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vedder.se forums • code to change the motor amp limit - Page 6
Page 6 of 14

Re: code to change the motor amp limit

Posted: 20 May 2017, 14:27
by rew
I was following you until "3".

If you think of the KV as: "how big a voltage do I get when I turn the motor mechanically?", (you'd be more likely to think of volts per RPM, than RPM/V, but it's the same thing)... Then you will see that the KV is independent of the wire thickness. Only the number of turns.

So... KV = Constant(motor) * C(termination) * turns.

C(termination) is 1 for Y or sqrt(3) for delta wiring.

Re: code to change the motor amp limit

Posted: 20 May 2017, 15:56
by devin

Re: code to change the motor amp limit

Posted: 20 May 2017, 21:26
by devin
in the change from wye termination to delta termination we see that when conductance increases to 3 times the original value, kv increases to 1.73205 [sqrt(3)] times the original value:

1) wye to delta retermination:
original conductance x 3
original kv x sqrt(3) [1.73205]

2) wye to wye rewinding with (1 / 1.73205) times less turns and (1 x 1.73205) times thicker wire.
original conductance x 3
original kv x sqrt(3) [1.73205]

3) wye to wye rewinding with (1 / 3) times less turns and (1 x ) same thickness wire.
original conductance x 3
original kv x ?? <-- is this also original kv x sqrt(3) [1.73205]?

to illustrate the change in conductance and kv in examples 1) and 2):

Square ADIJ is area 3-- 3 times the area of square AFGH which is area 1
^in wye to delta retermination this is equivalent to the increase in conductance

Line AD is 1.73205 [sqrt(3)] times the length of line AF which is length 1
^in wye to delta retermination this is equivalent to the increase in kv

Image

Re: code to change the motor amp limit

Posted: 22 May 2017, 16:53
by devin
Following this logic it would seem when the rotor and stator are identical, when altering a winding an increase factor in KV is proportional to the square root of the increase factor of conductance (as illustrated below):

1) Winding Conductance Increase Factor: x 1
KV Increase Factor: x 1

2) Winding Conductance Increase Factor: x 2
KV Increase Factor: x 1.41421 [sqrt(2)]

3) Winding Conductance Increase Factor: x 3
KV Increase Factor: x 1.73205 [sqrt(3)]

4) Winding Conductance Increase Factor: x 4
KV Increase Factor: x 2 [sqrt(4)]

5) Winding Conductance Increase Factor: x 5
KV Increase Factor: x 2.23606 [sqrt(5)]

6) Winding Conductance Increase Factor: x 6
KV Increase Factor: x 2.44948 [sqrt(6)]

Image

Can anyone verify this??

Re: code to change the motor amp limit

Posted: 23 May 2017, 05:31
by rew
IMHO, the conductance of the windings does not influence KV. It is the number of turns that influences the KV.

Consider I have a big motor with 10 turns of BIG wire. Now I measure the KV by turning the motor externally at 3000 RPM and measuring the voltage. If I change the 10 turns of BIG wire for thin wires, there will still be no current flowing, and the measurement will be practically the same.

Re: code to change the motor amp limitt

Posted: 23 May 2017, 08:40
by devin

Re: code to change the motor amp limit

Posted: 23 May 2017, 20:19
by rew

Re: code to change the motor amp limit

Posted: 23 May 2017, 21:18
by devin

Re: code to change the motor amp limit

Posted: 24 May 2017, 06:03
by Hummie
https://www.emetor.com/blog/post/bldc-m ... mulations/

I think inductance determines kv and resistance is just correlated. You could wind a motor with graphene, if you could get it, and have almost no resistance and if had let's say 30 turns before with copper and you did it with 30 of the graphene it would be the same kv but drastically different resistance

With the delta connection its only 2/3 of any phase resistance and wye is 2x a phase resistance, as already said.
If you removed 2/3 the copper from a motor that was wye and reterminate it delta, hoping to have the same kv, it would still need the same amount of turns....I don't think you could get those turns on and keep the same resistance with only 1/3 the copper. Either you aren't going to get the turns on, as it's too short, or you get them on and it has to be a thin wire and the resistance goes up.

Re: code to change the motor amp limit

Posted: 24 May 2017, 06:34
by rew