NEW ADDITION ( 7 April 2011) - Scroll down

Hey Guys, I thought of promoting EV's.
So here goes, with my experience, I think I will try and put stuff into words to make it an open source kinda handbook to build an EV from scratch.
Steps include:
1. Basic Calculations
2. Layout
3. Designing (3d modeling and 2d drawing considerations)
4. Simulations
5. Fabrication
6. Testing
7. Trouble shooting
8. FAQ

So here goes. Starting with step one. Deciding what you want.

Prior details like weight, drag, and other resistances to be calculated by users on their own. Its simple physics. If u are on a mission to build an EV yourself, Prior research should be peanuts for you. Next step is :

SOME BASIC EV Calculations Electric Vehicle Conversions: What’s - What?As with ICE (Internal Combustion Engine) vehicles, speed, distance, Kph, etc.. will vary between vehicles due to driving habits, road
conditions, etc.. The same will be for an EV (Electric Vehicle). However, here are some basic guidelines to help get you started.

SPEED:Voltage! The higher the voltage of your Battery System, the faster a given EV can go.


Trade Off:
As with ICE's, the faster you go the more fuel is used - the faster an EV goes the more power is used. This will impact how far you can
travel on a single charge.

Distance:Speed, Pack KW rating, driving conditions, aerodynamics, vehicle weight, hills, temperature, driving styles and several other factors play
into the distance question.

The basic formula for determining distance is: ( KW of pack / wh/k) = Distance
*note: there are adjustments that have to be made to this formula, see usable pack size below*Watt-Hour per Km (Wh/k):
The basic rule of thumb for vehicle is:
Small Vehicle 250-300wh/k
Small Pickup 350-400wh/k

The calculation is: Volts x (Amp Draw / KmPH ) = Wh/k

Battery Pack Size (KW):
Pack Voltage x Amp-Hour rating of battery = KW

Usable Battery Pack Size:Unfortunately, we can not use all of our battery Pack or we will kill our batteries extremely fast. To extend the life of the battery pack, we
do not want to discharge the batteries more than 80%.

In addition, because an EV will discharge the batteries faster than the manufacturer tested and rated, we get an effect called “Peukerts”.
Therefore, we will need to correct our calculations for this effect. LiFePO4 Batteries are only marginally effected and we can ignore
Peukerts effect. However if we use Lead-Acid batteries the Peukerts effect if considerable, where we only get to use about 55% of the
power in the Battery.

Usable Pack size: KW x 0.80 x Peukerts = Usable KW
Peukerts:
Lead-Acid = 0.55
LiFePO4 = 1.0

Yes, you get a BIG hit on your available power when using Lead-Acid. However, they are generally cheaper than LiFePO4 batteries.

Putting all this together - Example:
Vehicle: Reva
Batteries: 6 - 12V Lead-Acid, rated at 120 ah
Pack Voltage: 48V (8 batteries x 6V each = 48V)
Pack Size: 5760 Kw (48V x 120 ah = 5760 Kw - Remember, we can not use all this)
Usable Pack: 2535Kw (5760 x 0.8 x 0.55 = 2535 Kw usable)

From experience, we know that a Reva using a 48V system will draw around 40amps at 60KmPH.

Therefore, the Wh/k usage = 48V x ( 40Amps / 50KmPH ) = 38.4Wh/k

The distance our Reva will travel on this setup is: 2535kw / 38.4wh/k = 67 Kms (at 50 Kmph)

If we had a lithium pack of equal voltage and ah, the range would be 120 miles (because Peukerts effect does not play a role)
5760 x 0.8 = 4608 kw usable / 38.4 = 120
On a side note, 48 volt pack of lithium ( LifePO4) cells would consist of 15 of the lithium cells (they are nominal 3.2 volts each)


To CALCULATE this in reverse, (using LifePO4 cells)
say you need to go 120 Kms per charge at 50 Kmph and want to know what size batteries you need......
we will use the 38.4 wh/k avg.
wh per Km / pack voltage = ah per km
So in our "car/bike" 38.4/48= 0.8ah per Km
so you would need ah per km x km per charge needed x 1.2 (so you still had 20% charge left after the drive)
in our "car/bike" 1.8 x 67 = 120.6 Ah batteries at 48 volts needed to go the 67 Kms.

A lot of people wish to go close to 100 Kms in our experience. To make it simple, for this bike/car to go say 130 Kms (double than the
capacity now) the total KW of the pack has to be doubled. This can be done in a few different ways, most common would be to double
the AH rating of the batteries used or double the voltage by using double the amount of the same 120 ah batteries.

Keep in mind the components used must be rated for the voltage and amperage
Lets double the Voltage for instance.

Be careful here, just because you raise the voltage so high or don't need a long range, you should not use batteries much lower than
120ah rating, because of the "C" rating, see explanation below.
With today's Lithium batteries, it is not recommended to draw more than 3 times the C rating for more than @ 10 seconds. 1C for a 120ah
battery would be 120amp draw, and 3C is 360 amps. So if you limited your controller to draw the max of 300 amps from the batteries at
48 volts, the acceleration would be OK. With a 360 amp limit at 96 volts the acceleration would be impressive.
The usual recommendation is to use larger ah batteries, from 160-200 ah and adjust your voltage to get your needed KW pack, so that
3C is between 480 - 600 amps.

Some things to remember: A 5% grade requires twice the power that is needed on level roads.
Poor aerodynamics will use more energy
Poor wheel alignment, low tire pressure, other mechanical drags will use more power
Weight is very important-the lighter the less energy needed to move the vehicle
TEMPERATURE- battery temperature below 50 degrees will diminish the range of the vehicle. Generally, lead acid batteries will lose
30% of their useful ah at 30* F, and LifePO4 about 15-20%

Driving on hills Higher voltage comes in handy when going up hills- a long drawn out hill (remember a 5% grade doubles power needed) can easily
demand more than 3C for longer than the recommended time from our 100 ah batteries-putting them in an area that may reduce their
lifespan and create heat in the cell.
If the vehicle is to be used in mountainous areas or for high performance use, larger ah batteries are needed because of this C factor.
A side benefit of course would be longer range- but a costlier pack.

Performance Now we get to the fun part, calculating HP
V x A = watts, and watts/746 = HP so V x A / 746 = HP
Assume a small car with a setup or 12 batteries, of 12 volt each of 100 Ah rating.

With the 144 volt pack of 200ah batteries, and a 1000 amp controller, using the above formula, we could have 193 HP, (at a 5C draw)
and if we had 288 volt pack of 100ah batteries we could have potentially 386 HP ! (these are calculated without efficiency included,
figure about 85% efficient)
Only one problem, that much electrical power put into the motor could easily destroy it rather quickly ! The common "in the field"
estimate of KW power a 9" motor can handle (for short periods) is 100 KW. So using the above formulas, 144 volt system should be
limited to about 700 amps, and the 288 volt system to 350 amps. Still, 135 hp is pretty good for a small car. NOTE: use high power levels
at your own risk for motor damage.

Using a generator And for those looking to add a generator as a range extender.....
As you can see from the calculations above, the instantaneous watts needed to drive about 50 Kmph is about 12,000 watts. So to drive
your car strictly on a generator (at a steady speed), your would need a large one in the neighborhood of 15KW. For any type of
acceleration or resistance (hills) the load could easily be 50 KW, and up to 100KW ! If you used a smaller one, say a 2000 watt
generator, you can see it would add about 10 % to your range. It may be better to use the cost of a generator this size to just add more
cells and skip the generator and its complexity to the system (and exhaust emissions).


Now the disclaimer: These are all calculation based on theoretical values, averages and assumptions. There are several factors (such as
but not limited to weather, tire pressure, driving habits, battery condition, etc..) which effect all the calculations listed above which are not
used. All calculations should be considered estimates only and cannot be relied on as fact.

7 April 2011

Hi again.

Basic Classification of Motors

In Vehicle Propulsion system We would GENERALLY use the ones highlighted in blue

AC based
DC Based

AC motors can be further classified as:

• Classification Based On Principle Of Operation:

(a) Synchronous Motors.
1. Plain
2. Super
(b) Asynchronous Motors.
1. Induction Motors:
(a) Squirrel Cage
(b) Slip-Ring (external resistance).
2. Commutator Motors:
(a) Series
(b) Compensated
(c) Shunt
(d) Repulsion
(e) Repulsion-start induction
(f) Repulsion induction

• Classification Based On Type Of Current:

1. Single Phase
2. Three Phase

• Classification Based On Speed Of Operation:

1. Constant Speed.
2. Variable Speed.
3. Adjustable Speed.

• Classification Based On Structural Features:

1. Open
2. Enclosed
3. Semi-enclosed
4. Ventilated
5. Pipe-ventilated
6. Riveted frame-eye etc.