CleanCarTalk » Battery Technology for Hybrid and Electric Cars

GM Photo of Chevy Volt Crash Test Shows Protected Battery Packs

Cuong Huynh — Wed, 18 Nov 2009 23:47:53 +0000

GM released photos showing the orange T-shaped battery pack of the Volt is not impacted during frontal collision. (Credit: General Motors)

View the full presentation Chevrolet Volt development update Nov 17 2009

More from Autoblog.com article “GM provides update on Volt vehicle and battery development” and CNET News article “For Chevy Volt drivers, battery life will vary.”

GM Photo of Chevy Volt Crash Test Shows Protected Battery Packs is a post from: CleanCarTalk

Battery Pack Balancing – The Key to Maintain Top Hybrid and Electric Car Performance

Cuong Huynh — Fri, 28 Aug 2009 13:00:24 +0000

As the automobile industry moves toward alternative energy vehicles, near-term solutions include the already popular hybrid cars and the upcoming electric cars. Ironically, the single common performance killer among these new breeds of cars turns out to be their energy storage or battery packs that help them achieve their high mileage. Batteries tend to be unreliable and greatly affect the performance of any hybrid or electric car. Reliability of hybrid or electric cars can be improved with proper battery pack balancing.

Why is Battery Pack Balancing Needed?

Battery pack balancing is the maintenance of each battery cell, which centers on preventing the cells from reaching the minimum and maximum limits with every full charge and discharge cycle. Balancing the battery pack’s SOC, or state of charge, and making sure that the battery stays at an optimal level between full charge and full depletion can help your battery stay in great condition and can considerably lengthen the life of a single battery pack.

The full depletion of a battery pack is not advised since the extreme ends of a battery’s charge can sometimes cause changes to the electrode surfaces of the batteries. This sometimes happen due to SOC deposits that affect the original composition of the batteries. This may then lead to battery problems and possibly cell damage. To keep the battery pack balanced, the recommended operation is in the mid 30% to 50% of the SOC.

The Challenge of Battery Pack Balancing

Battery pack balancing is not a straightforward exercise. One of the most commonly advised practices is to charge each battery cell individually using separate low-voltage chargers instead of charging them together using a high-voltage charger. This will help prevent imbalance, though it could be a bit taxing and time-consuming to have to use multiple chargers. It is also advisable to shuffle the charges from high to low SOC, though this would require complex circuits and may be faced with certain limitations.

Battery pack designers also recommend the use of shunt clamps while charging. By shunting the current from one battery to the next each time a battery pack reaches the necessary clamp voltage, every battery will remain in the same maximum starting voltage. Aside from that, the use of a passive network may also be helpful. A passive network is an affordable and a manageable way of equalizing the voltage, but make sure to avoid deep discharges as this may affect the life span of the battery pack.

Battery Pack Monitoring

In order to ensure that the battery pack is optimally balanced, monitoring the pack closely is critical. Failing batteries should be identified and replaced when necessary. If a failing battery is not determined in a timely manner and left to continue to function within the pack, it can weaken the battery and its pack, and adversely affect the performance of your hybrid or electric car.

Battery pack monitoring is thus a significant function for proper battery pack balancing. Read more on “Design Considerations for Keeping Your Battery Pack in Top Performance: Balancing and Equalization vs. Pack Monitoring.”

Battery Pack Balancing – The Key to Maintain Top Hybrid and Electric Car Performance is a post from: CleanCarTalk

Design Considerations For Good Battery Pack Design & Integration

Tom Bartley — Wed, 27 May 2009 00:56:59 +0000

Battery pack technology is all about managing the temperature of the cells and low resistance of the interconnecting conductors, connectors, and switches. Battery pack technology is not the same as battery chemistry technology. The latter is about building functional individual battery units, while the former is about making those units work together effectively and safely to provide much higher capacities.

There is still a lot of room for creative pack designs in electric and hybrid-electric vehicles with different form, fit and function topologies and connection schemes. The most common requirement is the need for temperature management for high power performance and operational life of a pack. High current charging and discharging through parasitic resistances in the cells, connections, switches, and wire cables generate heat that must be dissipated without damaging the surrounding materials.

Here are some key factors governing good battery pack design.

Internal Heating Factor

Knowing where the heat originates is the first step in designing a cooling system. Just like ultracapacitors, cylindrical cells are rolled up like a jelly roll with an outside cover and dissipate the most heat through the electrode connections in the center at either end of the cylinder. Again just like ultracapacitors, prismatic cells are in the form of flat sheets and dissipate the most heat through the sides of the cell. Cells in the middle of the pack and at the end of the circulating air or coolant stream will be the hottest and deserve the most attention. The most stress on a cell occurs at high temperature and high voltage such as immediately after braking regeneration charging while going down a hill.

Quick, low cost, low resistance connections between cells are a challenge. One bad or corroded high resistance connection can create enough heat to destroy an entire pack very quickly during high current charging or discharging operations. Even if the cell chemistry can accept high current “quick” charging and discharging, resistive heating losses in the connections and wires can easily drop the stored energy efficiency to 50% from the 80%-90% efficiency of more moderate power operations.

MES-DEA Zebra Z5 battery pack Courtesy MES-DEA.

The challenge is to keep all the cells at a uniform cool temperature to prevent uneven cell aging and premature pack failure. It would be clever if the cooling system would start early in anticipation of high current downhill charging and startup accelerations. Today’s position locations systems make this a real possibility.

Low Ambient Temperature Factor

Keeping a pack warm is generally not a problem except during cold weather startups. Some batteries lose a significant amount of capacity at extremely low temperatures. Using part of the stored energy to power a heating blanket could work nicely prior to startup.

The “Zebra” Nickel Sodium Chloride (NiNaCl) battery requires an internal temperature of 300 °C (572 °F) to keep the NaCl electrolyte melted. Using the stored energy of the battery pack and excellent insulation, the temperature can be maintained over a number of days from the stored energy alone. The downside is that the battery must be preheated before use. Prematurely charging a cold Zebra will destroy an expensive pack.

Lithium Ion Factor

Lithium ion (Li ion) titanate is a unique battery chemistry that is endothermic (cools by absorbing heat from the environment) during moderate to low operational power currents. However, at high currents and with corroding connections over time a Li ion titanate pack has the same heat dissipation problems.

Tesla Roadster battery system – Courtesy TeslaMotors.com

The Tesla electric sports car battery pack uses an older Li ion battery chemistry that is more susceptible to thermal runaway. Even when passively sitting fully charged in a garage the Tesla pack uses the equivalent of two refrigerators power to continuously keep the pack cool.

Electromagnetic Radiation Factor

Often ignored, one final consideration in pack design is the high magnetic field surrounding the high current carrying conductors. The high current DC power of the battery leads to an inverter controller for control of the AC induction motor used in most electric vehicles. The high current AC coming out of the inverter creates enough electromagnetic radiation to drown out any nearby AM radio, so good shielding practices have to be followed in the wire and cable installation. Alternatively, this problem can be ignored if functioning AM radio reception is not a priority.

The Bottom Line

Very few battery pack manufacturers have successfully integrated all the pack thermal and electrical requirements into a mechanical structure that has to withstand the shock and vibration environment of transportation applications. With at least five new plug-in battery cars coming on the market within the next two years, resulting in thousands of electric cars driving on our roads, let’s hope the manufacturers are successful with their battery pack integration.

Design Considerations For Good Battery Pack Design & Integration is a post from: CleanCarTalk

A Short Primer on Ultracapacitors

Tom Bartley — Mon, 18 May 2009 19:48:50 +0000

Ultracapacitors are super high capacity versions of electric capacitor components that store energy in an electric field. These are devices that have raised the “capacity” of a capacitor so high that ultracapacitors or “supercapacitors” are now thought of as energy storage devices that can replace batteries in some applications. They are available in various cylindrical, square, and flat shapes and sizes. With increasing production volumes and economies of scale, their prices can be competitive with batteries.

Ultracapacitor Characteristics

Ultracapacitors, sometime called Ucaps, are high-power/low-energy devices while batteries tend to be high-energy/low-power devices. The lower equivalent series resistance of an ultracapacitor gives it higher roundtrip (in and out) energy storage efficiency, especially with lower losses at high currents. Ultracapacitor packs are ideal for storing high power braking regeneration energy and supplying quick acceleration energy. The original Honda FCX hybrid fuel cell car used ultracapacitors for the energy storage, as do some of the new hybrid electric transit buses.

Being a capacitor, the state of charge (SOC) energy is precisely determined by the square of the voltage (E=½CV²), where C is the capacitance. The SOC discharge profile is significantly different from a battery, but offers some unique characteristics and advantages. Low temperature performance down to a -40°C (-40°F) shows little degradation. Above 89°C (192°F) internal temperature the electrolyte will vaporize and cause a flash explosion. In general the cycle life is limited by the temperature history of the electrolyte, which slowly decomposes. Over a million complete 100% charge/discharge cycles can be expected.

Ultracapacitor Construction

Capacitors are electric components that store energy in an electric field between two electrically conducting plates or “electrodes”. Ultracapacitors or “supercapacitors” have electrodes are made from a high porosity carbon much like the carbon in air and water filters. This high porosity carbon (in some new devices carbon nanotubes) is somewhat like a microscopic sponge that has extremely high surface areas that increase the “capacity” of a capacitor to such a high density that ultracapacitors are now thought of as energy storage devices that can replace some battery applications.

Ultracapacitors are known as double layer carbon devices because the actual construction is like a layer cake with carbon electrodes on the top and bottom. In between the electrodes is an electrolyte to facilitate the movement of charged microparticles. A special separator sheet lies in the middle of the electrolyte to isolate the voltage between the top and bottom electrodes. Ultracapacitors are rolled up like a “jelly roll” to make cylindrical devices and stacked in flat sheets to make prismatic devices. The cylindrical devices dissipate most of the charging/discharging heat through the end electrode connections while the prismatic devices dissipate most of the heat through the flat sides.

Unlike some modern batteries of similar construction no chemical reaction takes place to store or release energy. One of the electrodes in a battery is made from a different material and different electrolytes are chosen to act as catalysts for the chemical reaction.

Ultracapacitor and Batteries

The combination of ultracapacitors with batteries offers potential advantages in power, energy, temperature range, and life. However, the different SOC voltage profiles make such combinations challenging especially in high power vehicle applications. There have been over 50 technical papers published on combining batteries and ultracapacitors.

I maintain that, for many applications, a simple parallel ultracapacitor pack combination with a battery pack could double the life of the battery pack and pay for the extra complexity.

At least one manufacturer is developing a type of hybrid battery/ultracapacitor cell for use in vehicles. An actual vehicle test using an energy storage pack built with hybrid battery/ultracapacitor cells more than doubled the pack life. The AFS Trinity hybrid SUV offered a combination of battery and ultracapacitor packs. Small scale testing in a camera circuit demonstrated the combination advantages and I suspect that there are some small cordless tool applications that have already implemented this design.

A Short Primer on Ultracapacitors is a post from: CleanCarTalk

Battery Options for Hybrid Vehicles and Electric Vehicles

Tom Bartley — Fri, 01 May 2009 00:47:34 +0000

The Institute of Electrical and Electronics Engineers (IEEE), the Society of Automotive Engineers (SAE), and others periodically publish magazine articles that provide update summaries on the leading candidate energy storage technologies. Research and Development (R&D) and production is on the upswing getting a kick from increased funding and tax credit support for electric vehicles (EVs) to reduce oil consumption and the generation of CO2 and other air quality contaminants. The American Recovery and Reinvestment Act of 2009 (ARRA 09) has designated $400 million for electric transportation technology and $2 billion for advanced car battery manufacturing.

Batteries or battery packs can make or break a hybrid or electric car. Here’s a look at the different battery options and their characteristics together with notes on key manufacturers. The list is in no particular order.

Lead-acid or valve regulated lead-acid (VRLA)

Most widely used for starting engines.
Cheapest option.
Good power capability.
Low energy density making it too heavy or too low capacity for some applications.
Reduced capacity at low and high temperatures.
Lead must be recycled.
Good shelf life.
Poor cycle life unless SOC (state of charge) range is limited during operation.
Improvements are still being developed, look for various “hybrid” energy cells.
Requires desulfation charge to extend the life an extra 25 to 50%.
Deep cycle versions are used for electric vehicles to keep the cost down.

Nickel Cadmium (NiCad)

Is going away because the biggest problem is the recycling of heavy metal cadmium.
Has a memory problem without deep cycling.
Requires watering maintenance.
Average cycle and shelf lives, power and energy densities, with reasonable temperature performance and cost.

Nickel Metal Hydride (NiMH)

Today’s standard for power and energy capacities and densities.
Millions of packs in use.
Shelf life requires charge maintenance.
Cycle life several times better than lead-acid, but SOC range must be limited during cycles to attain HEV and EV life goals.
Performance falls off at low temperature.
Cooling is required for high current charge and discharge cycles.
Panasonic is dominant producer and Toyota Prius dominant user.
U.S. producer Cobasys has yet to prove it can supply good reliable packs.

Lithium Ion (Li Ion)

High energy and power capacities and densities (lightweight) ideal for hybrid and EV applications. Ten-year shelf life and extremely high cycle life if SOC range is limited (40% to 70% or tighter); some low temperature performance drop off. Look for widespread production use by the middle of 2010.
Most of the world supply of lithium carbonate source material is located in Bolivia, Chile and Argentina. Early abundance reports suggested the supply was insufficient to supply the potential global demand. Later reports suggest otherwise.
Widely used in small electronics, early chemistries had a potential thermal runaway problem that led to a few explosions. More recent recipes must pass rigorous cell testing and have all but eliminated the problem, however there remains some residual concern about heat generated in pack designs.
Nissan now in partnership with NEC to develop and produce an in house pack design for an EV starting with fleet deliveries in 2010 and the general public in 2012. A 26-minute “quickie” is one of the charging options. Nissan and others will offer pack leasing to control fears about the cost of replacing a failed battery pack.
Magna Steyr in Austria is in volume pack production using A123 batteries for some European vehicle manufacturers. A123 is also developing some of its own pack designs.
Toyota delayed introducing Li Ion packs, but may do so in their new plug-in Prius.
Valence Technology Inc in Texas is in high volume production for electric bikes and scooters and has supplied larger packs to a limited number of plug-in hybrid school buses. The one negative is that these batteries tend to be a bit pricey. But I guess for extended EV range you get what you pay for at least for now.
ThunderStruck, a Chinese company, is in high volume low cost cell production with limited quality control; about 10% of delivered cells are bad.
Altairnano is leading the way in fast rechargeable cells with the lithium titanate chemistry. They give up some energy density to gain fast charging and high cycle life.

Nickel Zinc (NiZ)

Powergenix, headquarters in San Diego and production in China, offers AA and sub C size cylindrical cells with D size in preproduction testing.
The primary application so far is hand held power tools where they are a less expensive alternative to Li Ion and NiMH cells.
Higher energy density than NiMH because of higher cell voltage of the chemistry.
Easy recycle handling.
Apparently good shelf life.
Good efficiency (low cell resistance).
Good lower temperature performance.
Powergenix built a Prius replacement pack (it needs more R&D) and may find a niche market as a less expensive replacement pack supplier.

Ultracapacitors

These devices have extremely low internal resistance (~0.2 milliohm) per cell and extremely high capacitance (~3000 Farads) per cell, making them ideal high power devices.
However, they are generally low energy and need to work with a battery to achieve any driving range.
Ideally the combination of batteries and ultracapacitors offer the best of both worlds, but the voltage versus SOC profiles don’t match and there has been very little development of large pack combinations.
Hybrid cells may offer a way out.

This list represents a snapshot of various energy storage technologies available for upcoming hybrid and electric cars. Development in the industry is expected to move quickly in the next few years due to demands of the market and with the help of government regulations and financial stimulus packages. There are several major battery conferences on battery technology every year, both in the United States and around the world. For additional details, your favorite Internet search engine may be your best window into this fast moving, and critical, industry.

Battery Options for Hybrid Vehicles and Electric Vehicles is a post from: CleanCarTalk

Design Considerations for Keeping Your Battery Pack in Top Performance: Balancing and Equalization vs. Pack Monitoring

Tom Bartley — Sat, 28 Mar 2009 08:00:08 +0000

The history of battery packs for electric vehicles is filled with stories of early failures and fires. Optimum and safe pack performance requires balancing and equalization management of the pack state of charge (SOC). A battery pack SOC is the equivalent of a fuel gauge which tells you how much usable charge remains in the pack.

Battery pack balancing and equalization management is the regulation or protection of individual battery cells from hitting the maximum or minimum limits when fully charging or discharging the whole pack.

Here are several methods used by battery pack designers to keep a battery pack in balance in order to get top performance out of the pack.

Ignore it – For only few cells in series and a limited number of charge/discharge cycles (like a 12-volt starting battery with six cells) that don’t deplete the battery, balancing doesn’t add much to the battery life. For large numbers of individual batteries in a full parallel and series matrix connection the distribution of cells may be good enough to average out variations and provide some fault tolerance without balancing, however, it can create a huge connection and cooling problem. For example, the Tesla Roadster sports car is thought to have a matrix connected type of battery pack with over 8,000 small AA batteries and connections. It almost always turns out that the cells in the middle of the pack are the hottest and hardest to cool. I’ve suggested that a good university student project would be to model such a design and determine sensitivities to manufacturing tolerances, aging, and failures of individual cells.
Charge each cell or sub pack separately – For example, if a number of 12-volt packs are connected together for a higher voltage pack, each 12-volt battery is charged to a full voltage SOC with a separate 12-volt charger rather than charging the whole pack with a single high voltage charger. If this is done periodically, like once a day, the assumption is that the charge/discharge cycles during the day won’t result in enough unbalance to be a problem. Multiple chargers and connection points can make this a bit cumbersome and time consuming.
Use a shunt clamp - During charging, as each battery in the pack reaches a predetermined clamp voltage, shunt (switch) the current around the battery to the next battery in line. This process is better known as equalization because every battery in the pack is “equalized” to the same maximum beginning voltage. This requires extra switching circuits that can be tricky for high voltage and high current applications.
Shuffle the charge - During operation constantly move some charge (current) from batteries with a high SOC to batteries with a low SOC. This requires even more complex circuits and can be limited by how much current can be moved at any time. It works well if the batteries don’t go through a lot of rapid deep cycling because it could take a while to complete all the shuffling. A failing battery in the pack could put a heavy demand on the shuffling system.
Monitor the pack - Continuously monitor the individual battery voltages in the pack and create a maintenance flag to replace the failing battery. This can cause disruptive and costly down time if not well planned, and typically requires many sensors, extra wiring connections, data acquisition network, some form of processing and reporting (display). This approach is commonly used in addition to balancing and equalization.
Use a passive network - Connect a resistor in parallel with each cell in the pack. This is a cheap and easy equalizing voltage divider that may work well depending on the resistor value and the length of time available for voltage equalization. However, it can create inefficiencies, generate extra undesired heat, and shorten the battery pack life because of extra deep discharges.
Others - Dozens of issued patents and published patent applications offer a source reference for finding other schemes to solve this problem.

By managing the battery pack SOC and limiting the operation to stay between a full charge and full charge depletion, battery pack life can be significantly extended.

Why is it bad to fully deplete the pack? Some battery chemistries change the composition of the electrode surfaces at the extreme ends of the SOC (fully charged or full depletion). For example, lead acid batteries at a depleted SOC deposits a sulfate coating on the plates thereby reducing the available electrode surface area. The electrode surface area is where the electric action takes place and the amount available determines the battery performance. Other chemistries such as Li Ion seem to be much less susceptible to electrode damage. However, all chemistries are susceptible to individual cell damage due to imbalances at the extreme ends of the SOC. Most battery pack manufacturers will recommend operating in the middle 30% to 50% SOC for optimum battery pack life.

Take the Toyota Prius as an example. Toyota does extremely well in the battery pack design and operation in the Prius hybrid car. The Prius Nickel Metal Hydride (NiMH) battery pack has 800 to 2000 full charge cycles because of the nature of the battery chemistry. However, by allowing use of only 7% of available battery capacity (usually in the middle of the SOC, about 50-60%), Prius’ battery packs are achieving 8 to 10 years and 100,000 to over 300,000 mile life of the pack. When Toyota says you can drive the Prius on electric alone, this really means the system allows you to drive on electricity alone using 7% of available SOC before the engine comes on for recharging. Because pack life performance has been much better than expected, Toyota has increased the operating SOC range to 15% to increase driving efficiency by capturing more of the braking energy.

The only downside of all of this complex battery pack SOC management is the fact that you are carrying around all the extra battery weight that it appears does not get used. You charge the battery pack only to 50-60% SOC, then use only 7% of that before recharging again. You may be tempted to somehow shave off battery weight to lighten the load the car has to lug around. In reality, it’s actually cheaper to extend the life of the battery pack (through maintaining ideal SOC range, hence heavy battery pack weight) than to save fuel by carrying around less weight.

Similar considerations apply to plug-in hybrids and all electric vehicles that we are going to look at in future posts. You probably don’t need to know all this to drive your hybrid or electric car, but you can give yourself extra battery life by taking advantage of every convenient charging opportunity and not waiting until the battery is fully depleted. We’ll talk more about leakage depletion and how to avoid shelf life damage.

Design Considerations for Keeping Your Battery Pack in Top Performance: Balancing and Equalization vs. Pack Monitoring is a post from: CleanCarTalk

Building Reliable High Power Battery Packs: Here Are Some Practical Considerations

Tom Bartley — Sat, 21 Mar 2009 00:37:11 +0000

For the most part, today’s car batteries are driven by low cost mass production economies of scale. They are still the same fast discharge, slow charge energy storage device required to start an engine. Technology improvements have evolved in the areas of chemistries, shelf and cycle life, performance environment, maintenance, packaging, and recycling. They all contribute toward offering more choices to the discriminating battery consumer.

Lead-acid is still the most popular choice for battery chemistry because the elements are cheap and production techniques are well known. Recycling efforts have reduced much of the damage previously done by discarding old lead-acid batteries.

No matter what the chemistry, however, battery selection always starts with power and energy; the good old P and E. The battery has to have sufficient power over a long enough time to meet the peak load demand, e.g., turn the starter motor for a minimum of 3 10-second starting attempts. Because power equals current times voltage

P=IV, and

resistance heat losses (which is also expressed as a form of power) equal the current squared times the resistance

P(loss)=(I²R),

it is desirable to keep the voltage high and the current low for better efficiencies. Also, I²R not only describes the quantitative losses but also is real heat that must be dissipated to prevent high temperature damage to nearby materials. The resistance that causes heat loss can come from many components within the electrical system including parts of the battery itself or the wiring or connections.

Minimizing the resistance is always a challenge. And because there is a limit to minimizing resistance in the battery or heavy-duty cables, the discriminating vehicle designer must look toward using higher voltage batteries to get the power needed to drive the hybrid or electric car. That is why over 50 years ago car manufacturers switched from 6-volt starting batteries to the 12-volt car battery that is now common. Many heavy-duty buses and trucks use two 12-volt batteries in series to provide electrical power for 24-volt accessories. Several years ago there was an attempt to move to 42-volt car and truck batteries, but it didn’t catch on because of the proliferation of inexpensive 12-volt and 24-volt accessories.

In practice, for vehicle applications it is highly desirable to keep power currents less than 200 amps with only momentary spikes going higher. For example, if the power circuit has the small resistance of 1 ohm, at 200 amps the waste heat generated (I2R) is 40 kW, about the same heat put out by 40 hairdryers.

Making Battery Packs – The Key to Higher Voltage

The only way to get higher voltage battery packs is to “stack” or connect battery cells in series. Cells are essentially individual chemical batteries, and can be technically defined as “a vessel containing various chemicals which produce electricity as a result of the reactions taking place between these chemicals.”

So far so good, we’ll just stack the cells in series to get higher voltage and use larger cells or parallel stacks to get higher current and the problem is solved, right? Not so fast.

The first real world problem is that each of the stacked cells is not identical to the other cells in the stack because of slight differences in the fabrication processes and materials, i.e. manufacturing tolerances. The net result of differences in cell capacity, cell resistance, and leakage current is to cause the voltage to vary across each battery cell in a stacked pack.

When charging or discharging a series connected battery pack, each cell has exactly the same current as the whole pack. Because of the difference in resistance from cell to cell, repeated charge/discharge cycles of the pack cause the voltage variations between the cells to increase. Also, for the same charging current a lower capacity cell will wind up with a higher voltage than a cell with higher capacity; and for the same discharging current the lower capacity cell will have a voltage that drops faster than the cell with a higher capacity. Even if the pack sits on the shelf, over time the cells will have different voltages because of the variation in leakage currents (parasitic self discharge).

All this means that, as the state of charge (SOC) variations among the cells increase over time, some cells will eventually get excessively charged and some cells will get excessively discharged. In either case the cell is destroyed, typically resulting in a high cell resistance. Higher resistance means more heat generated during high currents and can result in a high enough temperature to melt materials and cause battery fires. If we’re lucky enough, the damaged cell will just short out, and the overall pack voltage and corresponding power capability will just be reduced. In either case, “unbalanced” voltages can result in destruction of the pack rather quickly as the best cells and the worst cells continue to be picked off from either overcharging or over-discharging. In a series connected pack it only takes one cell to fail in the open condition or “burn out” for the whole pack to fail.

So now you have some understanding on how high voltage battery packs can be built to power hybrid and electric cars. There are always challenges involved, and the best designs will have to take advantage of new materials, designs, and compromises between many important physical and operational considerations the system must withstand in both typical usage and worst-case driving scenarios.

How does all this affect my hybrid and electric car? Look for my next post.

Building Reliable High Power Battery Packs: Here Are Some Practical Considerations is a post from: CleanCarTalk

Rechargeable Car Battery Development: From Buggies to Hybrids and Electric Cars

Tom Bartley — Fri, 13 Mar 2009 01:40:40 +0000

Electric cars with an electric motor and rechargeable batteries developed quite early. However, the first person that experienced a dead battery before returning to the charging port realized that battery capacity and vehicle running range could be a problem.

Top: U.S. Army Neighborhood Electric Vehicle (NEV) courtesy my.barackobama.com; Center: Light rail photo courtesy Sound Transit; Bottom: EnerDel Lithium-Ion Battery courtesy transportation.anl.gov

The Rechargeable Car Battery

So, the gasoline powered “buggy” was much more accepted and the historical development of rechargeable car batteries satisfied the need for having a way to start the engine without having to rely on a “gorilla” companion to turn the engine crank. Thus, was born the battery, the starter motor, and the generator to recharge the battery.

Batteries were designed for rapid discharge (turning the starter motor) and slow charge from an engine driven generator. Once someone discovered that on-board electric power was available, they added electric accessories such as lights, radio, dashboard gauges and windshield wipers. Except for the accidental occurrence of someone leaving on an accessory (like headlights or vacuum tube radios) without the engine running, batteries were not slowly discharged during normal use.

Deep Discharge Batteries

Pushed by boats and RVs, eventually the lead electrode plates in lead-acid batteries were designed to be more tolerant of slow discharge deep cycle operation. These relatively cheap deep discharge batteries became the choice for electric cars and experimental hybrid-electric cars in the 1980s and early 1990s. The cost of electric energy compared to gasoline was starting to look more attractive, but battery range and replacement cost was still an issue.

Electric Golf Carts

The most successful relatively low power electric vehicles developed and still in operation today are electric golf carts. Golf carts worked very well for what they were designed to do, but they wrongly gave newly developed, road-going electric cars a reputation for being sluggish and slow. The number of miles a cart could be driven around a golf course on a single daily charge was not a problem. On the other hand, charge/discharge cycle life and replacement cost became the primary concerns.

Electric Street and Rail Cars

The very successful non-battery electric vehicles developed and still in use today are the self-powered electric street car and light rail cars with overhead electric power lines. The electric rail cars were efficient, but quite heavy and needed high power levels that could only be supplied by overhead high-voltage heavy-duty wires.

Neither the electric rail cars nor the battery electric cars addressed the capture of braking energy during deceleration because it was not yet realistic or deemed of any importance. With more attention given to fuel efficiency and obtaining higher miles per gallon of fuel, capturing of previously wasted braking energy now becomes much more important. It is in fact one of he major factors allowing modern hybrid and electric cars to increase their mileage performance.

Batteries for Electric Cars

This leads us to the modern electric cars and how they are shaping the development of batteries chemistries and battery packs. The challenge is and will continue to be designing hybrid and electric cars to function just like the fossil fuel-powered vehicles they replace, but with better fuel economy, lower emissions, and at affordable price points. Progress in battery development continues toward recharging a battery in the same time it takes to fill up a car, but can the infrastructure handle it?

Rechargeable Car Battery Development: From Buggies to Hybrids and Electric Cars is a post from: CleanCarTalk

Converting Fossil Fuel Energy to Battery Energy: Understanding Your Electric Car

Tom Bartley — Tue, 10 Mar 2009 06:41:21 +0000

A word about battery “power” and “energy“: Batteries store energy and supply power. It’s that simple.

But in casual conversation both words are tossed around to mean just about the same thing. Here is a primer to help keep your powers and energies straight. Warning: you’ll exercise your brain in this post, so read on at your own risk.

Electrical Power and Energy

First let’s look at units of measurement and how to convert from one unit to another.

In physics, power is strength; and energy is how long the power keeps going or, simply, energy equals power times time. Power and energy are both units useful to describing the performance and capability of batteries. Power is expressed in watts (W) or kilowatts (kW, or 1,000 W) and energy is expressed watt-hours (Wh) or kilowatt-hours (kWh, or 1,000 Wh).

To help explain power and energy in context, here’s an illustration. The San Diego Gas & Electric company (SDG&E) provides power to my home in San Diego and on my electric bill I am usually charged between $.13 and $.15/kWh of energy used. For comparison, typical amounts charged for electric energy in the U.S. range from about $.02 to $.20 per kWh with a surcharge if the power exceeds a threshold level. The national average is reportedly about $.08/kWh. The City of San Francisco pays about $.024/kWh because they own the hydroelectric dam. And Disneyland pays the City of Anaheim about $.04/kWh in the middle of the night when power demands are low.

So that’s how we quantify electrical power and energy. To compare energy from batteries with other sources of energy (natural gas or gasoline, for example), we need to know how to express energy in these fuels.

Energy in Fuels

Fuel combustion chemists like to use energy units of calories (cal) and British Thermal Units (Btus). Natural gas (CH4) is sold by the Btu and liquid fuels are sold by the gallon (or liter) with a specification of Btus per gallon. Again SDG&E provides my gas in San Diego and on my gas bill the average charge is about $.88/therm, where a therm is equal to 100,000 Btus, which is a little less than the energy content of a gallon of gasoline (about 114,100 Btus). To relate natural gas and electricity, 1 kWh = 3,414 Btus or 0.034 therms and 1 therm = 29.3 kWh.

Are you confused yet? Then forget what you just read above. Here’s a summary:

1 therm = 100,000 Btus
1 gallon of gasoline = 114,100 Btus
1 kWh = 3,414 Btus or 0.034 therms
1 therm = 29.3 KWh

Feeling smart yet? Then here’s a question: which is cheaper for me to use, my gas (natural gas) or my electricity? As you might expect, the answer is: My gas is cheaper (at $.03/kWh), because most of my electricity is generated by burning that same natural gas to convert to electricity and there are always energy losses in the process.

Energy of a Moving Car

Car designers like to talk about power and gallons of gasoline rather than energy. They like to use units of horsepower (Hp) where 1 Hp = 746 W. The basic energy content of gasoline is 114,100 Btus or 33.4 kWh before conversion to mechanical energy (by burning in an engine). Because of engine efficiency losses and other factors, less than 1/3 of the fuel energy is actually available as mechanical energy at the engine output with the rest being lost as heat energy.

The energy of a moving car can be calculated using the formula below. The letter x is used as the multiplication sign.

Energy = (Weight/64) x (Speed)²
where Weight is the weight of the car and Speed is its speed at a given time.

As you can probably guess, we’re really looking at a supply and demand situation. On the supply side we have energy provided by the fuel (gasoline energy through the engine or battery energy through the electric drive motor). On the demand side we have the car with a certain mass/weight required to go at a certain speed. As mentioned above, there is always efficiency or loss of energy involved when converting from the energy supply to what the car demands.

So knowing the energy of the moving car and how long it took to get to that speed, and the energy of the battery or gasoline engine expended to get there, we can start to understand the energy efficiencies of the car’s propulsion and the acceptable performance provided by the available power level.

To keep this analysis simple and easy to understand, I have ignored various other elements that need to be considered such as discussion on the weight and speed as related to the units of power (kW or Hp) and energy (KWh or Hph). However, to play in the intelligent bantering about of power and energy in transportation and vehicle efficiency issues requires a ready reference book of conversion factors between units and a reliable associate to check the calculations. (Even the most experienced professional can occasionally be caught forgetting that a pound force = 32 x pound mass.) I sometimes use the Internet and reliable websites for a quick source of reference conversions.

Using Batteries to Power the Cars

I hope you now have good background basics on gasoline and battery power and energy, and their relationship as applied to all kinds of vehicles, including cars. With the proper relationship and conversion factors in place, we can begin analyzing and comparing gasoline and battery electricity in plug-in and hybrid vehicles.

The next step is an exciting one. We’ll discuss how batteries, as the primary energy source, are put in cars and look at characteristics that determine range, operating cost, and battery replacement.

Converting Fossil Fuel Energy to Battery Energy: Understanding Your Electric Car is a post from: CleanCarTalk

Harnessing Electrical Energy: Batteries and Battery Packs Explained

Tom Bartley — Fri, 06 Mar 2009 05:03:03 +0000

Ever wonder what battery packs really are? Here’s a little bit of an introduction to help ease the mind into the pondering of batteries with hopefully painless acquisition of the required jargon.

What is a Battery?

In general terms (not scientific), a battery is a hunk of something that has some stored energy that can be accessed to convert into some other energy. Energy can come in a variety of forms, such as gravitational, heat, light, sound, motion, pressure, and electromagnetic fields. For practical purposes Newtonian physics is all you need to understand the principles and operations of batteries. Energy cannot be destroyed, but can only be converted into some other form.

I can argue that a rock held up in the air, just like the water behind a dam is a battery with potential energy (gravitational) waiting to be converted into kinetic energy (motion). Similarly, a rotating flywheel or a moving vehicle has kinetic energy that can be converted into other energy forms. Even a wound up spring or a pulled back catapult could be thought of as a battery with stored energy.

In electric circuits energy is stored as an electric field in capacitors and as a magnetic field in inductors. Batteries, as commonly referred to, store and release electrical energy by a chemical reaction of compounds inside the batteries. Batteries are either primary (single use) or secondary (rechargeable).

Harnessing the Energy

In today’s society almost everyone is familiar with the small button, small flat module, and cylindrical shapes for batteries that power all kinds of electric gadgets including, toys, watches, phones, cameras, radios, flashlights, computers, and model vehicles (air, surface and water). Larger battery packs start and run cars, trucks, boats and airplanes. Even larger packs provide backup power for communications, control systems, buildings, and transportation systems, or in smoothing out load and generation power spikes.

Looking from a different perspective, batteries can be considered a time buffer between the generation and the eventual use of energy. A perfect example is solar and wind energy that may be collected and stored for energy load usage at a later time. Or hydrogen could be thought of as a battery (though somewhat inefficient). First hydrogen is separated out from water through the electrolysis using electrical power. Then the hydrogen can be used at a later time in a machine such as a fuel cell or engine-generator set to deliver power and energy.

So again, a battery is a hunk of something that has some stored energy that can be accessed to convert into some other energy. And since energy cannot be converted with 100% efficiency from one form to another, the final form of energy you get will always be less than what you started with. Obviously the more times you convert, the more losses you’ll have, and the less you’ll have left to use.

So What Are Car Batteries Then?

Car batteries are electrochemical batteries for cars and trucks. Primary batteries (single use) are out of the question for this application and are appropriately limited to devices like flashlights and toys.

In car batteries the energy is stored as electrochemical potential energy in the battery materials that make up the battery electrodes and the electrolyte that provides a path for electrically charged particles moving between the electrodes. We refer to this as “the battery chemistry.” A chemical reaction occurs to store energy and the reverse chemical reaction occurs to release that energy.

I have attended conferences where electrochemists speak a jargon all their own to describe combinations of new electrodes and electrolytes that have various voltage potentials and other characteristic tradeoffs. For car batteries, there are multitudes of desirable characteristics, many of which can conflict with one another. Here are a few:

Safety,
Light weight (high energy density, high power density),
Quick charging,
High power,
Extended use (high energy storage capacity),
Operation over a wide temperature range,
Inexpensive,
Long shelf and operation cycle life,
Easily manufactured, and
Easily recycled.

This reminds me of something that I used to tell customers, “You want high quality, fast delivery, and cheap? Pick two!”

So what do you do when higher energy and/or power is needed? It’s actually pretty simple. Batteries can be assembled as multi-cell battery packs and packs of packs. In fact with all the buzz about hybrid and electric cars, battery packs are the hot devices (no pun intended) that currently propel the whole high-voltage, high-energy storage system industry. A battery pack manufacturer must follow an expensive process to bring its products to the consuming market. It has to spend time, money and effort in research, development, testing, production, distribution, charging, and salvaging/recycling. With many consumers still on the fence about buying hybrids and electric cars, the real question is, “where’s the money?”

If I’m thinking about buying a hybrid-electric vehicle (HEV) or electric vehicle (EV) what do I need to know about batteries? If I am converting a car or building a battery pack what else do I need to know? What is my current level of confusion? (Confusion is a prerequisite to understanding.)

All comments are welcome.

Harnessing Electrical Energy: Batteries and Battery Packs Explained is a post from: CleanCarTalk

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