18650 Motorcycle - Current question

**Zero_Phobia** · 01 August 2019

Hey guys so I'm building my 18650 motorcycle which is a revived project from 5 years ago and have a question that hopefully all the smart people on here can answer.

Below are the specs @ 48v for my ME1003 motor. Am I reading it correctly that it does a maximum of about 2100 RPM using about 130 amps? Unloaded of course.

What if I went to 72v and halved the AH capacity of my batteries (less batteries in parallel and more in series for 72v). Does the 130 amps drop due to the voltage being much higher?

Basically I am building this from tested but used laptop cells. I have 12S65p in order to limit current on each cell but this limits me to a 48v system (just less) due to pack size but I would love to rather run 72v. If the amps required drops when increasing volts then I may...just may be able to build packs into a 20S32P because with the higher voltage each cell will require less amperage.

Let me know, please don't persecute me, I'm still learning. Thanks guys!

Motor: ME1003 (200a continuous - 300a 1 minute)
Controller: AXE7245

**frodus** · 01 August 2019

Motenergy's graphs are a bit non-standard. What they do is set the motor to run at a certain RPM, and then gradually load it down. It's not a standard torque vs. RPM curve. They only load it down to about 130A, but it takes a lot more current at lower RPM (and at a stop to start moving).

Typically, for the same power, if you half the Ah, and double the voltage, 96V and 50Ah for instance, you would have the same power as 48V and 100Ah. The current on a 48V system would (most likely) be able to source more current if they're the same cells, because there are more in parallel.

For that motor, to achieve max power, you're going to need to hit 300A on the motor side, and fairly close to that on the battery.

**Zero_Phobia** · 01 August 2019

Thanks Frodus, I think that makes sense.

If I understand you correctly then you are saying that on a 48v system and a bigger pack (65P) can handle more amps even though the 96v setup is the same power rating. The 48v setup would devide the 300a evenly across all 65 cells but the 96v setup would divide the current among 32 cells.The 96v system would achieve a better overall RPM/Speed whereas the 48v would be slower but better current handling ability for the cells. They would both have theoretically the same range as its for the same power.

With this being used laptop cells (see below examples from my pack) with a max C rating of 2C,maybe 3C at bursts would you agree that the 48v setup would be better in this scenario? Each 65p pack is worst case 2ah per cell. 2C per cell which is 4a max current per cell. 65x4 = 260amps possible and at short bursts 3C per cell which is 390amps.

I can always adjust gearing for better speed with my sprocket configuration.

Thanks again!

**Spoonman** · 07 August 2019

Put very simply, power is power and energy is energy, but voltage is speed and current is torque.

Your low voltage high current pack will produce high torque at low RPM
Your higher voltage lower current pack will produce less torque but higher RPM
Everything after that is gearing.

It's worth considering that high torque places more stress on the drivetrain components, and the higher currents that go with it lead to greater heat related losses.

As for your battery pack - bear a mind to the fact that those packs will need to be able to shed heat if you're planning to draw a few hundred amps for prolonged periods.