X-File - The "Is My Math Right?!" Thread
#11
devin, post:21, topic:17037 Wrote:battery amps = motor amps x (% duty cycle / 100)

@Ackmaniac

if we use this ^

40 battery amps = 1440 W / Pack V: 36 V

battery amps = motor amps x (% duty cycle / 100)

can be rearranged to:

motor amps = battery amps / (%duty cycle / 100)

so:

1440W = 42.1052 motor amps = 40 battery amps / (%95 duty / 100)

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/22,2017-02-02 13:27:43 UTC
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#12
@Ackmaniac

@ 0 rpm

1440W = PWM Effective Voltage: 4.8V = Motor Amps: 300 A

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/23,2017-02-02 13:33:57 UTC
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#13
@Ackmaniac

0.1403 = Motor Amps @ %95 duty @ 1440W: 42.1052 A / Motor Amps @ 0 RPM @ 1440W: 300 A

%14.03 = 0.1403 x 100

In simple terms motor amps at 95% duty 1440w is %14.03 of motor amps at 0 rpm 1440W.

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/24,2017-02-02 13:37:04 UTC
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#14
devin, post:13, topic:17037 Wrote:If you are asking:

Which RPM does 1440W electrical = 95% duty cycle?

@Ackmaniac

we know that whenever duty cycle = 100%

it means:

battery amps = motor amps

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/25,2017-02-02 13:46:52 UTC
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#15
@Ackmaniac

from ohm's law we know that short circuiting the motor leads would lead to:

Battery Amps: 2250 A
Watts: 81000 W

",0,1,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/27,2017-02-02 13:55:11 UTC
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#16
@Ackmaniac

We know that % No Load Rpm is linearly proportional to % Battery Amps @ 100% Duty

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/29,2017-02-02 13:57:06 UTC
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#17
Ackmaniac, post:28, topic:17037, full:true Wrote:OK forget about it. I thought we can have a interesting talk. My fault.

@Ackmaniac

Since the question you asked is:

Which RPM does 1440W electrical = 95% duty cycle?

this is effectively the same as asking:

Which RPM does 1440W electrical = 100% duty cycle?

this is effectively the same as asking:

Which RPM does 40 battery amps = 100% duty cycle?

",0,5,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/30,2017-02-02 14:03:18 UTC
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#18
@Ackmaniac

We know that:

0% RPM @ 100% duty cycle:

2250 Battery Amps

100% RPM @ 100% duty cycle:

0 Battery Amps

So the question becomes:

Which XX.XX% RPM @ 100% duty cycle:

40 Battery Amps

It is the same as asking:

Which XX.XX% RPM @ 95% duty cycle:

40 Battery Amps

^*I think :thinking:

",0,1,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/32,2017-02-02 14:08:57 UTC
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#19
Ackmaniac, post:33, topic:17037, full:true Wrote:OK now that we asked multiple times it would be nice to see some posts that help us with the answer.

@Ackmaniac

Well if use

0.01777 = 40 A / 2250 A

%1.777 = 0.01777 x 100

In simple terms (1440 W @ 95% duty) 40 battery amps is %1.777 of 2250 A (%100 max) battery amps

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/34,2017-02-02 14:17:35 UTC
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#20
@Ackmaniac

you said:

Motor KV: 190 KV
Pack V: 36V

so:

6840 rpm (%100) no load max = 190kv x 36v

%100 - 1.777% Max A = %98.23

So if I had to hazard a guess I'd say:

1440w @ 95% duty = %98.23 of no load rpm

6840 no load rpm x 0.9823 = 6718.93 rpm

Ackmaniac, post:14, topic:17037 Wrote:Pack V = 36V, Ohm Resistance = 0.016, Batt = 1000 /Motor = 1000 /Absolute Max = 2000 Amp Limit Settings, and Motor KV = 190

devin, post:13, topic:17037 Wrote:If you are asking:

Which RPM does 1440W electrical = 95% duty cycle?

@Ackmaniac

In simple terms my back of the napkin guess is:

1440w electrical @ 95% duty = 6718.93 rpm

^^ take this with a huge grain of salt (probably wrong)

:thinking:

",0,1,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/35,2017-02-02 14:28:14 UTC
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