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Old 10-10-2019, 07:44 AM
  #1  
samx6
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Default Need help with Electronics

I am very new to this hobby and I am setting up my first drift car and would like some advice.
I plan on running a 120Amp Hobbywing Esc and Motor. I want to get a 2S 5000mah Lipo, but I am unsure what C rating to get.
The ESC has a continuous draw of 120A and Burst of 760A. I know a 25c would work for the continuous draw, but I am concerned about the burst.
Here's my math(could be wrong):
120A / 5A(5000mah) = 24, thus the 25c should be fine.
760A / 5A(5000mah) = 152, thus greatly straining the battery.
Would it be better to go with a lower Amp ESC, such as 60?
Thanks!
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Old 10-11-2019, 05:36 AM
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bill_delong
 
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You're on the right track, but need to be comparing everything to power draw or Watts in order to get your burst ratings.

You didn't specify which motor you plan to use, and that will be the first step.

For example, let's just say that you are planning to use the XERun Bandit 10.5T motor, you will want to click on the "Specification" tab and you will see that "Max. Output Power* (W)" = 325W for this particular motor. No problem if you decided to go with a different motor, just want to explain how the math works in general for you.

Now that you know the motor can pull up to 325W, you simply multiply the C rating times capacity of your battery time voltage of the pack:

25C x 5Ah x 8.4V = 1,050W

As you can see, the 25C pack is no where near the limit of power draw for the motor I referenced making the 25C pack perfectly acceptable for use with that motor.
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Old 10-11-2019, 11:52 AM
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samx6
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Ok, so I just looked a the specs on the Hobbywing Quicrun 3650 and it has a max of 240W, so 7.4V x 5Ah x 25c = 925W. I should be fine correct?
Also I have another question, The math that I did in the original post has nothing to do with it then? I thought I had to figure out the power draw of the ESC as well?
I plan on using the Quicrun 10BL120 ESC.
Sorry if this is a dumb question. I am very new to this.
Thank you!
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Old 10-11-2019, 12:03 PM
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A fully charged 2S LiPo is 8.4V which is what I like to use for my calculations, but 7.4V nominal is also perfectly acceptable too, we are calculating "ball park" estimates anyway.

You can use Ohms Law to figure out how many Amps your ESC needs to be:

Watts = Volts x Amps

240W = 8.4V x Amps

240V / 8.4V = 28.57A

Any ESC rated 30A or higher will suit your needs just fine
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Old 10-11-2019, 12:35 PM
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samx6
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Thank you for all your help! I appreciate it!
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