses. At that point, you may be better off going to a 3 blade turbine, which will have a TSR of around 4, but starts and runs better. Once you need to gear up, you could look at running your motor above 700 rpm to get even more power out, although your turbine would need to be bigger to output the extra power needed. The other thing is that you will need to have an amp hours balance between your generated amp-hours, and your load amp-hours. It is unlikely that your generated amp hours will completely meet even the small loads that you are looking at, but you can supplement the wind generation with a battery charger for the times that mains power is available. Oh yes, the second motor might just make a good fan motor, so at least you have most of what you need. Good luck! Don B |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi again Khalid, After having had a chance to do some sums on your wind numbers, I think that the 8 mph wind speed is too low to do much with. To get even 100 W out of your generator you would need the 14 foot diameter blades that you mentioned, and, even with a TSR of 10, the blades would still only run at 160 rpm or so. This would mean that you would need a 4.5 or 5:1 step up to your motor, and the gearing losses would probably be significant. You should also bear in mind that the power in the wind increases with the cube of the wind speed. If your wind speed doubles, the power increases 8 times, and your large but docile wind generator can suddenly become a monster. The best thing that I can suggest is that you look at a traditional type wind tower design on your roof that captures the wind in a scoop, and ducts it down to where it is needed. Low tech, but well proven! Regards Don B |
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