Originally Posted by Elegancec
Hi Im planning my drivetrain (BMW Z3):
Kostov K9 220V (ordered), Soliton Jr. Controller (not ordered until now),
The best weight ratio have the Sinopoly 60Ah cells (1,99kg per unit).
So will get at least 60 cells in series under the hood and 40 cells into the trunk.
So I have to reduce may be by 2 cells because of high voltage for the controller (max. 340V).
The controller is able to handle at maximum 600A, the motor has as its limit 220V and under full load 190V at 600A so its for short time 114kW under full load when I interpolate the graphic at 215Nm.
So the cells will provide at 300A @20 percent voltage drop/sag 82kW.
It seems to me not be able to get the full power of the motor, so I have to increase the Amps to round about 400-500A.
So what voltage drop would you expect in this constellation? Is 20 percent too much calculated for sag? In my opinion the accelleration phase is very short and if the car will break, the battery will not be charged, so it will idle.
I think it could work
Wait, where are you getting the full load 190v at 600 amps? I haven't yet come across that limit anywhere. It was my understanding that you could push a higher voltage than this under load. Also your 20% voltage sag calculation doesn't make any sense either. If you are using 98 cells as you propose, 20% sag of 3.2v puts you at 250v and if you are trying to say that you are going to be at 190v at 600amps, I don't think you will see that much sag. I'm just not sure where you are getting the numbers.
According to the Sinopoly 5C charts, if they are accurate, 5C should put you at about 2.8v per cell. 98 cells and you are at around 274v at 300 amps. With the voltage of pack you are running, if you are only going to pull 300 amps from them, sag is not a factor unless you are pushing either higher amperage or higher voltage than this 190v that you pulled out of wherever you got it from? I'm a little lost in your numbers and I'm also not entirely sure of the real limits of this motor because Kostov seems to think that if you are pushing over 220v to the motor that your RPM is through the roof, but if you want to push 600 amps to the motor up to 5500RPM, it looks like you'd really need about 280v going to the motor from what I'm seeing in the charts. I'm not sure what the short term thermal limits are of the Kostov 9 so don't take that as advice but there was a thread that seemed to suggest that pushing 250v to the motor would be fine. RPM limit is 7k RPM but you drop amperage if you don't raise the voltage off nominal. 190v at 600amps would probably cap your torque at high 3000's RPM.