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Electric Motors Winding and Repair Electric Motors Winding and Repair Discussion


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Old 09-23-2015, 08:55 AM   #1 (permalink)
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Default Efficiency governs power

Efficiency governs power/weight ratio
Higher efficiency does not only mean that the motor makes better use of the batteries' power, it also means the motor is able to handle a higher power input before hitting its maximum temperature mark.


An example
Say the motor has an efficiency η = 0.900 and it can handle 5.0kW input. That means it can get rid off (1 - 0.9 ) 5kW = 500watt excess heat. Now, by cramming in thicker wire (and/or using better stator-iron, segmented magnets), efficiency increases to 0.933. The motor's ability to loose those 500watt has not changed (by radiation, convection and conduction). This means the motor now can handle 7.5kW before it hits the 500watt (0.066 7.5kW) losses mark.
So, going from 90 to 93.3% efficiency gives an increase in power of 50%, factor 1.5 That's why efficiency plays such an important role, in any motor design: efficiency governs maximum power. All of this assuming the iron will not saturate. And the motors weight has increased (numberss and examples in Ralph's post #3 below).
A rather extreme example, just for calculation's sake/fun: going from 80% to 90% efficiency would increase the input power the motor can handle by a factor two (a.k.a. 2) Going from 90 to 95% efficiency would increase power again by factor 2


General case
Going from efficiency ηold to efficiency ηnew would give an increase in maximum power motor can handle by factor N
N = (1 - ηold) / (1 - ηnew)

Copper as thick as possible for ...
  • higher efficiency
  • more power
  • lower rpm drop under load
  • lower losses
  • lower temperature
  • at the cost of less cooling
Ignoring skin effect at high electrical rpm.


Vriendelijke groeten Ron

Last edited by ron_van_sommeren; 09-24-2015 at 10:45 AM..
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Old 09-23-2015, 05:48 PM   #2 (permalink)
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Very nice post Mr. Van Sommeren.....
Seems like you can get more copper in if you use square multistrand?

Thank You,
1BOHO
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Old 09-24-2015, 12:42 AM   #3 (permalink)
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Quote:
The motors weight may have increased a bit due to more copper.
practically seen it will not only a bit!
if you increase copperfill by 30% (this is for a normal rewinding) copperweight will increase into the same number.
and into an extreme rewinding the copperweight will go up up to 50%.

copperweight is normally round about 30% of motorweight.
so a good rewinding makes the motor 15% heavier.

cofe has 8,15g/cm^3; normal iron only 7,85g/cm^2.
so the usage of cobalt iron increases the ironweight by additional 8,15 / 7,85 = 4%.

same effects for a "complete thick" (shorted all magnetic field lines) backiron and for a stronger magnet system.
example:
scorpion 4035 V1 had 7,2mm broad magnets.
the more efficient and more powerfull V3 has 9,5mm magnets.
this increases the magnetweight by 9,5 / 7,2 = 32%.

pls. note my signature.
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Old 09-24-2015, 10:41 AM   #4 (permalink)
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Thanks for the numbers Ralph. I have changed my opening post accordingly.

Vriendelijke groeten Ron
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Old 09-26-2015, 04:46 PM   #5 (permalink)
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Ron

Isn't the ability to get rid of heat goes down due to higher copper fill = less vent? That is the result i see on my pyro 700-45 (copper is now similar to BE):

Max power has increased from 3000+ to 5000+ watt. Temp was significantly increased mesured up to 90+ Cel on a hot day.
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Old 09-27-2015, 09:56 AM   #6 (permalink)
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Quote:
Originally Posted by omerco View Post
... Isn't the ability to get rid of heat goes down due to higher copper fill = less vent? ...
Of course cooling ability goes own.
Hence my ...
Quote:
Originally Posted by ron_van_sommeren View Post
Copper as thick as possible for ...
  • ...
  • at the cost of less cooling
  • ...
Vriendelijke groeten Ron

Last edited by ron_van_sommeren; 09-27-2015 at 11:35 AM..
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Old 09-27-2015, 12:47 PM   #7 (permalink)
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Quote:
Originally Posted by omerco View Post
Ron


the ability to get rid of heat goes down due to higher copper fill = less vent? That is the result i see on my pyro 700-45 (copper is now similar to BE):

Max power has increased from 3000+ to 5000+ watt. Temp was significantly increased mesured up to 90+ Cel on a hot day.
Quote:
Originally Posted by ron_van_sommeren View Post
Of course cooling ability goes own.
Hence my ...


Vriendelijke groeten Ron
Isnt the bottom line output power if the components used and the surrounding environment can safely withstand the operation temperatures?

This is almost like a dragster not caring about BSFC? They dont care about mileage or fuel consumption only the output power. Is the point here that if we take two motors at the same output power the more efficient one runs cooler? So the whatever power output that would cause the more efficient motor to hit the same temp number would be its increase in output power over the less efficient?

Thanks for your time.
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Old 09-27-2015, 12:47 PM   #8 (permalink)
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Default cooling....

...

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Old 09-27-2015, 12:57 PM   #9 (permalink)
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Seems to me.

Iregaurdless of whether its criss crossed or layed perfectly a smaller wire is going to run hotter than a larger one with the same amperage running through it . When its full and you try to pull more through it the rest is basically heat.

In Saw boats Christian and I have considered cooling the stator with compressed C02 for increased output in the short burst required for two fast passes.Saw boats are pulling upwards of 400 amps in these burst.
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Old 09-27-2015, 01:05 PM   #10 (permalink)
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Quote:
Originally Posted by 1BOHO View Post
... So the whatever power output that would cause the more efficient motor to hit the same temp number would be its increase in output power over the less efficient? ...
A small increase in efficiency can give a much bigger increase in power motor can handle than one would expect. Going from 10 to 15% won't do much for max. power, going from 80 to 85% however, or even better, from 90 to 95% ... Just playing with numbers here to get the message across.

It's a bit like motorcurrent being proportional to voltage squared and proportional to Kv cubed (ignoring voltage sag in wires and motor). Current changes more than one would expect.

Vriendelijke groeten Ron

Last edited by ron_van_sommeren; 09-28-2015 at 09:24 AM..
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Old 09-27-2015, 01:13 PM   #11 (permalink)
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Thanks Ron,



A radial fan is something like a supercharger on a car. It adds and robs power. A higher pitched fan would pull more heat away but also use more of the motors power to operate. The more minimal load it is on the motor the less heat it pulls away. Better look for a very efficient blade design for the most benefit. This turnigy designed for a boat has a water jacket and radial fan.
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Old 09-27-2015, 02:24 PM   #12 (permalink)
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Funny about how the neatness airspace between in which the wires are lay'ed as far as efficiency is concerned. With lehners which use coreless designs similar to the attached photo there is no space as the photo shows between any wires and we know lehner produces some of the most efficient motors in the world. More copper may leave less space but it wouldnt heat up as much anyway as there is room for the current to pass. Of course space would help to ventilate everything but if there is enough copper to carry the current it shouldnt heat up as much anyway as compared to factory winds that neglect airspace for ventilation as well as enough copper to carry whats demanded of people living outside of factory limits. To me more copper seems much more important in reducing the heat for its output respectively than how neatly it is lay'ed. In turn a motors ability to cool is a motors ability to deal with waste.

http://physics.bu.edu/~duffy/PY106/Resistance.html
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Old 09-27-2015, 03:00 PM   #13 (permalink)
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Quote:
Originally Posted by ron_van_sommeren View Post
Of course cooling ability goes own.
Hence my ...


Vriendelijke groeten Ron
But you ignore that in your calculations. In the case of the pyro 700 i took a really coll motor and left close to zero air gap between the windings. Looks to me like a significant factor, but i might be wrong.

The biggest thing for sure is the much highet ability of the motor to drew amps - hence produce power - due to the lower R.
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Old 09-27-2015, 03:17 PM   #14 (permalink)
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Quote:
Originally Posted by omerco View Post
But you ignore that in your calculations. ...
Yes.
That's theory for you Engineering is about trade off's, decisions and finding the sweet spot for an application: lots of copper for short runs, less copper and thus better cooling for long flights. But I guess these little gems of wisdom (it's late already here) are not new to you, or anyone else here.

Just ignore anything I wrote there about copper and copperfil, and assume efficiency gain is from better materials (iron, wire).
Quote:
Originally Posted by ron_van_sommeren View Post
... Just playing with numbers here to get the message across.
Vriendelijke groeten Ron

Last edited by ron_van_sommeren; 09-28-2015 at 09:22 AM.. Reason: - long runs + short runs
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Old 09-27-2015, 03:42 PM   #15 (permalink)
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Quote:
Originally Posted by omerco View Post
But you ignore that in your calculations. In the case of the pyro 700 i took a really coll motor and left close to zero air gap between the windings. Looks to me like a significant factor, but i might be wrong.

The biggest thing for sure is the much highet ability of the motor to drew amps - hence produce power - due to the lower R.
Ask of you rewound motor the original motor out power output and see what temp it is of your new motor. If its higher your rewound motor isnt as efficient as what it was before.If it is temp at that same ouput level is lower Id think it would be more efficient based on whats been said here.

The other way is to load your old motor to the output power seen by the new motor and take a temp reading. Is it still running cooler than your new motor.



@ Ron
I appreciate your post please continue.....
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Old 09-27-2015, 08:58 PM   #16 (permalink)
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Quote:
Originally Posted by 1BOHO View Post
Ask of you rewound motor the original motor out power output and see what temp it is of your new motor. If its higher your rewound motor isnt as efficient as what it was before.If it is temp at that same ouput level is lower Id think it would be more efficient based on whats been said here.

The other way is to load your old motor to the output power seen by the new motor and take a temp reading. Is it still running cooler than your new motor.



@ Ron
I appreciate your post please continue.....
+ 2 for ron its still very interesting to see the numbers.

1Boho I don't think you are correct about the temp. I did what you wrote and it was running hoter (warmer) BUT also gave longer flight times :-) and more power :-) :-)

The heat comes from the fact that the air part of the cooling in the origonal motor with the much lower copper is very efficient. In the 80% higher copper one it is significantly reduced.
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Old 09-28-2015, 12:14 AM   #17 (permalink)
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Quote:
Originally Posted by omerco View Post
0

+ 2 for ron its still very interesting to see the numbers.

1Boho I don't think you are correct about the temp. I did what you wrote and it was running hoter (warmer) BUT also gave longer flight times :-) and more power :-) :-)

The heat comes from the fact that the air part of the cooling in the origonal motor with the much lower copper is very efficient. In the 80% higher copper one it is significantly reduced.
Nice. How did you perform the test?
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Old 09-28-2015, 12:44 AM   #18 (permalink)
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Absolutely agree.
My trex 500 uses a NEU 1706 (inrunner!) motor giving me 1/2 to 1 minute more flight time than Hacker, M500X motor.

I know this from flight time, battery temp, remaining % lipo(cellpro10s charger readout), and rpm at end of flight.

I could do some calculations and analyze the motor windings and specs...but fk it...I'd rather get my 12-15 flights per 2 hr quota!!!
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Old 09-28-2015, 04:09 AM   #19 (permalink)
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Quote:
Originally Posted by 1BOHO View Post
Nice. How did you perform the test?
Logo 600 with Castle 120HV ESC FOR DATA, both before and after the rewind.

Heat just by touch. Before was super cool and after it was warm.
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Old 09-29-2015, 09:23 AM   #20 (permalink)
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Quote:
Originally Posted by omerco View Post
Logo 600 with Castle 120HV ESC FOR DATA, both before and after the rewind.

Heat just by touch. Before was super cool and after it was warm.
Sounds like you simply logged both motors. That was not my suggested test. You will need real time data acquisition equipment unless you know how to look at the load you are putting on the original motor while its in operation. What I was saying is if you had a prop that would actually load the original motor to a point where it draws enough amps to output the same power as the new motor did with the original load and compare the temps of the original motor at the power level of the new motor it seems like a fairer comparison with respect to looking at the heat of both motors at the same power level your "control" if you will..... With the esc log you can only run it then download the log and look at it. You cant dial up a load this way. It may be difficult with a prop unless you have a series of them that load the motors differently. A good good handheld multi meter like a fluke or a knockoff like a VC97+come with a nice plug in temperature probe u can place right on the coils. Of course you would need to secure it away from the can somehow as to not get the probe wire spun up in the motor.
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