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Electric Motors Winding and Repair Electric Motors Winding and Repair Discussion |
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07-10-2016, 02:09 AM | #21 (permalink) |
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And with less current come less torque as defined by the torque constant which is derived from the Kv of the motor. Also Is the "same" power more power? I actually calculate about a hp between the packs. But if the motors are rated at the same power which yours will be if you only switch the pole count it seems to me the kv is more of a way to match the motor to the battery. The way to make more power is a lower Ri. and or pulling more amperage but if the wiring cant take it which a lower Ri would create/facilitate it just turns into heat creating less power in the end.
synchronous speed is ns=(120*frequency)/# of poles I would spend some time doing the calculations to plan out a strategy that will really yield more performance for the extra time or money involved I dont think as i posted initially that just swapping a different pole stator on the same wind will do it. No matter what wind is on the stator wye or delta in a dual layer the winding factor meaning its torque per amp output is still the same. The YY alows the motor to efficiently pass more amperage. |
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07-10-2016, 05:02 AM | #22 (permalink) |
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It would be nice to compare empirically and get some numbers from your logs to really get a feel of what would make the appropriate calculations. Things like efficiency your actual rpms at the loads etc. I certainly wouldn't take any of these pop shots at calculating things with so many unknowns as truly accurate if at all. But it is pretty certain that the addition of the poles will reduce the kv and rpm at a given voltage and make more torque. To calculate the true difference would take a lot more knowns i'd think.
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07-11-2016, 08:18 AM | #24 (permalink) |
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Hi Skylar,
I thought so too, but I still think my overall torque comparisons on the different motors at different voltages a bit skewed due to the fact of mixing "loaded" Hp and unloaded rpms . Nevertheless thanks for the intuitive insight. What I'm more curious about in my discipline is how "throttling" down doesn't lose anything .... voltage or at least some power (current) but I'm very unfamiliar with the commutation algorithms or topology of a Jazz. Is it a VFD? If it is then I pull back from my statement about single layers because the BLAC shows more dynamic efficiency than BLDC with dual layers. It seems speed planes would spend more time at WOT than a heli so It wouldn't seem much benefit to have the added dynamic efficiency by the use of BLAC drives and dual layers. With a BLDC single layers are a better choice for torque and efficiency so for me they make more sense. But still from my days in communication electronics a lower frequency ( seems the only other way to slow synchronous speed) will deliver less power. This is part of the reason 2.4ghz would be preferred over AM or FM more power delivery of the signal. Or am I missing something here? And so..... (10x12)/(14x12) x 415kv = 296 kv. Very elegant Skylar ! |
07-11-2016, 02:19 PM | #25 (permalink) |
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Hi Skylar ,
for true there is not this math relationship . This is only if you use it as a real magnetic gear as i have done in the counterrotating motor,where i used two 12 slot stator and let a 10 pole can run in front and a second 14 pole can at the back . Belong to the magnetsystem the cans run counterclockwise with a single controller . Need exact adjustment of propellers to find the right torque load . 10 pole run higher rev realy exactly like your math . But for true a 14 pole can rund higher speed as the statorplate shape has not changed and so the 10 pole can rund less speed as the math told you . |
07-11-2016, 03:25 PM | #27 (permalink) |
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Hi CHX2
It seems that you made that double motor from Torcman kit motor components. They were very nice motor kits. |
07-11-2016, 04:39 PM | #28 (permalink) |
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Correct way of writing Kv
Please note that the correct way of writing the speed constant is: Kv.
kV, kv and KV should be avoided. |
07-11-2016, 10:10 PM | #29 (permalink) |
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I wouldn't worry about it too much in general forum conversation.I doubt anyone thinks we are talking about 415 kilovolts maybe not, but It isn't truly "Kv" either as the "v" is truly a subscript of the "K" and that is not a usable feature in the advanced post option. If it confuses anyone you could always say rpm/V.
https://en.wikipedia.org/wiki/Motor_constants I'm kind of confused by the wording of the previous post on whether or not we can use your posted formula to find his 14 pole rpm/V based on 10 poles and 415 rpm/V. Can we or not? Based on the synchronous speed formula running at the same frequency from one controller on the same stator how does the 10 pole run slower and the 14 pole run faster as the wording has it in the last line of post #25? "But for true a 14 pole can rund higher speed as the statorplate shape has not changed and so the 10 pole can rund less speed as the math told you ." That defies the synchronous speed formula for a 3 phase motor. synchronous speed is ns=(120*frequency)/# of poles. 14 is a larger divisor If the frequency was arbitrarily 1 hz then rpm would be 8.571 with 14 poles and 12 with 10 poles. Isn't 12 rpm faster than 8.5 ? That is a nice counter drive though. Any videos of it running? |
07-11-2016, 11:11 PM | #30 (permalink) |
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Hi,
but the bldc motors are not frequenz related like synchronus motors run at a static frequenz net .The frequenz of the controller folowes the rpm of the motor and the load . If you load the motor the rev will go down and not hold by the frequenz . That's a big differenz . These motors are not geared by the number of poles . |
07-11-2016, 11:15 PM | #31 (permalink) |
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So in a BLDC motor the 14 pole motor on the same stator windings and controller is faster than a 10 pole? That is not what his math says either.
How can all brushless dc motors not be frequency related but you have brushless FOC controllers by a another name V.F.D. drives? variable frequency drives. http://vedder.se/2014/01/a-custom-bl...or-controller/ https://en.wikipedia.org/wiki/Vector...ol_%28motor%29 "Brushless DC electric motor (BLDC motors, BL motors) also known as 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. Additional sensors and electronics control the inverter output amplitude and waveform (and therefore percent of DC bus usage/efficiency) and frequency (i.e. rotor speed)." https://en.wikipedia.org/wiki/Brushl...electric_motor The formula is for ac synchronous motors and induction motors in which you would have to calculate in slip. well.... |
07-11-2016, 11:50 PM | #32 (permalink) |
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No Hugh ,
you are missunderstanding . The 14 pole motor turns faster than the math told you with the relationship of the number of poles . Not the 14 pole turns faster than a 10 pole rotor can . You have not to teach me about bldc motors ,you turn things like you want . If the 10 pole motor turns 321 kv the 14 pole motor will not turn 450 kv like the math say it will turn somthing about 460 or 470 kv and frequenz will be different as you run this motors on a open frequenz motorcontroller not on a fixed frequenz net . |
07-11-2016, 11:55 PM | #33 (permalink) |
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What you just said is they were not frequency related like a synchronous motor and that is not correct. So it seemed a lesson was needed. Your original post wasn't to my math but Skylars. I only used his reasoning to come up with 296 rpm/volt based of 415 which was the posted rpm/V of the OP. Yes the frequency will vary that how you vary the speed no one has disputed that. It is your wording that made it unclear not the fact that a BLDC speed isnt dependent of frequency and not a synchronous motor.
" If the 10 pole motor turns 321 kv the 14 pole motor will not turn 450 kv like the math say it will turn somthing about 460 or 470" Can you see this is still implying that the 14 pole will turn faster than the 10. I don't know what is significant about 10-20 kv in this case either. |
07-12-2016, 12:09 AM | #34 (permalink) |
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But the bldc motor workes like a brushed dc motor and is not frequenz related as it runs with a electronik that simulate only the comutation of the brushes . Under load it will not run with anfixed frequenz .This is what you have to understand . It runs not as a sinchronus motor . That's fact .
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07-12-2016, 12:15 AM | #35 (permalink) |
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What you have to understand is you continue to post the 10 pole at a lower Kv than the 14 pole and BLDC drives depending one the type most definitely are frequency related and the speed can be governed by a change in frequency and or its amplitude. It may not "run" as a synchronous motor but is in fact a synchronous motor.
It is also fact that none of this will make the 14 pole run faster on the same stator and wind than a 10 pole if you look closely at your quoted post you will see that is what you continue to write. " If the 10 pole motor turns 321 kv the 14 pole motor will not turn 450 kv like the math say it will turn somthing about 460 or 470" My argument is not about a 10 - 20 Kv difference in calculation do you see what you have posted? |
07-12-2016, 12:30 AM | #36 (permalink) |
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Op's ,yes i switcht the numbers . The 10 pole turns 450,460 or higher and the 14 pole turns the lower kv ov about 321 kv . This was a mistake by me as i am writing and not realy looking on the screen .But at the end they are running not on a fixed frequenz esc.
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07-12-2016, 12:33 AM | #37 (permalink) |
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No one has posted they do but that doesn't matter because you can put any frequency you want in vary it all you'd like 1 to infinity but the pole counts effect on speed remains the same. That is why the formula works to see the difference the different pole count would make. It always helps to look at what you are writing on the screen
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07-12-2016, 01:40 AM | #38 (permalink) | |
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Quote:
The "math" that I posted is not a hard rule or formula, but rather a "ball park" indication of what the Kv will be with a different number of poles. The 10 - 20 Kv difference in our example is probably due to magnet coverage and magnet size. @1BOHO Please note that I simulate the subscript 'v' in Kv by changing the text size to 1 or 2. (I trick I learned from Ron van Sommeren). |
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07-12-2016, 04:35 PM | #39 (permalink) |
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@ Skylar,
I never had any issue about your calculations because you had clearly stated the rpm/V numbers were nominal. Funny about "Kv" because after you posted that you see it still went all over the place "kv" "KV" and "Kv" I guess a smaller font is the best we can do but I doubt many will go through all that trouble in a best attempt. I have been on some forums that actually have the true subscript feature and u can also do it from the keyboard in windows office apps. with "shift""+" and "Ctrl" at the same time but when you try that trick within the forum it just zooms the entire page. I'm using google though and I haven't tried it in explorer. I think in the heat of typing it's probably very common to forget the technically correct symbolic representations. I've personally typed it every incorrect way it could be typed. For Scott's sake if you add 10 to 20 Kv to the 296 rpm/V estimate it should fall somewhere between 306 and 316. And so all the discussion actually yielded something useful toward his original question. That's the most important thing. Should be interesting to see how far off it will be from reality. I'm still very curious about the commutation algorithms and topology of a Jazz and "throttling" down scenario with no loss of voltage or current seen at the motor not the line voltage and what would be the correct math to estimate the Kv that extracts the additional 10 - 20 Kv . |
07-12-2016, 08:49 PM | #40 (permalink) |
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This is good to know and I apologize 1BOHO for doubting you on the two Pyro's being same stator/wind and Rotor Poles effecting the Kv.
My ESC is a Jive Pro, not a Jazz though basic function should be same. My understanding of how controller changes motor rpm is by varying pulse length, not Voltage. ESC pass' full V always but adjusts the time the FET's are 'open' which changes the rpm. Since the Jive has Active Freewheeling it can be used at much deeper throttle settings w/o heating up like some controllers. This is not the correct way to setup Gov, by gearing to low and slowing RPM by reducing throttle. But for my experiment it should be fine, especially since HS Calc show's I only need to drop about 10-15% to get where I want going from 10 cell to 12. I'll mess around with the different cell counts, including 6S when I can but the 14P rotor, assuming I can get one won't be till next season.
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