Power requirements for electric vehicle

[Jdin]

I want to verify that a vendor is giving me the correct sized electric motor for a vehicle (hp, amp, voltage, etc.) How can I do this?

The car must travel 8kph; carry 1000kg load (exclude driver). Top speed can be reached in 5-10secs. It runs on 4 vulcanised wheels (like golf carts). The entire length of runway is only 1.2km with slope 1:6 at the beginning and levels off then 1:6 incline at the end.

 

[quark]

Without data it is difficult to answer the question. However I will try to give some pointers.

8kmph corresponds to 2.22m/s. If the car weight is 1000kgs then the mass is 1000/9.81 kgs and the force for accelerating the car from 0 to 8kmph in 5 sec. will be 1000*2.22/5 = 444N (1000/9.81kgsx9.81N/kg)

If the car runs at 2.22m/s then power is 444*2.22 = 985.68W(1.34hp)

The low value is because we are neglecting wind resistance and friction.

Ideally, you should conduct a deceleration test by first running the car at some constant speed and then coming to neutral. Note the time 't'in which the car speed reduces from x to y m/s. x-y/t gives you the deceleration and using the above method you can get the hp required.

Regards,

 

[Jdin]

Thanks, Quark. This is also how I calculated the power. But it looks too low... even with drag and friction added.

For a normal Electric Vehicle I found on Web 'typical' hp is much higher than this, ~20hp.

Anyway, now I have Hp, how then do I select the correct DC motor? or how do I know what the supplier has offered is the right equipment? (Voltage, amp, torque, rpm, etc.)

 

[quark]

Yes, the required HP is actually low but there are some cases when you think you should have more power, like, you woke up 5 minutes after office timing and yet want to be in the office 5 minutes earlier.

That is a factor of safety when you have to drive against heavey winds and uphill etc.

Electrical engineering is not my cup of tea(or atleast it won't have the required ingredients). The experts here will help you out.

PS: Why can't you ask the manufacturer for a design qualification?

Regards,

 

[Jdin]

Can't take for granted what the manufacturer gives you is correct. Somehow u've to convince yourself or find a way to counter-check.

 

[itsmoked]

1.3HP is a lot of effort...especially if you are talking about a measely 8kph.. Sounds like you are making a prototype car. I would say if 1.34hp is what the quick numbers say... Install a 3hp motor and see how little you can demand from it. Unless you analyse this to death you may miss something and most the somethings will work against you in the long run. This would leave you with an overheated, unuseable tool.


Other things to consider:
Wheel bearing drag.
Steerage peak drag. (Tire scuffing.)
Windage.
Motor Efficency.
Gear box losses.
Differential losses.
Motor controller losses.
Maximum slope.