Electric motor help

Thread Starter

St.Paddy

Joined May 24, 2024
2
A friend of mine gave me a 3/4 hp Lindsey irrigation motor off a water pivot. And I’m trying to figure out if it is more efficient than an induction motor maybe? It says it’s only 48rpm 3 phase motor but it’s attached to a gear box so I’m sure it’s got step down gears to give it the low rpm. Either way I was going to see what kinda power I could get out of it and see if I can get over unity hooking a single phase motor and 3 phase in a closed loop. I’ve got 2 different ideas at what I maybe could do to build a generator it just depends on how efficient this motor ends up being. I’ll attach pictures of the sticker that it has on it and you guys let me know what you think. I was also thinking If it turns out to be on the higher efficiency side would adding n52 neodymium magnets to the armature raise my Efficiency up close to that of a a synchronous motor?
 

MrChips

Joined Oct 2, 2009
31,059
Welcome to AAC!

But don’t go there with any thoughts of over unity. Your thread will be instantly locked and you will be banned from the site.
 

MisterBill2

Joined Jan 23, 2018
19,366
The tag clearly states a 40:1 reduction and 43 RPM out, telling me that the base RPM is 40X43=1720 RPM. So it is a higher slip induction motor. To change to a synchronous operation you would need to design and fabricate an entirely new rotor, which would be a vastly complex project if you were already a master motor design engineer.
So this is not a super-efficiency motor, but a good farm quality motor.
To get any kind of efficiency you can use a single-phase supply, 3Phase out variable speed drive. But I am not sure just what a low speed gear-motor of that size and power would be used for. I used a half-horse reverseable gear-motor to power a dolly to move a travel trailer. That works quite well, it moves about 25 feet per minute, plenty fast enough.
 

MaxHeadRoom

Joined Jul 18, 2013
28,820
You also need to state the new application for the motor , you have in mind, if there is one, It is not worth the cost of converting it to anything more that it is, using a VFD could be one option and by using an encoder for feedback would give you tighter control.
They are usually ordered with the encoder feature option.
 

ThePanMan

Joined Mar 13, 2020
803
to see what kinda power I could get out of it and see if I can get over unity hooking a single phase motor and 3 phase in a closed loop. I’ve got 2 different ideas at what I maybe could do to build a generator it just depends on how efficient this motor ends up being.
see if I can get over unity
Over Unity (OU) is like paying a dollar for power and getting two dollars worth of energy back. If you could do that then everyone would be rich. But then a single grain of rice would cost well over a million dollars.

If I give you a dollar are you going to give me two back? Truth of the matter is that even if I give you a dollar you won't be able to give me a dollar back. There ARE losses that must be paid for. In other words, efficiency rating. If the motor is 80% efficient then for the dollar I gave you the most you can give me back is 80¢.
 

Tonyr1084

Joined Sep 24, 2015
7,989
Either way I was going to see what kinda power I could get out of it and see if I can get over unity hooking a single phase motor and 3 phase in a closed loop.
Can't be done. Energy can neither be created or destroyed. It can only be converted from one form to another. You can turn electrical energy into heat energy. You can turn dynamic energy into (heat energy) friction. Wires get hot. Motors get hot. Bearings get hot. Those are energy losses. And with motors there is windage internally from rotating parts. Many motors have fans to keep them from burning up. That last example is that of turning electro-mechanical energy into wind energy as well as other mechanical energy. You can never get more out than you put in. Never.

Quantum physics in its simplest understanding is that of an electron orbiting its proton. It orbits at a particular - happy - energy level. It's at its level, whatever that level is. When you excite it you pump it up to a higher energy level but it wants to get back to its happy place. You can change its charge but you can not create it. Nor can you get more out of it than you put into it. That electron that is pumped up - when it falls back to its happy place it emits a photon. That photon carries away some level of energy. I'm not a physicist so I know very very little about what I speak. I'm sure if I'm wrong in some fundamental way someone will correct me. But we all agree you can't get over unity out of anything. If you could you'd be a god. Really.
 

MisterBill2

Joined Jan 23, 2018
19,366
Really, the secret to APPARENT over unity is FAKING IT!! What you will be able to get from a 3/4 HP motor with an integral 40:1 gear reduction is quite a bit of torque. What could be rather interesting is to develop a scheme to drive it like a stepper motor, except only delivering power when a step was required. That would be good for a solar power array tracking system.
 

Tonyr1084

Joined Sep 24, 2015
7,989
It depends on how the motor is wired. But using one of the three phases to spin the motor and using the other two phases as a "generator" will still not produce more power than you put in. Suppose your motor is running at 100 watts (VA actually, but lets use watts for sake of understanding the point I'm trying to make). Your motor is running at 100 watts. the two other phases may be able to produce the same voltage as the driven phase but if you try to draw 100 watts out of the other two phases the motor will bog down. In a perfect world you'll get 100 watts total out of the other two phases. And if you put a load on the motor - your wattage will drop even further. Remember, I've used Watts in place of VA. VA (Volt•Amps). VA is the correct term for AC power. Unless (and I'm not 100% on this) a resistive load such as a light bulb rated in Watts may be the correct terminology.

Back to the point - You can't get more out than you put in. Don't think in terms of volts or even in terms of amps. Think in terms of "Power", measured either in Watts or in VA.
 

MisterBill2

Joined Jan 23, 2018
19,366
The way to get more ELECTRICAL power out of a motor than you put into it is to provide MECHANICAL power to spin it. I have read about that being done by spinning a motor with drive from a water wheel. You will need to spin the motor a bit faster than the synchronous speed to do that
But to achieve that from a motor with a 40:1 gearbox will take a lot of torque, and if the reduction is with a worm gear drive it will simply not be possible. So the best choice is to find a use for a gear reduction three-phase motor, or to sell it.
 
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