I have been looking at EV’s for a few years, and now I want to build one. Before building from scratch I want to build a convertion and have got as far as selecting the batteries and the car. My problem starts with the electric motor; there is lots to work out (math) and conversions which I dont know. So I though I would ask as many of you would have had to work this all out before in your builds and research.

Please correct me if im wrong.

[U]Power/performance[/U]
In a normal car engine, we gague the performance in HP in an electric car these dont matter as I believe that this is somwhat converted into the KW of the motor. that would mean that a 15KW motor would be 20.11HP.
BUT, if you put a 15KW motor on a car it wouldnt seem near this level of like for like performance. So how do we work out the performance?
is there a calculation where we use the torque to formulate a suitable answer of a rule of thumb that we can use?

[U]Battery and Motor[/U]
If we have 2x 12 volt 200ah batteries, this would give us a 24volt 400ah hour power supply(19.2KW).
If I use a 24 volt 9.6 KW motor, this motor would run at full load/speed for 2 hours, is that correct? (excluding 20%)

[B]Amps and the motor[/B]
If I use a higher voltage system, my amps that i would be using would be lower and the resulting power would be the same?
I say this as on the basis that KW is derived from volts x amps =KW therefore amps x volts would be the same answer.

and
If I use higher voltages, I should be able to use/draw less amps??

[U]Step-up voltage systems[/U]
I have read a lot about power, performance and volts and amps. On most EV’s that I have looked at I have not seen any mention of step up volting. Does anyone do this, of have they missed that bit?

just so that there isnt a translation issue on what the step up is… Steping up is a simple process of putting a current into a system and getting a higher voltage out. this is like a transformer but work in upping the voltage when the current is turned off.

WOW, what a quick reply lol…
so anyway I worked it out now. and it would seem that I can now fully calculate the cars power requirement, the acceleration, motor requirments , the 0-60. at last! that took a long time to work out…

if you want to know please feel free to visit my website which is the under name .co .uk and then you will find an email address on the site.

Power/performance
In a normal car engine, we gague the performance in HP in an electric car these dont matter as I believe that this is somwhat converted into the KW of the motor. that would mean that a 15KW motor would be 20.11HP.
BUT, if you put a 15KW motor on a car it wouldnt seem near this level of like for like performance. So how do we work out the performance?
is there a calculation where we use the torque to formulate a suitable answer of a rule of thumb that we can use?

15kw might be continous… peak you’ll need much more.

Battery and Motor
If we have 2x 12 volt 200ah batteries, this would give us a 24volt 400ah hour power supply(19.2KW).
If I use a 24 volt 9.6 KW motor, this motor would run at full load/speed for 2 hours, is that correct? (excluding 20%)

you calculated wrong. 2 12V batteries at 200Ah is 24V and 400Ah. In series, voltage adds, current stays the same. In parallel current adds, voltage stays the same. 24*200 = 4800Wh. I have no idea how you got 19,200W out of that.

If you had a 9.6kw motor, and were actually RUNNING at 9.6kw, you could only run it for part of 1 hour. First off, you can’t discharge to 100%, only 75-80%, ALSO, if you’re discharging higher current, you get peukert effects… so you might only get that for 30 minutes.

Amps and the motor
If I use a higher voltage system, my amps that i would be using would be lower and the resulting power would be the same?
I say this as on the basis that KW is derived from volts x amps =KW therefore amps x volts would be the same answer.

Yes, that is correct. Issues being, higher voltage controllers are spendy/impossible to find once you get above 72V/120V/144V/156V…etc.

Step-up voltage systems
I have read a lot about power, performance and volts and amps. On most EV’s that I have looked at I have not seen any mention of step up volting. Does anyone do this, of have they missed that bit?
Why step up? are you thinking AC or DC systems? Its better to just make a higher voltage pack and be close to lossless, than it is to build a high current/high voltage step up converter. It would be a huge power supply and cost a LOT.

just so that there isnt a translation issue on what the step up is… Steping up is a simple process of putting a current into a system and getting a higher voltage out. this is like a transformer but work in upping the voltage when the current is turned off.

buck boost… but the components needed to do high current/high voltage would be spendy.