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Forum Index : Other Stuff : M-G Set
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
When I was a kid, a friend's dad had a "motor-generator set" (M-G set), which was an electric d.c. motor on one end and a direct-coupled generator on the other that made a.c. Anyone here know anything about these things and where they could be found for sale without having to make one up from scratch? I thought it a more-novel way to make a.c. from d.c. than by using an inverter. My guess is you could size the motor and generator to handle a specific load. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
G'day MacGyver, I do have a schematic of a DC to square wave AC inverter, all it uses is a few resistors, a LM358 opamp, a hand made transformer to suit the voltage you need and a few caps. I made the schematic in splan5 and printed it out but splan crashed and I lost everything so I can scan the printout and post it you need.... Cheers Bryan |
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GreenD88 Senior Member  Joined: 19/05/2009 Location: United StatesPosts: 104 |
Find you an AC induction motor and drive it with a DC motor pretty simple. Surplus stores probably be the best place to find the motors. Here's a lil how to on getting induction motors to generate power. Induction Generator. I know around in central Kansas by Wichita, there some people selling Grid Tied Wind Turbines without inverters, what they use is large geared induction motors. And a Micro controller circuit to drive the relays for cut in and stuff.Prairie Wind Turbines I don't know where you could buy one already made up though, I know a lot of old buildings that needed three phase use to use this type of setup except they used a AC single phase motor to drive a 3 phase motor to power equipment. Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
These are MG-Sets , might be a bit big for what you want , they are used to convert AC to DC for 33,000 ton Draglines that I work on . 
PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Honeywell made portable units. 500W or about. used to be available before inverters came in vogue. units would fire up when the AC load was applied. Most were 12V type. Gordon. become more energy aware |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=GreenD88]Here's a lil how to on getting induction motors to generate power. Induction Generator. Daniel: Thanks for the two links. I'm fascinated by this one about induction motors. This may be key to simplifying building a small wind generator that is adequate for charging a deep-cycle 12-volt battery and may be just what I was looking for. I'm a great one for "reinventing the wheel" as it were. If I can simply modify an off-the-shelf item, I'd rather do so than slip into old habits! I'll research it further and maybe build something based on what I turn up. Thanks again. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi MacGyver, Yes, you can use an induction (ie standard squirrel cage) motor as a generator. In 60 Hz country like the USA, a 2 pole induction motor runs as a motor at just a bit less than 3,600 rpm. A 4 pole motor runs at just a bit less than 1,800 rpm, etc. The values of 3,600 rpm for a 2 pole, 1800 for a 4 pole, 900 for a 6 pole, etc, are the synchronous speeds for the number of poles. The amount that the motor runs below the synchronous speed is called the slip. A 4 pole motor may indicate on its nameplate that, at rated load, it will run at, say, 1,720 rpm. The 80 rpm difference between the nameplate speed and 1,800 rpm is the slip. To get this motor to run as a generator, you have to spin it up till it is running 80 rpm above its synchronous speed, or 1,880 rpm. At this speed, it should be generating at least its rated power. Note that you can probably get it to generate more than its rated power by increasing its speed a little more. The reasons that it works better as a generator than as a motor are because its fan is running faster, so that its cooling is better, and also the prime mover is now supplying the power for the fan and the friction losses. There is, of course, a catch, and that is that the motor will only work as a generator when it is connected to a grid. The other problem is that, if anything happens to the prime mover so that it looses power and slows down, the generator will again begin acting as a motor, and will drive back into the prime mover. Another problem for using an induction generator with, say, a wind turbine, is that the generator needs to operate at pretty much a fixed speed (1,880 rpm in the example given), and will not tolerate overspeeds. I hope that this helps. Regards Don B |
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| GreenD88 Senior Member Joined: 19/05/2009 Location: United StatesPosts: 104 |
You don't have to have it hooked up to the grid to get it generate. Although you can't start it up with a load on it. But being able to hook it up to the grid and having it put power back into the grid is a plus; though only do it if you have permission from your local power company. And with simple circuitry you can control when it connects to the grid and when it should disconnect to keep from acting like a motor. This can also be used if you want as a backup generator with a diesel,gas,steam,air... engine's. Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Sorry GreenD88, but I have to disagree with you. It is possible to use a capacitor to get a standard squirrel cage motor to self excite, but it is a really complicated exercise to control its output as a self excited generator. The following quote was found from Renewable Energies website when Googling induction generator, but it is typical. "What is an Induction Generator? An "induction" generator is essentially a special purpose motor that is run slightly above synchronous speed by the turbine. Induction generators receive their excitation from the grid, or electric utility and they have no means of producing or generating voltage until such time the generator is connected to the grid. Induction generators are direct-drive. The frequency and voltage of the power generated with induction generators are governed by the frequency and voltage of the incoming electric utility line. Induction generators can ONLY be run in parallel with the grid, which means when the electric grid goes down, or there is a blackout, ALL gensets, cogeneration and trigeneration power plants within the grid that has the blackout, also go down. This is why customers seeking greater power reliability should only consider cogeneration and trigeneration power systems that have SYNCHRONOUS generators." It should also be noted that the fact that an induction generator's output drops to zero when the grid goes down is a virtue for a grid connect application. Dropping the output to zero on failure of the grid is a requirement for all grid connect inverters or generators for the safety of supply authority workers who may need to work on the grid system fault. Regards Don B |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew: Thanks for all the input. Unfortunately, I'm reminded of that old saying, "There's no such thing as a FREE lunch." Just when something comes along looking pretty decent, something else comes along side and pulls the rug out from under it. Last evening I was tinkering in the shop (garage) and using several fingers and my nose, I held wires to light bulbs, then spun a small 12-volt d.c. electric motor with my thumb from the other hand and the bulb lit! Eureka! This morning (Hey! It's really an hour later! Just remembered it turned to Daylight Savings Time while I was snoozing.) I'll put together a "test stand" that should hold everything together at once and I'll experiment a little with motors and light bulbs. I have an idea of a way to excite the field windings of a 2-speed 12-volt d.c. electric motor, while turning the thing with either my fingers or a drill motor in an attempt to generate more d.c. I'll post the results here if it works. There just HAS to be a way to make a really simple direct-drive wind generator without all this fancy machining and epoxy and stuff. I'm not against building the ax-fx in general; I'm just extremely lazy. There, I've said it; now you know. That personality trait (lazy) is likely what turned me into a 300-pounder too, eh? I'm down 11 pounds, by the way! 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| GreenD88 Senior Member Joined: 19/05/2009 Location: United StatesPosts: 104 |
From what I've seen and read about them, you can get it to work rather easily with the capacitor's, and have seen videos of power tools and lightbulbs running off them. I'll try it when I come across a induction motor, I might even have one in my shed to use if I dig deep enough. I'll post it on here if I get it too work or not. Edit: I just read your post Mac, and yeah Daylight savings messed with me too this morning. Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=MacGyver]I'll put together a "test stand" that should hold everything together at once and I'll experiment a little with motors and light bulbs. Well, I got the test stand finished and even spun up the little 12-volt motor with my hand drill. It lighted a 7-volt automobile lamp very brightly. I didn't take time to get out the volt meter or take any pictures. Today was picture perfect weather, but as soon as the sun set, it got nasty cold in the garage shop. My hunch is the thing puts out somewhere between 6 and 14 volts, because I hooked it up to a 12-volt automobile LED tail light and it made that pretty bright as well. If I build this into a windmill, I'll have to concoct some kind of transmission that increases the shaft rpm for it to make any useable electricity. No problem, I like messing with belts, pulleys, gears and stuff! Pictures to follow as soon as I chip away the ice in the garage! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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