Electric kart 10/5kw ac synchronous motor

[thegala]

Hello,
This is my first post on this forum. Currently my friends and I are building a electric kart as student project. We are building our electronics(esc and bms). Battery's are lifepo4 110v, motors are two 5kw/96v. Now we are focused on electronic especially esc. We dont have a chassis and battery's yet but only motors and electronic is in a design phase. Pictures would come in next month's and some more information or change id any.

Bye

 

[itsid]

lifepo ?
Wow, that's going to be expensive...
but nonetheless... sounds like a plan

But allow me to ask, two motors?
Why so, you are surely aware that even the better quality products are not exactly identical, and even the slightest difference can lead to unwanted side effects using two motors.
I think that's why you talk about a speed controller in the first place
(otherwise a power controller would be easier and cheaper to make)

Oh and a battery management system?
isn't that too a bit overcomplicated (especially if you're going to make one your own)?

Anyways...
I'm waiting for your updates (and pics)
Oh and of course

'sid

 

[thegala]

lifepo ?
Wow, that's going to be expensive...
but nonetheless... sounds like a plan

But allow me to ask, two motors?
Why so, you are surely aware that even the better quality products are not exactly identical, and even the slightest difference can lead to unwanted side effects using two motors.
I think that's why you talk about a speed controller in the first place
(otherwise a power controller would be easier and cheaper to make)

Oh and a battery management system?
isn't that too a bit overcomplicated (especially if you're going to make one your own)?

Anyways...
I'm waiting for your updates (and pics)
Oh and of course

'sid

Well plan is to first install one motor and then after some modification to chassis we would be able to install second motor. And don't worry about differences between two motors and they speed they are basically none I mean it's very hard to do anything wrong if you do it with every precaution. Electronic can always eliminate them.

I am not working alone so in general we have time to build a esc and bms. It's more difficult to build a esc (5kW/100V=50A) then bms, just for you to know.

 

[itsid]

I know that the controller is more difficult than a battery manager..
But you MUST have a controller, the battery manager is optional IMHO...
so that could be left out to simplify things

depending on the motor and it's specs I need to inform you though, that you're NOT talking about a 50 Amp controller!

yes, 5kw/100V is 50 amps.. that much is true.
BUT the 5kw... what's that?
max rating electrical (in which case with security margin you'd want a 60Amp controller at least)
and your motor will likely have a mechanical power of ~2.4 kW (max electrical rating means always less than 50% efficiency)
or is that continous electrical (roughly an efficiency of 70-80% leaving you with 4kW mechanical power) which means the motor can draw up to 80 Amps (and you'd want a 100Amp controller again with tiny security margin)

or is that efficient continous mechanical power, which EV motors are rated mostly.
then things get nasty.. meaning it could be able to draw more like 110Amps from the batteries (and you need to have a 150Amp controller roughly)

making your own controller is already an "advanced project" to say the least.
don't have "underestimated powerdraw" be the cause for your failure

'sid

 

[thegala]

Well efficency of my motors (mechanical output efficiency) is about 90%. Electrical power of motor is about 5kW with peek of 7,5kW. So if a voltage of motor is 100V then max current is 75A. Battery current drain then is about 100A and esc should be rate at 150a at least.
So you are right I can't underestimate powerdraw.
I đon know if you read it but motors are AC synchronous.

 

[itsid]

Yes, but be carefull (I bet you are )
motor efficiency is variable, starting from generally significantly better than 50% and ending at always worse than 50% with a peak somewhere in between.

that peak is 90% in your case (that's a good value I must say... 90% is hard to reach)
anyways.. that 90% is at a specific and generally very narrow power band.
above that (towards peak power) it rapidly drops.. ALWAYS below 50%;
and that holds true for DC as well as AC motors, it's because of coppers conductivity dropping with heat

Best thing to do, is get the spec sheet with a power/efficiency diagram of the motor.

take the worst possible value to calculate your needed powersupply (add 15-20% safety margin) that helps keeping your controller cool too

'sid

 

[thegala]

Of course you are right but gear ratio will be made in that way that i will always be around most efficient motor point. But of course I will use 200A 600V Igbt bridge for esc.

My motor just pick 5kW 96V
http://www.goldenmotor.com/frame-bldcmotor.htm

 

[itsid]

...
I đon know if you read it but motors are AC synchronous.

...My motor just pick 5kW 96V
http://www.goldenmotor.com/frame-bldcmotor.htm

uhm... you are aware that this points to a DC motor, not an AC as you stated above?

Anyways, the good news it shuts down loong before it reaches critical temps. thanks to liquid cooling
bad news: it draws happily 127 Amps, so 150Amp controller might be a bit short..

200Amps (continous not peak) might be a better setup.. (depending on the cooling level that's roughly 300 peak or so)

'sid

 

[thegala]

No it's a ac motor with permanent magnet.

 

[itsid]

all motors on the page you linked are BLDC (brushless DC motors)
maybe it's the wrong link.. but those are in fact DC motors, no doubt about it.

'sid

 

[thegala]

No they called them that way because they purpose is to be powered with battery dc source. But you must control them with a ac of any shapn
e( triangle, square, sin). This ia probably reason for that wierd name. I know in start it was confusing, but it's a ac motor.
Just check Wikipedia about BLDC motors.

 

[itsid]

I'm sorry, but the confusion is on your side

it's a three phase motor but it's DC.. not AC;

Okay, let's be precise, to not mess this up some more..
it's an EC motor (electronically commutated motor)
They are powered by DC currents! (not just because of the batteries)
That's why BLDC is in fact correct and not misleading in any way.

And yes you need to create an artificial sinewave (or squarewave most likely)
to power it.
But a three phase motor will happily run with common ground when in WYE configuration ( star shape 'Y' connection) only switching the positive terminals on and off
(perfectly ordinary DC, could be realised with just a battery and three toggle switches)

delta shapes are trickier I admit.. they will need to shift the ground with the signal
which then gets closer and closer to AC.

Yes, if you're picky the signal is of course alternating, but from 0 to 1;
not necessarily from 1 to -1 (which it would if it's an AC motor)

I'm not sure, actually I cannot see why a threephase DC shouldn't be run with sinodial AC...
in fact the potential difference should be fixed anyways if the signals are properly offset, and I doubt the copper cares if it's 0 and 96V or -34 and +62 Volts *shrugs*

Anyways, they're meant to run 0-96V especially if it's a four terminal shared ground WYE configuration, which is impossible to run on AC (it'd buzz and slightly wiggle... not turning at all) or worse, you'd create a short ...

'sid

 

[thegala]

Have you read a Wikipedia article they clearly state

electronically commutated motors*(ECMs, EC motors) are*synchronous motors*that are powered by a DC electric source via an integrated*inverter/switching power supply, which produces an AC electric signal to drive the motor. In this context, AC, alternating current, does not imply a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform.
[/QUOTE ]

 

[itsid]

I did, and I understand it's misleading for some
it's not the "AC" you think it is, it's a pulse width modulated alternating signal.
depending on the position of the rotor. but it's still DC although that alternating signal has a current flow.
But it is what it is.. a brushless dc motor, we can turn in circles and you can call a pig a sheep, it's still a pig

Uhm, how do I make the difference more clear...

Motors produce Back EMF, that much you will agree upon.
Now, a DC motor creates a square wave
(I think we can accept that a single phase potential difference is a infinitely wide square wave)
And so does a BLDC motor it produces a square wave,
or well let's say trapezoidal wave that's a better match; still square'ish .

An AC motor on the other hand produces sinusoidal back EMF.

And since motors like to be powered in the same way they produce back emf, that's the optimal way to excite them.

That's what your wikipedia article means with "does not imply sinusodial..."

There are many mechanical as well as electrical differences between the two.
the rotors are different, the way they like to be powered is different..
But most important of all:
An AC motor has all three stator coils ALWAYS ENERGIZED,
which you simply cannot do with a BLDC.

So please, if you build your controller, make sure you build a Brushless DC motor controller;
Do not build an AC motor controller not even an brushless AC motor controller, it will not power your motor.

'sid

 

[thegala]

Ac motor is every motor that use alternating current so BLDC motor uses a AC current of any shape so you can use a sin or square wave. Electronic for BLDC or to be precise a transistor or bridge layout is a same if we talk about same phase power inverter and esc. So what for you is ac synchronous motor or ac motor and BLDC motor. I mean they physical layout is a same and they can ne controled with same electronic(well program and parameters sholud be slightly different). I think we are talking about the same thing but using different names. And just for end you can connect my motor on 100V from network and it will work properly.

 

[thegala]

Ac motor is every motor that use alternating current so BLDC motor uses a AC current of any shape so you can use a sin or square wave. Electronic for BLDC or to be precise a transistor or bridge layout is a same if we talk about same phase power inverter and esc. So what for you is ac synchronous motor or ac motor and BLDC motor. I mean they physical layout is a same and they can ne controled with same electronic(well program and parameters sholud be slightly different). I think we are talking about the same thing but using different names. And just for end you can connect my motor on 100V from network and it will work properly.
And yes they back emf is different.
, because of different stator design.

 

[itsid]

their physical layout is not and I repeat : IS NOT! identical!
there are few but important changes, that's why there is a difference in the first place.
And that's what differntiates the BLDC from a brushless AC motor.
You can ignore the fact as long as you like; I don't care enough to go on with this discussion ...
Just keep in mind that it's called BLDC for a reason

'sid

PS read this: http://www.mpoweruk.com/motorsbrushless.htm that should cover all I could ever argue with,
if that's not convincing enough for you; you're on your own.

 

[thegala]

Yes they are not identical to AC synchronous motors only difference is their stator. Rotor is in both permanent magnet. BLDC motors are sometimes called a PMSM. Or you could define it this way BLDC motor with a trapezoid back EMF and a BLAC a motor with a sin Back EMF. But they are controlled with AC current both.
P.S
And almost all AC motors are brushless.

 

[thegala]

Just to prof look at this pages
http://www.researchgate.net/post/What_is_the_difference_between_BLDC_and_PMSM_motors
http://control.com/thread/1026172925
And this video
http://www.youtube.com/watch?v=ZAY5JInyHXY

Well you see in video that for control of BLDC you should use a reverse polarity which lead as to using a AC current.
I personally don't have a problem calling that motor a AC motor nor my professor.
Basically they are both very same and so a driving techique. (but also a very different) At least a power transistor layout is the same and electronic also. Program or algorithm you will put in mcu is not the same.

 

[itsid]

cough...
you read that??

National Metal and Materials Technology Center
The BLDC and PMSM motors can be the same or different depending on the researchers' views. Basically they are synchronous motors with permanent magnets attached on their rotors.
Some researchers define a BLDC motor is a PMSM with trapezoidal BEMF, while a BLAC is a pmsm with sinusoidal BEMF.
The drive techniques for BLDCMs and sinusoidal PMSMS are quite different, as I said, depending on BEMF shape, but drive techniques for BLDCMs (typically 2-phase excitation) can be applied to PMSMS, and vice versa.
Hope my answer helps.

Oh and.. NO that's a three phase excitation you're dealing with.. so that part's not applicable

and I guess you refer to Curt Wilson (who is simply wrong..)
but congrats on finding someone as confused as you are..
scroll down and read the rest to know the truth

And yes that video is a perfect explanation..
explaining the commutation (electronically commutated)
as opposed to mechanically commutated brushed DC motors.

QED

But thanks for proving my point

'sid