rew wrote:That's what I've been saying all along.
In practice, copper volume does not change. When you rewind you always try to cram in as much copper as you can, resulting in, hopefully, the same copper fill (about 100%: as much as will fit).
^Using half the turns with the same thickness wire, the copper volume is 1/2
. If wire with twice the girth was placed within the motor on the right, KV [rpm per volt] and KT [torque per amp] would stay the same as when the thinner, more modest wire was used.Left Motor: 30 turns, delta, 47.9V, 23856erpm, 3408rpm, 71.14kv | Right Motor: 15 turns, delta, 47.6V, 47444erpm, 6777rpm, 142.3kv | 71.14kv Left Motor x 2 = 142.3kv Right Motor@rew I agree you’ve been saying KV changes in proportion to turns and termination only and not wire thickness
, which is technically true.
But it would also be true to say KV changes in proportion to conductance and copper volume only (and not termination), both of which are SI base unit derived variables in contrast to “turns and termination.” (https://en.wikipedia.org/wiki/SI_base_unit)
My aim since May has been to uncover why re-termination from wye to delta changes kv by a factor of exactly 1.73205 or the square root of 3... which I don't think anyone has yet fully described the correct answer to this but I intend to in my next posting...
...But for now there's 2 accurate formulas to calculate kv from winding changes... a new one and an old one... let's compare their differences:
K = kv = max rpm per volt no load
N = turns = # of wire turns per tooth
C = constant = original kv x original # turns
T = termination = 1 for wye | 1.73205 for delta
kv x turns = constant x termination
100kv x 30 turns = 3000 constant x 1 termination
now we change the number of turns:
50kv x 60 turns = 3000.00 constant x 1 wye termination
now we change the termination:
86.62kv x 60 turns = 3000.00 constant x 1.73205 delta termination
-Accurately predicts KV changes from winding “turns,” “constant,” & “termination” changes.
-Unfortunately, variables “Turns,” “Constant,” & “Termination” are not derived from internationally recognized SI base units
such as “Kilogram,” “Second,” “Meter,” etc.
S = Change Factor of KV
C = Change Factor of Conductance
V = Change Factor of Copper Volume
100kv, 30 turns, 0.05ohm, 1 copper volume
now we change the number of turns (same wire thickness, assuming there was extra space):
50kv, 60 turns, 0.1ohm, 2 copper volume
C = (1/0.10ohm new resistance)/(1/0.05 original resistance) = 0.5 = Change Factor of Conductance
V = 2.0 = Change Factor of Copper Volume
S = 0.5 = Change Factor of KV
New 50kv = Original 100kv x (S = 0.5 = Change Factor of KV)
-Accurately predicts “KV” changes from winding “conductance” and “copper volume” changes
-Accurately predicts “Conductance” changes from winding “kv” and “copper volume” changes
-Accurately predicts “Copper Volume” changes from winding “kv” and “conductance” changes
-Formula #2 has one less variable than Formula #1 -- works for both delta & wye without explicitly specifying which termination style is used
-In contrast to Formula #1, variables “Conductance,” & “Copper Volume” in Formula #2 are indeed derived from internationally recognized SI base units
such as “Kilogram,” “Second,” “Meter,” “Ampere,” etc.
-Formula 1 highlights the correlation between # of turns, termination, and KV, regardless of wire thickness, but requires one additional variable & doesn’t utilize exclusively SI base unit derived variables.
-Formula 2 highlights the correlation between conductance, copper volume and KV, regardless of termination -- only requires 3 instead of 4 variables (termination style delta/wye is not needed to be specified for the formula to work), and unlike Formula 1, Formula 2 utilizes exclusively SI base unit derived variables.
devin 14 May 2017, 23:54 wrote:i'm trying to conceptualize in my mind how sqrt(3) enters into the equation of the difference in kv between wye and delta...
The whole point of this is since mid-May I've been trying to fully understand exactly why re-termination from wye to delta results in an increase factor in rpm per volt of exactly sqrt(3) or 1.73205
So... why exactly does re-termination from wye to delta result in a change factor of kv equal to irrational number square root of 3?
I’m pretty sure I’ve solved it, & will answer this in my next post…