Arranged by topic with an Automotive, EV conversions point of view. Wikipedia and Google of course have much broader detail on many of these topics.
- EV: Stands for Electric Vehicle. The broadest classification, basically covering any car or truck that is capable of driving at useful speeds and distances on electric power alone.
- BEV: Battery Electric Vehicle: an EV whose sole source of power is an onboard traction battery. No generator, gas engine, fuel cell, or other sources of energy on board. Example: Tesla S, Nissan Leaf. Not a hybrid, in other words.
- HEV, or Hybrid: A car with both a gas engine and electric drivetrain, with gasoline being the primary source or energy. The electric drivetrain is used to supplement the gasoline engine and recover some energy during braking to add up to an overall increase in efficiency and/or performance over a gasoline only vehicle. Example: Toyota Prius.
- PHEV: Plug-in hybrid electric vehicle. Like a hybrid, but with a larger battery and the ability to operate for significant distances in electric only mode, and the ability to recharge the battery from the grid. Example: Chevrolet Volt.
- FCEV: Fuel cell electric vehicle. A vehicle where a fuel cell provides the main source of energy. A fuel cell takes in a source of hydrogen, mixes that with oxygen from the atmosphere in a catalytic reaction to produce electricity and water as waste. There is a small traction battery as well since fuel cells cannot deliver surges of power, for example when accelerating or climbing a hill. Rarely seen outside California. Still a million dollars a vehicle and many technical, environmental and economic hurdles before these vehicles will live up to their promises. Example: Honda FCX clarity.
- NEV: Neighborhood electric vehicle. A classification of electric vehicle that is legal to operate on roads up to 25mph or 35mph posted speed limit (depending on jurisdiction). Essentially, road legal golf carts. This classification of EV sold in modest numbers but is fading out now that full sized production EVs are commonly available. Niche markets such as small islands, campuses, and theme parks may continue using them. Example: Zenn, Miles, Zap
- EV Conversion: Or, just Conversion. An EV (virtually always a BEV) that was constructed by taking a gasoline or diesel car and removing the ICE components and replacing with a traction battery, motor, controller, and other EV components.
- ICE vehicle: Internal combustion engine powered vehicle.
- Range Extender: A built in or detachable device that can be attached to a BEV to increase its range. Homebuilt examples most often consist of a trailer carrying either a gasoline engine and generator, or a secondary battery pack and mechanism for transferring charge to the battery pack of the tow vehicle. In production vehicles the BMW I3 REX is a ‘range extended’ BEV. This is more of a grey area as like the volt, the range extender is a gas engine built into the vehicle. The BMW though has about 100 miles of electric range and 100 miles of REX capability from about 2 gallons of fuel capacity.
- Glider: A car with its ICE and all related components removed. Term used to refer to a rolling chassis that is ready for EV conversion component installation.
- Curb Weight: The weight of a vehicle ready to drive, but with no passengers or cargo. ICE curb weight is useful to know when selecting a chassis. EV curb weight is useful to know for calculating rolling resistance and overall efficiency.
- GVW: Gross Vehicle Weight. The maximum rated weight for a given vehicle, including its curb weight and the weight of passengers and cargo.
- Cd and CdA: Measures of aerodynamic efficiency. See efficiency section.
Electrical Power and Energy
- Ampere (Amp): The unit for measurement of electric current, or flow. A water synonym would be gallons per hour. By itself, this measure does not say anything about power available. Most EVs can pull up to a few hundred amps from the battery at full throttle. High performance EVs can pull a couple thousand amps from the battery. In most electric motors, Current is directly proportional to torque.
- Volt: The unit of measurement for electrical “pressure”. A water equivalent would be pounds per square inch. Like amps, by itself this measurement says nothing about the power available. Most EVs run with battery voltage from 72V up to about 400V. In most electric motors, volts are directly proportional to RPM.
- Watt: Often, expressed in Kilowatts (KW; 1000 watts) or Megawatts (MW; one million watts). A unit of instantaneous power. Not to be confused with Watt Hours, KWH, or MWH; units of energy. One watt is equal to one volt at one amp. One thousand watts, or one kilowatt (KW) is one volt at 1000 amps, one amp at 1000 volts, 10 volts at 100 amps, etc. The watt can be expressed in terms other than electricity. 746 watts is equal to one horsepower, the commonly used english unit for mechanical power. Most modern EVs have about 80KW (about 100 horsepower) while the most powerful EV dragsters can put out up to one megawatt (over 1000 horsepower).
- Watt Hour: Often, expressed in Kilowatt Hours (KWH) or Megawatt Hours (MWH). A unit of energy. Not to be confused with Watt, Kilowatt, or Megawatt; units of power. Energy is defined as Power delivered for a length of Time. Hence, one watt hour is one watt delivered for one hour. One Kilowatt hour is 1000 watt hours, and one megawatt hour is 1000 kilowatt hours. The size of EV battery packs are usually described in terms of Kilowatt hours. The Nissan leaf has a 24KWH battery; The top end Tesla Model S has an 85KWH battery. One gallon of gasoline contains approximately 33.6KWH worth of energy. One watt hour is equivalent to about 3.41 BTU. The Kilowatt hour is the unit of energy that your electric utility bills in; with a kilowatt hour costing anywhere from about $0.05 up to $0.20 or more in the USA depending on the region of country, season, time of use rates, and cumulative usage.
- AC electricity: Alternating Current electricity. Type of electrical current which rapidly switches direction. (60 times per second for US household electrical power). AC current and voltage follow a sinusoidal pattern. AC electricity is what powers your home, and is also what powers the electric motor in production EVs and some conversions. AC comes in two common forms: Single phase, and Three Phase. Single phase AC is what supplies homes and most smaller buildings. It can run smaller induction motors and brushed motors. Three phase AC is used to power larger buildings, industrial motors, and the motor in many EVs. (Note for industrial history nerds: there is such a thing as two phase AC power, but it has not been widely used since the beginning of the 20th century)
- DC electricity: Direct Current electricity. Type of electrical current that has constant voltage and current. This is what comes from batteries and is what most electrical devices run off of internally. AC power is often converted to DC within devices by their power supply circuitry. In most modern EVs, the DC power coming from the battery is converted by the inverter into three phase AC with variable frequency and voltage, in order to power the motor at the desired speed and horsepower output. In DC powered EV Conversions, the motor controller (taking the place of the inverter in this type of conversion) efficiently steps the voltage and current down from the full battery voltage but still puts out DC power that is compatible with the motor.
Mileage and Efficiency
- Efficiency: Simply, the ratio of power out to power in, OR energy out to energy in stated in equivalent units, regardless of what form that power or energy takes. For example, an electric motor that is taking 100 volts at 100 amps (10KW) of electrical power in, and is putting out 10 horsepower, or 7460 watts of mechanical power, is approximately 7460/10000 or 75% efficient. If it takes 30KWH at the meter to fully recharge a 100% depleted 24KWH battery, then the charging process is 24/30 or 80% efficient. Note that if you compute or measure an efficiency greater than 100%, you are doing it wrong. Your typical EV is about 70% efficient wall-to-wheels and 80% efficient battery-to-wheels. Compare this to a similar gasoline vehicle, which will be lucky to achieve 20% efficiency pump-to-wheels under the same conditions. Typically, the energy lost due to less than 100% efficiency takes the form of heat. It can also be light, noise, or other forms of energy.
- WH/Mile: Watt Hours per Mile. This is the EV equivalent to miles per gallon. Also commonly used is Miles per kilowatt hour which expresses the same thing in a slightly different way. If you are in a part of the world other than the USA, you would use WH/km or kilometers per kilowatt hour. Most full sized, production EVs achieve between 200WH/mile and 400WH/mile. 200WH/Mile is the same as 5 miles per kilowatt hour. To further confuse things, WH/mile can be given two ways: “wall to wheels” and “battery to wheels”. The difference between these two is the efficiency of charging. When figuring how much actual energy an EV uses, you want to use the wall-to-wheels measurement. If figuring how far you can go on a battery pack of a certain KwH capacity, you use the battery-to-wheels measurement. Usually, wall-to-wheels WH/Mile is about 20% higher than battery-to-wheels WH/Mile, owing to the efficiency loss in charging the batteries. Note that an EV that gets 300WH/Mile wall-to-wheels (Nissan Leaf, and most production EVs are in this ballpark) is getting the equivalent energy efficiency to a gasoline car getting about 110 miles per gallon.
- MPGe: Miles-per-gallon-equivalent. This is an attempt by the EPA to design a efficiency description that non-EV-owners can understand to compare the efficiency of a gas car to that of an EV. Simply, it is the miles that an EV could travel on the electrical energy equivalent of 1 gallon of gasoline, or 33.6KWH.
- Range: Simply, the total one-way distance an EV can travel on one charge. Range should be given assuming a safe and repeatable level of discharge for the batteries, and a realistic WH/Mile measurement that factors in realistic driving conditions.
- Cd and CdA: Measurements of aerodynamic efficiency of a vehicle body. Cd is Coefficient of drag, which is a dimensionless number representing the Aerodynamic drag generated by a particular three dimensional body at a particular angle to oncoming wind. CdA is simply Cd multiplied by the frontal surface area of the body. This accounts for the overall size of the body and can be plugged into a mathematical formula involving speed, density of air, and CdA to give you the resistive force caused by motion. Drag increases in proportion to CdA and in proportion to the square of speed. Aerodynamic drag almost doubles going from 45mph to 60mph, as an example. Aerodynamic drag at freeway speed for a full size, reasonably aerodynamic passenger car is over 100 pounds. For vans and SUVs it can be several hundred pounds easily. At freeway speeds, this is the biggest factor impacting range in an EV.
- Rolling Resistance: The friction forces caused by tires against road, brake drag, and friction in the drive line of a vehicle. It varies with vehicle type but for a typical EV, the rolling resistance is usually measured as a force around 1 to 2 percent of the overall weight of the vehicle. Rolling resistance is relatively constant in relation to speed, but can be affected by weather and road surfaces. It is not uncommon for an EV to experience an increase in rolling resistance of 10% to 20% in cold, wet weather relative to warm, dry conditions, and this can cause a noticeable reduction in range under those conditions. At lower speeds, (under about 40mph) rolling resistance exceeds aerodynamic drag for most road going cars.
- J1772: The standard charging protocol as defined by the SAE. All US market production EVs, and many conversions, are compatible with this standard. J1772 can provide Level 1 and 2 (L1 and L2) charging rates. The charging protocol includes various safety mechanisms designed to be usable outdoors and in all weather conditions. The plug somewhat resembles a gas pump handle.
- L1, L2: Different charging rate standards likely to be seen at household installations. L1, or level one, indicates 120V charging at up to 20 amps. This is standard household wall plug power. A full sized, roadgoing EV will charge at the rate of 3 to 4 miles of range per hour of charging at L1. L2, or level 2 charging, is 240V at up to 70 amps. Most production EVs charge at 30 amps and 240V. This charging rate will recover about 20 miles of range per hour of charging. The top end of this range can recover up to 50 mile of range per hour for cars that support it. This standard puts the actual charger onboard the car, and the charging station itself is typically an automatic switch with some safety circuitry included.
- L3, CHAdeMO, DCQC: Different standards for high power, fast charging. Not all production EVs, are compatible, and very few conversions are likely to be anytime soon. This standard puts the charger off board of the vehicle owing to its large size. The voltage and current is negotiated between the car and the charging station and can be delivered at rates that will recharge compatible EV battery packs in under an hour. There are several competing standards here. Most US market production EVs that are capable of DC fast charging use CHAdeMO which is the japanese standard. The SAE has a different standard, and Tesla has their own network. Eventually there will be consolidation down to one standard.
- ICEing: Or: Getting ICE’d. When an EV charging station is blocked by a gas powered vehicle. A common problem, especially when charging stations are located in prime parking locations.
- Battery Swapping: As literally described. A mechanism for “instant” recharge by literally removing the depleted battery and replacing it with a fresh one. While this method does not seem terribly practical in many circumstances, there are usage models, such as buses/fleets where it might make sense. Tesla is also building capability into their Model S to support it. The Better Place project tried it in parts of Europe and Isreal but folded.
A lot here, as batteries are a complex topic, and the heart of an EV.
- Cell: Technically, “Battery” is the plural. “Cell” is the singular. A single Duracell “AA” cell is a single cell. Put one or more together in series or parallel, and you have a true battery. A 12V car battery is a true battery, in that it consists of six individual lead acid cells. That said, nobody in the EV conversion world will look at you funny for calling a cell a battery. Usually.
- Traction Battery: Refers to the battery that provides the power that moves the EV. Distinct from the SLI or House battery. For most EVs, between 72 and 400V, and between 50 and 200AH.
- SLI Battery: The “starter, lights, ignition” battery. Technically, there is no starter in an EV but this is the 12V battery that serves the same basic function as the battery in a gas car, that is to provide startup power and backup power for the 12V system should the DC/DC converter fail. Sometimes referred to as the house battery, from RV/Camper terminology.
- AH: Amp Hours. This is watt hours, divided by voltage. This is the most commonly used capacity unit for batteries. A battery that can output 100 amps for one hour, or 1 amp for 100 hours, has a capacity of 100 amp hours. Note that because voltage is not a factor in the unit, this is not a complete unit of energy capacity. E.G. a single 100ah cell has a capacity of 100ah, and so does a traction battery consisting of one hundred 100ah cells in series. The difference is in the voltage. Note that while EV sized batteries pretty much all give an AH capacity, how much of that capacity, and how fast it can be used, is a big variable.
- Peukert’s Law: This basically states that with all batteries, the rate at which you use the energy stored within affects the ultimate amount of it you can recover. In other words, the more power you use, the less total energy you get. Type of battery, age, temperature, and other factors all play a part here. Peukert is the bane of lead acid batteries, because typically you could only get about 1/2 to 1/3 the rated capacity of the batteries, or 30 to 50ah usable capacity from a 100ah rated battery. With modern lithium batteries, the impact is much less, but still nonzero.
- Energy Density: How much energy per unit weight, or unit volume. For example, a typical energy density by weight for lead acid is 15 watt hours per pound. This means a 70 pound lead acid battery can store about 1kwh of energy. This is your typical golf cart battery. For LiFePO4 lithium most commonly used in conversions, energy density is more like 60wh/lb. More exotic lithium chemistries are well past 100wh/lb and in the laboratory energy density of several hundred wh/lb has been achieved.
- Power Density: Like energy density, except how much instantaneous power a battery of a certain unit weight or volume can deliver. This is often boiled down to “C” rate, or the maximum current in amps the battery can delivered, given in terms of a multiple of the battery’s AH capacity. For example, a 100ah battery with a 3C power density can deliver 300 amps continuously (for 20 minutes) without damage. In the EV conversion world, a properly sized 3C battery will make for a perfectly satisfactory road going car, and most LiFePO4 chemistries are rated near there. Drag racing EVs which need much more power use 10C to 20C batteries. Often there is a tradeoff between energy density and power density, though with modern batteries you can get a considerable increase in power density without sacrificing much energy density.
- “C” Rate: A way of describing the power density of a battery. Bigger is better. 3C is typical for road going cars, 10C for drag racers. See above.
- BMS: Battery management system. Electronics that monitor every cell in a traction battery during charging and discharging, looking for temperature and voltage out of bounds, and acting to balance and preserve the battery. A requirement in any lithium powered EV, unless you want to risk your investment.
- Prismatic Cells: Refers to large format (40ah and up, usually) individually package cells (typically lithium these days) with rectangular housings. Most common format found in roadgoing conversion EVs. Easy to package, easy to mount, easy to connect to.
- Cylindrical Cells: Refers to cylindrical cells, like your typical AA sized duracell, though for lithium they come in sizes up to about 20ah. Often a higher C rate than prismatics, and thus more often found in motorcycles and high performance EVs. Easy to connect to for EV sized cells, a little more challenging to mount.
- Pouch Cells: A cell packaged in a flexible plastic pouch, not unlike vacuum sealed food package. This is a common packaging scheme for Lithium polymer cells and is lighter and smaller than hard plastic prismatic cells. The downside is that these cells must be packaged in an outer enclosure to protect them and electrically connect them together and the terminals must be contact welded or sandwiched into bus bars as there are no screw terminals.
- Super Capacitors: Not really batteries, as they operate on a completely different principle, but another device for storing electrical energy. Extremely high power density, very low energy density. A modern super capacitor bank sized similarly to a lithium EV battery could propel the same car a couple of miles. Major disadvantages of capacitors relative to batteries, is when putting them in series you increase voltage, but lose capacity rapidly , while with batteries voltage goes up and AH capacity is constant. Also the voltage discharge curve of any capacitor is an exponential decay curve, while with a lithium battery it is largely flat.
There are many. I am listing here only ones that are rechargeable and have seen usage in EVs to some degree or other, at some point in history. Listed roughly in historical order of appearance (and also, increasing energy density)
- Nickel Iron: Thomas Edison’s battery. About 1.2V/cell. Like most of his inventions, revolutionary at its time but mostly eclipsed now. Used in EVs at the turn of the last century. Still used in railroad and backup power applications, but not nearly as common as lead acid these days. Very robust, very long life span. Some railroad NI batteries are over 100 years old and still work; lead acid is lucky to last 10 years in backup power applications and 5 years in a car by comparison. Another advantage: Could be recharged via electrolyte swap, e.g. you could literally “fill up” (after first draining) your Edison battery powered EV.
- Lead Acid: The successor to the Nickel Iron battery for most applications. About 2V/cell. The Old standard for EV conversions until about the mid 2000’s, and for production EVs until the early 2000’s. In EVs, basically the same technology as used in car starting batteries for most of the last century, but optimized for longer life and deeper cycling.
- NiCd: Nickel Cadmium. About 1.2V/cell. A similar, but older, chemistry to NiMH. Originally built as flooded cells. The flooded versions of these were most commonly used in military applications and aircraft starting batteries. The flooded cells are rather high maintenance but are very robust and have very high power density and can remain serviceable for decades if not completely neglected. Never commonly used in production EVs, and only a few conversions used them due to difficulty in sourcing them and the high maintenance. NiCd batteries of smaller sizes were common in the consumer electronics market but have been mostly replaced by less toxic and higher energy density NiMH.
- NiMH: Nickel Metal Hydride. About 1.2V/cell. This type of battery replaced lead acid batteries in production EVs in the early 2000’s and some of those batteries are still going today 10 years and 100K miles later. This type of battery never made it into many conversions, as the only source for large enough cells was surplus and salvaged production EV battery packs. This technology has been eclipsed by lithium batteries for EV purposes, though you can still find small rechargeable NiMH batteries for use in consumer electronics.
- Molten Sodium chemistries: These batteries are a high energy density, relatively low (but perfectly usable for roadgoing vehicles) power density and typically were provided in a modular package with built in BMS. They require heating to several hundred degrees farenheit to operate hence the provision with built in care and feeding. They are durable and made from extremely common and cheap materials, but the care and feeding requirements have limited their use in EVs. These were being used in some European fleet vehicles until lithium got cheap enough to put them into the why-bother category. If lithium becomes scarce and nothing better has come along after all the oil runs out, expect this one to come back.
- Lithium Chemistries: The current state of the art. 3V to 4V/cell. There are many different chemistries, too many to list. Common ones used in EVs are LiFePO4 (lithium iron phosphate), LiMnPO4 (lithium manganese), LiPo (lithium polymer; many variants). Less often used in EVs due to poor lifespan and tendency to catch on fire are all the Lithium cobalt chemistries. As the state of the art, there is much happening in this field. It is worth noting that your typical Lithium battery used in a modern EV has about 5 to 10 times the usable energy capacity of an equivalent weight lead acid battery and stuff that has not made it out of the lab yet is promising another tenfold increase in energy density. Think about EVs with a 1000 mile range, or with range similar to a contemporary gas car but with the battery smaller than a normal gas tank. The next decade is going to be revolutionary for batteries. The lithium iron phospate chemistry is among the least powerful of the lithium chemistries, but is still light years ahead of lead acid and also among the cheapest and most robust. This means LiFePO4 is most commonly used in EV conversions though we are now starting to see prices and availability of some of the better chemistries come into reach for EV conversions.
- CALB, Winston, GBS, Thunder Sky, Headway, Sky Energy, and others: Various Chinese manufacturers of LiFePO4 batteries which are available for EV conversions. These all have reasonably OK reputations, and several are owned by the same parent company. Currently, pricing is about $1.30-$1.50/ah plus shipping from US based distributors.
- Enerdel: The only US based manufacturer of LiPo lithium that is willing to sell to end users for EV conversions at realistic prices. The Jury is still out, but these are promising in quality. performance and price. While these are LiPo pouch cells they come prepackaged in larger modules to make attachment/installation easier.
Again, there are many varieties of electric motors ranging in size from literally microscopic up to weighing many tons. I am only briefly describing the types used in roadgoing EVs.
- AC (3 Phase): Invented in the early 1890’s. this type of motor is probably the most common industrial motor design out there. They are found in sizes from a few horsepower up to thousands of horsepower. No brushes or commutator, and usually a fully enclosed frame allows for very high reliability. This type of motor is commonly used in modern EVs. Advantages include simple design, no exotic materials, reversible with software when powered by a three phase inverter, and will easily operate as a generator. While not as sophisticated and slightly less efficient than BLDC, these motors are still very competitive.
- BLDC/Synchronous: Brushless DC. Similar advantages to 3 phase AC motor in that there is no commutator and rotation is produced by creating rotating magnetic fields, but utilizing permanent magnets and allowing for very high power to weight ratios and very high efficiency, sometimes into the high 90’s percent range. Easily operated as a generator, easily reversed. Downside is higher expense and use of expensive and strategic rare earth materials for the magnets. Common in production EVs.
- DC (Series): Invented in the early 1800’s, but not practical and did not begin to resemble modern motors until later that century. Series wound means the field and armature windings are wired in series with each other. This is the most common type of motor used in EV conversions. As a DC motor, simple to set up and use, and requires a simpler controller than any AC or BLDC motor does. Can be extremely powerful if properly set up. Downside is the potential for runaway under no load conditions. Difficult to use as a generator, meaning regenerative braking virtually never found on DC powered EV conversions. Requires reversing polarity of the field relative to the armature windings to reverse motor.
- DC (Shunt): Shunt wound DC. This is very similar to series wound DC motors, except that the armature and field windings are in parallel, not series. This type of motor is not often seen in EV conversions, but it is very common in golf carts and other small industrial electric vehicles. This motor type has the advantage of not running away under no load, but has reduced starting torque versus series wound. Works fine as a generator.
- DC (Compound): A DC motor with both series and shunt field windings. There are several configurations, and this type of motor splits the difference in operational characteristics between series and shunt. Rarely seen in EVs, but was often used in large industrial machinery that required speed control. Less common these days now that modern power electronics allow fine grained control of AC motors.
- DC (Permanent Magnet) A DC motor with no field windings, and instead permanent magnets. Otherwise, identical to series or shunt motors. Not commonly found in EV motor sizes, but may be found up to a couple of horsepower in electric lawn mowers, treadmills and other such things. This type of motor is found in pretty much all battery operated motorized toys and battery operated power tools as well.
- Regen: Regenerative braking, or operating the motor as a generator to recapture some electrical energy when decelerating. All modern production EVs utilize this, as do AC powered EV conversions. Regenerative braking can improve the overall efficiency of an EV by up to 10% or so.
- Rotor: In an AC motor, the rotating portion of the motor within the field.
- Armature: In a DC motor, the rotating portion within the field.
- Commutator: in a DC motor, the large copper rotary electrical contact that transfers electricity from the brushes to the armature and back.
- Brushes: In a DC motor, the carbon electrical contacts that run against the commutator. There are at least two, and often four or eight in a large DC motor.
- Field: In an AC or DC motor, the stationary windings around the rotor or armature.
- Warp, Advanced DC, Prestolite, GE, Kostov: Various DC motor manufacturers seen in conversion EVs. Only the first two typically are sold new expressly for conversions. The others are often found surplus from forklifts or other equipment and adapted for the purpose. Size is usually described by diameter, e.g. a 9″ advanced DC or an 11″ warp. Larger diameter motors are capable of producing more torque, but have lower peak RPM speeds and require higher voltage to get there.
- Solectria, Azure, Curtis/HPGC, Siemens: The most commonly found manufacturers of 3 phase AC motors found in conversions. Solectria/Azure is now out of business but there are a fair amount of their systems out there (including mine). Siemens motors are very expensive but can be bought new. The Curtis/High Performance Golf Carts motor is the most economical new equipment option in AC drives for conversions right now.
- Horsepower: Electric motor horsepower is rated as a continuous load, unlike gasoline engines where horsepower is given as a peak rating. Most stock EV electric motors can put out 3 or 4 times their rated horsepower on a temporary basis, and racing prepared motors can do a lot more than that. What this means is that a 30 horsepower rated 9″ advanced DC can put out similar power to a small block V8 if properly prepared.
- Torque: In most electric motors, torque is directly proportional to the amps flowing. For example, series wound DC motors have an attribute unique to each motor design called the torque constant. This number, multiplied by amps, give torque, regardless of motor speed. (However, at higher speeds, higher voltage is required to create the same amount of current)
- RPM: In most electric motors, higher voltage across the motor yields higher RPM. Again, there is a relationship with torque, but generally speaking higher voltages are required to get higher RPMs. This is why freeway capable conversions typically need at least 120V while NEV class vehicles with top speeds of 35mph could get away with 48 or 72V batteries.
- Controller: In a DC powered EV conversion, this is the device that controls the flow of electricity from the battery to the motor. It is essentially a giant light dimmer circuit. Curtis, Soliton, Zilla, Netgain, and others manufacture controllers for the EV conversion market.
- Inverter: In an AC powered conversion, this does the same job as the controller in a DC powered car. It is called an inverter because it converts DC power from the battery into AC power for the motor. However the basic purpose is the same, to allow throttle control of the electric motor. In AC powered cars, the inverter also regulates regenerative braking, as this can be done with no additional hardware. Unlike with DC motor controllers, the AC inverters are often provided as a matched pair with an AC motor. This is mostly because many more parameters are required to be programmed into them in order to efficiently run an AC motor. However there are some AC inverters, such as the Reinhart models, that can be programmed to run pretty much anything.
- DC to DC converter: In any EV, this component converts traction battery voltage down to SLI battery voltage. It acts as the equivalent to an alternator in a gas powered car, to keep the SLI battery charged and the 12 volt system powered.
- BMS: See description under batteries. The system that monitors the traction battery and prevents it from being damaged due to heat, overcharge, or over discharge.
- Low Rolling Resistance (LRR): Refers to a type of tire that is designed, as the name implies, to reduce rolling resistance. This is done by some combination of making the tire run at higher pressure, using different rubber compounds, tread patterns, and internal structure of the tire to either reduce flex, or allow it to flex more easily. A low rolling resistance tire can require anywhere from 10 to 50 percent less energy to roll down the road under the same conditions as a normal all season tire of the same size, and well designed ones do this without compromising handling and traction. The difference in energy lost to rolling resistance equates to a few percent of the overall efficiency in a gas car (owing to the relative amount of the original fuel energy making it as far as the wheels) but a considerably larger percentage difference in an EV, where much more of the battery energy makes it as far as the tires. This makes tire selection (and proper inflation and alignment) a very important part of optimizing your range with an EV.
- Overunity, Perpetual Motion: The idea or hope that there is some way to get more power out of something than you put into it, or an efficiency greater than 100%. As applied to EVs, it often starts with “can’t you attach a generator to the wheels and recharge your car as you drive?” or “can’t you put a wind turbine on the roof to recapture wind power while you drive?” Many people seem to desperately want to believe in this, and I have run into several people who were very insistent about it. Not I nor anybody else has actually SEEN a WORKING overunity device, because they do not exist. If they did, everybody would have one in their car and their basement and their Ipod and we would all live in a free energy utopia. Perhaps this is why the idea of it is so compelling. This reality does not mean nobody will ever again discover a new source of energy, but it will not be an over unity device.
- Free Energy: OK, there is no such thing, But this is less of a fantasy than overunity and perpetual motion. You can invest in equipment (such as rooftop solar (most people with a house), wind or microhydro (many fewer, but a lot of rural people) , etc. which will produce energy over time and ultimately pay for itself. After that, a well designed renewable energy system will continue producing energy for the balance of its (long) lifespan thereafter. If you want free energy, this is the way that works. Of course, it requires an up front investment. No free lunch and all.
- My Hummer is greener than your Prius/Leaf/Tesla/etc: And similar sentiments. This sort of argument usually revolves around the additional ecological impact or carbon footprint of the battery manufacturing process for an EV, and how that compares to that of the manufacturing a similar sized gas car. While it has been shown to be true (for now) that the embodied energy of producing an EV is higher than that of a similar gas car (by about 20% to 50%), it is not so much higher that the EV will not surpass the gas car and over a normal lifespan use far less energy, and cost the owner less overall. The comparison is almost comically in favor of the EV in areas with large proportions of hydroelectric or wind power on the grid. In areas with mostly coal fired power, highly efficient diesel vehicles and hybrids can be similar in ecological impact to a battery electric vehicle. Assuming you can keep your local nuclear plant from melting down, an EV powered from that source is also free from any incremental ecologic impact per mile driven.
- EVs don’t make sense because they are powered by polluting coal plants. Coal is ecologically speaking the worst case source for grid electricity production, and despite that an EV powered solely from that source is still comparable in overall emissions to a similar hybrid or clean diesel vehicle. However, In the USA, nationally, the percentage of coal fired electricity on the grid is around 40% and dropping. Many areas near the coasts the percent of coal is much less than that. Seattle City light, for example gets over 90% of its electricity from hydro and other renewables and basically zero from coal. An EV is as clean as its electricity source, so when powered purely by renewables the incremental impact of driving it is zero in terms of atmospheric emissons. As the grid gets cleaner, an EV will get cleaner too. ICE vehicles by comparison get dirtier and leak noxious fluids as they age. It is worth pointing out that the electricity generated from coal pollutes just as much whether it powers an EV or your house. The above argument is an argument against coal, not against the proliferation of EVs.