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Topic: +, -, GND (Read 2557 times) previous topic - next topic

Grumpy_Mike

Quote
the document is WAY too long and complicated!
In a nutshell please...

It is a motor. It requires no sensors and has no brushes.

One wire is for each of the phases. You need to supply a three phase signal to make it turn. That is three sin waves 120 degrees apart. The frequency of the sin waves will determine the speed of the motor.

faisalfasi

Ground is basically connected to the main switch in house as we do not give ground to every device (some may not need ground so ground do act as negative in devices) so the two wires attached to motor are two,one + and other - which is also ground.

Grumpy_Mike

Sorry but that doesn't make any sense and does not address the problem in this post.

winner10920

I think you are referring to how the physical earth ground in a regular electrical service is connected at the main panel with the neutral, and how essentially grounding the motor casing gives it the same potential as the neutral(hopefully assuming the ground is electriclly clean) and would provide protection from shock in the case of instead of electrifying the outer case due to a failure, the breaker would trip disconnecting power to the circuit
however in this case it seems this motor isn't going to be connected to the mains, and so it wouldn't protect it from say the 12v supply shorting to the case, not that that would hurt anyone anyway
All your questions could be answered if you were to find the datasheet

retrolefty

There are obviously two different subjects being interleaved in this thread. First is about the definition and usage of the word 'ground' as it applies to electronics. While the OP used it his original posting, it's pretty clear he really wanted to know what/how to wire up a 3 phase brushless DC motor, which has no use for nor applicable to 'ground'. So while most post responces here talking about ground are not incorrect, they are not what the OP really meant to ask for, nor requires to understand what he needs to get his motor to run.

The motor in questions has more in common with a 3 phase AC motor then a true DC motor. It requires a motor driver/controller to generate the proper 3 phase signal at the proper frequency, voltage, and current capacity required for the motor. In reality one never just purchases such a motor without also purchasing a driver/controller module compatible to the actual motor selected. These are usually called ESC, for electronic speed controller. Then one controls the ESC by sending in standard +5vdc servo ppm control pulses. There is usually a start-up 'arming' sequence one has to send to the ESC before the motor will actually obey the servo control pulses, for motor start-up safety. Most ESCs also output a regulated +5vdc power source pin suitable for powering things requiring up to around 2-3 amps for +5vdc loads, this is usually called a BEC feature, for battery eliminator circuit. The main power source for a ESC is usually battery power specified for a certain voltage range and rated to be able to supply the peak current demand for the ESC and motor. Again the main battery, brushless motor, and ESC must be selected as a set to insure they are all of a compatible voltage and current range suitable for the motor.

Lefty

yosler

majenko:    I'm not exactly positive that the other one is ground or -. What it could be? - I don't think it's for noise reduction/safety etc. Probably something to do with some other function; backwards, maybe a command line or an emergency power line, I don't know. Or, like a lot of people were saying, maybe a 3 phase sensorless motor?

In regards to the 3 phase motor, I Wikipedia-ed it and came up w/ http://en.wikipedia.org/wiki/Three-phase_electric_power
If don't really understand what a 'phase' actually is, that would help.

retrolefty: Thank you for helping to clarify it. Correct....... I have a 30mA ESC. Remember, I have a 1000kv 400xt brushless motor. www.hobbypartz.com/40tyoubrmo.html  I also have a BEC.
I'm 13 and I'll frequently be wordy, not writing to the point.
But don't worry, I know somethings about electronics.

majenko

A three phase brushless DC motor, which is what you have, consists of three coils of wire arranged in a triangle, with one wire attached to each point of the triangle.  Different signals are applied to each coil to create a moving "wave" of magnetism.  This wave drags the magnet around to turn the motor.

You cannot drive a 3-phase BLDC motor directly.  Instead, you need to create three AC waveforms with each wave offset by 120 degrees from each other.

Nick Gammon


If don't really understand what a 'phase' actually is, that would help.


Here's one description:

http://en.wikipedia.org/wiki/Phase_(waves)

In essence, for (say) a sine wave, the phase describes how "far along" the wave you are at a particular moment. Electricity distributions systems usually use 3-phase power, the idea being that the 3 phases will roughly cancel out when added together, reducing the size of the "ground return" wire that is required.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

retrolefty

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Electricity distributions systems usually use 3-phase power, the idea being that the 3 phases will roughly cancel out when added together, reducing the size of the "ground return" wire that is required.


LOL Best to stick to software Nick.  ;) 3 phase electrical distrubution systems have several advantages over single phase in higher power systems, but none of those advantages match your guess. The power from each individual phase will actually add, not cancel, to the total power being consumed by the load(s). If a 'ground' wire even carries working current depends on if it's a delta or star Y 3 phase system.

Lefty


Nick Gammon

Yep, I'm no hardware expert. :)

However: http://en.wikipedia.org/wiki/3-phase_power

From that page:

Quote
The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load.


I said "the 3 phases will roughly cancel out when added together", Wikipedia says: "The phase currents tend to cancel out one another, summing to zero".

Isn't that the same thing?
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Nick Gammon

I probably got "ground wire" wrong, it would be "neutral wire".
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

retrolefty

#26
Aug 10, 2012, 03:31 am Last Edit: Aug 10, 2012, 03:37 am by retrolefty Reason: 1

Yep, I'm no hardware expert. :)

However: http://en.wikipedia.org/wiki/3-phase_power

From that page:

Quote
The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load.


I said "the 3 phases will roughly cancel out when added together", Wikipedia says: "The phase currents tend to cancel out one another, summing to zero".

Isn't that the same thing?


Real power consumption requires voltage and current, summing to zero wouldn't to very useful for a power distribution system, would it?  ;)

In reality high power 3 phase systems and large power consumers like large motor windings, the main advantages is that the current can be supplied by multiple conductors rather then having to move all the current in just two wires. I squared R losses in wires is costly in high power distubution and the higher a voltage they can run the distrubution system at the smaller wire they can use for the same wattage delivered. But of course that requires step-down transformers at the consumer's location.

The earliest consumer power systems used simple DC generators and distribution systems (Edison?), but that limited it to many but smaller generation sites with limited distance to the customers due to wire losses. Tesla's 'invention' of AC allowed one to use very high step-up transformers to allow the distribution system to run at thousands of volts keeping line losses manageable by lower current and allowing for large power generation stations to supply larger populations at longer distances. 3 phase is just another wire loss management method.

Lefty

yosler

There is some special feature to the motor when it turns on. It plays some music.
I'm 13 and I'll frequently be wordy, not writing to the point.
But don't worry, I know somethings about electronics.

majenko

Quote

The earliest consumer power systems used simple DC generators and distribution systems (Edison?), but that limited it to many but smaller generation sites with limited distance to the customers due to wire losses. Tesla's 'invention' of AC allowed one to use very high step-up transformers to allow the distribution system to run at thousands of volts keeping line losses manageable by lower current and allowing for large power generation stations to supply larger populations at longer distances. 3 phase is just another wire loss management method.


... which is why HVDC is being used more and more now for power distribution ...  ?

yosler

By the way, the motor works perfectly.  :) When turned on, it plays some "song" and spins extremely fast. Probably a 3-phase motor. The 3 wires connect to the 3 wires on the ESC. All works well!! 8)
I'm 13 and I'll frequently be wordy, not writing to the point.
But don't worry, I know somethings about electronics.

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