code to change the motor amp limit

General topics and discussions about the VESC and its development.
rew
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Re: code to change the motor amp limit

Postby rew » 16 Aug 2017, 06:31

There are a few things where the units "drop out". The unit is "1".

Assignment: You live in an area with 50Hz AC current from the wall. How many cycles in a minute?

Answer: The Hz unit is actually 1/s. Maybe "cylces/s", but according to SI it is really 1/s. the cylce (just like turn) is dimensionless. 60 seconds per minute (min = 60s), N = F * t = 50Hz * 1min = 50 (1/s) * 1 min * 60 s/min = 3000 (cycles). That 3000 is dimensionless.

Another example is resistance of sheets of material. The resistance is expressed as "ohms / square". where the "square" is dimensionless (1m/1m).

Similarly the "turn" and "termination" parameters/factors are dimensionless quantities.

If you like the quantities in your formula better than those in the standard formula: Good for you!

The whole motor-KV-calculation is a bit tricky: if you send an object moving at 10ms you can calculate how long it will take to travel 20m. But for a motor starting with say a CAD model of the motor, the materials used, go ahead and calculate the KV. Very difficult. I'm sure there are expensive motor-design-software-packages that can do it, but there is probably just a numeric simulation involved to solve some equations that we can't analytically solve.

So you have this motor with 100kV and say 100 turns. Now I rewind that motor with aluminium wire because I heard aluminium is also a good conductor of electricity. I use the same thickness and manage to cram in the same 100 turns. So you predict my kV with your formula. The conductivity of aluminium is 61% of that of copper.

devin
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Re: code to change the motor amp limit

Postby devin » 16 Aug 2017, 15:53


devin
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Re: code to change the motor amp limit

Postby devin » 17 Aug 2017, 15:59

This formula may in the end be a bit more simple and practical because:

-It's based on changes in resistance and resistivity rather than changes of conductance and conductivity.

-It uses only one square root operation instead of 2

-It still calculates KV changes using SI base unit derived variables, rather than legacy non-SI derived units "turns and termination"

----------------------------

D=sqrt(E/(V*N))
E=N*V*D^2
V=E/(N*D^2)
N=E/(V*D^2)

D = Change Factor of KV (rpm/v)
E = Change Factor of Conductor Resistivity (ohm-meters)
V = Change Factor of Conductor Volume (meters^3)
N = Change Factor of Conductor Resistance (ohm)

--------------------------------

100kv 30 Turns 0.6ohm Wye Copper -> 173.205kv 30 turns 1/2 Cross Section 0.671432ohm Delta Aluminum

D = 1.73205 = Change Factor of KV (rpm/v)
E = 1.67858 = Change Factor of Conductor Resistivity (ohm-meters) Copper to Aluminum
V = 0.5 = Change Factor of Conductor Volume (meters^3)
N = 1.1190533 = Change Factor of Conductor Resistance (ohm) = 0.671432 new ohm/0.6 original ohm

D=sqrt(E/(V*N))

D=sqrt(1.67858/(0.5*1.1190533))

1.73205=sqrt(1.67858/(0.5*1.1190533)) <—Correct

100kv 30 Turns Delta -> 57.73kv 30 turns Wye

D = 0.5773 = Change Factor of KV (rpm/v)
E = 1 = Change Factor of Conductor Resistivity (ohm-meters)
V = 1 = Change Factor of Conductor Volume (meters^3)
N = 3 = Change Factor of Conductor Resistance (ohm)

D=sqrt(E/(V*N))

D=sqrt(1/(1*3))

0.5773=sqrt(1/(1*3)) <— Correct

------------------

^Verified

devin
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Re: code to change the motor amp limit

Postby devin » 20 Aug 2017, 04:21

Last edited by devin on 22 Aug 2017, 23:44, edited 35 times in total.

Hummie
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Re: code to change the motor amp limit

Postby Hummie » 20 Aug 2017, 05:13

actually forget it I remember now
Attachments
Delta_diagram.gif
Delta_diagram.gif (27.97 KiB) Viewed 2908 times
Wye_diagram.gif
Wye_diagram.gif (14.71 KiB) Viewed 2908 times

devin
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Re: code to change the motor amp limit

Postby devin » 23 Aug 2017, 17:56

One could say the change factor of IKEACVE@CCV@S@FDC (individual kinetic energy of average copper valence electron @ constant copper volume @ stall @ 100% [full] duty cycle) = change factor of KER@NLR (kinetic energy of rotor at no load rpm)

CFOIKEACVE@CCV@S@FDC = CFOKER@NLR

For example at constant copper volume, if we double the voltage, the average copper valence electron has 4 times as much kinetic energy, and therefore the rotor has 4 times as much kinetic energy at no load rpm, & CFOIKEACVE@CCV@S@FDC = CFOKER@NLR.

It's a fancy way to say when the electrons go twice as fast, the rotor goes twice as fast.

Image Source:
Image

Image Source:
Caption: "The s-orbital electrons create a spherical shape based on probability"
Image

Image

devin
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Re: code to change the motor amp limit

Postby devin » 26 Aug 2017, 21:54

If it turns out copper and aluminum wire at the same number of "turns" have different KV, in theory it's the result of different electron drift velocities in the copper vs aluminum windings with the same geometry. For example a copper wire with half the turns has double the electron drift velocity, and double the rotor rpm at no load speed.

Image

rew
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Re: code to change the motor amp limit

Postby rew » 27 Aug 2017, 06:56

The power of a good theory (formula) is that it can make accurate predictions about the real world.

So my theory/formula predicts that with aluminium wire and the same number of turns you get the same KV. Just a little bit less efficient motor overall.

devin
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Re: code to change the motor amp limit

Postby devin » 27 Sep 2017, 15:36



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