Industrial 3-Phase Motor conversions

Making a wind generator from an industrial motor

If you are willing to compromise a little on performance, and you have access to suitable industrial motors, then the conversion of these motors may be a great tool for producing electricity. Converting the industrial motor to be used as a wind turbine alternator should not be thought of as “the easy way”. Since you are taking something that was designed for one purpose, and using it for another, you are bound to sacrifice something (usually performance) to gain something else (ruggedness and most of the wiring done for you).

Before you start

You should have the following things:
  • The motor, of course. Read MORE HERE about how to pick a motor – some are better than others!
  • A machine shop with a lathe (whether you just turn down the rotor, or make a new one from scratch)
  • A vernier or machinist’s caliper (try to find the plastic ones that won’t stick to the magnets)
  • Wrenches, screwdrivers, wire cutters/strippers, etc.

At the very beginning, you have a choice between 3-phase motors and 1-phase motors. If the motor is single-phase, then you probably have a motor with an auxiliary winding that is designed to work with a combination of capacitors and/or centrifugal clutches. Some of the wiring is wound at 90 degrees to the main wiring, and this may not have the same wire, resistance, or number of turns as the main wiring. You will have to work around this limitation, either by stripping out all of the wire and starting fresh, or by leaving it all in, and running the motor at an over-speed to produce electricity. 

If it is a 3-phase motor, then it is much more suitable for use as an alternator. When the output AC is rectified, the DC is fairly smooth. If the alternator is actually going to produce electric heat, say in a water heater, then install three AC heating elements.

When you are considering a motor for conversion, start by simply looking at it carefully. Is it in good condition? Is anything bent or damaged? If the motor is old, then a thorough inspection is due. Open it up and examine the wire in both ends for scratches, burning, un-tying, bare copper, or worse, corroded copper. Check the leads coming out the side, are they intact? Take note of how many there are. Using a CHART of typical motor wire connections, identify each wire coming out, and take some rough resistance measurements to confirm that all phases are roughly the same.

If the motor is new, the manufacturer has no warranty for what you’re about to do to it!

Your motor's specifications

Next, read the data plate. At first glance you should see this much information:

  • Power
  • Speed
  • Voltage
  • Amperage

Funny enough, you won’t need the Power number any more. Converting the motor makes the dataplate power rating irrelevant.

The next number, speed, is very important. The speed number tells you how many poles are in the motor. Round the speed number up to the nearest hundred. For example, if it’s 1740, round up to 1800. If it’s 1120, round up to 1200. When you divide that number into 7200, you get the number of poles in the motor. So 7200/1800=4 poles, 7200/1200=6 poles. The number of poles is extremely important, it tells you how many groups of permanent magnets you must install on the rotor.

Note, for Europeans, and others whose local electricity has a frequency of 50Hz (not 60Hz like in North America), you need to be careful to divide your speed into 6000. In that case, a motor with a speed just under 1000 RPM has 6 poles (6000/1000=6). The data plate should tell you for what frequency the motor is designed, if there is any doubt.

At this point, I expect you have a 3-phase motor with either 2, 4, or 6 poles. If your motor has more than 6 poles, then it might be very heavy. If you were to set two motors with the same power rating side by side, the one with more poles will probably be the heavier one. This is because for every pole, there must be at least one winding of wire. The more windings of wire, the more slots are required in the stator, and the more slots there are, the bigger the motor must become, hence heavier. I have two salvaged 5 horsepower motors. The 2-pole motor weighs about 25 pounds. The 6 pole motor weighs almost 200 pounds! I doubt I will ever raise that beast on a tower!

Operating voltage and power

The next part is either difficult, or obvious. What voltage range are you designing your motor for? Are you thinking of starting with a 12V battery bank? Will the voltage output fluctuate in a water heating element? Maybe you already have a battery bank and it’s wired for 48V? These are important considerations, and they will have a very large impact on the success of your alternator. Typically, industrial motors are designed for high voltage; at least 208V, if not 460V or more. You have to de-rate the motor according to the voltage of your system, although the floating-voltage water heating case is a bit of an exception. Let’s assume from now on that you intend to use the wind turbine to charge a battery system, in which case the voltage doesn’t vary too much.

The motor’s data plate also lists the rated current. As a motor, it would draw that much current when it was delivering its rated output. Different motor behave differently, but almost all motors draw a high inrush of current before getting started. Also, if they are turned on when the shaft is locked, a high current would be drawn. The locked rotor current can be twice as much as the full load current. When you make this motor into an alternator for the wind turbine, you may choose to leave the wire as-is. In that case, then the wire’s current rating still holds. You cannot expect much more than the full-load amps when turning the windmill blades. Any more current than that will heat the motor up, and exceeding the locked-rotor current rating will damage it quickly.

If that much current is not enough for your needs, then you must either re-wind the wire in the stator, or use a different motor. Keep in mind that the motor’s current rating is for an individual phase of AC, but if you rectify the motor conversion’s output, then you can get more DC current. Don’t mix up the two. When rectifying the AC, there are at least two phases providing current at any time, so overall DC current can be 73% more than the rated AC current per phase (as written on the data plate).

Now that we’ve established that your wind turbine motor will work at a constant voltage, and the current is limited by the existing wire, the power you can expect is easy to calculate:

  • P = V x A
  • eg. 24Volts DC x 20Amps DC = 480 Watts DC electric output (empty battery)
  • eg. 28Volts DC x 20Amps DC = 560 Watts DC electric output (full battery)

Is that all I get?

In a nutshell, yes. I said that the motor conversion was a compromise. For the same mass of magnets, you could probably generate twice as much power from an AXIAL FLUX ALTERNATOR. The compromise comes from having the mounting, enclosure, and wiring all done for you. The motor’s ability to suffer abuse and extreme weather up there on the pole surpasses that of the Axial, which uses glue as a major structural component.

The motor conversion that I currently have flying, the GE, easily delivers 500 Watts in strong winds, and I have seen peaks upwards of 700W. Usually it puts out 100W, because there is usually only a breeze blowing around here. This is more than satisfactory for the needs of my barn and other animal shelters. I even have excess that I can “dump” into heating the water in the animals’ troughs from time to time, relieving the need to heat them with electricity off the grid.