inside electric car

8/13/2019 Inside Electric Car

1/16

Research & Development Centre, Automotive Division,

INSIDE ELECTRIC CAR

Chetan Bhavsar

( R&D Proto Development)


2/16


Inside Electric Car

The heart of an electric car is the combination of:

Theelectric motor

The motor's controller

The batteries

ASIMPLE DCCONTROLLER CONNECTED TO THE BATTERIES AND THE DCMOTOR.

IF THE DRIVER FLOORS THE ACCELERATOR PEDAL,THE CONTROLLER DELIVERS THE FULL

96VOLTS FROM THE BATTERIES TO THE MOTOR.IF THE DRIVER TAKES HIS/HER FOOT OFF

THE ACCELERATOR,THE CONTROLLER DELIVERS ZERO VOLTS TO THE MOTOR.FOR ANY

SETTING IN BETWEEN,THE CONTROLLER "CHOPS"THE 96VOLTS THOUSANDS OF TIMES

PER SECOND TO CREATE AN AVERAGE VOLTAGE SOMEWHERE BETWEEN 0AND 96VOLTS.

The controller takes power from the batteries and delivers it to the

motor. The accelerator pedal hooks to a pair of potentiometers (variable

resistors), and these potentiometers provide the signal that tells the controller

how much power it is supposed to deliver. The controller can deliver zero

power (when the car is stopped), full power (when the driver floors the

accelerator pedal), or any power level in between.
http://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/battery.htmhttp://electronics.howstuffworks.com/battery.htmhttp://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/motor.htmhttp://electronics.howstuffworks.com/battery.htmhttp://electronics.howstuffworks.com/motor.htm


3/16


The controller normally dominates the scene when you open the hood,

as you can see here:

THE 300-VOLT,50-KILOWATT CONTROLLER FOR THIS ELECTRIC

CAR IS THE BOX MARKED "U.S.ELECTRICAR."

In this car, the controller takes in 300 volts DC from the battery pack. It

converts it into a maximum of 240 volts AC, three-phase, to send to the motor.

It does this using very largetransistorsthat rapidly turn the batteries' voltage

on and off to create a sine wave.
http://electronics.howstuffworks.com/amplifier.htmhttp://electronics.howstuffworks.com/amplifier.htmhttp://electronics.howstuffworks.com/amplifier.htmhttp://electronics.howstuffworks.com/amplifier.htm


4/16


When you push on the gas pedal, a cable from the pedal connects to

these two potentiometers:

THE POTENTIOMETERS HOOK TO THE GAS PEDAL AND SEND A SIGNAL TO THE

CONTROLLER.

The signal from the potentiometers tells the controller how much power to

deliver to the electric car's motor. There are two potentiometers for safety's

sake. The controller reads both potentiometers and makes sure that their

signals are equal. If they are not, then the controller does not operate. This

CABLEPOTENTIOMETER


5/16


6/16


The controller's job in a DC electric car is easy to understand. Let's

assume that the battery pack contains 12 12-volt batteries, wired in series to

create 144 volts. The controller takes in 144 volts DC, and delivers it to the

motor in a controlled way.

The very simplest DC controller would be a big on/off switch wired to the

accelerator pedal. When you push the pedal, it would turn the switch on, and

when you take your foot off the pedal, it would turn it off. As the driver, you

would have to push and release the accelerator to pulse the motor on and off

to maintain a given speed.

Obviously, that sort of on/off approach would work but it would be a pain

to drive, so the controller does the pulsing for you. The controller reads the

setting of the accelerator pedal from the potentiometers and regulates thepower accordingly. Let's say that you have the accelerator pushed halfway

down. The controller reads that setting from the potentiometer and rapidly

switches the power to the motor on and off so that it is on half the time and off

half the time. If you have the accelerator pedal 25 percent of the way down,

the controller pulses the power so it is on 25 percent of the time and off 75

percent of the time.

Most controllers pulse the power more than 15,000 times per second, in

order to keep the pulsation outside the range of human hearing.The pulsed

current causes the motor housing to vibrate at that frequency, so by pulsing at

more than 15,000 cycles per second, the controller and motor are silent to

human ears.
http://health.howstuffworks.com/hearing.htmhttp://health.howstuffworks.com/hearing.htmhttp://health.howstuffworks.com/hearing.htm


7/16


AN ACCONTROLLER HOOKS TO AN ACMOTOR.USING SIX SETS OF POWER

TRANSISTORS,THE CONTROLLER TAKES IN 300VOLTS DCAND PRODUCES 240VOLTS AC,

3-PHASE.SEEHOW THE POWER GRID WORKS FOR A DISCUSSION OF 3-PHASE POWER.THE

CONTROLLER ADDITIONALLY PROVIDES A CHARGING SYSTEM FOR THE BATTERIES,AND A DC-

TO-DCCONVERTER TO RECHARGE THE 12-VOLT ACCESSORY BATTERY.

In an AC controller, the job is a little more complicated, but it is the same

idea. The controller creates three pseudo-sine waves. It does this by taking

the DC voltage from the batteries and pulsing it on and off. In an AC controller,

there is the additional need to reverse the polarityof the voltage 60 times asecond. Therefore, you actually need six sets of transistors in an AC

controller, while you need only one set in a DC controller. In the AC controller,

for each phase you need one set of transistors to pulse the voltage and

another set to reverse the polarity. You replicate that three times for the three

phases -- six total sets of transistors.
http://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htmhttp://www.howstuffworks.com/power.htm


8/16


Most DC controllers used in electric cars come from the electric forklift

industry. The Hughes AC controller seen in the photo above is the same sort

of AC controller used in the GM/Saturn EV-1 electric vehicle. It can deliver a

maximum of 50,000 watts to the motor.

Electric-car Motors and Batteries

Electric cars can use AC or DC motors:

If the motor is a DC motor, then it may run on anything from 96 to 192

volts. Many of the DC motors used in electric cars come from the electric

forklift industry.

If it is an AC motor, then it probably is a three-phase AC motor runningat 240 volts AC with a 300 volt battery pack.

DC installations tend to be simpler and less expensive. A typical motor

will be in the 20KW to 30KW range. A typical controller will be in the 40 KW to

60 KW range (for example, a 96-volt controller will deliver a maximum of 400

or 600 amps). DC motors have the nice feature that you can overdrivethem

(up to a factor of 10-to-1) for short periods of time. That is, a 20 KW motor will

accept 100 KW for a short period of time and deliver 5 times its rated

horsepower. This is great for short bursts of acceleration. The only limitation is

heat build-up in the motor. Too much overdriving and the motor heats up to

the point where it self-destructs


9/16


10/16


Battery Problems

You can replace lead-acid batteries with NiMH batteries. The range of

the car will double and the batteries will last 10 years (thousands of

charge/discharge cycles), but the cost of the batteries today is 10 to 15 times

greater than lead-acid. In other words, an NiMH battery pack will cost Rs.

12,00,000 to 13,00,000 (today) instead of Rs.80,000. Prices for advanced

batteries fall as they become mainstream, so over the next several years it is

likely that NiMH and lithium-ion battery packs will become competitive with

lead-acid battery prices. Electric cars will have significantly better range at that

point.

Just about any electric car has one other battery on board. This is the

normal 12-volt lead-acid battery that every car has. The 12-volt battery

provides power for accessories -- things like headlights, radios, fans,

computers,air bags,wipers,power windowsand instruments inside the

car. Since all of these devices are readily available and standardized at 12

volts, it makes sense from an economic standpoint for an electric car to use

them.

Therefore, an electric car has a normal 12-volt lead-acid battery to power

all of the accessories. To keep the battery charged, an electric car needs a

DC-to-DC converter. This converter takes in the DC power from the main

battery array (at, for example, 300 volts DC) and converts it down to 12 volts

to recharge the accessory battery. When the car is on, the accessories get

their power from the DC-to-DC converter. When the car is off, they get their

power from the 12-volt battery as in any gasoline-powered vehicle.
http://science.howstuffworks.com/radio.htmhttp://auto.howstuffworks.com/car-computer.htmhttp://auto.howstuffworks.com/airbag.htmhttp://auto.howstuffworks.com/airbag.htmhttp://auto.howstuffworks.com/airbag.htmhttp://auto.howstuffworks.com/wiper.htmhttp://auto.howstuffworks.com/wiper.htmhttp://auto.howstuffworks.com/power-window.htmhttp://auto.howstuffworks.com/power-window.htmhttp://auto.howstuffworks.com/power-window.htmhttp://auto.howstuffworks.com/power-window.htmhttp://auto.howstuffworks.com/wiper.htmhttp://auto.howstuffworks.com/airbag.htmhttp://auto.howstuffworks.com/car-computer.htmhttp://science.howstuffworks.com/radio.htm


11/16


The DC-to-DC converter is normally a separate box under the hood, but

sometimes this box is built into the controller.

Charging an Electric Car

Any electric car that uses batteries needs a charging systemto recharge

the batteries. The charging system has two goals:

To pump electricity into the batteries as quickly as the batteries will allow To monitor the batteries and avoid damaging them during the charging

process

The most sophisticated charging systems monitor battery voltage,

current flow and battery temperature to minimize charging time. The

charger sends as much current as it can without raising battery

temperature too much. Less sophisticated chargers might monitor

voltage or amperage only and make certain assumptions about

average battery characteristics. A charger like this might apply

maximum current to the batteries up through 80 percent of their

capacity, and then cut the current back to some preset level for the

final 20 percent to avoid overheating the batteries.

Using a 240-volt circuit, The car might be able to receive 240 volts at 30

amps, or 6.6 kilowatt-hours per hour. This arrangement allows significantly

faster charging, and can fully recharge the battery pack in four to five hours.


12/16


PLUG THE CAR IN ANYWHERE TO RECHARGE.

In this car, the charger is built into the controller. In most home-brew cars,

the charger is a separate box located under the hood, or could even be a free-

standing unit that is separate from the car.


13/16


14/16


ACHARGING SYSTEM IN THE TRUNK OF THE CAR

The charging station is hard-wired to a 240-volt 40-amp circuit through

the house's circuit panel.

THE CHARGING SYSTEM SENDS ELECTRICITY TO THE CAR USING THIS INDUCTIVE PADDLE.


15/16


THE PADDLE FITS INTO A SLOT HIDDEN BEHIND THE LICENSE PLATE OF THE CAR.

The paddle acts as one half of a transformer. The other half is inside the

car, positioned around the slot behind the license plate. When you insert the

paddle, it forms a complete transformer with the slot, and power transfers to

the car.

One advantage of the inductive system is that there are no exposed electrical

contacts. You can touch the paddle or drop the paddle into a puddle of water

and there is no hazard. The other advantage is the ability to pump a significant

amount of current into the car very quickly because the charging station is

hard-wired to a dedicated 240-volt circuit.

The competing high-power charge connector is generally referred to as

the "Avcon plug" and it is used by Ford and others. It features copper-to-

copper contacts instead of the inductive paddle, and has an elaborate

mechanical interconnect that keeps the contacts covered until the connector is

mated with the receptacle on the vehicle. Pairing this connector with GFCI

protectionmakes it safe in any kind of weather.
http://home.howstuffworks.com/question117.htmhttp://home.howstuffworks.com/question117.htmhttp://home.howstuffworks.com/question117.htmhttp://home.howstuffworks.com/question117.htmhttp://home.howstuffworks.com/question117.htm


16/16


Equalization charge

An important feature of the charging process is "equalization." An EV

has a string of batteries (somewhere between 10 and 25 modules, each

containing three to six cells). The batteries are closely matched, but they are

not identical. Therefore they have slight differences in capacity and internal

resistance. All batteries in a string necessarily put out the same current (laws

of electricity), but the weaker batteries have to "work harder" to produce the

current, so they're at a slightly lower state of charge at the end of the drive.

Therefore, the weaker batteries need more recharge to get back to full charge.

Since the batteries are in series, they also get exactly the same amount

of recharge, leaving the weak battery even weaker (relatively) than it was

before. Over time, this results in one battery going bad long before the rest ofthe pack. The weakest-link effect means that this battery determines the range

of the vehicle, and the usability of the car drops off.

The common solution to the problem is "equalization charge." You gently

overcharge the batteries to make sure that the weakest cells are brought up to

full charge. The trick is to keep the batteries equalized without damaging the

strongest batteries with overcharging. There are more complex solutions that

scan the batteries, measure individual voltages, and send extra charging

current through the weakest module.

inside electric car

Documents