Creating a 3 phase output from a single 12v AC or DC rail.

[Life4Never]

Computer BLDC fans can be hacked for 3 phase output 

they are 3 phase but to shift the phases you need 0.1uF caps

I'm pretty sure that a BLDC fan is a 2 phase system since I opened one up a few days ago.

So I'm kinda wondering how to get a 3 phase out, there is a way to manipulate this or are there fans which have 3 pole system?

Or is it 4 and we just get rid of a phase and so some shifting of the waveform?

Also I need some information on how to wire up the 3 phase power. Would it connected like so:


Because right now it is like:

Where there are 6 wires comming out from our design.

[T4P]

It's exactly like that, you just have to break open many fans to look for a 3 phase ... you'll never be sure
But the PWM ones might because 3 phase is easier to control precisely the RPM

[ivan747]

Brushless RC motors make terrible generators unfortunately.


You could generate your 3phase signal without too much work using..
- An Arduino with DAC module (3 channels required)
- 3x simple mono audio amplifiers (or 2 stereo) 

Just program the Arduino to generate 3 sinewaves 120deg apart and use the audio amp to get some power behind it.

The code could just be a 3x64 array of hardcoded DAC values.
Then loop through the array setting the 3 values and doing a simple delay.
You could add more elements but 64 is probably enough to get a reasonable sinewave


Or you could forget the DAC module and just find an Arduino library that can do PWM analog output and feed that into the audio amps.

No need for a DAC, just use the "Analog output" (PWM) of the Arduino and filter it using a low pass filter. PWM is a technique used to get kind of an analog output. It switches a digital output on and off very fast. Here is a tutorial:




If you filter this PWM value you can end with a basic digital to analog converter. You can generate a sine wave with software with this "analog" output. But, to make it a real sine wave you will have to filter the fast on and off switching so you can get a real clean sine wave. You can do that with a low pass filter




Then you can that signal though the audio amplifier. Maybe if the PWM frequency is high enough you won't even need a filter because the audio amplifier will take care of that by itself.

An amplifier like this should work a treat: https://www.quasarelectronics.com/3097-2w-mono-amplifier-module-lm380.htm




Have fun!

[ivan747]

P.S. another way to move a 3 phase motor would be using RC equipment like many people has suggested before. Get a cheap ESC (electronic speed control) for a 3 phase motor, a compatible motor and a servo tester. Servos receive signals from the RC receiver the same way an ESC does, so by getting a servo tester, the ESC will "see" that it was pugged int to a receiver. You can even control the speed with the tester. You can also make your own if you want to have some fun.

[Life4Never]

P.S. another way to move a 3 phase motor would be using RC equipment like many people has suggested before. Get a cheap ESC (electronic speed control) for a 3 phase motor, a compatible motor and a servo tester. Servos receive signals from the RC receiver the same way an ESC does, so by getting a servo tester, the ESC will "see" that it was pugged int to a receiver. You can even control the speed with the tester. You can also make your own if you want to have some fun.

This seems to be the most simple way to get this project working. Since these have be obviously designed for small motors, i wonder how well, if at all, they will work for one with an approximate diameter of 15 centimetres. Though looking at the specs of these ESCs, they should output a decent enough current though I am worry if this would trip the power supply's safety to cut at 5A. I can see a problem when it is furst turnt on but when the motor is actually moving this should more be an issue.
Plus this is an induction motor and not the standard found in RC motors which contain magnets.

Time wise, we have about a month to do this, so I might have to go on a whim and just buy it and see if it works or not. If not, then onto the next idea.

[T4P]

"Small" motors
Indeed. 30A @ 11.1v ... not small
The ESC's themselves are usually limited by the mosfets, like the cheap one i know was 50A@5-26v

[Life4Never]

Computer BLDC fans can be hacked for 3 phase output 

they are 3 phase but to shift the phases you need 0.1uF caps

As a backup to the RC motor controller idea, how would you hack the actual fan? Snip off the wires and then connect add some capacitors in parallel and run the wiring off?

It would be an interesting project. I might just do it on the side as a little side project.

[T4P]

Computer BLDC fans can be hacked for 3 phase output 

they are 3 phase but to shift the phases you need 0.1uF caps

As a backup to the RC motor controller idea, how would you hack the actual fan? Snip off the wires and then connect add some capacitors in parallel and run the wiring off?

It would be an interesting project. I might just do it on the side as a little side project.

Should be it. Remember to drive with AC

[SeanB]

Strictly speaking most of the cheap fans i have looked at are 2 phase motors, with a skewing that makes them run in one direction only. The common drivers I see have a 4 wire hall and power driver integrated circuit, with only 2 phases driven, and a open collector on a transistor to give an output for RPM sensing if used.

A drive motor out of a floppy drive or a cdrom is 3 phase though, but you will need to either drive the second coil in parallel or figure out how to fake the hall feedback to it.

[Life4Never]

Okay, after some research on how ESC works ie (3 phase square wave generator) I have some more questions on the effect of it on the actual motor.

Firstly: Will an induction motor be able on this square wave? I am wondering if current would be induced in the rotor using square waves at all. Has anyone run a inductor motor such as a fan off a UPS? The cheaper ones produce square waves.

Second: How much current would the ESC draw? I am thinking of 2 solutions for power. The first is straight off a power supply, either the ones supplied or a PC ATX PSU, or running it off a LiPo and charging it before use.

Thirdly: Does the cheap ESCs have any feedback to determine how to deliver current to each of the 3 leads? Or are they just delivering square waves through 2 of the 3 wires to create the illusion of a moving field without any feedback.
 

[Psi]

My 230v desk fan runs on my square wave inverter, however it doesn't sound very happy about it.
Speed is normal though.

But i dunno what type of motor's inside it.

[T4P]

They use back EMF as their sensor on the third wire the other two wires are square waves

[Life4Never]

They use back EMF as their sensor on the third wire the other two wires are square waves

Hmm that might be a problem. Theres no magnetic field in the rotor to actually cause any back emf if the third wire is not producing a square wave to at least induce a current.

What will happen if it detects nothing on the sense?

[T4P]

the ESC stops.

[David_AVD]

I was pretty sure those brushless RC motors are 3-phase.  If they were 2-phase, how could they run backwards when required?

[T4P]

I was pretty sure those brushless RC motors are 3-phase.  If they were 2-phase, how could they run backwards when required?

Oh okay  Cheers.

[Psi]

Pretty sure the motors are 3 phase, but the ESC only drives them with 2 phases while using the 3rd for monitoring.

It's not static though, it switches around in all combinations.
(If you looked at it over many cycles you would see all motor wires used for both power and monitoring at different times)

This is how it can control direction as well as speed.

[Life4Never]

So judging by the information so far, an ESC won't work on an INDUCTION motor. It might work for BLDC motors but thats because it has magnets inside which can set up back emf.
There will be no back emf as it is an induction motor (no magnets). <--- There should be back emf on the 2 powered wires as we induce a current and then that can create back emf but then on the sense, I'm assuming its unpowered, there will be no back emf and therefore the ESC wont work.
Is this correct so far?

Or, does the "sense" wire generate an electrical pulse and measures back emf from that? If so then it might work.

[Life4Never]

Anyone?
Answer the above questions as I'm planning to buy the parts required this week.

If not then can anyone suggest another simple method with easily sourced parts in the local Sydney area? (I don't plan to do any programming. Out of the box, almost no setup required like the RC ESC and controller)

If all else fails, I will create a generator connected to an LED or bulb to demonstrate the generation of electricity by changing magnetic fields. I will need to buy some flat neodymium magnets though. A local source on the cheap?

[Panduit]

Computer BLDC fans can be hacked for 3 phase output 

they are 3 phase but to shift the phases you need 0.1uF caps

I'm pretty sure that a BLDC fan is a 2 phase system since I opened one up a few days ago.

Oh no


Ic driver NJM2624 3phase controller

[T4P]

Holy lord, hmm, i wonder what's inside a PFR1208XHE now