Want to build DC motor, coils in Stator, Magnets in Rotor...

[Enrique15]

build dc motor

Hello, folks.
Here I am again with another question.

I've read about new DC motors for Radio-control cars. They are Brushless, and so more efficient. How "Brushless"? Well, instead of current flowing through windings in the rotor (needing the Brushes to feed with dc current the windings while the rotor is spinning), the rotor is made up with magnets. But it seems they lack of popularity for now (because of bussiness matters, for example, companies that make a lot of dc motors with brushes).

Well, maybe bussiness people don't want this motor to be too popular for now, but I got the idea of building one for myself. Of course, a larger dc motor (maybe for making myself an ELECTRIC CAR :wink: )

So, in this idea of making such kind of motor, but in a larger size, would it work if I only use electric current through windings in the stator, and MAGNETS in its rotor ?

Let me be more specific: If I only use current in the stator, for example, with 6 pairs of windings simulating the poles of a magnet, and each pair being fed up with current at a time, so to obtain a spinning magnetic field (as in AC induction motors):
WOULD IT BE POSSIBLE TO MOVE WITH ENOUGH FORCE A ROTOR MADE UP OF ONLY MAGNETS ???

I have studied about AC and DC motors in college, and I still review some books about the topic... but thinking of this new sort of motor, the DC MOTORS theory doesn't work (I think)... it seems more likely that AC motors theory will adjust to it, even though it's controled with dc current, because it'll be "transient" dc current (like a "DC current-AC current" converter).

I don't know if I made myself clear, so you understand my point.
In a phrase:

If I want to work in a project of making myself an Electric Car (taking out the gas motor of an old car and installing the "brushless type" electric motor), would it be possible ?

Because I'm not sure of how much FORCE a motor needs to move its weight, and of course, I don't know how much Current would it need to apply that Force ???
I still need that kind of Numbers to do my calculations... 8O

What do you think ?
Do I need a little help, or BIG help ?
Am I crazy, or could it be done ?

I'll appreciate any pointers you could give me...

Also, is it possible to buy ON-LINE (on Internet) magnetic cores for transformers and motors ??? Because I'm now with the idea of making my own motors and transformers. And in my country the only think I'll get is already-made transformers and motors. And what I want is to do my own desings as a way to practice what I learned in college.
And to do so, I need magnetic cores with datasheets that will tell me the facts and numbers I need to know for my calculations.

Thanks A LOT for any help.

See you later. 8)

 

[hock]

how to make a stator

permanent magnet moters will be able to give you power in the range of few 100s of watts.
also the tarque to weight ratio will be much smaller in case of permanent magnet moters.

why dont you use a induction moter driven by a power electronics controller?
hock

 

[Enrique15]

how to build a stator

permanent magnet moters will be able to give you power in the range of few 100s of watts.
also the tarque to weight ratio will be much smaller in case of permanent magnet moters.
why dont you use a induction moter driven by a power electronics controller?
hock

Thanks for the FAST answer to my topic, Hock.

What you tell me about using an induction motor, I supose is due to the fact that magnets only have ONE LEVEL of magnetism, while the induction motor will have LEVELS of magnetism due to the spinning speed and magnetic field cutting the rotor.

So, in conclution, instead of "building" a new motor, I just have to take an Induction motor, and feed it with "Controlled DC current", so the DC current would act similar to AC current ???
So simple as it sounds ???

But then it comes this question:
If I'm trying to make a DC motor because I want to feed it with Car Batteries (Acid batteries), not with the "120V AC" voltage line...
Will it be very difficult to feed the motor with just the car batteries, even if I use more than one (in a parallel structure) to provide more current (assuming that the motor needs a great amount of current to move) ???

Because if that's the problem, I was thinking of using a Generator coupled to the motor, so while the motor rotates, the generator will recharge the batteries ???
Of course, there's the problem of regulating the rotating speed of the generator, because the motor will rotate at different speeds (when increasing or decreasing acceleration).

It seems like a hard project. Or is not ?
Maybe is easier than I thought, but because I don't have ALL the knowledge, I see it like if it's very difficult.

What can you tell me.

More ideas ???

Thanks a lot, again, for all the help.

Regards.

 

[hock]

build a stator

the power required will remain the same in either using low or high voltage motors.
The weight will also be almost constant. For your power electronic driver stage. For battery charging stage you will need some kind of kug converter to generate a fixed output voltage.
I will advise you to go for the following

1) Use high capacity 24 v batteries.
2) Use high efficiency aircraft grade induction motor, they run at 400 Hz and hence more compact and less bulky.
3) Look for invertors for above motors, should be available as a standard.
4) Use photo voltaic method for battery charging on the run.
5) use dynamic breaking on the induction motor to feed power back to the battery when motor is slowing down or you are breaking
6) try to keep the dead weight as low as possible

let me know if you need further help
hock

 

[VVV]

building a dc motor

Brushless DC motors can be built the way you intend. Many are in fact built like that. The problem is that you need sensors on the rotor, to tell you when to switch the voltage to which coil in the stator. In brush motors, all this switching action is done by the brushes thmselves, as the rotor rotates.
But here you need sensors (usually Hall effect ones) and you need some transistors to do the switching. Your motor becomes a more complicated piece of equipment.

 

[Enrique15]

make a stator

Hi there, fellows. Thanks for replying.

VVV said:

Brushless DC motors... problem is that you need sensors on the rotor, to tell you when to switch the voltage to which coil in the stator... and you need some transistors to do the switching. Your motor becomes a more complicated piece of equipment.

That's right, it has its complications. I've read about building this kind of DC brushless motors, and about the extra work it has to be made with sensors and other things to control the magnetism direction in order to move correctly the rotor.

But that kind of control circuit won't be as complicated as the one to switch the DC current and voltage in order to convert it into AC current and voltage, if using an induction motor (because for induction I need AC voltage, while feeding it with DC battery) :?:

hock said:

1) Use high capacity 24 v batteries.
2) Use high efficiency aircraft grade induction motor, they run at 400 Hz and hence more compact and less bulky.
3) Look for invertors for above motors, should be available as a standard.
4) Use photo voltaic method for battery charging on the run.
5) use dynamic breaking on the induction motor to feed power back to the battery when motor is slowing down or you are breaking
6) try to keep the dead weight as low as possible

1) The fastest way to build my "Electric Car" would be buying an Induction Motor. But those motors are for 120 V, aren't they ??? Or can I get one of big size (to push heavy weight) that works with 24 V ???
Because if there's no motor for 24 V, then I'll have to "coil-up" my personal made-up motor, as I was planning from the beginning.

2) and 3) "aircraft grade induction motor". It can be get in the market ?? Or do you refer to it as a "model" to use for my design??

4) For the "battery charge" I was thinking in something similar to the method: "alternator + voltage regulator" scheme that use the gasoline cars nowadays.
The problem is that this "Voltage Regulator" regulates the current fed to the rotor coils, and therefore, it uses brushes. And that's what I don't want to use: brushes.
If I use "magnets" in the rotor of my alternator, would it be enough to generate good voltage ?
The trouble will be to regulate the voltage because of the rotation speed.
Where can I get theory about the "photo voltaic method" you suggest ? To see if it can work with the "rotation-changing voltage regulation problem".

5) "dynamic breaking on the induction motor". I'll have to search for some theory about that. I know about the use of Eddy's currents to slow down machines. Is that related to what you refered me to here ??

6) about the weight... my idea is to make a personal "Electric Car" with this "motor+generator+battery" system. So I'm planning to carry at least 4 people and a little more weight. Of course, not adding a lot of metal parts... just the ones to support the electric system and the people.
Would a 24 V motor move this kind of weight ?

It's just that I'm convinced that "current" is the important matter regarding a motor. Because the current is what generates the magnetism.
That's why I believe that a 12 or 24 DC battery can do the work, if it has a good amount of "Amperes-hours". Because the main idea is to maintain recharged the battery so it could keep feeding the motor.

I was planning maybe a system of switching batteries. Having two batteries, one for feeding the motor first, and when its voltage is falling, disconnect that battery from the motor and connect it to the alternator, while connecting the second and full battery to the motor to continue feeding it... and so on the cycle.

Any comments... suggestions... ???

As I said before, maybe I'm crazy for trying doing it.
Because if millionaire car companies haven't done such a car, with all their experience, why could I ?
Even if I have the idea, maybe it's more difficult than I think to make ir reality.
Of course I'm not trying to make a car to sell, hehehe. Because it won't even have roof or doors. :lol: I just want to do a little machine to ride without using gasoline and without the trouble of charging energy back in some station.
It could be helpful for a Master degree work, or at least for trying a different use of electricity.

See you later. And thanks for your help.
Regards.

 

[hock]

how to make a dc motor

As I said before, maybe I'm crazy for trying doing it.
Because if millionaire car companies haven't done such a car, with all their experience, why could I? Even if I have the idea, maybe it's more difficult than I think to make ir reality. Of course I'm not trying to make a car to sell, hehehe. Because it won't even have roof or doors. Laughing I just want to do a little machine to ride without using gasoline and without the trouble of charging energy back in some station. It could be helpful for a Master degree work, or at least for trying a different use of electricity.

No you are not crazy.
Other companies have not done it for one simple reason. They do not fiend economical.
Some have developed hybrid cars but they are very expensive luxury cars.
the second problem is run time and distance limitation as battery can not be charged very fast.

I was planning maybe a system of switching batteries. Having two batteries, one for feeding the motor first, and when its voltage is falling, disconnect that battery from the motor and connect it to the alternator, while connecting the second and full battery to the motor to continue feeding it... and so on the cycle.

It is a waist of energy. you should connect both or all the batteries together.
This will increase your power level and torque to weight ratio.

It's just that I'm convinced that "current" is the important matter regarding a motor. Because the current is what generates the magnetism.
That's why I believe that a 12 or 24 DC battery can do the work, if it has a good amount of "Amperes-hours". Because the main idea is to maintain recharged the battery so it could keep feeding the motor.

Current can be converted in to voltage, what matters is power. You can use a transformer to step up or step down the voltage, current will follow the reveres pattern as VI must remain constant

The fastest way to build my "Electric Car" would be buying an Induction Motor. But those motors are for 120 V, aren't they ??? Or can I get one of big size (to push heavy weight) that works with 24 V ??? Because if there's no motor for 24 V, then I'll have to "coil-up" my personal made-up motor, as I was planning from the beginning.

Induction motor is the best choice for you. You can use any voltage motor for your need. Use a standard rating motor.

) "aircraft grade induction motor". It can be get in the market ?? Or do you refer to it as a "model" to use for my design??

Aircraft uses 400 Hz motors in place of 50 Hz motors to reduce core weight.

For the "battery charge" I was thinking in something similar to the method: "alternator + voltage regulator" scheme that use the gasoline cars nowadays.
The problem is that this "Voltage Regulator" regulates the current fed to the rotor coils, and therefore, it uses brushes. And that's what I don't want to use: brushes.
If I use "magnets" in the rotor of my alternator, would it be enough to generate good voltage ? The trouble will be to regulate the voltage because of the rotation speed.
Where can I get theory about the "photo voltaic method" you suggest ? To see if it can work with the "rotation-changing voltage regulation problem".

read any good nook on power electronics. You will find a lot of good material on ac drives. Power electronics and ac drives by b. k. Bose is the best book.

]"dynamic breaking on the induction motor". I'll have to search for some theory about that. I know about the use of Eddy's currents to slow down machines. Is that related to what you referred me to here ??

When the DC motor is running faster its terminal voltage is higher then the supply voltage, this higher voltage will feed power to the dc battery.
Same can be done in case of an induction motor.

about the weight... my idea is to make a personal "Electric Car" with this "motor+generator+battery" system. So I'm planning to carry at least 4 people and a little more weight. Of course, not adding a lot of metal parts... just the ones to support the electric system and the people.
Would a 24 V motor move this kind of weight ?

You are expecting very much. just expect the car to carry you only.


i hope i have replied many of your quarries.
hock

 

[Enrique15]

make stator

Thanks A LOT, hock, for taking the time in helping me further with my doubts.
It's a great aid what you tell me here.

About what you said:

You are expecting very much. just expect the car to carry you only

Thanks for putting it clear. I needed to know if I was "expecting too much".

I shouldn't be asking for more help, but is about your previous reply, where you said:

use dynamic breaking on the induction motor to feed power back to the battery when motor is slowing down or you are breaking

Here you said: feeding power back when "slowing down".
But in your last reply you said:

When the DC motor is running faster its terminal voltage is higher then the supply voltage, this higher voltage will feed power to the dc battery.
Same can be done in case of an induction motor.

This time you speak about feeding power back when "running faster".

And what gave me doubt is the one that says: feeding power back when SLOWING DOWN the motor. How can this be done ?

Again, thanks a lot for your support!!!

Hope I can make a "24V motor" car that can give me a ride (at least one or two blocks before exploding, hehehe :lol: )

Regards.

 

[hock]

dc motor coil

when you are going down the hill you get more speed due to gravity.
now your car is moveing faster then the motor and hence you can feed back power.
in case of breaking you can reduce the power generated by motor by reducing the speed. in this case also the car speed will be more the the moror speed. hence in this case also you can feedback power to the motor.
hock