Joined
·
118 Posts
I'm trying to find out what performance I can realistically expect for my EV project and am trying to fine tune my spreadsheet. I need to approximate a DC motor torque curve and have attached some figures to see if I have understood what I have read.
Chart 1 is just the torque curve from Netgain for a 9" motor formatted how I'm used to looking at torque curves. It seems that torque is very proportional to motor amps, and I just assumed that the 334 amps at maximum torque is the controller rating and the Red torque curve is just flat from 0 rpm to 2158 rpm.
Chart 2 is just the torque curves.
Red is at the rated 72v and 334amps.
Yellow is at 115v and 334 amps and all points are shifted right by the proportion of 115/72.
Gray is at 115v but with a controller that has the motor amps and battery amps limited to 500amps, so all points from the yellow line are shifted up by the proportion of 500/334.
Blue is at 115v but with a controller that has the motor amps limited to 1000 amps, and the battery amps limited to 500amps. I just figured if the maximum power out of the batteries was 115v*500amps at the knee of the curve, then the curve would start declining at 500/1000 * rpm of max power. That's assuming electrical power would be similar to mechanical power, but I haven't a clue to the efficiencies in this area, so I don't know how close I am.
Does this look right, or is there any data that would shed some clarity on this? And is this how a controller works if the controller is rated at 1000amps with the batteries limited to 500amps? And which controllers can do this?
I'll post my spreadsheet, once I've tuned it up a bit. You should be able to plug in various bit about your car and find your ET's from 0 to 85mph. You can also see where to shift for maximum performance. I plugged in tomofreno's SwiftE using the AC50 motor and he said the numbers look close.
Edit:
I'll post updated spreadsheets (Excel format, zipped) here so you don't have to search the thread for the latest. Also, the charts below have been corrected in the next few posts.
Chart 1 is just the torque curve from Netgain for a 9" motor formatted how I'm used to looking at torque curves. It seems that torque is very proportional to motor amps, and I just assumed that the 334 amps at maximum torque is the controller rating and the Red torque curve is just flat from 0 rpm to 2158 rpm.
Chart 2 is just the torque curves.
Red is at the rated 72v and 334amps.
Yellow is at 115v and 334 amps and all points are shifted right by the proportion of 115/72.
Gray is at 115v but with a controller that has the motor amps and battery amps limited to 500amps, so all points from the yellow line are shifted up by the proportion of 500/334.
Blue is at 115v but with a controller that has the motor amps limited to 1000 amps, and the battery amps limited to 500amps. I just figured if the maximum power out of the batteries was 115v*500amps at the knee of the curve, then the curve would start declining at 500/1000 * rpm of max power. That's assuming electrical power would be similar to mechanical power, but I haven't a clue to the efficiencies in this area, so I don't know how close I am.
Does this look right, or is there any data that would shed some clarity on this? And is this how a controller works if the controller is rated at 1000amps with the batteries limited to 500amps? And which controllers can do this?
I'll post my spreadsheet, once I've tuned it up a bit. You should be able to plug in various bit about your car and find your ET's from 0 to 85mph. You can also see where to shift for maximum performance. I plugged in tomofreno's SwiftE using the AC50 motor and he said the numbers look close.
Edit:
I'll post updated spreadsheets (Excel format, zipped) here so you don't have to search the thread for the latest. Also, the charts below have been corrected in the next few posts.
Attachments

19.8 KB Views: 389

24.4 KB Views: 416

109.2 KB Views: 728