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1512 Views 9 Replies 5 Participants Last post by  Killzilla
Hi all,

I am building a custom EV (three wheels; two front wheels, one rear) for driving on road. The rear wheel is the driven wheel. My specs are listed below:

Vehicle curb weight - 500 kgs (two seats)
Battery - 48 V Lead Acid 100 Ah (4 of these) - total weight 125 kgs
Motor - Golden Motor 3 KW Fan cooled
Motor Controller - comes with the motor
Drive - Using a CVT, final drive ratio of 10:1 which goes down to 6:1 based on speed.

I am trying to get the vehicle to have a max speed of at least 80 km/hr. However while testing I maxed out at around 35 km/hr. I have a feeling the motor is grossly under powered. The RPM maxes out at a range of 3000-3200 RPM, providing around 10-12 Nm of torque. I am using lead acid because it is way cheaper for the testing phase at least. I am planning to buy a 5 KW motor to maybe try it out, or should I go ahead and buy a 10 KW motor for the speeds that I want to reach.

I used a very basic equation to derive how much power I require and came up with 7.3 KW minimum. The equation I used was:
Power in Watts = ((Mass in kg) (9.8m/s²) (Velocity in m/s) (Rolling Resistance)) + ((0.6465) (Coefficient of Drag) (Area in m²) (Velocity^3))

Any help regarding this would be helpful.
Thanks!
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Discussion Starter · #3 ·
Thanks for the link. I read through the entire thread and it seems that he wasn't able to reach the desired speed even with the new gear ratio. This is kinda worrying coz I only have the budget for a 10 KW motor as my last bet. Any way I can make this work with a 10 KW motor? :confused:
 

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I used a very basic equation to derive how much power I require and came up with 7.3 KW minimum. The equation I used was:
Power in Watts = ((Mass in kg) (9.8m/s²) (Velocity in m/s) (Rolling Resistance)) + ((0.6465) (Coefficient of Drag) (Area in m²) (Velocity^3))
What did you use for the Rolling Resistance factor and the Coefficient of Drag?
 

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Discussion Starter · #8 ·
Reading on the forum, it seems a 10 KW motor powered by 48 V batteries may not be enough to actually achieve the speed that I am looking for. Has anyone used 10 KW motors to get anywhere close to 50 mph speed? Even if it is using higher voltage battery pack? :confused:
 

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Has anyone used 10 KW motors to get anywhere close to 50 mph speed? Even if it is using higher voltage battery pack? :confused:
Me. With my 950 kg Smart fortwo I can drive at 50 mph with only 10 kw from the battery on a flat road. And you will be able too if your vehicle doesn't have an horrible aerodynamic.
Of course, in my car, I have acces to over 100 kw if I need for acceleration and to climb hill.

But the trick is to really have 10 kw at the motor.
First point is to have 10 kw from the battery and this can be dificult from a lead acid battery. Voltage sag can be terrible.
Second, if you are single speed, you can't load the motor to obtain 10 kw exept if you have the perfect gearing. And if you have it, it will only be good at particular condition.
Finally, if you have CVT, his efficiency probably eat a part of the power and his ratio is maybe not appropriate.


A solution for you can be to go with a cheaper, but more powerful drive system: http://www.evdrives.com/category_s/1860.htm
 

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Discussion Starter · #10 ·
Yesterday I did another trial run, used the 5 KW motor I had in stock and was able to get to 50-55 kmph on a flat road. The gearing was 8:1 and was able to accelerate at a fairly lousy rate of 0-40 kmph in 12 seconds. Which is alright as I know the 5 KW isn't doing much. Hopefully things improve with the 10 KW motor, may try different sets of gearing and see what gives me the best acceleration vs speed.
 
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