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Electric Motors Winding and Repair Electric Motors Winding and Repair Discussion


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Old 11-06-2019, 09:32 AM   #1 (permalink)
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Default Half speed Loading

Hi,
Since we know you are still here, Ill continue my journey... I want to examine running in the half speed region which should be full power. My quest is to find how much heat needs to be dissipated to run continually in this region. It is well known in the field that motor has a peak efficiency around 50-75% of the load but max power does not lie there. I want to see how rapidly the temperature climbs in the winding at this loading point and see if there is a way to cool the motor enough to broaden the efficiency band out to the max power point. I have no decided on what motors I want to test but the bench is under construction now. I also would like to find a good way to predict stall current with a fair level of accuracy if possible. I need this because the bench drives may no withstand the load.





Gauging temperatures by touch is never recommended, because depending on the motor, or application, proper or normal operating temperatures may be way above what could be considered safe to touch. Measuring the temperature at the surface of the motor is not a useful indicator of the temperature of the winding or bearings.

"Practical electric motors are designed for optimum cost and performance. Since they are never operated at full load in the field, they are designed for maximum efficiency around 85% of full load because that is the normal region of operation. By changing the design, highest efficiency can be made at full load. At maximum efficiency, the I^2*R losses are approximately equal to the no-load losses. At higher load, the efficiency falls again due to increase of I^2*R losses with increase of current. At 50% load, the efficiency may be typically 80% of the maximum value. It falls faster at reduced load. High-efficiency motor and custom designed motor characteristics will differ, depending on their design philosophy adopted. "

~Sujit K. Biswas
Jadavpur University~



100*C is boiling and no one can touch that or would consider it cool but the motor would operate just fine with good efficiency and is making great power.

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Old 11-06-2019, 01:35 PM   #2 (permalink)
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Default For your eyes only.

Here is my braking load. 5kW per phase. The load is a motor/generator in a cradle with a 1 ft torque arm to a 0-25 pound load cell for true ft pound measure. I bring the wye bundles or Delta wire out an put a thermistor there to measure the winding temperature. Lastly a QTI optical sensor to record the bell rpm. All it need on the black bell is a white line or dot. If it were srm the pattern would be grey code. It would resemble a repetitive bar code. The data acquisition will be handled by a basic stamp's "stamp plot" with a real time clock module.





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Old 11-07-2019, 06:25 PM   #3 (permalink)
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Default A lesson on torque and speed in a BLDC machine from da hood.

Define power in a rotating electrical machine.

Prot = Torque(τ) x Angular velocity (ω)

In a dc machine the torque and angular velocity are inversely proportional. You can see this better by looking the torque speed characteristic of a dc machine. This line can be approximated by connecting two points, no load speed and stall torque. The equation of this line can be defined in terms of torque or angular velocity. This relationship is bounded to a inverse trade off between torque, rpm, and power.

τs = stall torque
ωn = no load speed

τ = τs - ωτs/ωn
or
ωn = (τs-τ)ωn/τs

The charts explain the trade off.
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Max power occurs at the square of half the maximum free no load speed (ωn) and half the maximum torque (τs) in the rotating machine.

Pmax = (.5τs)(.5ωn)

This is observed here in this chart.
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Substitute the line equations back into the original definition of Prot. and this will give u the power curve eq's as they are defined by torque (τ) or angular velocity (ω) .

Pmotor(ω) = -(τs/ωn)ω+τs^ω

Pmotor(τ) = -(ωn/τs)τ+ωn^τ

From these u plot the torque/speed line and power curves.
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Half speed is full power.

Inexperienced pilots have no answer for predicting stall torque. So I will suggest one that is very simple to understand. The phase conductor Preece value and the torque value at that amperage. If we ignore the permanent magnets we can assume the max current value the phase conductor could see is its Preece or Onderdonk value.

The Preece (10sec.) fusing value for only 2 10Ga conductors will be a bomb @ 666 amps the Onderdonk (1sec) fusing value will be the devil @3.2 kA!

Do you really think blathering pilots 100 watt motors and benches are significant here or could sink this motor at stall ?


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Old 11-07-2019, 08:23 PM   #4 (permalink)
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The PMFSM maintains high torque through most of its speed and power range.The SRM and induction machines also observe different speed torque character than a bldc.
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Old 11-08-2019, 10:13 AM   #5 (permalink)
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Default Motor parameters

To make calculations we record motor parameters
  1. Motor Voltage Constant Ke(volts-sec/rad)
  2. Motor Torque Constant Kt(lb-in/amp)
  3. Motor Resistance Ra(ohms)
  4. Motor Inductance La(Henries)
  5. Motor Inertia Jm(1b-in-sec^2)
  6. Load Inertia reflected to the motor shaft Jload(lb-in-sec^2)

In a BLDC machine these are phase values.
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Old 11-08-2019, 10:42 AM   #6 (permalink)
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Default Motor Voltage Constant(Ke)


In the hood we measure the Ke by turning the shaft at a know speed and measure the generated line to line voltage. With a bldc motor the voltage measure will be taken between any two phases then converted to the phase voltage by dividing the measured value by the square route of 3 (1.73).
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Old 11-08-2019, 01:03 PM   #7 (permalink)
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Default Torque Constant (Kt)

A bldc motor torque constant (Kt) can be computed from the voltage constant (ke). I simply divided 1 by the Kv multiplied this value by the highest winding factor potential for a 22 pole 24 slot machine which was. .95766. This seems to agree well enough with Neu specifications.Extrapolated from his Kt values I found a factor of .956828(1/Kv)=Kt throughout the 46 series so were pretty close with this calculation. You could use either and the number wont change significantly.

For a 4638(289) as an example I calculate the Kt to be 33.137 mNm/A or .0244 ftpounds/A from this we can easily predict a stall torque based on the 10 second Preece and 1 second Onderdonk fusing values of the phase conductor.
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Old 11-09-2019, 11:06 PM   #8 (permalink)
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In the middle of this I work on a 24 slot 22 pole stator for the bipolar dream.The PMFSM.
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Old 11-10-2019, 04:25 PM   #9 (permalink)
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Here is the dimension ed 46 series stator. Im greater than 50% fill here which should be adequate for an exceptional machine. I can do more as you can see. This is 2mm conductor so the preece value would be summed from 2 of these
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Old 11-10-2019, 04:41 PM   #10 (permalink)
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Here is the sheet by itself.
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Old 11-10-2019, 04:57 PM   #11 (permalink)
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Default Tooth geometry and slot area 46 series 24 slot Neumotor


Here was the measurements I took of the slot and teeth everything was slightly over but this would be the un-insulated iron. Please enjoy what you actually get here from me. It all takes real time and effort what I do and I chose to share it for anyone that may have interest.
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Old 11-10-2019, 09:19 PM   #12 (permalink)
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PMFSM Rev.1 Permanent magnets added to model and cut goes further into yoke. 22 poles I believe will do better with teeth simulations will know better but from theory slot opening has less benefit as the pole pairs go up, but I need to consider the stator tooth geometry of the reference machine. This was just for interest in the midst of the thread topic.
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Old 11-17-2019, 08:34 PM   #13 (permalink)
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Preece conductor value X .0244 ft/lbs is ??? U can do math right. So a lil practice never hurt anyone We will call that stall torque. A very conservative one because the Preece value should hold for 10 seconds. That's adequate time for a pull through a precious F3S speed trap.

Can a 100 watt drive hold 666 amps for 10 seconds?

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Old 11-17-2019, 10:37 PM   #14 (permalink)
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Default 16.25 ft/lbs @ Preece

If this evil number is what we choose we can say half speed is 333 amps. we should be able to do this with our motor and drive.
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Old 11-17-2019, 10:41 PM   #15 (permalink)
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Look again the torque density of the reference PMFSM. It is greater torque than the 4638 at stall @ less than 3 kW. It is not some huge motor. It is in our size on the larger end of things.

At these power levels these are hardly toys!!
So be careful with the editorial u get on my work in other places by people that have no experience with any of this. The posted idea that because these are "toys" you can ignore the torque speed character of the machine is absolutely wrong.

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Old 11-19-2019, 10:06 AM   #16 (permalink)
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Have the notes on Ke (post#6) been downloaded so much ( 45 x's) b3cause jt is new information? Sure seems to be a lot of interest in those formulas u got here . I would have thought that should have already been known..You see the parallel coil configurations I'm using on the the first layer of the 4632 22 pole machine.
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Old 11-20-2019, 01:43 PM   #17 (permalink)
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Progress here since I've done all this. No winds, no test, no half speed running, just the usual forum topic hijack of my work......




.... and in general as there is nothing useful shown or any specific information for a better rotating machine and will not be from the editors. Don't waste your time.
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Old 11-22-2019, 01:39 AM   #18 (permalink)
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Default https://www.clughmotors.com/

From here we will always have protection from forum folly, then u can always see what I do.I created safe place for positive capable persons in "my hood" It is not meant to be an exclusive site but there will certainly be no bad apples there. If there is over cite and it is corrected you wont have to endure themed post, rants ,or personal solos.

We can consolidate all the threads here to one Clugh's corner and never worry about these type of things again. Everything posted there will be of no reflections, liabilities, or consequence to the non professionally based social site communities. We wont have to argue, I can just cut out the unnecessary fat, and keep going.

https://www.clughmotors.com/ The site is no where near completely built yet but when it is the readers can interact with US and it will all make sense. This way the cdromulans can have there precious space back.

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Old 01-03-2020, 05:58 PM   #19 (permalink)
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Is my cryogenic blast effective at cooling? Is this one way to extend the duration of full power running? Previous ideas from the "group" editors it wouldn't work seem to be 20F below zero.
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