Topic: the doran kitset car

[piersdad]

 A friend asked me on my thoughts on this car and its conversion  so here is my reply

 
this is my views on ac motors.
They are the way of the future and the brushless motors used on model aeroplanes are a good source of info as they have had a lot of work in their design that relate to the larger motors.

The prius car has a 230 volt motor battery system.
The use of high voltage means the small amp hour batteries  of the life04 can be used.
I suspect the larger the amp hour capacity of these batteries the less reliable they may be (just a thought )

With ac drive the frequency determines the speed so the torque of the donor motor is the suitability of the motor for the car.

Ev album has a lot of conversions and the donor vehicles used will give you an idea of the power to drive these vehicles

Some 3 wheel freeway cars
 http://www.evalbum.com/type/FRWY

most of the electric bikes are brushless and up to 2.5 kw.
So the first  thing to find out just how much torque you will need and this will determine the size of the motor as there is just so much torque from so much surface area of the motors rotor.

Getting the horsepower/power rating of an ac  motor as well as the speed at that rating will determine the actual torque available and this means if the frequency is low and the speed is low then the torque there will be the same as the torque at very high speed as well though not always used.

When I looked at a huge catalogue of motors I saw the same motor at 2 hp  24 v was identical to a 4 hp at 2 time the voltage and speed.

20 hp =550 foot lbs per minute time 20 =11,000 ft lbs per minute  (sorry cant get head around the metric newtons)
At 3000 rpm  we get 11,000 /3000 =3.6 pounds of torque at one foot away from the centre of the shaft.
A 20 hp 1500 rpm motor will be 2 times as big and have 7.2 pounds at one foot.torque.

So perhaps imagine the EV going up a 1 in 4 grade and bottom gear and work out with maths what torque will be needed.
Then find out what power will be needed to go at 100 km/h or max speed you want and see if the torque and speed of the motor and voltage will match
A search of the net could give you some ideas on this calculation..

So when the motor the car the voltage  and the gear ratios are balanced then start the project

 
so good luck and any queries are welcome as the stretch my brain and it does not get too much exercise lately


doran electric car kit and conversion using 80-89 subaru hatchback parts

this site has very good support to amature builders

Kitset car using subaru car front running gear
Length: 144 inches
Width:  67 inches
Height: 46 inches
Front Track: 58 inches
Curb Weight: 1490 lb
Test Weight: 1650 lb
Front Weight Distribution: 74% (with driver)
Rear Weight Distribution: 26% (with driver)
Wheelbase: 90 inches
Ground Clearance: 5.7 inches
Trunk Space: 10.2 cubic feet
Motor: Traction, DC series wound
Controller: Transistorized pulse width
    modulated
Continuous Rating: 27.4 hp @ 5000 rpm
Intermittent Rating: 53.6 hp @ 5000 rpm
Torque, lb/ft @ stall: 85
Batteries: 9 deep cycle lead acid
Front Brakes: 9.5 vented discs
Rear Brakes: 7.1 X 1.2 drum
Body: Foam-core composite
Frame: Steel backbone
Steering Type: Rack and pinion
27.4 hp= 15070 ft lbs per minute (hp =550 ft lbs /min)
Speed = 5000 rpm
Torque at rated current  = 15070/5000 = 3.014 lbs ft

For an AC motor  and very low frequency the stall torque would have to be reasonable.
Check out brushless motors that use permanent magnets and AC coils driven by electronics  some of the old fisher paykel smart drive washing machines had a similar motor but not powerful enough.
DC motors with permanent magnets have a limitation of the actual size of the magnets as when physically too big they self demagnetise
They over come this by using multiple small magnets
One small powerful dc motor I have has 4 magnets with 4 brush sets and is the equivalent of two motors wound into one frame to overcome the limitations of individual magnet size.
 
Stall torque is for DC motor at saturation and would be many times the rated current
Ie as above 28 times running current

Ok the construction will start with a  1980-89 Subaru Hatchback.car wrecked and the parts from it.
automotive hardware, along with coil-over shocks from a 1987 Honda Prelude.? Wrecker $50 approx
The welding of the frame will have to be by certified welder. I have a friend that is certified welder and wants casual work and keen on EVs.
 
Keep the original registration of the wrecked car alive as it costs heaps to re register and things like airbags, abs brakes etc  would have to be installed if registered as a 2009 car
 
I like the batteries in front and if lighter batteries are used here, a foam filled crash adsorption  barrier to protect them will be a good idea.

 

The body is first built of foam, and then it's fiberglassed over to create a super-strong, high-impact  enclosure
The kiwi solar powered car is similar