Steven Fahey
31st January 2009, 00:33
Hi,
Months ago, I obtained an old Toshiba 7.5 HP three-phase motor. I began converting it for use as a wind-turbine generator by installing magnets on the rotor back in the fall, but since the assembly I haven't been able to get back to the project and finish it off. The complete motor weighs 125 pounds, so even moving it around is difficult.
Here is a link (http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1320&PN=2) to some earlier forum discussion about the assembly process. 24 magnets = BIG FORCES! :-)
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Assembly.jpg
The cogging is noticeable, but not excessive. It seems bad when turning it by hand, but with a suitably sized propeller, there will not be enough resistance to prevent early start-up. I get a laugh out of my GE motor-conversion, whenever I see it tick-tick-tick to a stop, so I expect to see the same from this one, if I ever get it up a tower.
Early bench tests showed me that cut-in will be very slow in this one. Wired in series-star, the 24V cut in is just 40 RPM! It just begs to be wired in parallel, or operated with a 48V battery bank. Later tests show that very high voltages are present at high RPM's, making direct electrical water heat a serious consideration. I had to take unusual precautions while running it up to avoid electric shock. More on this later.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Lathe_Test1.jpg
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Lathe_Test2.jpg
To give Toshi a complete run-up test, I used a lathe at work. This lathe has a 5 HP motor, which sure seemed like enough before I started, but I was wrong! I chucked the main shaft into the jaws and the tail (fan) shaft into the tailstock. Then I bolted a board over the mounting lugs to serve as a torque beam. Sorry if the messy pile of stuff beside the lathe makes it hard to tell how the torque was measured. I just dropped a board on the floor, put an eyebolt through it, and weighed it down with bags of lead shot. It was just a convenient way of anchoring something to the floor under the torque beam. A spring scale connects the torque beam to the floor. Load on the scale indicated torque (force X arm). In all tests the arm was 36.0" (91 cm). If you can see it, sticking out the back was another arm to which I taped a counterweight to get the scale to read somewhere close to zero when the machine was stopped. I still had to deduct a "tare" from the scale reading.
I brought a pile of batteries with me for this test; enough for 24V and 48V trials. Quite a mish-mash here. The smallest battery, from my tractor, was far too small. It suffered a lot of gassing and spilling during the test! This actually affected the test results, so I had to make allowance for the over-voltage when calculating the output that it would actually show if a charge controller was regulating the voltage.
There were a lot of combinations available to test. Unfortunately, I did not have time, nor the extra rectifier, to test "Jerry" connections. I really regret this because it was the perfect opportunity to make comparisons for myself. Not since Flux wrote his "Matching the Load" thread on Otherpower have I seen such a clear comparison of Star, Delta, and Jerry connections, and he wasn't using a motor conversion to do then.
The choices I did have were 24 & 48 volts, series & parallel, star(Y) & delta(D). In the end, I had time for parallel-Y in 24+48V, series-D in 24+48V, and series-Y in 48V. I did not test in parallel-D because the vibration in series-Delta was frightening! The lathe was putting out more noise than I've ever heard it make. After realizing that I should have checked the data plate on the lathe's motor, I discovered that I was on the verge of locking it up! In the end, fear, not power, was the limit to my run-up tests. Hehehe.
It makes for quite a mess to plot all of the curves on one graph. Here they are anyway. Splitting them into separate graphs for Inputs and Outputs will make more sense.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_In.gif
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_Out.gif
Some results aren't surprising, like the output curves at 24V in parallel-Y and 48V in series-Y, which match up very well, because the increase in voltage is proportional to the decrease in current. What WAS a surprise was more output power in series-delta at 24V than parallel-Y. I did not expect that. Nor would I have guessed that the Parallel-Y curve at 48V would line up with the Parallel-Y curve at 24V like it does at 300 RPM!:huh:
Another surprise is how closely the input power required for 24V series-Y and 48V parallel-Y are. You would think that the higher current necessary to make the same power at lower voltage would incur a resistance loss, which would show up in greater input power demand. And yet, the two curves are nearly the same. If anything, it took more power to turn at higher voltage. I'm still scratching my head about that.:wacko:
None of the output power curves are straight lines. They bend down at higher RPM. This is probably a characteristic of motor conversions, where the copper is wound around iron teeth. The windings have a certain amount of reactance to current, due to the iron laminations, which increases when the AC frequency increases. Delta was least affected by this. It is possible that the output would plateau at some speed. I couldn't explore such high speeds due to the immense power required to do so.
Delta-connections seem to be the winner looking at the curves, but something I haven't mentioned yet is the vibration! Sure there was noise during all of the tests, but nothing compared to the heavy vibrations running in Delta! The torque measurements are, in fact, averages of the scale readings, which were often 20 pounds +/- 4 or 5. Windmills have enough trouble with vibrations coming from blade imbalances, tip tracking differentials, cogging, and wind turbulence, I don't think I really need to add any more... Too bad. I can only imagine what parallel-Delta would have yielded, but alas, I didn't dare! Perhaps if I decide to try some Jerry connections, and haul the genny and batteries back for more tests, I will risk a few parallel-delta tests to see what happens.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_Eff.gif
Here's the last graph, where the rubber meets the road, so to speak. After wondering if Parallel-Y would be worth anything at all, here it rises to the top, though only under certain conditions. The P-Y connection offers the highest efficiency in both 48V and 24 Volts. There may be other combinations that give the same or more output power, but more power at the prop is needed to get there.
Which leaves me with the next question: What size and TSR would make a good prop for each of these combinations? Higher TSR is needed for the faster connections, bigger diameter for the less efficient ones. Matching the cubic wind power to the square power generator curve will be interesting to say the least!:rolleyes:
Months ago, I obtained an old Toshiba 7.5 HP three-phase motor. I began converting it for use as a wind-turbine generator by installing magnets on the rotor back in the fall, but since the assembly I haven't been able to get back to the project and finish it off. The complete motor weighs 125 pounds, so even moving it around is difficult.
Here is a link (http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1320&PN=2) to some earlier forum discussion about the assembly process. 24 magnets = BIG FORCES! :-)
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Assembly.jpg
The cogging is noticeable, but not excessive. It seems bad when turning it by hand, but with a suitably sized propeller, there will not be enough resistance to prevent early start-up. I get a laugh out of my GE motor-conversion, whenever I see it tick-tick-tick to a stop, so I expect to see the same from this one, if I ever get it up a tower.
Early bench tests showed me that cut-in will be very slow in this one. Wired in series-star, the 24V cut in is just 40 RPM! It just begs to be wired in parallel, or operated with a 48V battery bank. Later tests show that very high voltages are present at high RPM's, making direct electrical water heat a serious consideration. I had to take unusual precautions while running it up to avoid electric shock. More on this later.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Lathe_Test1.jpg
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Lathe_Test2.jpg
To give Toshi a complete run-up test, I used a lathe at work. This lathe has a 5 HP motor, which sure seemed like enough before I started, but I was wrong! I chucked the main shaft into the jaws and the tail (fan) shaft into the tailstock. Then I bolted a board over the mounting lugs to serve as a torque beam. Sorry if the messy pile of stuff beside the lathe makes it hard to tell how the torque was measured. I just dropped a board on the floor, put an eyebolt through it, and weighed it down with bags of lead shot. It was just a convenient way of anchoring something to the floor under the torque beam. A spring scale connects the torque beam to the floor. Load on the scale indicated torque (force X arm). In all tests the arm was 36.0" (91 cm). If you can see it, sticking out the back was another arm to which I taped a counterweight to get the scale to read somewhere close to zero when the machine was stopped. I still had to deduct a "tare" from the scale reading.
I brought a pile of batteries with me for this test; enough for 24V and 48V trials. Quite a mish-mash here. The smallest battery, from my tractor, was far too small. It suffered a lot of gassing and spilling during the test! This actually affected the test results, so I had to make allowance for the over-voltage when calculating the output that it would actually show if a charge controller was regulating the voltage.
There were a lot of combinations available to test. Unfortunately, I did not have time, nor the extra rectifier, to test "Jerry" connections. I really regret this because it was the perfect opportunity to make comparisons for myself. Not since Flux wrote his "Matching the Load" thread on Otherpower have I seen such a clear comparison of Star, Delta, and Jerry connections, and he wasn't using a motor conversion to do then.
The choices I did have were 24 & 48 volts, series & parallel, star(Y) & delta(D). In the end, I had time for parallel-Y in 24+48V, series-D in 24+48V, and series-Y in 48V. I did not test in parallel-D because the vibration in series-Delta was frightening! The lathe was putting out more noise than I've ever heard it make. After realizing that I should have checked the data plate on the lathe's motor, I discovered that I was on the verge of locking it up! In the end, fear, not power, was the limit to my run-up tests. Hehehe.
It makes for quite a mess to plot all of the curves on one graph. Here they are anyway. Splitting them into separate graphs for Inputs and Outputs will make more sense.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_In.gif
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_Out.gif
Some results aren't surprising, like the output curves at 24V in parallel-Y and 48V in series-Y, which match up very well, because the increase in voltage is proportional to the decrease in current. What WAS a surprise was more output power in series-delta at 24V than parallel-Y. I did not expect that. Nor would I have guessed that the Parallel-Y curve at 48V would line up with the Parallel-Y curve at 24V like it does at 300 RPM!:huh:
Another surprise is how closely the input power required for 24V series-Y and 48V parallel-Y are. You would think that the higher current necessary to make the same power at lower voltage would incur a resistance loss, which would show up in greater input power demand. And yet, the two curves are nearly the same. If anything, it took more power to turn at higher voltage. I'm still scratching my head about that.:wacko:
None of the output power curves are straight lines. They bend down at higher RPM. This is probably a characteristic of motor conversions, where the copper is wound around iron teeth. The windings have a certain amount of reactance to current, due to the iron laminations, which increases when the AC frequency increases. Delta was least affected by this. It is possible that the output would plateau at some speed. I couldn't explore such high speeds due to the immense power required to do so.
Delta-connections seem to be the winner looking at the curves, but something I haven't mentioned yet is the vibration! Sure there was noise during all of the tests, but nothing compared to the heavy vibrations running in Delta! The torque measurements are, in fact, averages of the scale readings, which were often 20 pounds +/- 4 or 5. Windmills have enough trouble with vibrations coming from blade imbalances, tip tracking differentials, cogging, and wind turbulence, I don't think I really need to add any more... Too bad. I can only imagine what parallel-Delta would have yielded, but alas, I didn't dare! Perhaps if I decide to try some Jerry connections, and haul the genny and batteries back for more tests, I will risk a few parallel-delta tests to see what happens.
http://www3.telus.net/faheydumas/Wind_Turbine/3_Motor_Conv/Toshi/Toshi_Tests_24-48_Eff.gif
Here's the last graph, where the rubber meets the road, so to speak. After wondering if Parallel-Y would be worth anything at all, here it rises to the top, though only under certain conditions. The P-Y connection offers the highest efficiency in both 48V and 24 Volts. There may be other combinations that give the same or more output power, but more power at the prop is needed to get there.
Which leaves me with the next question: What size and TSR would make a good prop for each of these combinations? Higher TSR is needed for the faster connections, bigger diameter for the less efficient ones. Matching the cubic wind power to the square power generator curve will be interesting to say the least!:rolleyes: