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Old Dec 05, 2003, 06:01 PM
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Question
Building a power supply for brushless motors

I learned that an ESC converts DC into AC to run brushless electrics. Since I want to build a power supply (or buy one) to directly power a motor(s),what type of AC supply should I build/buy?

Is it a pure sine wave source?

Do I need to vary the voltage to vary the motor speed?

Where can I learn about the power requirements of these brushless motors?

Thanks!
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Old Dec 05, 2003, 06:25 PM
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Unfortunately there is a lot more to it than that. If you search this forum (look in power systems section) there are a few plans for homemade ESC's. They are far more complex than a power supply.

Good luck!

Larry
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Old Dec 05, 2003, 08:00 PM
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Idea: Buy a controller big enough for your use and build a DC power supply. Much easier and more fun.
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Old Dec 05, 2003, 09:26 PM
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little bit off topic, but Feathermerchant, where is Euless? Sounds familiar. Thanks
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Old Dec 05, 2003, 11:32 PM
Use the 4S Luke
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Hey, I was serious. I'd just use a fused wire off a car battery if all you need is 12V
Just SW of D/FW airport
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Old Dec 06, 2003, 07:59 AM
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What he said. You don't just feed a fixed rate AC into the motor. You have to fire each winding with pulsed DC, and monitor rotor position carefully to ensure the motor operates correctly. That's what ESC's do.
..a
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Old Dec 08, 2003, 04:37 AM
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What Andy said; BL motors do NOT run on AC. They run on pulsed DC, i.e., the output voltage from the ESC never swings negative - it's either on or off. Each set of coils (phases) get rapidly pulsed on then off in sequence thereby causing the magnetic rotor (whether outrunner or inrunner) to rotate. The faster the on/off sequence between phases, the faster the motor runs.
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Old Dec 08, 2003, 12:34 PM
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Besides, regular old house current is only single-phase AC. Brushless motors are technically three-phase.
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Old Dec 08, 2003, 08:06 PM
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Miami Lakes, Florida, USA
Joined Mar 2003
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Re: Building a power supply for brushless motors

Quote:
Originally posted by BillBrian
I learned that an ESC converts DC into AC to run brushless electrics.
Yes, that's correct. The brushless motors we use run on synthesized three-phase alternating current. The waveform from ESC's isn't sinusoidal and the voltage is never more negative than the negative terminal of the battery pack, nevetheless it's still bona fide three-phase alternating current.
Quote:
Since I want to build a power supply (or buy one) to directly power a motor(s),what type of AC supply should I build/buy?
You might be able to find the information you need with this Google search for "three phase ac power supply". What are you building anyway?
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Old Dec 10, 2003, 04:49 AM
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The difference between a brushless controller and three phase mains voltage is a lot.

Three phase motors are desined to run at constant RPM, can not be throttled, and work best in a fairly narrow power band.

What our ESC's do is chop DC about to give variable frequency variable voltage outputs. In a fiarly copmp[lex way, because they also sense RPM and throttle position and adjust everythung to (hopefully) get the best mix of pahse advance, frequency and voltage for every possible throttle setting prop load and rPM and inpout voltage...

Or to put it another way, do you REALLY want to follow in e.g. Castle Creations last 3 years of R & D? Or just buy a controller from them
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Old Dec 10, 2003, 05:59 AM
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The Netherlands, GE, Nijmegen
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How a brushless ESC works, waveforms, diagrams:
http://www.torcman.de/peterslrk/SPEEDY-BL_eng.html

Met vriendelijke groet Ron van Sommeren
diy outrunner brushless e-motor discussion.
Electric fly-in & lrk meet, June 27th, 2004, Nijmegen, the Netherlands.
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Old Dec 10, 2003, 05:37 PM
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Vintage1 Good post. There are now many variable freq drives out there for things from locomotives to chiller drives. They allow better mechanical efficiency for many processes without the need for brushes and the associated maint.
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Old Dec 11, 2003, 07:42 AM
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Re: Re: Building a power supply for brushless motors

Quote:
Originally posted by Miami Mike
Yes, that's correct. The brushless motors we use run on synthesized three-phase alternating current. The waveform from ESC's isn't sinusoidal and the voltage is never more negative than the negative terminal of the battery pack, nevetheless it's still bona fide three-phase alternating current.You might be able to find the information you need with this Google search for "three phase ac power supply". What are you building anyway?
Indeed there are three phases, but this doesn't mean they are alternating current (AC). Alternating current implies that the voltage swings both positive and negative. Each of the phases for a brushless motor, on the other hand, is a "chopped" direct current (DC) voltage which in turn are 120 degrees offset from each other (120 x 3 = 360 degrees = one rotation of rotor). Another way to visualize this is to imagine a three cylinder engine where each of the cylinders represents one of the phases. Each cylinder fires in sequence one after the other to rotate the crankshaft.
If one where to connect a brushless motor to a three-phase AC power supply it would not run, but instead just sit there buzzing and humming due mainly to the fact that it uses permanent magnets. AC motors do not use permanent magnets unless there is a rectifier built-in which converts the AC to DC first. My mini-lathe uses such a motor.
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Old Dec 11, 2003, 06:50 PM
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Re: Re: Re: Building a power supply for brushless motors

Quote:
Originally posted by babblefish
Indeed there are three phases, but this doesn't mean they are alternating current (AC). Alternating current implies that the voltage swings both positive and negative.
Sorry, but that's just plain wrong. "Positive" and "negative" are relative concepts that depend upon one's frame of reference (what one chooses to call "ground"), and have nothing to do with the concept of alternating current.

One type of alternating current that we're all familiar with is that which comes from the electric company through power lines in the form of a sine wave, but that's by no means the only type there is. All electric current is either direct or alternating, and if there's any regular change in current, then by definition that change represents alternating current. Current that is capable of steadily flowing through a capacitor is alternating current. Current that can transfer energy from the primary winding to the secondary winding of a transformer is alternating current. (The current produced by a brushless motor controller is capable of both.)

The brushless motor controllers we use in our models work by synthesizing three-phase alternating current from direct current provided by battery packs. It's as simple as that.
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Old Dec 11, 2003, 07:48 PM
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Re: Re: Re: Re: Building a power supply for brushless motors

Quote:
Originally posted by Miami Mike
The brushless motor controllers we use in our models work by synthesizing three-phase alternating current from direct current provided by battery packs. It's as simple as that.
Brushless DC motors will not start and run on 3 phase AC. Brushless controllers perform the same function as the brushes and commutator do in a brushed motor. The difference being the FETs are doing the switching.

Steve
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