bmc/puma windings

[solarbbq2003]

noticed on a picture of insides of bmc/puma motor looks like some of the windings (coils) might be connected in parallel, changing to series connection in the motor would allow to run on higher voltages, would change rpm of the motor and maybe torque ( not sure on torque)......................dont have one to play with as yet....not sure if the windings are in parallel at all just going from a picture of the motor
On the fisher/paykel washing machine motor ( same type of motor as bmc/puma ) you change from series connection coils to parallel to run on lower voltages, so same should apply in other direction, change parallel windings to series to run on higher voltages.
just a thought

 

[fechter]

I'm not sure on the Puma, but my BMC scooter motor has the windings in parallel (delta).

If I wanted to run a higher voltage, but lower current and keep the output the same, then re-configuring to wye would make sense.

Crystalyte hub motors seem to be in series (wye), so if you rewired one, you could run a lower voltage/higher current. Or you could go really really fast at the same voltage.

 

[The7]

I'm not sure on the Puma, but my BMC scooter motor has the windings in parallel (delta).

If I wanted to run a higher voltage, but lower current and keep the output the same, then re-configuring to wye would make sense.

Crystalyte hub motors seem to be in series (wye), so if you rewired one, you could run a lower voltage/higher current. Or you could go really really fast at the same voltage.

For ac synchronous motors and ac induction motors, they could be configurated to run at a high voltage at Y and low voltage at delta.
The ratio between high volt and low volt is 1.73 : 1.

But for BLDC motors with hall sensors, the story will not be the same. The relative phase between the hall signal and the phase back emf will change for the Y and delta config.

Let us use AL1020 hub motor as an example

Phase-sequence = A-B-C
A= yellow winding
B= blue winding
C= green winding

HA = Hall signal of yellow
HB = Hall signal of blue
HC = Hall signal of green.

HA, HB and HC are spaced at 120 elect deg.

Case 1 (Normal config)
The winding is Y connected
Voltage between A and B = Vab
Vab leads HA by 60 deg ( by the controller)
Then voltage in yellow winding leads HA by 30 deg which is the designed phase shift.

Case 2 (Not normal)
The winding is delta connected.
Vab leads HA by 60 deg ( by the controller).
Then voltage in yellow winding also leads HA by 60 deg which is not the designed phase shift.
The phase shift in the case has "advanced" by 30 deg.
I think the motor could still run but it may take an relative higher current at the same load.


Comments:
A) If the orignal design is Y and it is connected as delta, the relative phase between the voltage of winding and Hall signal is advanced by 30 elect deg. The motor could still run at a higher current for the same load. Similar to an poorer power factor in ac syn motor.

B) If the orginal designis delta and it is connected as Y, the relative phase between the voltage of winding and Hall signal is retarded by 30 elect deg. The motor may not run at all.

C) The Hall signals could be inverted and re-aranged to have an 60 deg phase-shift change such that (B) becomes "advanced by 30 deg".

 

[safe]

The ratio between high volt and low volt is 1.73 : 1.

That's a very interesting "magic ratio".

My gearing experiences on electric bikes have given me the insight that you need a range (from whatever is low to whatever is high whether it be electrical or mechanical) of about 3 : 1. This is assuming that you use street legal power (750 watts) and want to extend that power as far as possible in both directions, up hill and at high flat land speeds.

The question really becomes whether it's even possible for an electric motor that is SMALL (since using excessively large motors or overvolting is one way to escape the high/low problem) to be electronically manipulated so as to reach the more desireable 3 : 1 ratio?

It's at the 3 : 1 ratio that mechanical gears become unnecessary...

 

[The7]

Further Comment:
D) X408/4012 motor uses two sets of windings to achive high and low speed. If Y/delta switching could be used for the same simple controller then why should they border to have two sets.

E) If an "advanced" controller is so designed to compensated for the 30 deg phase shift, then Y/delta switching is possible. This trigger me to design such advanced controller for y/delta connected winding.

 

[Toorbough ULL-Zeveigh]

The ratio between high volt and low volt is 1.73 : 1.

That's a very interesting "magic ratio".

The square rooot of threee is trés masonic.

 

[xyster]

The ratio between high volt and low volt is 1.73 : 1.

That's a very interesting "magic ratio".

The square rooot of threee is trés masonic.

That's why they call themselves the Threemasons. One of the three was sentenced to life in a South American prison for trying to spark a democratic uprising; another lost a leg while attempting to topple Castro. So there's 1.73 masons left in the world. And nobody knows what they're up to.

 

[Malcolm]

Found an informative little wiki on brushless motors here:
http://en.wikipedia.org/wiki/Brushless_DC_electric_motor
It probably has nothing new for most people here, but if motor theory is a bit of mystery (which it is to me) there's an interesting section about star/delta configurations about half way down.

 

[solarbbq2003]

i thought delta gave more torque, says opposite on the wicki page

 

[The7]

i thought delta gave more torque, says opposite on the wicki page

Both of you and wicki are "Right and also WRONG"

Have to go out now. Will give an explanation when I come back.

 

[maxwell]

Star (Y) and delta are used quite a lot for starting big induction motors (start in Y run in delta) this is all fine for sinusoidal voltages. Our BLDCs have a square wave drive, whilst this works on a delta connected motor you do get so called 'circulating currents', this wastes some power. Y connected motors can't have these currents as there is no loop for them to go round.

I have no figures for the extra losses when in delta but would like to know (anyone). Crystalytes are easy to convert (well the windings anyway) as the centre point of the star is accessible on the wiring board in the motor.

 

[The7]

Star (Y) and delta are used quite a lot for starting big induction motors (start in Y run in delta) this is all fine for sinusoidal voltages. Our BLDCs have a square wave drive, whilst this works on a delta connected motor you do get so called 'circulating currents', this wastes some power. Y connected motors can't have these currents as there is no loop for them to go round.

Agreed.
But the BLDC have a taperzoidal wave form drive.

The taperzoidal wave could be resolved into the fundamental, 3rd harmonic, 5th harmonic etc.

The fundamental current will produce an FORWARD torque. This is what we want.

The 3rd (and odd multiples of 3rd) harmonic will cause the 3rd harmoinic current ("circulating currents") in an delta connected motor. The value of the 3rd harmonic current" could be determined from the inductance and resistance of the winding. So you will have exta heat loss in the motor.
The worst effect of the 3rd harmonic current is to produce an BRAKING torque on the motor.
With Y connection (and no return star-point connection), the 3rd harmonic current cannot flow. So there is no ill-efffect. That is why is preferable to use Y-connection for BLDC motors .

The 5th harmonic current will produce an REVERSE torque at 5 times the speed. It occurs both in Y and delta connections. Luckily its net torque effect is small.


Wonder whether you still remember "Maxwell Equation"? I don't.

 

[The7]

i thought delta gave more torque, says opposite on the wicki page

Both of you and wicki are "Right and also WRONG"

Have to go out now. Will give an explanation when I come back.

I am back.

The motor will have the same output, same torque, same efficiency and same speed when it is supplied at its rated voltage and rated current in Y and in delta connected.

The salient potint is that the rated values in Y are not the same as in delta and have an magic ratio of 1.73.

Rated voltage in Y : rated voltage in delta = 1.73 :1
Rated current in Y : rated current in delta = 1: 1.73.

Case 1
There is not motor current limiting and for the same voltage.
Torque of Y is lest than the torque of delta.

Case 2
There is motor current limiting.
Torque of Y is greater the torque of delta.

 

[The7]

Crystalytes are easy to convert (well the windings anyway) as the centre point of the star is accessible on the wiring board in the motor.

If the X-motor is re-connected from Y to delta, there will be an additional phase advance of 30 elect deg of the winding voltage with respect to the Hall signal. Please read my previous reply in this post.

 

[maxwell]

"But the BLDC have a taperzoidal wave form drive."

The back EMF is trapezoidal, the drive is square (well rectangular to be precise).

And I did say "the windings anyway", I do read the posts.

 

[The7]

"But the BLDC have a taperzoidal wave form drive."

The back EMF is trapezoidal, the drive is square (well rectangular to be precise).

And I did say "the windings anyway", I do read the posts.

The back emf waveform of the BLDC is sinusoidal.
When the the motor is turned by hand, the voltage waveform between any two motor phase as observed from scope is very sinusoidal.

The motor has a 6-step drive from the 6-step controller as ref to pdf file. Each step is 120 deg.
( Some controllers use square (180 deg step) as you say, but not common. Sorry we are referring to different controllers.)

The waveform of the voltage between any two phase from the controller when connected to a Y-connected resistor load is in stair-step as shown.
This stair-step waveform is the resultant between two phases of the 6-step drive.

When it is connected the the motor, the wavform becomes trapezoidal.

 

[fechter]

My bench test motor has a very trapezoidal looking waveform when the motor is running. I hadn't considered the shift in hall sensor timing when changing configuration. On an induction motor, this doesn't matter.

I suppose if we had sensorless BLDC controllers, you could switch configuration.

Another interesting thing you can see in the O'scope is the ringing in the windings. On my test motor, the ringing appears to be about 5x the PWM frequency.

What would happen if the PWM was synchronous with the resonant frequency of the windings?

 

[maxwell]

A BLDC is (usually) wound to give a trapezoidal BEMF, this is done so it can accept a rectangular voltage waveform efficiently. The AC syncronous motor however is wound for sinusoidal voltages. The two tend to get a bit mixed in the real world.

The Crystalyte 400 series has a remarkably trapezoidal BEMF as it uses windings that span 3 slots (the phases are spaced one slot) with magnets that span three slots (per pole), those slots are also skewed 1 slot pitch making it even better. Next time I get a rig on my bench I will take some voltage and current waveforms.

The advantage of a trapezoidal BEMF where the rectangular drive pulse fits the plateu is the current is constant (well it would be for a perfect trapezoid) over the drive pulse. A motor with sinusoudal BEMF would have a peak of current in the middle of the pulse. As losses are proportional to I(amps) squared the trapesoidal BEMF motor has lower losses and less torque cogging, all other things being equal.

Fecher, if the PWM was in sync to the ringing it would probably get very big and blow the FETs

 

[The7]

My bench test motor has a very trapezoidal looking waveform when the motor is running.

Is the voltage between two motor wires?
The flat top of your waveform spaces 120 deg which is not a typical 6 step drive.
The flat top of my waveform spaces 60 deg which is a typical 6-step drive.

I hadn't considered the shift in hall sensor timing when changing configuration. .

It is an important issue which should not be overlooked.

On an induction motor, this doesn't matter.

I suppose if we had sensorless BLDC controllers, you could switch configuration.

Agreed.

Another interesting thing you can see in the O'scope is the ringing in the windings. On my test motor, the ringing appears to be about 5x the PWM frequency.

Ringing is very common in switching circuit. By-pass capacitor (order of 0.1 uF across the big electrolytic cap) could help to reduce the magnitude of ringing.

What would happen if the PWM was synchronous with the resonant frequency of the windings?

Then high magnitude of resonant frequencncy current could flow in the motor circuit. High intensive of resonant frequency sound will be produced. They could be annoying to some animals like dogs and bats.

 

[The7]

The Crystalyte 400 series has a remarkably trapezoidal BEMF as it uses windings that span 3 slots (the phases are spaced one slot) with magnets that span three slots (per pole), those slots are also skewed 1 slot pitch making it even better. Next time I get a rig on my bench I will take some voltage and current waveforms.

Would like to see the Back emf on X400 motors!

I don't have any X400 motors.
But on my AL1020 motor, the back emf as observed from scope is very sinusoidal.

 

[The7]

Photo of Back emf of AL1020.

The waveform was taken by spinning the drive wheel backward because the motor has internal free-wheel. The motor was not connected to the controller during measurement.

Looking forward to see back emf of X400. Have never seen an taperzoidal back emf of BLDC motor.

 

[fechter]

My bench test motor has a very trapezoidal looking waveform when the motor is running.

Is the voltage between two motor wires?
The flat top of your waveform spaces 120 deg which is not a typical 6 step drive.
The flat top of my waveform spaces 60 deg which is a typical 6-step drive.

The voltage is between one phase wire and battery negative.

My motor also looks pretty sinusoidal between phases if I just spin it by hand.
I wonder if it would look more trapezoidal if I put a load resistor across the windings?

 

[The7]

The voltage is between one phase wire and battery negative.

Then it is correct to have an 120 deg top. Your controller is a typical 6-step dirve.

The waveform of one phase to battery negative of my AL1020 is similar to yours.

 

[The7]

My motor also looks pretty sinusoidal between phases if I just spin it by hand.
I wonder if it would look more trapezoidal if I put a load resistor across the windings?

To my uderstand, the waveforms will remain unchange for a balanced Y-connected R ( or delta-connected R). The magnitude could becomes a bit smaller due to loading effect.


Please note I use connectors similar to yours.

 

[The7]

The Crystalyte 400 series has a remarkably trapezoidal BEMF as it uses windings that span 3 slots (the phases are spaced one slot) with magnets that span three slots (per pole), those slots are also skewed 1 slot pitch making it even better. Next time I get a rig on my bench I will take some voltage and current waveforms.

Thanks for tell us the distribution of the windings of X400 motors.
This construction would give an trapezoidal Back emf.

Grateful if you post its back emf waveforms when available.