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Forum Index : Electronics : induction motor as generator

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BenandAmber
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Joined: 16/02/2019
Location: United States
Posts: 791
Posted: 02:08pm 15 Nov 2019
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I'm sure many of you on here already have explored this subject

I have read this about induction Motors

When plugged in and running

if you spin it faster than its normally running speed

it will start to produce Electric and back feed

Some wind Mills take advantage of this

Seems like this would have to be how the electric company does is it also

is this something that could be took advantage of

Like when trying to get a generator to sync to a inverter

This may be a very stupid question

please understand it's just an idea

Don't forget my lack of knowledge and understanding on this subject
( and many others)

Second question

Could a large Industrial type motor be used as a alternator

(like car alternator)

if so what would have to be done to the rotor

I'm not talkin about adding magnets

I'm talking about being able to control it
By varying the input voltage

I know brushes and coils would have to be added to the rotor

I was just wondering if anyone has heard of a hack to make it easily done

If special Machining is needed that's okay too

It would definitely be worthwhile because large heavy duty alternators are so expensive

big heavy duty industrial Motors are  inexpensive ( usually scrap value)

I come across them every once in awhile at very cheap prices

Most people aren't able to use them because they are three phase

These Motors are very impressive built to last with continuous use and abuse

These big industrial Motors are made so well a person could depend on one for their lifetime

I have converted a few with magnets and they are very impressive

I don't like having to change the RPM to change the output

Getting one of these to work like a car alternator is the Holy Grail for me

Thanks for your thoughts and your time
 
SimpleSafeName

Regular Member

Joined: 28/07/2019
Location: United States
Posts: 86
Posted: 04:59pm 15 Nov 2019
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You are absolutely correct, I built test stands for Lovejoy that had a 4 pole motor driving a 6 pole motor. This provided a load for their VFDs and generated electricity back into the system. It worked very well.

To your second point, yes you can. You rely on the residual magnetism of the motor feeding into some run capacitors to make this happen.

This was the best video that I found on it:

https://www.youtube.com/watch?v=OML8LjGegrQ
 
Davo99
Senior Member

Joined: 03/06/2019
Location: Australia
Posts: 297
Posted: 02:28am 17 Nov 2019
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There was a comprehensive thread on this recently. Can't remember what it was called now but have a search.

To answer the basic questions:

Yes, spinning an induction motor ( preferably 3 Phase will turn it into a generator over synchronous speed.

Is it practical/ Worthwhile?

In limited Circumstances.
If you want to use it like a normal generator to plug your house hold varying loads into, Forget it.  If you want to run a fixed load like lights you don't switch on and off but rather have the just going, yes.

If you want to direct couple it to the mains and offset your power usage of feed back to reverse your meter, Yes.

You cannot control an induction motor by input voltage. There is no winding on the rotor to do that. You can only control speed and capacitance depending how you hook them up. They are EXTREMELY sensitive to load, speed and capacitance.
Trying to get them to balance between overloading which will crash the Field in standalone mode and not run away with 600V+ is a delicate balancing operation and is only vaguely possible with Constant, non varying loads.

Your best bet to get one to work like an alternator is to put a 3 phase Motor on a Bridge rectifier and send the DC to a Solar inverter that is grid connected.

It's a LONG way from perfect but will work.

Anything beyond this requires HIGHLY complicated or expensive electronics, usually with a dump load to make it work.

On the last thread Tony spoke of his experience with trying this. In a nut shell, He put it in the too hard/ not worth while basket as stand alone so I think that's about all anyone needs to know.   :0)
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 2915
Posted: 03:09am 17 Nov 2019
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This has only one useful application that I can see, and that is bulk recharging a high voltage battery. But even that is tricky to control when the battery reaches the end of bulk charging.

Much better to hook up one or more treadmill motors for recharging a high voltage battery.
At least you can throttle back the engine rpm to reduce the charging current as much as you want, as the battery nears full charge.

With a resonant self excited induction motor used as an alternator, as soon as you try to reduce engine rpm, the whole thing drops out of resonance and stops working altogether.
So you get either flat out full bulk charging current, or nothing at all, with nothing in between.

The internet is full of u-tube examples of guys running 15Hp motors as generators to light a pair of 100 watt light bulbs.  
They very carefully adjust the rpm so it works and say how clever it all is.  
If one light bulb is switched off the voltage shoots up to a fairly destructive 300 volts.  
If a third bulb is switched in the voltage sags to a dull orange 160 volts.
 
Hardly a useful or practical way to generate power for your home or anything else.

Its all jolly good fun, and interesting, but a complete waste of time.
Edited 2019-11-17 13:16 by Warpspeed
Cheers, Tony.
 
BenandAmber
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Joined: 16/02/2019
Location: United States
Posts: 791
Posted: 11:47am 17 Nov 2019
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I have ran induction Motors as generator before

You are right it sucks

if you try to start a motor it stops producing electricity

Just figured it would be an easy way to sync

Now that u explained full out or nothing it sounds pretty silly

I want to change a 3 phase induction motor to a alternator

so it can be controlled

I want itl to work the same way as a car alternator does

How could this be done

Would the windings have to be changed hopefully not

Could a person make a new rotor with slip rings and coils

If a new rotor could be machined and you were able to use the original winding it would be worth while

Thanks for your wise thoughts and time warpspeed
 
Davo99
Senior Member

Joined: 03/06/2019
Location: Australia
Posts: 297
Posted: 10:42pm 17 Nov 2019
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  BenandAmber said  

I want to change a 3 phase induction motor to a alternator

so it can be controlled

I want itl to work the same way as a car alternator does

How could this be done


By going and buying a proper generator would be the best way to do it.  

Converting an induction motor would be an exercise in Futility basically. I could not see a DIY conversion possibly coming in cheaper than buying a proper ready made unit.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 2915
Posted: 12:24am 18 Nov 2019
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  Quote  By going and buying a proper generator would be the best way to do it.


Agree 100%.
Cheers, Tony.
 
BenandAmber
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Joined: 16/02/2019
Location: United States
Posts: 791
Posted: 12:31pm 18 Nov 2019
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I have a old very well built on Onan generator

My whole thing is these 3-phase industrial Motors are built so well

They are also available free or very cheap

I converted one using magnets and I am very impressed with it

I used the motor and the big belt off of a old clothes dryer as a lathe

I'm machined down the rotor with a handheld grinder while the homemade lathe spun it

It was very easy and very accurate

I used the strongest epoxy I could buy to bond on the magnets

I can turn the shaft with two fingers and light up a high output flood light bulb LED of course

I think it would be perfect for hydro

Or a gasoline battery charger

It's not a real large one it's only two horsepower

I have read that the output will be three times the amperage rating on the tag

That is only if you're rectifying the three phase to dc

On a large battery Bank the batteries ought to keep the voltage down

But you can turn it to hard or too fast and burn the windings up

So for it to be used as a good alternator it would need something to prevent this

It would also be nice to be able to control the charge rate



Thanks again for all your thoughts
 
arthur8
Regular Member

Joined: 08/05/2019
Location: Brazil
Posts: 69
Posted: 08:41pm 18 Nov 2019
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  BenandAmber said  I have a old very well built on Onan generator

My whole thing is these 3-phase industrial Motors are built so well

They are also available free or very cheap

I converted one using magnets and I am very impressed with it

I used the motor and the big belt off of a old clothes dryer as a lathe

I'm machined down the rotor with a handheld grinder while the homemade lathe spun it

It was very easy and very accurate

I used the strongest epoxy I could buy to bond on the magnets

I can turn the shaft with two fingers and light up a high output flood light bulb LED of course

I think it would be perfect for hydro

Or a gasoline battery charger

It's not a real large one it's only two horsepower

I have read that the output will be three times the amperage rating on the tag

That is only if you're rectifying the three phase to dc

On a large battery Bank the batteries ought to keep the voltage down

But you can turn it to hard or too fast and burn the windings up

So for it to be used as a good alternator it would need something to prevent this

It would also be nice to be able to control the charge rate



Thanks again for all your thoughts


Hey Bernard, post some photos of it so we can appreciate it. I just love those old Onan's.
 
arthur8
Regular Member

Joined: 08/05/2019
Location: Brazil
Posts: 69
Posted: 08:41pm 18 Nov 2019
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  BenandAmber said  I have a old very well built on Onan generator

My whole thing is these 3-phase industrial Motors are built so well

They are also available free or very cheap

I converted one using magnets and I am very impressed with it

I used the motor and the big belt off of a old clothes dryer as a lathe

I'm machined down the rotor with a handheld grinder while the homemade lathe spun it

It was very easy and very accurate

I used the strongest epoxy I could buy to bond on the magnets

I can turn the shaft with two fingers and light up a high output flood light bulb LED of course

I think it would be perfect for hydro

Or a gasoline battery charger

It's not a real large one it's only two horsepower

I have read that the output will be three times the amperage rating on the tag

That is only if you're rectifying the three phase to dc

On a large battery Bank the batteries ought to keep the voltage down

But you can turn it to hard or too fast and burn the windings up

So for it to be used as a good alternator it would need something to prevent this

It would also be nice to be able to control the charge rate



Thanks again for all your thoughts


Hey Bernard, post some photos of it so we can appreciate it. I just love those old Onan's.
 
BenandAmber
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Joined: 16/02/2019
Location: United States
Posts: 791
Posted: 10:38pm 18 Nov 2019
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Haven't used it in a long time

I've had no use for it after finishing the first inverter build

Not that I can remember anyway

If I needed it it would start up very quickly

I drained all the gas out of it last time it was used

It takes a 12 volt car battery and it does charge the 12 volt battery

It has two outlets in one metal box

I have done absolutely nothing to it except putting new points in it and changing the oil





I would like to figure out how to change it over to a DC battery charger

It is 2000 watts 120 volts ac

It is ginormous and weighs probably three or four hundred pounds

It was built to last forever

It is on a four wheeled cart

it was on this cart when I bought it

It makes it easy to move around
Edited 2019-11-19 09:46 by BenandAmber
 
brucedownunder2
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Joined: 14/09/2005
Location: Australia
Posts: 1361
Posted: 11:28pm 18 Nov 2019
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Hi Arthur ,  Bruce and Ilda here..

How is that inverter build going ..

Maybe you start a new thread on it ,thanks

Bruce
Bushboy
 
Davo99
Senior Member

Joined: 03/06/2019
Location: Australia
Posts: 297
Posted: 05:34am 19 Nov 2019
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  BenandAmber said  

I converted one using magnets and I am very impressed with it


Your thread title and what you are saying/ asking now are 2 Different things.

Converting an induction motor with magnets makes it a permanent magnet generator.
That is different, VERY different to an IMAG.

Far as I'm aware, the only way to control a permanent magnet generator is by speed and although I have had nothing to do with them, I don't think it would be a great way to do it.  If you are charging batteries for instance the load would vary and so would the output and the same goes for any switched loads.

If the load increased the voltage would sag and vice versa. There may be some control in an engine governor but I doubt the permanent magnet generator output would be linear.  

Again, as with an IMAG, probably the best control would be to run a fixed speed and control the output with a dump load and something like a PWM controller that held the output constant by varying the power into the dump load.
Again you cannot control the output internally as you would have to vary the magnetic field. That is done on a regular generator by the windings on the rotor which is basically an electro  magnet.

What exactly do you want to use this for, what are you intending to drive it with and how much power are you looking to get out of it?
 
BenandAmber
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Joined: 16/02/2019
Location: United States
Posts: 791
Posted: 06:09am 19 Nov 2019
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I was originally asking if anyone new of a good way to build

A rotor with windings so it could be controlled by the magnetic field

A lot like a car alternator

This would be idea for a three phase motor

This was the original question

I Already have made one with magnets

And I have a generator already

I just thought it would be a very affordable way to build a gasoline or diesel powered battery bank charger

As far as power output I haven't got that far yet

Just looking for ideas on how to build the rotor first
Edited 2019-11-19 16:14 by BenandAmber
 
arthur8
Regular Member

Joined: 08/05/2019
Location: Brazil
Posts: 69
Posted: 06:56am 19 Nov 2019
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  brucedownunder2 said  Hi Arthur ,  Bruce and Ilda here..

How is that inverter build going ..

Maybe you start a new thread on it ,thanks

Bruce


Hey Bruce, my dear friend.  

I'm slowly making progress on the inverter boards, waiting the components to arrive from China.

If everything works as expected, the inverter should be running on the next few weeks!

Here is my topic about a generator we bought: https://www.thebackshed.com/forum/ViewTopic.php?FID=4&TID=11840

And the original inverter topic, i will post new follow ups soon:
https://www.thebackshed.com/forum/ViewTopic.php?FID=4&TID=11433

Wish you and Ilda the best and i still owe you a beer.      
 
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