Relation between electric motor and battery current, peak etc.

[Jon Zimmer]

Good afternoon guys,

I was making some researches about building my own EV and its' specifications but I have a few no direct answered questions and some of them I humbly ask the help for you guys, based on the configuration example below.

Considering that I hypothetically have an electric DC motor with a minimum operating voltage of 48v, nominal input 72v and peak 96v with DC current limitation of 100A (peak 9.6kW) and an LFP battery pack of 72v and 20aH (with discharge max of 4C):

- Does the motor will draw only 80A from the battery-via-controller as it is the maximum the battery can provide/supply?
- How the motor can achieve its' peak of 96v as the battery has only 72v? How could it happen (if/or happens)? Or the battery has to be arranged/set to/with 96v to match the motor?
- Is there a proportional reasonable ratio between battery-motor that I can have a good range and performance.
- In the sometimes referred "continuous rate" of motors and batteries are there a base/average that I can stipulate/calculate (even if not described by the manufacturer) or it depends on the fabrication process? Is it the same for the minimum current the motor draws from the battery?

* I apologise for the amount of questions and any mistakes (even if technical or linguistic) which can sound stupid, this is my first time/post on the forum and I'm doing all by myself as I'm not an engineer or physicist and would be grateful with some advice or missed point :) .

Beforehand, thank you all for the attention and help!

 

[anorlunda]

with DC current limitation of 100A (peak 9.6kW)

That makes no sense, amps and kW are not the same thing.

But in general, I think you are confusing max ratings with actual numbers. The tires on your Corolla may be rated for up to 200 mph. That does not imply that your Corolla can really reach 200 mph. If you have a 9.6 kW battery, then you shop for motors rated 9.6 kW or more. It is likely that the best choice is rated at 10 kW or some other round number, not exactly 9.6.

If your real question is "How do I optimize the EV motor and battery design?" it is a big job. You need to consider the entire range of demands the car is expected to meet, speed, hill climbing, range, cost, max and min temperatures, weight, size, lifetime, and so on. Then compare those requirements with several proposed designs. An engineering company assigned to do that might produce an inch thick report.

But the key point is that it does not begin with design choices. It begins with requirements. What cost/performance features do you require the EV to meet to declare it a success. "Best possible" is not an answer. Take range for example. Do you require at least 400 miles range? or 40 miles?

 

[Jon Zimmer]

Thanks for your point of view, it helps me somehow, but does not answer on the hypothetical setup I posted (I wrote that the motor peak is 9.6kW (96v*100aH), not the battery as you answered). Actually, on the '1 inch thick report', there are a few years I've been constantly reworking by my own with all its variations and variables included before starting building it. The type of vehicle, if it is a car, bus, bike or else and it's expected/approximate electrical setup (motor-battery) I kind of already have and recalculate the needs based on the variables as you mentioned. These few details posted are the ones which I can't get the closer or exact answer. Thanks anyway.

 

[berkeman]

Thanks for your point of view, it helps me somehow, but does not answer on the hypothetical setup I posted (I wrote that the motor peak is 9.6kW (96v*100aH), not the battery as you answered). Actually, on the '1 inch thick report', there are a few years I've been constantly reworking by my own with all its variations and variables included before starting building it. The type of vehicle, if it is a car, bus, bike or else and it's expected/approximate electrical setup (motor-battery) I kind of already have and recalculate the needs based on the variables as you mentioned. These few details posted are the ones which I can't get the closer or exact answer. Thanks anyway.

Can you say what your background is in EE and electricity and electrical motor+battery systems? As @anorlunda has pointed out, there are several issues with your initial question that seem to show misunderstandings about how power is transferred from a battery to a motor. We would like to help you with this project, so it would help us know at what level to address our responses. Thanks.