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Forum Index : Electronics : Question about three phase conections?
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WindyMiller Regular Member  Joined: 05/04/2011 Location: United StatesPosts: 62 |
GidDay! In my quest to build an induction generator from a 2 HP Dayton motor I have run across this article http://www.redrok.com/cimtext.pdf which explains how to get 120 Volt output from a 230,415 volt motor. However I found a link in the Internet Archive service http://web.archive.org/web/20090417050403/http://users.aber. ac.uk/iri/WIND/TECH/MISC/MotorsAsGenerators.html that points out that there is an error in the above link in that the neutral wires should go to the center of the phase taps? Is this correct? Or am I heading towards destroying a nice 2hp electric motor if I connect it like the drawings? Living in the US I am looking for 120 volts and nothing else. I do want to use the three phase motor for the benefits it offers when converted to a generator. Robert |
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Three phase motors are usually always rated by the voltage from phase to phase. Most three phase motors don't use the mid point of the star connection, even if it is there, as these motors are most commonly connected in delta. Now the relationship between phase to neutral, and phase to phase voltage is always 1.73 Here in Australia phase to neutral voltage is 240v, and phase to phase voltage is 415v, or (240 x 1.73 = 415) If you want 120v nominal phase to neutral voltage when star connected, (as shown in that article), you will need a 208 volt rated three phase motor. The circuit shown in that article is correct. You need three 120 volt outlets connected one each across each star winding, and the correct tuning capacitors connected from phase to phase are a vital part of the system. You will need to run your generator up to nameplate rpm, as it will only work very close to that speed, and the tuning capacitors also need to resonate the windings to that speed too. Fine for being driven by a constant speed governed gasoline engine, for example, but hopeless for wind or water power drive where the rpm varies up and down. It will also need to be loaded fairly equally on all three phases, and the output voltage regulation is not going to be very good. Expect to see voltages much higher and much lower than the expected 120 volts, and that can damage some types of load. These self excited alternators certainly work, but they are tricky and temperamental enough to cause some significant problems which many users find quite unacceptable for normal everyday use. Cheers, Tony. |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Warpspeed, Thankyou for the response. I am sorry I did not get back here sooner. I do not check in here regularly, Or very often at all really. I just drop by a couple of times of year looking for suggestions, or hints on how to sort out an issue I am having with building my first turbine system. As for the induction machines? I have not given up on it but time is scarce and I have alot of other projects I am messing with right now. I hope to get back to the IDG later this winter? Robert |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Hi Robert, In order to use an induction motor as a wind generator, one must either machine down the rotor or make a new one then pot magnets on the machined down rotor. The output is then wild AC and is generally recitfied then used for charging batteries. I have made a 2hp motor conversion and it has been going well for years and I am in the process of doing a full conversion on a 4kw motor. With both projects I machined new rotor shafts out of solid bar stock. With the 2hp(1.5kw) I used 8 off 2x1x1/2" neo magnets and used the offset method. Now with my 4kw conversion I used 84 off 16x13mm round N50 grade neo's and put a 0.8mm deep counterbore in to locate each magnet. Now by using the counterbore I did manage to have 22 of the small but strong magnets sitting side by side without any of them moving. Then I potted each pole separately using epoxy. Below is a picture of the 4kw rotor showing 1 of the magnet poles epoxied in and the counterbore on another pole. Each line of magnet is skewed 10 degrees to stop any cogging and I will be doing a full rewind of the motor too. 
I hope this gives a bit more understanding of what is needed in order to use an induction motor as a wind generator. Regards Bryan |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Bryan, I have been considering doing a hybrid induction permanent magnet generator using a 3 phase 3/4 Dayton? It is one of the 9 lead triple voltage 208, 240, 415 motors being I am here in the USA. It is a 1800 RPM unit and I am just wondering if you think it would work? What kind of output can I expect maybe? I do not have the resources for rewinding or machining of the rotor so I want to use this method http://research.ee.sun.ac.za/emr/files/u1/Paper29JHJPotgiete r.pdf http://www.rpi.edu/cfes/news-and-events/Wind%20Workshop/Deve lopment%20Challenges%20of%20PM_Generator_RPI_Qu_v8.pdf Along with a Induction Generator/ Permanent Magnet voltage regulator scheme. This is something I am designing myself at this time. I do need to get wires 10, 11, 12 brought out of the unit yet? Unless I can find the type of leads and connectors a professional motor shop would use so I can do it myself? I want to try the star, delta, jerry connections using a massive mess of diode bridges. I guess I need 6 diode bridges for Jerry as that is the connection I am leaning towards. I plan on using 50 amp 1000 volts diode bridges for their reliability. This motor has a rotor with 5 or 6 holes running the length of the rotor making it very thin and not possible to machine much or drill holes in for round magnets. But if I press in round bar magnets in the North South North method to excite the machine and make it a hybrid induction generator I should be able to use it for a wind turbine I hope? I live in North Carolina and we only get winds in the 5 to 10 MPH range. Right now in the fall and winter we have the wind. In the spring and summer we get no wind at all. So I am thinking of a gear box, or pulley and belt arrangement? The motor rotor looks like this drawing. 
I have a little 1/2 HP GE water pump motor that is 3450 RPM, 115 Volts at 7 amps. With a tiny rotor which makes it difficult to put the magnets in it? I only need one North and one South pole as this motor is only a 2 pole machine. However I cannot find any proper half curved magnets anywhere? I am using this article for this machine and it's conversion. http://www.otherpower.com/otherpower_wind_alternators.html I am only experimenting right now and not looking for any serious output as I am only trying to learn at this point about induction motors and permenant magnet conversions? Blades and towers, etc. I started out 4 years ago on this project and I need to get one of these machines running as I am losing confidence, and faith in myself regarding these projects as I need to just get one unit going to watch and study. The 2HP Dayton I want to use as a induction machine driven by a gas engine so I am not thinking of converting it for wind power at this time. However if my above scheme works I may go ahead and make a bigger wind turbine by using the 2HP machine. Robert I like to try things that have never been accomplished before because no one else has done it! |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Hello Robert, I tried both of those links in your last post and both came up with a 'page not found' error. I was hoping to have a read of them so I can get a grip on what you are really trying to do. Now guys have used servo motors out of welding robots etc, put some blades on and they have made quite good wind generators. Now Tony (Warpspeed) has given a very good insite into trying to use a motor as a AC power source. The motor MUST be run at the name plate rpm or slightly over and caps ARE needed aswell. Trying to go star,delta or even Jerry rigged on a standard induction motor with no magnets on the rotor won't give any real world voltage figures or amps either for that matter. Sorry mate your on your own with this one but before you go too far go and take some AC readings from one phase when the motor is doing 300 rpm and see what you get. If is nothing then simply multiply that nothing with the other phases and that will be your output. Cheers Bryan ( who loves to be proved wrong at times ) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
My feelings as well. Knew a bloke once, he was going to make a carburettor that delivered 200 miles per gallon and would also make his car go at 400 miles per hour. He totally scorned over a hundred years of conventional engineering wisdom, and was going to prove everyone else totally wrong, and relished the challenge. He simply could not understand why nobody was really interested in his revolutionary ideas. Cheers, Tony. |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Byran, I am not trying really reinvent the wheel here or anything. What I hope to accomplish is simply using magnets in an induction motor to provide some excitation while using the caps to make the Induction Generator bit of it work as well to get the full output see here http://research.ee.sun.ac.za/emr/files/u1/Paper29JHJPotgiete r.pdf Note to get the link to work copy and paste the link into your browser and back space the R as it should not have any spaces? For some reason it keeps spacing on me when I try to summit this post. http://www.rpi.edu/cfes/news-and-events/Wind%20Workshop/Deve lopment%20Challenges%20of%20PM_Generator_RPI_Qu_v8.pdf For this one to work remove the space in developement. I do not know why the site keeps spacing my links for some reason? I do want to apologize for my rather rude comment about wanting to try and do the impossible. I do not wish to do the impossible. I wish to make the idea in the above article work if possible? Robert |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Robert, this forum has a hyperlink feature, perhaps that's the reason for the spacing. To use the hyperlink feature click the fourth box (has a globe and chain link picture) on top of the reply page and go from there. The first question is for the click on text that gets shown blue in your message - type a short word - and the next is for the exact hyperlink. Klaus |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Links Permenant Magnet Induction Generator Theory Magnetic Flux Examples Robert |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
GidDay Everyone! I have decided to post some pictures of the motor I am working with in the hopes that what I am trying to do becomes clear? The two links above are the core of what I am trying to do. This link PMIG is the one I am using the most as it shows the PMIG stator and the flux fields. I just don't see why putting round bar magnets in the holes seen in the rotor would not energize the machine enough to start it generating and then use the normal cap method for full power from the machine? Should it not cause the unit to start generating at the slower speeds? 
Robert |
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