Motor vs Generator

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Dennis Alwon

Dennis Alwon

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I don't mind showing my ignorance here so....

As I understand it a generator is basically the reverse of a motor but there has to more to it than that. If I take 2 corded drills and chuck them together and plug one in to turn the other am I going to get voltage on the cord of the other drill that is not plugged in? I assume the direction or rotation of the motor won't matter.

If the 2 drills won't work then what would be needed. I know how a simple generator can be built with magnets, coil etc but the 2 drill things got me thinking and that is sometimes a bad thing. Sure I can test it but this way you guys can feel smart.... :D

It seems a bit different. If so then How so?
 
Dennis Alwon said:
I don't mind showing my ignorance here so....

As I understand it a generator is basically the reverse of a motor but there has to more to it than that. If I take 2 corded drills and chuck them together and plug one in to turn the other am I going to get voltage on the cord of the other drill that is not plugged in? I assume the direction or rotation of the motor won't matter.

If the 2 drills won't work then what would be needed. I know how a simple generator can be built with magnets, coil etc but the 2 drill things got me thinking and that is sometimes a bad thing. Sure I can test it but this way you guys can feel smart.... :D

It seems a bit different. If so then How so?
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My understanding is limited, but basically if your two motors are permanent magnet motors your drill thing would work. Small exhaust fans for example. Many motors require power on the rotor and the stator, one to create a magnetic field and the other to be influenced by the magnetic field. A generator usually has an exciter that requires at least a small amount of power.
 
A generator of any type needs two things: a magnetic field and energy input to spin it, or spin something in it. The energy input is your prime mover; an engine, water wheel, wind turbine or in your case, drill motor #1. The magnetic fields can be created by permanent magnets, or by electromagnets. To be created by electromagnets, you need to get electricity to the coils of those electromagnets, wherever they are.

In the case of a typical portable drill motor, those are “universal motors” that are basically DC motors that are designed to run on AC. The AC both powers the stator coils and, through brushes and commutators that create pulsating DC, puts power on the rotor coils to form the rotor magnetic field at the same time to make the rotor spin. But they have no permanent magnets, so there is no field excitation on the rotor coils to speak of. There is a small amount of residual magnetism in the iron core of the stator that can be used to generate a small amount of electricity on the stator, about 1-1/2V. I’ve seen demos on YouTube where someone then fed that small voltage back into the armature of the motor to excite its own windings (called a self exciting DC generator) and they got about 24V out of it, maybe 20-30W, but that’s about it. Then in your case in order to get even that little bit, you would have to disassemble drill motor #2 and access the wiring on the motor itself.

There are types of motors out there that would do better at becoming generators, but they are not the type easily found in cheap tools or appliances. Permanent magnets are relatively expensive to use in motor construction compared to these little universal motors.
 
Jraef said:
A generator of any type needs two things: a magnetic field and energy input to spin it, or spin something in it. The energy input is your prime mover; an engine, water wheel, wind turbine or in your case, drill motor #1. The magnetic fields can be created by permanent magnets, or by electromagnets. To be created by electromagnets, you need to get electricity to the coils of those electromagnets, wherever they are.

In the case of a typical portable drill motor, those are “universal motors” that are basically DC motors that are designed to run on AC. The AC both powers the stator coils and, through brushes and commutators that create pulsating DC, puts power on the rotor coils to form the rotor magnetic field at the same time to make the rotor spin. But they have no permanent magnets, so there is no field excitation on the rotor coils to speak of. There is a small amount of residual magnetism in the iron core of the stator that can be used to generate a small amount of electricity on the stator, about 1-1/2V. I’ve seen demos on YouTube where someone then fed that small voltage back into the armature of the motor to excite its own windings (called a self exciting DC generator) and they got about 24V out of it, maybe 20-30W, but that’s about it. Then in your case in order to get even that little bit, you would have to disassemble drill motor #2 and access the wiring on the motor itself.

There are types of motors out there that would do better at becoming generators, but they are not the type easily found in cheap tools or appliances. Permanent magnets are relatively expensive to use in motor construction compared to these little universal motors.
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I admitted limited understanding but did get it "right". But to go a little deeper then, and I know I could do the research but you obviously just know. How does you typical generator maintain the stator excitement? I know they have an exciter, but what is that, a separate permanent magnet generator that gives off the small electricity needed?
 
Strathead said:
I admitted limited understanding but did get it "right". But to go a little deeper then, and I know I could do the research but you obviously just know. How does you typical generator maintain the stator excitement? I know they have an exciter, but what is that, a separate permanent magnet generator that gives off the small electricity needed?
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Yes, that’s one way to do it, for what’s referred to as “island mode” operation where the only source of electricity is the generator in question. You can also have a DC battery system that
supplies power initially, then taps off of the AC that is generated to make the DC field power once it is producing.

Otherwise, if the generator is “grid connected”, the excitation power just comes from the existing grid via an excitation power supply.

An Induction Generator is basically just an induction motor that has the prime mover turning it faster than its synchronous speed. In that case, they can ONLY be grid connected, because the rotor field is energized BY the grid (as a motor at first). This is what most of the big windmills are.
 
Jraef said:
An Induction Generator is basically just an induction motor that has the prime mover turning it faster than its synchronous speed. In that case, they can ONLY be grid connected, because the rotor field is energized BY the grid (as a motor at first). This is what most of the big windmills are.
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So the disadvantage of an induction generator is lack of control, or that you have to vary speed to control the power flow? Whereas a synchronous machine you can control the excitation field to control the power generation, is this correct?
 
Strathead said:
My understanding is limited, but basically if your two motors are permanent magnet motors your drill thing would work. Small exhaust fans for example. Many motors require power on the rotor and the stator, one to create a magnetic field and the other to be influenced by the magnetic field. A generator usually has an exciter that requires at least a small amount of power.
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So are you saying that 2 small bath fan motors connected as I stated would give me voltage at the end of the unplugged end? DC or AC voltage?
 
Dennis Alwon said:
So are you saying that 2 small bath fan motors connected as I stated would give me voltage at the end of the unplugged end? DC or AC voltage?
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If they are permanent magnet motors - but those are DC motors.

Small bath fans are typically PSC or shaded pole induction motors, you would have to add things to them to control field excitation before they will become generators.

You may have some residual magnetism that allows it to produce a low voltage - but just coupling one motor to drive the other isn't going to produce 120 volt AC output from the second motor.
 
kwired said:
If they are permanent magnet motors - but those are DC motors.
Small bath fans are typically PSC or shaded pole induction motors, you would have to add things to them to control field excitation before they will become generators.
You may have some residual magnetism that allows it to produce a low voltage - but just coupling one motor to drive the other isn't going to produce 120 volt AC output from the second motor.
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There are several type motors that can be altered, modified to act like a generator. Deciding on which type you want, depends on what end result you want to achieve.
OP's aim is basically trying to prove that motors can be converted to generators. . . fine and dandy.

After all, motors are designed using a lot of principles, theories, suppositions etc, that produce electricity as in generators. Save for electro-chemical reactions that we get from batteries.

The easiest type of motor to convert is the synchronous type that employs earth magnets.
OP's approach (using two motors) which in essence is utilizing one motor as the prime mover and the other acting as generator with no modification to either motors.
This scheme is similar to the so-called ROTOVERTER.

The power from this RotoVerter is derived by using a rotating magnetic field from a regular motor mostly a medium sized with three phase winding.
Unlike OP's scheme from the above instance, requires breaking into the motor stator and modifying the connections in order to be able to run this prime mover on a single phase source.

Now, someone will scream “why do we need a motor using the same energy to make energy”.

This is a valid retort. . .but isn't this what OP is trying to do?

The advantage of the RotoVerter scheme is: with the right combination of components (capacitor , inductor, resistor etc) it can produce a higher and much more stable output.

There is more to this than the basic practical approach that's presented here. The main thing is: understanding the basics without having to deal with tedious and often boring (to those lacking the fundamentals) of having to dig through the vagaries that are often associated in electrical engineering textbooks.
 
Another example of an "induction generator" is the old hillbilly 3phase converter. Just take an old three phase motor and wire it single phase. Spin it to get it going and it will act as a somewhat poor three phase generator.

In all fairness these can actually work pretty well if augmented with caps and proper engineering design. There are commercial units you can buy for small shops.
 
kwired said:
If they are permanent magnet motors - but those are DC motors.

Small bath fans are typically PSC or shaded pole induction motors, you would have to add things to them to control field excitation before they will become generators.

You may have some residual magnetism that allows it to produce a low voltage - but just coupling one motor to drive the other isn't going to produce 120 volt AC output from the second motor.
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Looks like you are correct

I took a drill and turned a small squirrel cage bath fan at 1500 rpm and only got .7 V ac
 
The most common large permanent magnet motors that you can find around the home or scrap yard are the drum motors for some front loading washing machines. A very large number of poles and driven by pulsed DC from the control board. Strange looking beasts.
 
GoldDigger said:
The most common large permanent magnet motors that you can find around the home or scrap yard are the drum motors for some front loading washing machines. A very large number of poles and driven by pulsed DC from the control board. Strange looking beasts.
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ECM furnace blower motors also.

But these aren't simple two wire input motors either.
 
Jraef said:
... An Induction Generator ... can ONLY be grid connected, because the rotor field is energized BY the grid (as a motor at first). This is what most of the big windmills are.
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If I understand you correctly, this is quite distressing. So big windmills ("big" = 1 megaWatt and up) require grid excitation, which means that the grid must be up & stable before they can put any power onto the grid?

Hypothetically speaking, what would happen in a region where the majority of power came from these big windmills? What, if anything, would stabilize the grid frequency? How would you get them started during/after a grid outage? Could you disconnect a small region of the grid and use locally-produced power locally, or would it be necessary to wait for the rest of the grid to come back?

On the original topic, I once ran an automobile alternator as a 3-phase 14-pole synchronous motor by applying 6 volts DC to the rotor winding and 3-phase 20.8-volt 60-Hz AC to the stator windings. (from three 12-volt buck-boost transformers) It wasn't self-starting but it did run. I didn't have a dynamometer available to to measure how much torque it could deliver.
 
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drcampbell said:
Hypothetically speaking, what would happen in a region where the majority of power came from these big windmills? What, if anything, would stabilize the grid frequency? How would you get them started during/after a grid outage? Could you disconnect a small region of the grid and use the locally-produced power, or would it be necessary to wait for the rest of the grid to come back?
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You said hypothetically speaking.

Real world, where is such a source the primary method of generation? If wind stops blowing there is no generation period. You can't even rely on such system to be a majority of your generation, if wind stops blowing you aren't going to instantly transfer to more conventional sources without a delay in there. If that alternate source is from a steam driven turbine, that boiler has to be on line and up to pressure at the time of transfer or there will be a shortage of power.
 
myspark said:
There are several type motors that can be altered, modified to act like a generator. Deciding on which type you want, depends on what end result you want to achieve.
Click to expand...

That's how regenerative braking on electric cars works, innit?
 
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