VESC Motor Current Max vs Battery Current Max

I am new to ESK8 build and have spent many hours reading before posting. I have some basic questions I am hoping an expert can quickly answer or point me to the right thread. This site has been inspirational and hope to eventually build my own monster off-road board. But for now, I am trying to learn by tweaking an existing board.

I bought a Propel Endeavor 2 Pro board and it simply doesn’t have enough low end torque and I am trying to increase better grass hill climbing capability. It uses a Flipsky VESC and I have been working with Propel’s support which has been good but wanted to get expert opinion on this site for education and verification.

Please kindly allow me to provide some background info on the setup:

A - Battery Pack: Samsung INR21700-50G. 12S5P. Total output 44.4V. Continuous Amp 25A. 1110wH. The individual Samsung battery spec shows battery can provide PEAK current discharge at 14,700mA each which equates to 14.7A x 5 series = 73.5 amp PEAK output

B - The board has a Flipsky Dual FSEC6.7 Pro 140A base on VESC 6.6. The VESC specs are = Continuous current 140A, instantaneous current: 400A

C - Remote = Flipsky VX2

D - Motor is 6374. Max amp / KV unknown (waiting to find out exact specs)

E - BMS specs unknown.

F - 15 teeth on motor with 68 teeth on Wheel. The wheel is 8"x2" pneumatic (800mm x 200mm)

Here is my setting for my VESC picture below.

Questions:

  1. In the current factory setting, the “Battery Current Max” is set to 25A, which makes sense since the 5P series can provide 25A continuous to each motor. Question is … how does the 25A from the battery provide enough power to both motors which has factory setting of “Motor Current Max” = 50 A each. So the battery has to provide 50A x 2 motors = 100 A. How does the 25A setting allow 50A output to each motor?

  2. Is it correct to set the “Battery Current Max” to the continuous battery specs? The battery pack peak Amp output is 73.5 A. (I read somewhere these peak output can only be sustain for a few milliseconds).

  3. Since my battery pack can provide peak current output 74 amp and the factory default for “Motor Current Max” is at 50.00 A, Is it OK to set my “Motor Current Max” at 60 A permanently? I did set it to 60A each motor to test some short run and the low end torque was better for grass hill climb. At this setting will I damage the battery long term?

  4. At “Motor Current Max” at 60A setting, how long can I do a full output for hill climb and be safe? Is two minutes of full throttle OK for the battery’s health?

  5. In the “Motor Current Max” of 60A setting, I did notice a pretty significant battery sag. I was on a paved hill, and battery was at shows 57% at rest on my remote. I did a full throttle and the battery capacity dropped down to 30% for a split second and recovered back to 56% at rest once I reached the top of the hill. Is this acceptable battery sag? My main concern is not damaging the battery long term.

  6. What is the largest value you would recommend for the “Motor Current Max” and “Battery Current Max” without damaging the current battery pack?

Thank you in advance for everyone’s patience as I am a newbie and really trying to learn and understanding.

  1. So, lets see for your battery INR21700-50G specs: comtinious current discharge is 9.8a. You have 5p battery. This makes max battery output as 49A. So its max your battery can output. 2. Battery current max 49A as pes spec of 9.8 a for cell. 3-4.I dont see reason to put more than 24.5 a on each motor, battery wont gove more than restricted by max battery output anyway. 5.sag may be verified with moosh battery tests if it has for this battery. But cells sag whrnon on maximun current for them. This is ok probably

Hope this is clear now. Ask if not

Just personal thoughts: i would never consider peak current in esk8. Also, cells with 9.8A current are on low side. For future projects check milocel 21700 P42a or even newer p42b. Both of tgem has continious current of 35a with susteinable 45a if consider tempreture monitoring. To not damage battery - do not store fully charged or fully discharged. Do not try to discharge with higher current than it can output as per spec ang you would be ok. Also good thing to check your battery health (p groups voltages from time to time)

@OleksiiF Thank you so much for the prompt reply. It’s very kind of you to take the time to help out a newbie. What you say makes complete logical sense and it’s what I would have concluded too. Thanks for clarifying for me that the Battery Current Max (continuous) should be no more than 49A. I am assuming Propel rounded the 24.5 up and just allocated “Battery Current Max” 25A for each motor (25x2 = 50).

The weird thing is that Propel support said that the factory default for “Motor maximum current” should be 50A and when I didn’t get enough low end torque they told me to dial it up to 60A. I have a specific hill I tested the board on and at 50A, the board would not make it up the hill… but at 60A it made it up without stalling.

That’s why I am so confused as I would have thought that by setting the “Battery Current Max” to 25A, there is no reason to set the “Motor Current Max” any higher than 25A. However in real life it’s making a difference in how the board’s provide torque and power for motor value of 50A vs 60A which both motor values are way above the battery value of 25A.

Still unclear why it makes a difference on the higher setting of “Motor Current Max” and in real life. Any additional insight?

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I looked up Molicel P42A… wow… max continuous current is 45A. Which means 5P = 225A. That’s crazy. It does seem like the storage capacity is about 14% lower than the Samsung… but the cost isn’t any more than Samsung. Maybe when these original factory battery wears out… I will replace it with Molicel batteries instead.

Thanks again for your help.

Well, to say thuth, its kind of unexpected to me that increasing motor max without increasing battery max made any difference. There is always place for knowlage improvement, right? I would advuse to check telemetry if you have one for current in such load(or if you dont have one, make test with laptop connected or somth) just to make sure what are current drain on battery. Wish you a good luck.

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If your battery pack is 70A.

Battery Current Max:

  • 70A / 2 motors = 35 amp
  • To be safe, keep it at 30 amp

Battery Current Max Regen:

  • (5P * 4A) and divided by 2 motors = 10 amp.
  • Because recommended charging for lithium battery is between 2A or 4A max.

The correlations between Motor current and Battery current changes based on the percent of motor power. Example: 6355 Motor is rated at 2500 Watts and 80 Amps.

So if you are pulling 1250W of power with a 44v battery.
That is 50% rated of the motor’s power.

The amps on the Battery side would be 1250W / 44v = 28.4amp.
Then your Motor current is at 56A = 1250W /(44v * 50%).

But now consider this, 36v is minimum voltage for 12s battery pack.

  • 1250W / 36v = 34.72amp
  • Your Battery Current is 35 amp (rounded)
  • Your Motor Current is 70amp = 1250W / (36 * 50%)

How you calculated bat current max?