TLDR: Acedeck puts 50E batteries that can only output 58.8 AMPs with 140Amp ESCs. What’s the point of putting such high Amp ESCs in the board when it can only have 58.8 Amps to work with? They used to have P42A cells, but they quietly changed the batteries to 50E. With a 14S6P configuration, i think this will impact performance by quite a bit? am I wrong?
Need help doing math. Acedeck has the Z1 with 14S5P 50E cells. 50E cells have a discharge of 9.8A. So (5P) x (9.8A) = 49 Amps Max output by the battery pack. What’s the point of putting an ESC that can use 145Amps? when the battery pack can only output 49 Amps? I have a shallow understanding of battery electrics. can someone explain if I missed something here? The board still feels super torque and powerful, not at all like a 50Amp board.
Similarly with the Z3. it uses a 14S6P 50E battery pack, so the battery can only output 58.8 max current. and 58.8 Volts of max peak discharge. This means the battery can at best sustain a max peak discharge of 3,457 Watts. Yet the motors on the Z3 are rated for 7500 Watt seach motor for a total of 15,000 Watts. Why use use such high powered motors if battery pack can’t support them?
I’m genuinely asking this as I don’t know if the math is nuanced? or if there’s something I’m missing? Maybe the motors will run cooler?
I think there’s a couple pieces of the equation that are missing here.
First off, are you familiar with the difference between battery and motor current?
(I suspect they’re getting the 140a number from motor current which will not draw 140a from the battery)
This thread has some good info especially near the beginning.
But the gist of it is for motors:
Voltage in=RPM out
Current in=torque out
Your speed controller is capable of “converting unnecessary voltage to current”
If your board is geared for 50mph and you have a 50v battery (simplified numbers)
Your ESC will accept 50v but will only need to output 50v when riding at or near 50mph
Your ESC can accept 100a at 50v and output 25v at 200a which will increase your motor torque while under top speed. (More simplified numbers)
This is correct, however this is rated under the assumption these cells are charged to full, and used at 9.8a until they’re dead. While I can’t recommend drawing more than @Battery_Mooch ratings per cell. It is worth keeping in mind that we will likely do less damage with 3-10 second bursts of drawing 10+a than we would do at 9.8a for sustained periods of time.
50E’s max discharge current is 9.8A for continuous and 14.7A for non-continuous according to the data sheet. However, these limits are set to avoid over-stressing the cells, not the physical limitation of what the cell can output. As an extreme example, if you directly shorted the positive and the negative ends without a BMS or a fuse, you sure as hell will get more than 9.8A continuous. But that will heat up the cell like crazy and destroy it. So, technically speaking, 50Es can output more than 9.8A continuous and 14.7A in short bursts, but at the cost of shortened cell life, extreme heat production and risk of explosion. So the 5P pack of 50E can output more than 49A max. It will output to either the limit set by the discharge BMS (many production boards do not bypass BMS for discharge), or what the ESC will draw, whichever is lower. Acedeck probably set the BMS or the ESC to allow more than 49A, especially in bursts.
The ESC’s current draw from the battery multiplied by the voltage is the total power consumed by the board (minus some heat/efficiency losses). By the way, 58.8V x continuous 49A = 2881W is not insignificant amount of power (close to 4HP). When you are cruising at 30 mph on flat terrain, you probably use 400-500W.
I will not get into battery current (ESC input) vs motor phase current (ESC output) as I don’t understand the details either, but the motor phase current is delivered in phases through three phase wires, varying rapidly through the motor’s rev cycle, so it can be higher than the battery current at one instant and lower than the battery current at another instant. But for the sake of discussing the total power output, you use battery current (ESC input) x voltage. If the BMS/ESC truly allows peak 140A (70A per side), that’s 8232W. That’s a lot of power if it really delivers.
Lastly, a smaller motor would be fine. For marketing purposes, many production manufacturers tend to inflate their advertised power to the motors’ max rating, although the motor’s max rated power is not the bottleneck. And yes, a bigger motor tends to heat up less than a smaller motor while producing the same power.
Because the amp rating they use for ESCs is more often than not referring to the Motor Amps, not the Battery amps. Motor amps are always higher than battery amps.