Is it possible to create a brushless DC motor that runs solely on DC current?

In summary, it is possible to make a brushless motor which runs solely off of DC current, without any electronics or AC. However, this may not be a practical option due to the difficulty of creating a motor with an unswitching DC current.
  • #1
Low-Q
Gold Member
284
9
Hi,

I use brushless DC motors for my hobby things (planes, cars, helicopters). These motors have a special ESC which outputs a 3-phase AC current to the motor. These motors have stationary coils, and a rotary magnet array. The motors have an incredible torque for the size. I have, however, though of a brushless motor which runs on solely DC current, no electronics, no AC anywhere. A motor that can be ran solely by a battery with no fancy ESC to run the motor. Is it possible to make such motors - in theory, perhaps in practice?

PS! Brushless, and no ordinary DC motor with rotating coils.

Vidar
 
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  • #2
There are two types of brushless dc (BLDC) electric motors. Larger ones have internal Hall Effect sensors to sense the permanent magnet rotor orientation and switch the dc polarity to the stator coils. Smaller sensorless BLDCs use external sensing of the Faraday-induced voltages to switch DC polarity.
 
  • #3
It can also be done by winding two sets of coil with the current flowing in opposing directions alternately.
 
  • #4
I was thinking of a motor which do not change polarity at all, not externally or internally. It is fed with DC, it works with DC, it is DC internally, no cogging, no polarity change, no sensors or fancy electronics - just pure DC all the way. I think more like a brushless homopolar motor. Maybe I think too much outside the box :uhh:
 
  • #5
You could take a look at a homopolar motor. It works off very low voltage very high current. You may be pleased to know it doesn't even have coils! However, in a conventional configuration you need some contact at the outer edge, a brush is usually used but you could use a roller or geared arrangement.

In theory, however (and it may well have been done already) you could run two of them in a way that geared them together at the edge. This would avoid the need for a brush.

The same principle was, in fact, the very first 'motor' ever built. It was Faraday's first demonstration of electricity turned into mechanical motion. He used a dish of mercury as the conductor of the electricity and the outer conductor, whereas a homopolar motor uses a rotating conductor.

I do not know of any other means to achieve a motor with an unswitching DC.

It might be amusing for you to take a look at all the various electrostatic generators, and try to figure out if you could make any of those work in reverse, as a high voltage DC motor.
 
  • #6
Is it possible to build a homopolar motor with several windings in order to increase voltage and decrease current?
 
  • #7
Low-Q said:
Is it possible to build a homopolar motor with several windings in order to increase voltage and decrease current?

A hompolar motor has no windings. It works simply by a big fat radial current discharged acorss a metal disc, the current then interacting with a magnetic field normal to the disc.

To make it operate on a bigger voltage, you make the disc bigger. But then you end up with big magnets to find.
 
  • #8
I guess you're right CMB. I have seen and tested homopolar motors myself with small nickel plated disc neodymium magnets. I have understood that the conducting coating on the magnet is a wire too. As long the magnetism in this part of the "wire" can escape from the magnetism in the magnet, it must be brushed - or using a gear ofcourse - but that will not make it possible to wind several windings in the same motor. The motor works more or less like a rotary "rail gun".

What about a looped speaker driver motor system? The coil is aligned in a magnetic field. The longer the coil is the longer the stroke, but I can't imagine how this coil can be looped like a toroid with a pole piece in the middle and a magnet around it - AND make it work. The magnetic flux must return to the other pole, and by that crossing the windings again, which in turn will stop the motor from running...

I think I will continue to use my regular brushless motors.

Vidar
 

1. What is an electric brushless DC motor?

An electric brushless DC motor is a type of motor that uses electronic commutation instead of mechanical brushes to control the speed and direction of the motor. It is a more efficient and reliable alternative to traditional brushed motors.

2. How does a brushless DC motor work?

A brushless DC motor works by using a series of permanent magnets on the rotor and electromagnets on the stator. The electronic controller sends signals to the electromagnets to attract or repel the permanent magnets, causing the rotor to rotate. This process is repeated rapidly to create smooth and precise rotation.

3. What are the advantages of using a brushless DC motor?

There are several advantages to using a brushless DC motor, including higher efficiency, longer lifespan, and lower maintenance. They also have a wider speed range, better speed control, and can operate quietly and smoothly.

4. What are the common applications of brushless DC motors?

Brushless DC motors are used in a variety of applications, including electric vehicles, drones, robotics, HVAC systems, and industrial machinery. They are also commonly used in household appliances such as washing machines, refrigerators, and power tools.

5. How do I choose the right brushless DC motor for my application?

When choosing a brushless DC motor, consider factors such as the required torque and speed, voltage and current requirements, and environmental conditions. It's also important to consider the quality and reputation of the manufacturer and the availability of spare parts and technical support.

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