We're using AC BL, what about DC BL?

[aqwut]

Hey guys,

We are using AC brushless motors right? I was thinking are there any DC brushless motors out there that can handle higher RPMS?.. I found some that can run 25000rpms, but very low power ratings (wattage)... I was thinking maybe they have more torque than the motors that we are using.. ? The feigaos, Neus, Lehners, Pletts, etc.. are 3 phase AC right?...

[BrianG]

Well, we're sorta using both. AC means alternating current, which usually refers to a voltage that goes positive and negative in reference to a neutral or ground point. So, technically, we're using "pulsed DC".

Yes, all these motors are simply 3-phase AC motors. However, in absence of a true since-wave generator, pulsed DC works fine. Besides, a variable frequency-drive ESC would be a bit larger and more complex.

[sikeston34m]

The traditional definition of AC as it pertains to electricity is "Alternating Current". Household single phase current is 60hz, or 60 cycles per second. In other words, it reverses line voltage polarity 60 times a second.

DC current, of course, only flows in one direction.

With the method that brushless ESC's use, I think a more precise term would be "chopped DC".

There are tricks from several different electrical types at work here. Yes on the 3 phase, but it's not AC current.

With Industrial 3 phase, the motors are AC AND 3 phase. Industrial 3 phase has three hot leads. They fire in a 1-2, 2-3, 3-1 pattern, much the way that your ESC sends power pulses to your brushless motor. The difference is, the frequency of the pulses doesn't change AND the power being fed is cycling AC at 60 times per second.

I hope this helps.

[sikeston34m]

Well said Brian.

[aqwut]

How would these motors work in a RC vehicle.. and they would use the regular Brushed ESc right?..

http://www.brushlessmotor.cn/Brushless.htm

Originally Posted by BrianG

Well, we're sorta using both. AC means alternating current, which usually refers to a voltage that goes positive and negative in reference to a neutral or ground point. So, technically, we're using "pulsed DC".

Yes, all these motors are simply 3-phase AC motors. However, in absence of a true since-wave generator, pulsed DC works fine. Besides, a variable frequency-drive ESC would be a bit larger and more complex.

Man Brian, you really know your BL stuff lol

You got PM also

[aqwut]

Originally Posted by BlackedOutREVO

Man Brian, you really know your BL stuff lol

You got PM also

Don't get him a few other guys get started... it would be an alien language to me...

[zeropointbug]

Originally Posted by sikeston34m

The traditional definition of AC as it pertains to electricity is "Alternating Current". Household single phase current is 60hz, or 60 cycles per second. In other words, it reverses line voltage polarity 60 times a second.

DC current, of course, only flows in one direction.

With the method that brushless ESC's use, I think a more precise term would be "chopped DC".

There are tricks from several different electrical types at work here. Yes on the 3 phase, but it's not AC current.

With Industrial 3 phase, the motors are AC AND 3 phase. Industrial 3 phase has three hot leads. They fire in a 1-2, 2-3, 3-1 pattern, much the way that your ESC sends power pulses to your brushless motor. The difference is, the frequency of the pulses doesn't change AND the power being fed is cycling AC at 60 times per second.

I hope this helps.

Well, technically, an AC motor (3-phase motors), each phase is firing ALL the time. 3-Phase AC machines have what is called a 'rotating magnetic field', created by the 3 individual, constant sine waves (phases) being 60degrees out-of-phase of one another, thus creating what appears a rotating field.

And, for example, the AC Induction motor (the standard industrial workhorse motor type)... to control the speed and torque of one of these motors, you must change the 'frequency' of the 3 phases (Brian mentions the 'variable frequency drive'). These motors are A-synchronous, meaning that there is NO commutation (electronic (BL motors), or brushed motors) going on....

First, the speed is proportional to the 3-phase frequency being fed to the motor by the drive, or 3 phase power lines if it is not running from a motor controller (or 'inverter' is the standard term).

Second, torque is proportional to the magnetic 'slip' between the 'stator' (stationary) and the rotor... this magnetic slip is the difference between the rotating magnetic field frequency, and the rotors physical rotating fequency... think, the faster the stators 'rotating magnetic field' is turning, the more force (torque) is created at the rotors surface, and ultimately the output shaft.

I can see advanced types of AC Induction replacing brushless DC motors that we use in the near future (if is utilized), such as RaserTech's new AC induction technologies. Reason being is that these types of motors will, and do NOT COG; they can spin at ultra low speeds, and they have 'glass smooth' torque, unlike the BL motors which have alot of torque 'ripple'.

[sikeston34m]

Wow ZPB. You're a wizard with words.

You are correct.

At work, we have discussed installing VFD's on the compressors to increase overall effiency. They are Frick Twin Screws that are variable compression ratio. We have 1300 Compressor Horsepower on site contained in 4 units. The smallest being a 250 Horse Booster compressor and the largest being a 450 Horse High stage compressor.

We hold a 5 million cubic foot freezer at 20 below zero. Frozen Distributor mainly focusing on Ice Cream. We can hold 22,000 pallets of ice cream.

Simple rule of how they vary compression ratio, the longer the refrigerant is held in the screws, the tighter it's compressed before being released into the discharge port. Slide Stop setting is what it's called. They unload by blowing compressed vapor back into the suction header. This really hurts effiency.

VFD's would allow capacity to be controlled by speeding up and slowing down the drive motor, instead of loading/unloading the compressor head to maintain a given suction pressure range.

VFD's also greatly improve magnetic harmonics, thus improving the overall power factor. They have built in power factor correction.

I've always wondered how the power company can tell how efficiently you are using their power? But they can and do.

[zeropointbug]

Whow, now we are talking giant freezers!

I can see them being very useful in that application for sure; in particular, power factor, they would be unity power factor, or at the very least, 0.99 factor.

But, anyways...

[BrianG]

Uh oh, I can see this thread starting to get a little deeper than aqwut probably intended, but good info nonetheless.

Brushless motors aren't really complex all in all. Just about every motor you find in your house (airconditioning/refrigerator compressor motors, washing machine, etc) use a "squirrel cage" motor, which is similar in construction/principle to a 3ph BL motor, except single or dual phase. 3ph motors are generally used in industrial apps where there is a 3ph service.

All our BL motors would spin just fine on straight house A/C, provided it was 3ph and the voltage was a "tad" lower. The issue comes when we want speed control. Can't simply reduce the voltage since that would create tons of heat (operating much like a linear regulator), so you have to either vary the A/C sine wave frequency and/or the DC pulse duty cycle to change the speed. Problem is these aren't the most simple things to make.

[aqwut]

Here at the mushroom farm.. all we have are thos big *ss 3phase Brushless A/C motors.. we use them for giant conveyors and Compost Prewet machines... I'm aware of the VFDs.. we use Allen-Bradley Powerflex(s).. We use them in our coolers for the mushrooms spawn.. and growing rooms.. we have over 1 000 000 ton of cooling capacity.. we buy used compressors from Chrysler, Fords, GM.. etc.. anywhere we could get our hands on one... We use them for wash pumps, wet lands, and pumps for Glycol for cooling and heating... blalablalblablablabllablalblabllblab

Okay guys.. back to English.. Please.. LOL

[zeropointbug]

Originally Posted by BrianG

All our BL motors would spin just fine on straight house A/C, provided it was 3ph and the voltage was a "tad" lower. The issue comes when we want speed control. Can't simply reduce the voltage since that would create tons of heat (operating much like a linear regulator), so you have to either vary the A/C sine wave frequency and/or the DC pulse duty cycle to change the speed. Problem is these aren't the most simple things to make.

I am not sure on this, but wouldn't you have to have some type of capacitor start for a BL motor? They are Synchronous motors after all. Correct me if I'm wrong.

[BrianG]

Those caps are to help tame the surge currents that motors call pull on startup. If a motor's working current is say 10A, the surge can be as high as 50-60A, which might be hard on wiring, circuit breakers/fuses, etc.

[sikeston34m]

OMG Aqwut, I just about snotted tea out of my nose when I read that! LOL

It is English!