My latest EV project

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Regular Member

Joined: 12/08/2016
Location: Australia
Posts: 99
Posted: 01:09am 20 Sep 2021      

The 90 to 100KW is no problem. Both power and torque taper off quickly as revs rise. Just the opposite of what you experience in a combustion vehicle. Yes there is a gearbox. In 1st gear you have the gearing advantage but run out of revs at about 50kph. In 5th you loose the gearing advantage and still run out of revs at about 110kph. The problem is back EMF which resists high revs. The way around it is higher voltage.

I did the math on super capacitors. To make a noticeable difference you would need enough capacity in the capacitors to cover the upper portion of the power curve for a typical period of acceleration. This would mean about 4 sets of capacitors. That is too much space and weight for my purposes. With Super capacitors amps are no issue but capacity is an issue.

1000amps is from the controller to the motor not from the batteries. The Controllers always take the power from the batteries in the form of maximum voltage (172v in my case). At low RPM and full acceleration they lower the voltage and increase the amps (within the power limits of the system).

So at initial acceleration the output is around 1000amps and 90volts (90Kw) and the input would be 523amps at 172v (still 90kw).

The 1000amps output 523amps input literally only lasts a portion of a second before it begins lowering dramatically.

As the revs increase the controller decreases the output current and increases the voltage until the maximum voltage is reached. At that point the system reaches the limit of speed. Increasing the input voltage allows the system to achieve higher revs equalling higher speed. But it comes at the expense of added battery weight.  

Davo: Thanks for the tip. I haven't looked at those yet. But I will. I doubt they will suit my requirements though. I have very small physical space and low weight requirements because it is such a small car. So I can't afford inefficient batteries. I have some in mind that would fit in the space (I think) and would weigh about 100KG. They will give me about 14Kwh which I think will give me about 150km of range if driven responsibly. Am I missing something though 48v at 600ah is 24kwh. That would be massive and $1200 is very cheap.