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Forum Index : Windmills : Servo motor for wind turbine
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
If this is a 2Kw servo motor, the current rating will be 200 volts at ten amps total. 3.3 Amps per phase. Much higher current than that, and you will cook it for sure. It will run fine at 12v, but don't expect it to last long at sustained power levels much greater than 120 watts. Cheers, Tony. |
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piggweed Newbie  Joined: 09/01/2012 Location: United StatesPosts: 29 |
You have to love those Texas winds, for two days we had 15 to 30 mph winds, currently 18 mph with temperature of 32 deg and wind chill of 20.5 deg. The low this morning 26 deg with 22 mph winds, wind chill 11.5 deg, yesterday it was 63 deg. The name plate data on the motor is 200 vac, 2000 rmp and full load current on name plate is 14.6 amps. I believe I can go 10% over that should let me get 5 amps per leg at max speed, Would this be correct? Would the max speed be the motor shaft or the outer blade dia on a wind turbine. I am reading alot about wind turbines, as I know nothing about them but, I have an application that I need power out at my barn and it would cost to much to run power to it plus I don't want to run power to it. I want to try to get 12 amps @ 120 vac at the barn, Any recomendations on the correct way to achieve this goal would be greatful. |
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97fishmt Regular Member  Joined: 19/04/2010 Location: United StatesPosts: 77 |
The current rating on these motors are the recommended slow blow fuse per leg of the 3 phases in a working environment. This motor I'm sure is like one of mine with a line to line resistance of 0.5 ohms or less. I've looked up the data sheets on many motors of this type and they do list a maximum amp that the winding can handle and it is 3-5 times what the name plate says. So used as an alternator with wind cooling it up on a tower. Connecting a 3 phase full wave rectifier 20 amps times 1.73 = 34.6 amps. It will probably do more I've only gotten them to do about double the amp rating used as an alternator pushed with a blade set. The trick is to get the right blades on it to work with the power curve the motor puts out. The whole point of using these motors is just what someone pointed out the size and being large. That's exactly what we have going on here. 2000 watts, 200 volts at 2000 rpm. We're turning it at 200 rpm for our purpose and getting 20 volts, just an easy way to look at motors for me just knocking off a decimal, and getting a fraction of the watts. Yes it is limited to the winding I guess some folks just have to try and find one of these gems to play around with. |
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Bub73 Senior Member  Joined: 10/12/2009 Location: United StatesPosts: 116 |
As 97fishmt pointed out the tag amperage on many of these servos is the safe Stalled amperage it can withstand as a stalled motor. When up and flying I look for that tag amperage per phase or x3 as a safe max amperage DC and no smoke yet. Looks to me like you've got a nice motor for a first project, I wish I'd started with a servo a long time ago. Good to see you posting here Mike. Bob |
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| 97fishmt Regular Member Joined: 19/04/2010 Location: United StatesPosts: 77 |
I agree with you Bob. 3 times should be just fine and a simple way to look at these kind of motors. (and there is still more head room) I just am trying to get out what I have done. There was someone a few years ago on this site coupling a servo motor to a gas engine and it would go 3 times and no further but with no signs of getting hot. I know you have followed what I have wrote in the past and now you are doing it also. Congratulations on your success!! 
There are many old stories about AC servo motors used as alternators if someone was to try and look for them.  |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
All of the above but please remember a couple of points, there will be a maximum output current that your motor will settle at. As a servo motor it is probably a little underrated as it is designed for frequent starts ( assumption, dangerous I know). Although it is up in the wind the core temperature of the windings is the overriding factor and they are inside this nicely sealed motor. A of j "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
So 200v x 14.5 amps x 3 = 8.7 Kw About the same heat generation as as seven 1.2Kw electric radiator bars. How long can it stand that do you think? Cheers, Tony. |
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| Bub73 Senior Member Joined: 10/12/2009 Location: United StatesPosts: 116 |
Well Warpspeed, you have a valid point and I don't mean to mislead anyone this was the way I look at these motors when I use them as alternators, also I wasn't thinking of charging a 200 volt battery. More like a 12 volt battery bank; 14.5 amps x 3 = 43.5 amps x 15v = 652.5 watts. Bob |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Whats that they say "Everything in moderation" No reason to run anything at max. rateing, always adviseable to back off atleast 10% of that for longevity. Mac46 I'm just a farmer |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi again Piggweed, There is much conjecture about what your servo is capable of as an alternator, so here is how you can get a feel for what it can do. Set up the servo in your variable speed lathe, connect an AC ammeter hard across one winding, and short circuit the other windings. Raise the speed until your ammeter is either up to its full scale (maybe 10A?), or the reading is at the servo rated current (14.5A?). Note the speed, stop the lathe, and remove the ammeter and short circuits, then spin the servo again at the same speed, and measure the open circuit voltage on each winding (they should all be the same). The servo winding “resistance” is then the open circuit voltage divided by the short circuit current. You should also calculate the Volts per rev by dividing the open circuit voltage by the shaft speed. The open circuit Volts per rev will be more or less constant within the operating shaft speed range of the servo, however, the “resistance” will increase as the shaft speed increases due to the increasing frequency and the inductive component of the “resistance”. You could maybe do further sets of short circuit/open circuit readings at different currents to get an idea of the trend. When the servo is connected to an external circuit such as a rectifier and battery, no current can flow until the servo shaft is spinning fast enough to produce a voltage equal to the sum of the battery voltage and rectifier voltage drop. As an example, if the battery voltage is 12V, and the rectifier voltage drop is, say, 1.5V, then no current will flow until the alternator voltage equals 13.5V. At this point current will begin to flow when the peaks of the servo voltage just exceed 13.5V, even though the measured AC voltage would be nearer to 9.5V. You can use your Volts per rev figure to calculate the shaft speed for this point. Note though that, as the servo begins to deliver current, the measured terminal AC voltage will increase until it more or less equals the DC voltage. The point where current begins to flow is the point where the servo “resistance” figure becomes important. For the servo to actually charge the battery, the servo must produce sufficient voltage to drive current through both its own “resistance”, plus that of the load which, in this case, is the rectifier and battery. The rectifier and battery keep at more or less constant voltage so, as the charge current increases, the effective resistance of the rectifier/battery combination drops (resistance equals volts divided by current). Unfortunately though, the servo “resistance” increases as the shaft speed increases, and it will be the dominant element in determining what shaft speed is needed to drive a useful current through the battery. This is the reason for my previous comment that the higher resistance windings of a high voltage (and relatively high speed) servo make it less useful for duty as a wind generator alternator. When you have some actual numbers, you will be able to calculate the sort of shaft speed that you need to send, say, 15A through a 12V battery, this amounts to a load of around 200 Watts. Assuming that the servo has 3 windings, this means that each winding would be contributing 5A to make the total 15A. To calculate the servo Volts needed for this example, you would use Servo Volts = 5 X “resistance” + 13.5. Servo shaft speed for this would be calculated Servo Volts/Volts per rev. You then need to find your average wind speed, and look up a “power in the wind” chart (on this website) to see what area and hence diameter of turbine you would need to get, say, 200W at your average wind speed. Note that the power in the wind varies with the cube of the wind speed, so you can get very substantial power increases from only a small wind speed increase. Next, you need to select the number of blades that you would like to use, as this will determine the tip speed ratio (TSR) band that applies to that number of blades. Tip speed ratio is the speed of the blade tip relative to the wind speed. A three blade turbine (which is a popular choice for a number of good reasons) has a TSR band centred around 4 to 5. Less blades permit a higher tip speed ratio, while more blades require a lower TSR. The TSR is a fundamental figure used in the design of the blade, and is more or less a given for a particular number of blades. Operation of a turbine at speeds above or below its design TSR results in significantly lower power extraction. If you have a TSR of, say, 5, and your average wind speed is, say, 5 metres per second, then your blade tip speed for this wind speed would be 5 X 5 = 25 metres per second. If you then look at the diameter (D metres) of turbine necessary to extract, say, 20% of the power available in the wind at 5 metres per second in order to generate 200 Watts, you can calculate the shaft speed from 25 X 60/pi X D rpm. If the turbine speed happens to equal the servo shaft speed to provide 200W then you are laughing. Unfortunately, though, the servo shaft speed is likely to be much higher that the turbine speed. Your choices are then to reduce the turbine diameter, which will permit it to run faster, but you can not then extract as much power, or to consider some form of gearing or belt drive to match the speeds. Most usually, you will need to go around this calculation several times to get the best compromise between turbine diameter, power, and shaft speed. Then you need to either make some blades to suit your requirements (check out turbine blade design sites), or to find something on the market that is close to what you need. You need though to resist the temptation to bolt on the propeller off great grandad’s Wright Flyer, just because it looks vaguely like a wind turbine. Proper turbines are purpose designed for specific applications, with the object of getting maximum power from minimum wind, not the other way around. Regards Don B |
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| 97fishmt Regular Member Joined: 19/04/2010 Location: United StatesPosts: 77 |
http://www.baldor.com/products/servomotors/c_series/bsm_cser ies_spec.asp?CatalogNumber=BSM100C-4150AF This is just one example of a motor like we are talking about. Look at the stall amps and the peak amps. Also look at the resistance and the V/KRPM. Maybe even look at the performance graph. It will obviously work differently being an alternator. I don't know all the electrical theories but servo motors work very well for me. I see 30 amps @15 volts all the time from a motor like this. Mike |
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| piggweed Newbie Joined: 09/01/2012 Location: United StatesPosts: 29 |
Don B, I am not sure what you mean, I can short two windings together and put an ampmeter on the other, but won't I need to connect the lead with the ampmeter to some type of load? I will test as soon as I here back from you. I just machined my hub and cut out 3 48" blades(out of pvc for testing). I should be able to put it in some wind tomorrow just to get a wind speed and rpm. I have designed a 35' tower that will swing up and dpwn for maintance with 1/4" steel cable and boat winch. it have 6' 3" pipe in the ground and 2' above groung with welded cap on it. There will be a 3/4" x 1" x 4" piece of steel welded to the cap for the pivot point. If anybody see's anything wrong with this setup please let me know. I am very thankful for all the information that I've received. This is the first forum i have ever used, and am vary pleased with all the good information I have gotten. |
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| piggweed Newbie Joined: 09/01/2012 Location: United StatesPosts: 29 |
Don B are you taking about using a vom set on amp's and using the vom in series to groung to get an amp reading? |
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| piggweed Newbie Joined: 09/01/2012 Location: United StatesPosts: 29 |
Warpspeed what are electric radiator bars? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
 Cheers, Tony. |
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| Bub73 Senior Member Joined: 10/12/2009 Location: United StatesPosts: 116 |
Here is a servo in Michigan winter with the deicer's on using up some of the extra amps!! 
Piggweed be careful when you put that motor in the lathe those WILL BE LETHAL VOLTAGES and it may want to spin the whole thing when you put the load to it be safe! Be careful welding on pipe as some is galvanized and can make you sick and the weld also causes a stress point and cause cracks . THIS IS PIGGWEEDS first project let's help him work it out.!! There are people here that know how to make these servo's work that was a nice post DanB. Isaiah on Bub's computer |
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| piggweed Newbie Joined: 09/01/2012 Location: United StatesPosts: 29 |
Warpspeed, I have always called them heater elements, I learned something new. Bub73, I layed boards on the ways of the lathe, it runs vary smooth. For a quick test I ran it up to 2500 rpms.In the eightys I taught welding, mostly tig with id gas for sanitary food pipe. I will post some pictures of my progress so all you good people can see how it's going and give your input. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
An Anglo Saxon heritage, and old age, puts me well behind modern times. But electric "radiators" were a very inefficient (and expensive) way to keep warm in winter. These days, it is all fan heaters with microprocessors and hand held remote controls. I am a bit into welding myself, just bought a Transmig 310, and a bottle of Argoshield light to play around with. Looking soon towards buying an ac TIG welder with pure argon to destroy some aluminium in the future, when the piggy bank recovers from shock. Great stuff on the servo motor, keep us all in the loop. Cheers, Tony. |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Piggweed, In answer to your query re the ammeter, the intent was to connect it directly across the terminals so that you are measuring the current circulating in the winding only. There is no need for an external load. Most multimeters withan AC amps range will measure to 10 or 20 Amps. That being said, you should realise that shorting the windings is like applying the brake to the servo, so that it does need to be well secured. It also will probably not turn at great speed, and will load your lathe. When you remove the short circuits to test the open circuit voltage, the lathe will probably run faster because it then has no load - even at the same speed setting. If you have some sort of tachometer that would help to ensure that the same speed can be set for each test. The recent post from Mike gives data for another servo, and I must say that I am surprised at the low resistance of the windings considering the voltage rating of the servo. I am not sure if there is any manufacturer and model number on your servo but, if there is, it would be well worth Googling it to see if you can find comparable data on your specific servo. If you can get this data it would save you having to carry out these tests. Regards Don B |
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| 97fishmt Regular Member Joined: 19/04/2010 Location: United StatesPosts: 77 |
http://www.sanyo-denki.com/wc_sanmotion_q2_motor200v.htm Is your motor like this one? (go down to 2kw) The new ones are sure awesome and they make sweet alternators 
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