ESC and motor Amp relation ??

[wings_of_fire]

Hi,
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Motor Specifications:

• Resistance: 290m
• No Load Current @ 7V: 0.9A
• No Load RPM @ 7V: 7030
• Max Torque: 123.4mN
• Max Current: 18A
• Max Efficiency: 68%

ESC Specifications:

• Power: 4-7 Cell NiMH/NiCd, 2 Cell LiPO
• Input Voltage: 6V-8.4V
• BEC Output: 5V/1A
• Constant Current: 240A, Forward: 240A, Back: 160A
• Size: 26 x 26 x 16 mm
• Motor Range: 540 8 - 60T motor
• Waterproof: Yes
• Fail Safe Protection: Yes
• Low Voltage Protection: Yes (5V cut-off)
• Over Voltage Protection: Yes

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Considering the above specs for motor and ESC..


1] Why is the ESC current rated at 240 A when in actual the ESC will never send out a current above the 18 A rating of the motor?



If we calculate max power output of motor we get

7 volt x 18 A = 126 watt power


In a max power condition if 240 A current had to be reached then voltage will drop to

126/240= 0.525 Volt.
But again as I said the ESC cannot exceed the max Amp rating of motor which is 18 A other wise the motor winding will get burnt.



Is this high Amp related to Pulse width modulation in any way?

[Johnnysplits]

The motor draws current. The esc doesn't push current. You have a motor rated at 18A max current and that's all it will pull from the esc. When you try to pull more (overgearing) is when motors get cooked. Your esc is way overkill for that motor but you can use it.

[wings_of_fire]

Originally Posted by Johnnysplits

The motor draws current. The esc doesn't push current. You have a motor rated at 18A max current and that's all it will pull from the esc. When you try to pull more (overgearing) is when motors get cooked. Your esc is way overkill for that motor but you can use it.

Yes you are right that motor draws current and esc don`t push it.

What Amp rated esc would be right for this motor?

And in fact most of the ESC have high Amp rating than what is actually required and that gets me confused.

[Olle P]

Most ESCs are designed for racers using high amp motors.
There's a larger customer base for those, and the manufacturing cost doesn't rise as much with higher current rating compared to the selling price.

Some noobs will also think that higher rating is always better...