# Motor sizing



## Ravishankar (Jan 26, 2009)

Hi EV'ers

I am sure that this type of motor power sizing question has been asked before. But I need some sort of confirmation. So please help me out.

Here goes: I am planning to convert FIAT Uno to electric and my calculations show me that I need a 10KW motor:

ehicle Curb weight = 700kgs (gasoline version)

Vehicle Remove engine + add batteries + passengers = 900kgs gross weight (I expect)

Top speed I want is = 90kmph = 25m/s

Total Power = Power to overcome rolling resistance (Prr) + Power to overcome aerodynamic drag (Pad)

Caculation of Prr:

Urr of Michelin Energy XM1 tires = 0.015 (I expect)

Prr = Urr * Mass * veclocity

= 0.015 * 900 * 9.8 * 25

= 3307.5 Watts = 3.4 KW

Calculation of Pad:

A = 18m2

p = 1.25 kg/m3

Cd = 0.34

Fad = 1/2 * Cd * A * p * v * v

Pad = Fad * v

= 1/2 * 0.34 * 1.83 * 1.25 * 25 * 25 * 25

= 6066W = 6KW

I think I require a motor of atleast 10KW nominal and 20KW peak for adequate performance. 

But this motor: 
http://www.chennic.com/show-products.asp?id=107&BLD7.5

is 7.5KW nominal and 18KW peak. 
The question is: Is it OK (i.e Safe) to go ahead with this motor or should really and only be this:
http://www.chennic.com/show-products.asp?id=105&JCUBLD11

Thanks in advance to all.


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## ken will (Dec 19, 2009)

How do you find the prices?


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## Ravishankar (Jan 26, 2009)

You mean what are the respective prices ?


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## ken will (Dec 19, 2009)

Ravishankar said:


> You mean what are the respective prices ?


I mean I went to www.chennic.com and could not find prices for anything!
For me the price is very important when comparing.


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## Ravishankar (Jan 26, 2009)

ken will said:


> I mean I went to www.chennic.com and could not find prices for anything!
> For me the price is very important when comparing.


Yeah, sure the price difference is making the choice difficult for me too. The 7.5Kw motor costs $1130 and the 11Kw motor costs $2750 (excl. differentials).

Another point of consideration for me is the system voltage which is 216V..


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## Ravishankar (Jan 26, 2009)

ken will said:


> How do you find the prices?


By sending a mail to [email protected]


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## ken will (Dec 19, 2009)

Thank you very much for getting back to us with the prices.


Now I am going to rant for awhile so everybody can skip the rest of this message.
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One of my pet peeves are companies that don't show prices!
I was helping a friend yesterday trying to pick out a watch, the first store had all the prices hidden, the sales lady said all the stores do that. The very next store we went to proudly displayed the prices.

The slimball companies that hide the prices want you to make a decision, then when they tell you how much it costs, even though it is more than you wanted you to spend, to save face you will go ahead and pay the ridiculous price. ( especially if Daddy is paying the credit card! )

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Okay, end of rant. Sorry I just had to get that off my chest.


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