This section gives you more information on specific topics. Click on the links in the short sections below to be taken to the more detailed information section.

Charging my EV

An EV can be charged anywhere there is a socket. You need at least the basic charging cable that is supplied by the vehicle manufacturer. Most include a level 1 (120V) charging cable that plugs into a regular domestic 3-pin wall socket. (It is recommended that you have a fast charging 240V socket and charger installed in your garage or where you park the car overnight. The charging duration is reduced substantially). The time it takes for a full charge can vary depending on what type of a setup it is. Plugging into a socket or charger specifically built for EV charging in a house or an outside location will charge the battery in shorter time due to the fact that it will most likely be wired for higher power. Based on power level (and consequently the time it takes to charge), EV chargers are classified into different charging levels

Cable standards

Rather than a one size fits all approach or one global standard for cabling and power, there are different standards and each EV manufacturer supports one or two different cable standards. You can learn more about this by scrolling to the cable standards section.

Regenerative braking

Regenerative braking is a mechanism which uses the vehicle's motion during coasting or braking to recharge the vehicle's battery. This is an energy saving feature that is specific to a vehicle type that uses a battery to power some or all of its forward motion. Click on this regenerative braking link for a more detailed explanation.

An electric car needs only a single gear

In an EV there isn't a need for a transmission for most road-going applications and in addition it imposes weight and cost on the vehicle. An EV typically has one reduction gear that reduces the motor's rotational speed at the wheels and is called 'final drive ratio' in its specifications. Click on this an EV has no transmission link to scroll to this section.

The Lithium-Ion battery on my BEV

It is currently the battery technology used for propulsion of a pure electric vehicle. It is the most energy dense and the best practical rechargeable battery technology solution currently available for EVs (and for many other applications). Think of it as your typical smartphone or camcorder battery except much larger. More information about this topic can be found in this section.

Charging levels

Level 1

Level 1 charging is the slowest way to charge your EV and is accomplished by plugging in your electric car to any available standard domestic 120V 3-pin socket. The manufacturer supplied charging cable is the only equipment needed to charge at this level. Any apparatus related to charging an EV is frequently referred to as EVSE (Electric Vehicle Supply Equipment). Level 1 normally increases range by 3-5 miles per hour of charging. Increase in usable range is typically obtained by charging the vehicle overnight for at least 8 to 10 hours or more.

                               

                                                                                          Level 1 charging

Level 2

This is the next level up. For home charging, a 240V domestic AC socket or line is required. This would be similar to one that a kitchen oven or clothes dryer is plugged into. An external charger with a charging cable is installed on this 240 volt line along with a compatible EV connector at the other end of this cable (Ex. a SAE J-1772 connector). Level 2 chargers are available from various vendors starting at around $450 + installation costs. Most public charging stations within an urban area (in parking lots of retail locations, office buildings or those installed by the city) are level 2 charging stations. Depending on the model of EV, a useful range is obtained by charging your EV for around 4 to 6 hours.

                               

                                                                                            

                                                                                           Level 2 charging

Level 3

This is typically referred to as DC (or AC) fast charging. Public supercharging stations with J-1772 CCS, CHAdeMO or the Tesla supercharging network are level 3 DC fast charging stations (more about these standards and connectors in a later section). These stations are usually located in urban areas and along popular highway routes.

You can use the Plugshare plugin available in this website to map out the locations for Level 2 and level 3 charging stations.

CHAdeMO stations that make up the most number of installations around the U.S and primarily compatible with Nissan Leaf models operate at up to 500V DC, and deliver up to 62.5 kW of power.

Since Current = Power / [Voltage * Power factor (pf)], doing some basic math calc (and assuming pf=1), reveals that these stations can deliver up to:

                                                         62,500 watts / 500 volts = 125 amps (A)

This is way beyond what a domestic level 1 (around 12 A) or level 2 (up to around 30 A) setup can possibly deliver and therefore can charge an electric car much faster depending on how much power your EV can accept. A useful range can be obtained in 30 minutes or less. The ability to DC fast charge an EV is offered as an option that costs extra in some models.

                                                                                                              

                                                                                           

 

                                                                                             Level 3 charging

 
Cable standards for charging

A basic charger is an electrical device that converts AC from your wall socket to DC (direct current) energy to top up the battery in your EV. Most electric car makers supply cable connectors and inlets that adhere to a certain standard set up by standards bodies, like SAE. In the U.S, connectors support at least one of the three standards J-1772, CHAdeMO or the proprietary Tesla standard.

The shape of the connector, power levels, circuit configuration etc. are specifications that define the standard but to an end-user a standard is essentially the shape of the connector that fits the vehicle charging inlet or port. Some of these standards are specific to level 3 or fast charging. The main standards used in the U.S are:

SAE J-1772

A popular U.S standard supported by many EV manufacturers in the U.S, Europe and Asia. Connector cable looks like this:

                                                 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CCS or SAE Combo connector

SAE standard for fast charging and currently supported by several U.S, European and Asian marques. This standard is an extension to the J-1772 standard with added support for fast charging. Connector cable looks like this:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAdeMO

Japanese fast charging standard that has been adopted by many Japanese and other Asian EV manufacturers.

 

 

 

 

 

 

 

 

Tesla connector

Proprietary connector on Tesla vehicles and Tesla supercharging stations.

Other types of connector standards (non-U.S)

Type 2 or Mennekes connector - Germany

Type 3 - Italy

GB/T 20324 - China

The table below shows the standard port(s) supported on each EV by brand and model.

 1 & 2: 120V to 240V power to on-board battery charger

 3: Ground pin

 4: Pilot signal - Detects presence of car connected to cable and initializes current to charge battery etc.

 5: Proximity detection - Detects movement of vehicle and cuts off power if cable is disconnected

     

 1 & 2: 120V to 240V power to on-board battery charger

 3: Ground pin

 4: Pilot signal - Detects presence of car connected to cable and initializes current to charge battery etc.

 5: Proximity detection - Detects movement of vehicle and cuts off power if cable is disconnected

 6: DC power and ground for fast charging

     

   1: DC Power (+) - DC power for fast charging

   2: DC Power (-)

   3: Ground   

   4: Charger start/stop 1 - First step. EV is initialized            for charging by this signal

   5: Charging enable/disable - Charging is enabled                after Connection check at pin 6

   6: Connection check - Compatibility check, lock                check and insulation check

   7: CAN (H) - SoC (State of Charge) check within               the Control Area Network

   8: Charger start/stop 2 - Closing the connection

   9: CAN (L) - SoC (State of Charge) check within the           Control Area Network

                                ** Charging from J-1772 outlets possible with included J-1772 adapter.

                                                                      Table 1: Supported cable standards in the U.S

 

1

9

 

3

4

5

2

6

7

8

Regenerative braking

In a vehicle, slowing or stopping is accomplished by friction braking (not counting some degree of engine braking, air resistance and so on). Friction is created between the brake pads and the brake discs coming in contact with each other as you depress the brake pedal. In the process of slowing down or stopping, the kinetic energy of the vehicle is converted to heat energy that is eventually lost. In regen braking however, some amount of this kinetic energy can be recovered by converting it to electrical energy and fed back into the battery pack.

 

 

 

 

 

 

 

 

 

 

Modern electric vehicles have one or two electric motors that drive the wheels while consuming energy from the battery pack.

 

The motors are mostly common ones like the AC induction motor or an AC synchronous motor. These motors are similar to the ones that drive a household fan or a leaf blower but in this case they are adapted to the characteristics and needs of an electric vehicle. Battery current which is DC, is inverted, conditioned and filtered through some kind of a controller before it's fed to the motor.

Regenerative braking is only possible in a hybrid or a pure electric vehicle. In normal operation, the battery powers the motor to drive the wheels and gradually depletes the energy stored. But when the vehicle is coasting i.e., forward motion with not enough (or no) electricity supplied to the motor and during braking, the motor in turn acts like a generator that produces electric power; essentially converting some of the kinetic energy to electrical energy. The major components of an electric vehicle involved in the regenerative mechanism are the wheels, the electric drive motor, the battery pack and the wiring between the battery pack and the electric motor.

This phenomenon can be clearly demonstrated in an electric vehicle coasting down a hill. When the car ends up at the bottom of the hill it will have more energy in the battery than when it first started its descent. Some, not all of this kinetic energy is thereby recovered.

So how does regen work?

The figures below give you an illustration of how this mechanism works. The normal forward motion of an electric vehicle is depicted in figure 1. The battery supplies the specified power to the variable speed drive controller that inverts the DC power to 3-phase AC. This power drives the motor that in turn drives the wheel all while depleting energy from the battery. The torque applied to the wheel is in the same direction as the direction of wheel rotation.

The regenerative mechanism is illustrated in figure 2. Here, the reverse torque acted upon the wheel during coasting or braking is generating current in the system and charging the battery pack replenishing some of the lost energy. The torque referred to above is the twisting force that is acting in the opposite direction of motoring mode torque. During coasting or braking this reverse (braking) torque generates current in the windings of the motor (which is a generator at the moment) and sends it to the battery pack after conditioning and rectification (conversion to DC) in the controller block. In both the induction motor and the synchronous motor when the rotor speed is greater than the synchronous speed, current is generated. In other words, if synchronous speed of the motor is reduced to less than the rotor speed (negative slip) and there is a braking torque the motor becomes a generator for this duration.

 

The amount of electrical energy recovered depends on a lot of factors including how you drive, terrain, size of the motor and how much braking was done in the course of the trip.

 
An EV has no transmission

The reason an EV does not require a transmission for most situations is because whatever the rpm of the motor, it produces reasonably good torque across the range and losses due to heat and friction are low. But in a gasoline engine, we need proper gearing that is appropriate for the rpm to compensate for the lack of torque at low rpms.

Without gearing, it would be difficult to maintain speed or torque in a usable range in a gas vehicle. Heat and other losses are also very high in an internal combustion engine -it is only around 30% efficient in converting fuel to output.

The AC motor's rated speed, given in revolutions per minute (rpm) is directly proportional to the frequency of the current supplied (in the motor's operating voltage and current range) as seen in the graph below. In case of a motor connected to a standard U.S domestic supply this is a fixed 60 Hertz. But in an EV, the rotational speed can be varied by independently varying the frequency (f) of the current and the voltage (V) supplied to the drive motor based on the torque and speed required at that moment. The graph also shows that we have high instantaneous torque even when speed is zero.

 

 

                                              Figure 3: Torque speed curves for induction motor with constant V/f ratio

Some EV electric motors can operate at very high rpms, even up to 18,000 rpm for short bursts. However, at these high revs proper cooling of the rotor and bearings become important. An ICE car on the other hand typically has a limit of only around 5,500-6,500 rpm. This limit is called the redline of the engine. 

All is required is a reduction gear as a final drive to reduce the motor's output to the wheel. The conceptual figure below depicts an example of a reduction gear how the rotational speed is reduced at the wheel by the larger gear. The ratio of the number of teeth of the larger gear wheel to the number of teeth in the smaller gear wheel gives you the gear ratio of the gear train below.

                                                                           Figure 4: Reduction gear

In this example the final drive ratio is:

                                                                           24/16 = 1.5:1

                    

The final drive ratio in EVs are typically higher. 

 
Lithium-Ion batteries
Li-Ion battery is a single term that encompasses many types of Li-Ion batteries, classified (mostly) on the chemistry of the cathode material. Some battery types are especially suited for EV propulsion owing to factors like lower cost, high energy and power density and good cycle life --which is the number of charge/discharge cycles a battery can go through before capacity falls to 80% or less of initial capacity.
Like all batteries, a Li-Ion battery cell is also made up of the following components: A positive electrode (cathode), a negative electrode (anode), electrolyte (liquid or dry coating), separator and an enclosure. A regular flashlight or TV remote alkaline battery has a similar basic structure and stores energy similarly. A depiction of a Li-Ion cell is as show below in figure 5. In reality one form factor of Li-Ion cell looks somewhat similar to the regular cylindrical alkaline cell rather than what is depicted below. That Li-Ion format has the cathode, separator and anode sheets rolled into a 'jelly-roll' inside a cylindrical enclosure with a powdery damp electrolyte in the middle.  
 
 
 
 
 
 
 
 
 
 
                                                       
                                                                       
               
                                                                         Figure 5: Li-Ion battery cell diagram
Li-Ion batteries do not usually have a liquid electrolyte as in a wet lead-acid car battery but are mostly the type absorbed by the internal materials but the material used as electrolyte here in most cases are of a flammable type which leads us to the topic below; how to keep the battery in an optimal and safe operating range. 
 
Battery Management System (BMS)
An electric car should be capable of operating optimally even in relatively harsh conditions that include extreme ambient temperatures, hot/cold battery temperatures, a battery pack with a history of having been charged/discharged at different charge/discharge rates, different loads, different states of charge, battery age etc. There is need to maintain the battery pack in the safe operating range always and for the battery to deliver adequate performance. A battery management system (BMS) is used for this purpose. The BMS monitors the above mentioned conditions. It employs sensors to detect any metric that should be corrected. It should be able to direct cooling/heating of the battery when it detects high/low temperatures or shut off when it detects very high charge/discharge rates or physical impact for instance. Below is a list of conditions that should be managed by the BMS, up to its capability, to maintain the life of a Li-Ion battery.
Overcharge/Overdischarge 
Occurs when the battery is brought to a state of charge (SOC) that is greater than 100% or when SOC falls to 0% or lower. It can lead to permanent damage to the cells of the battery or thermal runaway that includes cell overheating, venting or fire/explosion. Full discharge cannot always be prevented by the BMS and therefore it is recommended that SOC doesn't drop to 0% (fully discharged battery). Some EV models come with apps or settings that limit charging the battery beyond a set SOC; useful when the EV is being charged overnight or while unattended. An SOC of 80%-85% is a commonly floated number for 'full' charge.
High temperature 
Internals of the cells in the battery degenerate at high ambient temperature or high operating battery temperature caused by very fast charging or very fast discharge (going very fast or excessive load). Batteries start degrading at temperatures above 45 Celsius (113 deg F).
Low temperature
Charging at low temperatures, below 0 deg C (32 deg F), can cause plating of Lithium metal on the anode leading to permanent capacity loss and other structural issues. 
State of Charge (SOC) and State of Health (SOH)
Monitors the SOC and the SOH as the battery ages. The SOH is a measure of current health versus the battery's original metrics. Capacity loss, power loss/impedance growth and increased self-discharge are some of the metrics measured.
Self-discharge or leakage is another metric that is of interest to an EV owner. Li-Ion batteries have very low self-discharge compared to other batteries. However, this depends on and may increase with battery age, exposure to high temperatures and other factors. 
Longevity of the battery pack is affected by temperature, high or low SOC, and charge/discharge rates. Also as the battery ages, it will suffer from capacity loss and power loss. Capacity loss is the natural decrease in the amount of energy in kWh a battery can hold. Power loss is a result of increase in internal impedance (resistance) caused by events like high or low operating temperatures (this can be managed by the BMS) and number of charge/discharge cycles.
To maintain optimum battery life, it has been shown that it is best to maintain SOC at moderate levels around 40%-50% at cool to moderate temperatures [around 40 to 80 deg F (4 deg C to 27 deg C)]. The enemies of a long Li-Ion battery life include charging to 100%, draining it to a fully discharged state, high ambient or high battery temperatures, and very high charge/discharge rates.

 
 
                     Table 2: Maintaining optimum Li-Ion battery life
Quick comparison of Li-Ion battery types
The table below compares the characteristics of a few types of Li-Ion battery. NMC and NCA are the popular ones used for EVs owing to their advantages over other types. Here energy density is measured by the capacity in Wh/kg (or kWh/kg), is how much energy can be stored per standard weight.
 
As far as cycle life is concerned, what the numbers in table 3 means can be explained with an example. In case of an NCA battery it is capable of going through a complete charge/discharge cycle 1000 times before its capacity begins to drop. Suppose we have a battery that has a 150 mile range and is charged to 80% every time. This means that we get about 100 miles of range on every charge before we need to recharge again (it is 120 miles but we don't want to discharge our battery completely before we go back to recharge). We can do this around a thousand times and at the end effectively see 100,000 miles on the odometer (about 6-7 years on average) before seeing reduced range from that point on. Of course, 1000 cycles is an approximate number and depends on several factors, as discussed earlier. 
So based on these calculations, it appears that longer range batteries like the ones on any Tesla model or the Chevy Bolt can actually give you many more years of service all else being equal. There is some data online that indicates that this may indeed be true as batteries on some of these models are holding up pretty well.
                     Table 3: Li-Ion battery types

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