hemank

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.

sunilg

Topic moved and approved.

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ROCKRZ

Infomative post. However, i have some queries starting with the basics of this..
can you put this calculatioms on an excell sheet so that we can get the values easily?

Also, how is the voltage varied when the output of the batteries is constant??

By the generator, will this be rather called a hybrid??

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hemank

Excel sheet. Nice idea. Is possible. But I dont need it.
Any ways, When you draw current from the battery, it will show a drop in voltage. That is nothing but discharging. and inorder to force charge (voltage) into the battery, the battery needs to draw current from an external source (charger) which is at a higher potential (Voltage). Thus ur flow is from the charger to the battery, and thus the voltage at the charger will drop and at the battery will increase, totally showing an avg of the two. This is called charging. Its simple.

hemank

First of all. Excel sheet - nice idea.

Voltage of the battery is never constant. Voltage shows the amount of charge in your battery(When not under load condition). A 12V battery is fully charged when its voltage measured at the teminals is 13.5 to 13.7 V . And is DEAD when its voltage measured at the terminals is 10.5 or below. 11 to 12 is discharged condition. When you apply electrical load on the Battery, basically you are connecting a device with a lower potential. For example. When a bulb is connected to the Battery, the Bulb is at zero potential initially. When you connnect it to the battery in a parellel type of connection, it will pull energy from the battery to light itself up. How much charge is pulled purely depends on the Resistance of the object. For example, a metal piece, would have a very low resistance value and would thus pull maximum charge. A bulb would have a very high resistance and thus would pull less amount of charge. Its simple. You cannot drink a glass of pepsi entirely in one second using a straw (straw = high resistance). How ever, it would get over in a second if flipped upside down. (Almost Zero resistance). So same is the case with electricity. When you increase the torque demand on ur wheel (by user input or hill slope, or ..etc) the motor, in order to maintain the required speed will compensate the charge it pulls in. This is the controllers job. Thus the Voltage drops on the battery as a result to power the moter by supplying current (Charge). This is called discharging. And in a charger, ur charger is at a higher potential, and thus the battery would pull charge(current) out of it to increase its potential(Voltage ) untill it reaches the potential of the charger. When both are on equal potential, your battery is full charged . Get it?
Cheers
Ride Safe

antz.bin

#1 If you use a generator, you make it a plug-in, serial hybrid eg. Chevy Volt.

#2 If you use the motor to power the wheels (and use a dynamo + regenerative braking to charge the battery), you make a parallel hybrid (power from both petrol / diesel motors is used to power the wheels in 'parallel') eg. Honda Civic Hybrid, Toyota Prius.

The advantage of using it like a #1 Hybrid is that you can keep running the generator of the car at its most fuel efficient RPM regardless of what speed your vehicle was running / not running at (and hence converting the most petrol into electricity to run the car further / faster). Moving parts are also reduced, so a simpler / cheaper to produce design by principle. (I hope this was correct ) eg. For a Chevy Volt, The engine only starts when the State of Charge (SoC) of the battery reaches 25% and its subsequent job will be to maintain the battery at a SoC of around 30%, and will do so by continuously matching the average power requirement of the car once it is turned on. Those power requirements will roughly be about 8 kW in the city, and 25 kW on the highway.

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insane_x97

nice thread,
any links to decent bldc motors, controller could be more helpful.....

hemank

Basic concepts of DC Motors:

TYPESOFDCMOTORS

AC Motors:

AC motor - Wikipedia, the free encyclopedia

I think We should not go too deep down to the basics, people can Google their own problems, when it comes to silly ones. Complicated, yes definitely, is a nice thing to ask on forums, and is fun to discuss too.

I was planning a Workshop on EV / hybrid conversion in Pune. may be 2 or 5 ppl. Not interested in Money much. Just for fun. Anyone interested? PM me. :P

abhijeet080808

Nice initiative. Practically looking, what the the dimensions for a 100HP motor? Also, how much of storage area are we looking at for 200Ah batteries?

Looking at the Reva, we can calculate the following -

Power Req - 6000KW

10x 5Ah 12V battery - 120V, 50Ah - 6000KW

The difference being in 3C = 150A instead of 360A.

But since we now have 120V at our disposal (instead of 48V), we will not need that much current anyway. So, either setup should do fine.

Am I correct?

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hemank

Partially.
The reva uses a different type of battery. It does not use conventional Lead acid. Thus the calculations vary a little bit. The reva is equipped with a 10KW motor, and a 48V, 120Ah batt pack ({6V, 120 Ah} x 8)

I also forgot to mention a few things. check the edited text