How to Determine your desired Kv rating before rewind

[Inkslinginmofo77]

How to find out desired Kv rating of brushless rewind project using your curent specs.
This formula is to find out the Kv you are aiming for without having to wind it first. I find the other methods require you to wind it first and use a drill and tester but if u are off then u need to unwind and rewind and can be a headache. So this helps u pre-determine the kv u want.

Things u'll need

Current motor kv
Current motor wind specs (wire size, no. Of strands, number of winds)
Desired wind specs (wire size, no. Of strands, number of winds)
Wire winding calculator
Microsoft excel or equivalent
Winding scheme (delta or wye for both)

This is super easy and haven't found any cut and dry explanations or formulas to do this so I figured this out on a wimb. I've tested it and shows accurate

I am using a dji 2212 920kv motor for an example. It has 9 turns delta of 2 strands. The wire is .32mm but will be using the closest size given by the calculator which is .315mm. I want 730kv so will be using 24gauge wire which is indicated in the calculator as the calculator displays both metric and awg size.

Once u have found your current motor specs u can use the calculator. U will need to enter the number turns in the first field and the number of strands above the curent wire size field from your current specs. Hit enter to calculate. This is a Microsoft excel program so u will need that or equivalent to use calculator

Example: no. 9 turns with 2 strands of .315mm wire = 1.403mm2 in the calculator (current)

Now u need to enter your desired number of turns and desired number of strands above the desired wire size in the calculator to find out the calculation. U may need to try different wire sizes or number of strands in formula to reach desired Kv.

Example: 9 turns with 1 strand of 24 gauge wire = 1.767mm2(desired)

Now take the two mm2 results and divide them.
Example: 1.767 / 1.403 = 1.259
Always divide in this order (Desired mm2 / current mm2)

Now take the current kv rating and divide it by the above result
Example: 920kv / 1.259 = 730kv

730 kv is my result of rewinding this motor with 24gauge wire, one strand, of 9 turns delta from 920 kv .32mm wire 9turns of 2 strands delta.

This is an easy formula and I hope it is helpful as I haven't found any other explanation easily found. I will include the calculator file u will need for the excel program. Just enter your info in the proper fields. I have tested and show accurate. However it may vary a couple kv depending on how accommodating the calculator wire sizes are to your current wire size. Which shouldn't matter as long as it's extremely close. I am open to comments or suggestions. Enjoy!

here is the link for the calculator. after u click it it will show a snapshot and above is a download button that looks like an arrow pointing down at a line. click that to download.

https://drive.google.com/file/d/0B8Z...ew?usp=sharing

[Jmann841]

I am a bit confused, Are you saying that the wire size makes a difference with the Kv?

From my understanding, the wire thickness is not important other than if it will fit or not, it is the amount of turns that changes the Kv.

I can wind a motor with 9 turns delta with 24 gauge wire or with 20 gauge wire and both will have aprox. the same Kv.

[omerco]

Also confused...this shouldn't work like this. are you sure you did the same number of T and same scheme and termination?

By the way from my (short...) experience i found any calculation is and estimate but only a test wind will give you the true final result.

For example: i tested my pyro 450 before unwinding to be exactly 450KV.

Then i calculated:
change to YY termination - 450/1.73*2 = 520Kv
change from 13T to 15T - 520 *13/15 = 450Kv

did the winding. got 438-440....

So now i do test winding every time...

[krtek2k]

Dont fall with first post
I done two windings on same motor 12N8P scorpion HK 4025 few days ago:
1,6mm 7(4+3)YY and measured as 1400kV
http://krtek2k.rajce.idnes.cz/Scorpi...C6mm_7_4_3_YY/
than done
2x1,2mm 7(4+3)YY and measured again 1400kV
http://krtek2k.rajce.idnes.cz/Scorpi...C2mm_7_4_3_YY/

Is here some moderator?

[Manuel V]

If using Turn Calculator 7 will not have problems.
http://www.rcgroups.com/forums/showthread.php?t=2228201

[ron_van_sommeren]

Originally Posted by Inkslinginmofo77

How to find out desired Kv rating ...

• The Kv constant is not a rating, not a figure of merit, in that higher or lower is better, it's just a characteristic. More windings will give lower Kv, less windings will give higher Kv, that's all there is to it. No big deal, anyone can do that.
  Rewinding a motor with more (thicker) copper will give you a more efficient (Pout/Pin), more powerful and cooler running motor.
• A motor's Kv constant says nothing about ... max.current and max. power a motor can handle, it is no indication for efficiency, rpm, quality, torque, propsize etc.
  Both a 10watt motor and a 10kilowatt motor can have the same Kv motorconstant.
• Motorcurrent is proportional to voltage squared, and proportional to Kv cubed!
  Motorpower is proportial to voltage cubed.
  Way more than one would expect. (Worst case, ignoring voltage losses/sag due to the higher current ).
  Whether motor can handle those current- and powerlevels is a different story.
• Simple instructive table giving the extra current when you add one extra cell to a pack
  (a.k.a. "why did my motor and/or controller and/or battery go up in smoke ???")
• Motors have just one Kv, not e.g. 1000Kv's.The motor Kv constant is physical quantity (length, weight, time, current, ...) measured/expressed in rpm/volt. It is not a physical unit (meter, kg, s, ampère, ... ). Therefore, Kv=1050rpm/volt.

Prettig weekend Ron