Keeping electric-vehicle batteries cool

Keeping electric-vehicle batteries cool

By: Karel Smrcka

27th July 2012 

Batteries provide the ‘fuel’ that drives electric cars – in effect, the vehicles’ lifeblood.

If batteries are to have a long service life, overheating must be avoided. A battery’s ‘comfort zone’ lies between 20 ºC and 35 ºC. But even a Sunday drive in the midday heat of summer can push a battery’s temperature well beyond that range. The damage caused can be serious, as operating a battery at a temperature of 45 ºC instead of 35 ºC halves its service life.

Batteries are expensive – a new battery can cost as much as half the price of the entire vehicle. That is why it is important to keep them cool. Thus far, conventional cooling systems have not reached their full potential. They are either not cooled at all – which is the case with those that are simply exchanged for a fully charged battery at the ‘service station’ – or are air-cooled. But air can absorb only very little heat and is also a poor heat conductor. What’s more, air cooling requires big spaces between the battery cells to allow sufficient fresh air to circulate between them. Water-cooling systems are still in their infancy. Though their thermal capacity exceeds that of air-cooling systems and they are better at conducting heat away, their downside is the limited supply of water in the system, compared with the essentially limitless amount of air that can flow through a battery.

In future, another option will be available for keeping batteries cool – a coolant called CryoSol-plus – a dispersion that mixes water and paraffin, along with stabilising tensides and a sash of the antifreeze agent glykol. The advantage is that CryoSol-plus can absorb three times as much heat as water and functions better as a buffer in extreme situations like trips on the freeway at the height of summer. This means that the holding tank of the coolant can be much smaller than that of water – saving both weight and space under the hood.

In addition, CryoSol is good at conducting heat away, moving it quickly from the battery cells into the coolant. With additional costs of just €50 to €100, the new cooling system is only marginally more expensive than water cooling systems. The coolant was developed by German researchers at the Fraunhofer Institute for Environmental Safety and Energy Tech- nology, in Oberhausen.

As CryoSol-plus absorbs heat, the solid paraffin droplets within it melt, storing the heat in the process. When the solution cools, the droplets revert to their solid form. Scientists call such substances phase-change materials, or PCMs.

“The main problem we had to overcome during development was to make the dispersion stable,” explains Tobias Kannels, a scientist at the institute.

The individual solid droplets of paraffin had to be prevented from agglomerating or – as they are lighter than water – collecting on the surface of the dispersion. They need to be evenly distributed throughout the water. Tensides serve to stabilise the dispersion, depositing themselves on the paraffin droplets and forming a type of protective coating.

“To find out which tensides are best suited to the purpose, we examined the dispersion in three different stress situations. How long can it be stored without deteriorating? How well does it withstand mechanical stresses? And how stable is it when exposed to thermal stresses – for instance, when the paraffin particles freeze and then thaw again?” asks Kappets.

Other properties of the dispersion that the researchers are optimising include its heat capacity, its ability to transfer heat and its flow capability.

The scientists’ next task will be to carry out field tests, trying out the coolant in an experimental vehicle.

Edited by: Martin Zhuwakinyu

Industry says there will be enough lithium - but will there be enough graphite?

cars21.com - Everything Electric

The Leaf's battery needs 20kg of lithium but 40kg of graphite, the Tesla Roadster's battery needs even 100kg of graphite. While discussions about the scarcity of lithium were vivid 1-2 years ago and have now ebbed down, nobody has discussed yet the supply of graphite, indispensable anode material, to facilitate a large uptake of electric mobility.

While EV uptake might be not as fast as forecast last year, investments into battery plants are still high. GS Yuasa invests $300 (~ €245) million to expand their battery production facilities, LG Chem invests the same amount in a li-ion battery plant in the US to supply the Chevy Volt, Russia had announced to put $420 (~ €342) miilion into completing the world's largest li-ion battery plant.....

But if only 5% of cars worldwide were to become electric, current graphite production would need to double, says Greg Bowes, CEO of Northern Graphite (see exclusive interview tomorrow), who has a graphite mine development project in Bissett Creek, Ontario, Canada.

Graphite - the anode material of choice

Graphite has already been the anode material of choice for the alkaline batteries in the 1950ies, passing by the nickel hydrogen batteries in the 1970ies, the nickel metal-hydride in the 1980ies and finally the lithium-ion batteries since the 1990ies. Batteries are the fastest growing end use for graphite and EVs hold the potential to see graphite demand boom.

Why is graphite so popular as anode material? 

The anode requires a porous carbon material and graphite is the optimum match. Graphite is also:

• easy to machine (not true of natural graphite, only synthetic)
• very resistant to thermal shock
• does not melt in the battery (melting point at above 3,600°C) which reduces wear
• has a density 5x lower than copper and is therefore lighter
• is insoluble in water, acids & bases;
• is not corrosive

How much graphite does one EV battery pack need? 

There are 3-10 kgs of graphite in the average HEV and 25-50 kgs in an EV. Estimates are that increasing demand for lithium carbonate will reach 286,000 tonnes by 2020. This would mean a six fold increase in annual flake graphite production to provide material for that many batteries. Graphite demand in li-ion batteries in 2008 was already estimated at 44,000 tonnes, i.e. ~ 10% of the flake graphite market - with a persisting upwards trend.

The Nissan Leaf, for example, is equipped with a 24kWh battery pack containing 20 kg lithium carbonate and 40 kg graphite. The Tesla Roadster needs 100kg graphite for its 56kWh battery pack. The average recharge time of the Tesla Roadster is 3.5h, average range 400 km and average battery life 160,000km.

Only spherical (potato shaped) graphite can be used in batteries. This requires flake graphite to be upgraded to 99.95% purity - an expensive process that wastes 70% of the feedstock of flake graphite. Therefore, spherical graphite sells for more than 3 times the price of flake graphite. currently $6,000-8,000 (~ €4,900-6,500 per tonne.

World Production

China dominates world graphite production and represents 75% of total output. India is the second largest producer followed by Brazil, north Korea, Austria and Canada.

EVs always cheaper to charge than ICEs

According to a study from Northeast Group, 6% of all utilities located in the United States had implemented special electric vehicle (EV) tariffs as of the end of June 2012. Electricity tariffs designed specifically for EV charging are a key driver to EV adoption, as EV tariffs are cheaper than standard residential electricity tariffs.

The study, ”United States Smart Grid: Utility Electric Vehicle Tariffs,” includes a benchmark of the EV tariffs of ten different utilities in six different US states (California, Georgia, Michigan, Nevada, Oregon and Texas).

“In all scenarios we studied, the costs to recharge an electric vehicle were cheaper than fueling a gasoline-powered car. In the most likely EV charging scenarios, costs were approximately one-tenth to half the costs of fueling a conventional vehicle with gasoline,” according to Northeast Group, LLC.

Eleven US states concerned so far

In just the past year, utilities in Arizona, California, Indiana, Michigan and Virginia have added new EV tariffs. In Hawaii, Michigan and Nevada, more than 90% of state residents already have access to EV tariffs through their various utilities. California and Georgia are next in line, where more than 80% of state residents have access to EV tariffs. The large California utilities were early pioneers in launching EV tariffs. As EV numbers grow over the coming years, EV penetration rates are likely to be higher in states with utilities offering their customers special tariffs.

Smart charging without smart grids

EV tariffs offered by utilities have been structured in two main forms to-date: time-of-use (TOU) tariffs and flat rate tariffs. TOU tariffs typically provide for cheaper overnight and off-peak rates for those recharging EVs. Flat rate tariffs charge customers one fixed monthly fee for recharging EVs. In addition, sliding scale tariffs – where rates increase with usage - can also be incorporated in some form with both tariff structures above.

“With the TOU tariffs, customers receive cheaper rates when they charge during off-peak times (typically nights and weekends). With the flat rate tariffs – e.g.$40 (€33) per month – all charging is typically covered. Utilities are now studying which tariffs will best accommodate the increasing number of electric vehicles on US roads” according to Northeast Group, LLC. “. EV tariffs can save approximately half the cost per year for EV owners, compared with standard electricity tariffs.“

State of art in Europe

Nothing exists at the European-level regarding EV tariff. However, off-peak rates exist and OEMs have tried to make it easy for EV owners to set up the charging of their EV at a chosen time through smart meters or via a smartphone application such as Nissan.

Nevertheless, there is interest in Europe for having EV tariffs implemented, such as Narec's Chief Technical Officer,Steve MacDonald, who, speaking at Utility Week's electric vehicle (EV) conference in June 2012, said that “energy suppliers should offer consumers home charging points with smart functionality and a specific tariff for EV owners to help support the take up of EVs.”

cars21.com - Everything Electric

Headline Story | equities.com

Qualcomm and Renault Announce Memorandum of Understanding on Wireless Electric Vehicle Charging Technology

 | equities.com

Qualcomm Incorporated (NASDAQ: QCOM) and Renault s.a.s. today announced a Memorandum of Understanding (MoU) concerning their intended cooperation on the London trial of Qualcomm Halo™ Wireless Electric Vehicle Charging (WEVC) technology, and their intent with respect to conducting preliminary studies of the integration of this technology into Renault vehicles. Renault will also join the London trial steering committee.

One-Stop Shop

KTA Services offers a multitude of services to its customers. KTA creates the opportunity for individual and professional converters to find the products and services in one unique place, making the purchasing experience convenient and efficient at the same time.Compared to visiting a separate institution for each area of need, the "one-stop shop" concept saves our customers a lot of time, effort and money.

Sample Kit

KTA is a distributor of new, competitively priced, parts and components that come with full manufacturers' warranties. We stock and sell the largest variety of the very best components and parts manufactured by the industry's most well known names.

To name some of our products, we carry controllers from Curtis Instruments, Evnetics and Alltrax; Motors from Advance Motors & Drives, Netgain and Hi-Performance; Battery Management Sysyem (BMS) from Elithion; Battery Pack Kits (Lithium and Lead Acid) and many other products that can be viewed in our Web-Store. We can tailor our  kits to fit the most diverse needs, in terms of power and price, to save your customers time and money.  Or, we could also help you to find a specific product or distributor using our extensive network and knowledge of the market .

KTA Vacuum System

Become a Preferred Partner

We provide free personalized Technical Support from beginning to the end of our client’s project. For established Conversion Shops, our Customer Service provides the support and peace of mind necessary to see your project come to a successful end. For those considering starting a new conversion business, we have the means to provide a more comprehensive support package including, but not limited to, business start-up consulting and marketing strategies. We are in a position to provide our partners with leads of customers looking for a shop to do their actual conversion project.

For those business partners interested in increasing their internet traffic to their websites, we can provide a link from our web-store. At the same time we can give some important pointers in how to increase your web ranking.

We also have developed for our preferred converters, a discount scale tied to the volume of sales in a determined period of time. This system allows small businesses to achieve its financial goals in an efficient and productive manner. Again, we are here to support your venture from beginning to end in every aspect of your business.

Overview of the Soliton1 & Soliton Jr Motor Controllers by Evnetics

The Soliton1 and Soliton Jr are motor controllers specifically designed to drive brushed DC motors (more specifically, series field) in electric vehicle applications. These motor controllers employ cutting edge technology and have a vast array of unique features: the main contactor with automatic precharge is built-in, a heatsink with both liquid and fan cooling, a state-of-the-art film capacitor on the input rated for the full ripple current (one-half to as little as one-fifth is typical!), and an ethernet interface that continuously streams live performance data and allows configuring the controller with an ordinary web browser! You run Linux or MacOS? No problem. Don't have a serial port on your computer? No problem. Despite the fearsome level of technology inside the controller, it is even easier to install and use than the venerable Curtis 1231C!

There are lots of details to consider and specs to compare when choosing a motor controller for your EV, but one of the most important considerations is how long you can get peak motor current and how often? Unlike the typical “shoe-box” style controller with little intrinsic ability to shed heat, Evnetics controllers have a massive machined aluminum, fan-cooled heatsink which give them unparalleled continuous power capability even before liquid cooling – which they also feature – is used. Other controllers may deliver a higher peak current for some brief (and usually unspecified) amount of time, but none can deliver the same amount of current for as long as the Soliton1. Period.

Raw power might be great at the drag strip, but without the ability to precisely and safely control that power, everyday driving situations like rush-hour congestion or pulling into a parking space quickly turn tedious. The throttle input to Evnetics' controllers directly controls motor current for an exceptionally smooth and natural driving feel, even at low currents and 0 RPM, and without emitting an annoying whine through the use of random pulse skipping, rather than an abrupt change in switching frequency.

Unlike other companies making EV-related products, Evnetics is comprised of a core development team with interlocking and complementary expertise in mechanical engineering, power electronics and embedded software design. To put it simply: we make better products not only because we want to, but because we can...

The Evnetics Core Development Team

Sebastien Bourgeois – Management/Mechanical Design

Jeffrey Jenkins – Hardware Design

Martin Persson – Software Design

Soliton1/Soliton Jr Specs and Features

•        9V-340V battery voltage range (output current reduced above 310V).

•        1000A max current (battery or motor) for the Soliton1; 600A max current (battery or motor) for the Soliton Jr.

•        Thermal derating smoothly reduces allowed current with temperature.

•        Main contactor and precharge/discharge control built-in!

•        Splash-proof (approx. IP55 rated) nickel plated aluminum enclosure.

•        Rugged design based on 600V industrial IGBT modules.

•        High reliability 600V film capacitors in the power stage – no electrolytics!

•        1.5V max voltage drop at max output current (0.8V is typical).

•        PID loop to idle the traction motor (for A/C, automatic transmissions, etc.).

•        State-of-the-art laminated bus structure extracts maximum performance from the IGBTs by ducing noise, ringing and spikes.

•        Full optical isolation between traction battery and 12V system.

•        Fully configurable with an ordinary web browser!

•        Performance data continuously streamed to the ethernet port.

•        Throttle directly controls motor current (torque) for a natural driving feel.

•        Motor current ramp rate can be set from 100A/s to 25kA/s.

•        Randomized pulse-skipping (“dithering”) maintains precise control of motor current all the way down to 0A for smooth starts and easy low speed driving without emitting an annoying whine.

•        Switching frequency selectable between 8kHz (Performance) and 14kHz (Quiet).

•        All low voltage connections protected against reverse polarity, spikes and treat 5V as maximum but tolerate up to 15V for convenience.

•        Tachometer input (1, 2, 3, 4, 6 pulses per revolution) for protecting against overspeed and idling automatic transmissions, a/c compressors, etc.

•        Brake input overrides throttle when active for added safety.

•        Reverse input reduces max throttle and motor voltage when active.

•        (3) programmable inputs (analog/digital) for reverse, throttle limit, start, etc.

•        (3) programmable outputs for driving analog meters, cooling pump control, etc.

•        Error light output can directly drive the “Check Engine” light in the dash.

•        3D CAD drawings of both controllers for planning installation ahead of time.

•        And, perhaps most importantly, we constantly strive to improve our products and add new features and functions!

Safety Recommendations for Electric Conversions by Wistar Rhoads & Ken Koch

INTEGRITY OF BODY, BRAKES & WHEEL BEARINGS

Most EV conversions wind up being from 400 to1200 pounds over stock weight. This represents additional strain on the body, wheel bearings, and brakes. Don't convert any vehicle that has cancer (road rust) because the additional strain could eventually cause structural failure of the body. It's mandatory that a conversion have the best brakes possible. When performing a conversion, always put on brand new brakes; use the best materials available. If the vehicle you're converting has power brakes, be sure to restore vacuum to the brake servo with a vacuum pump system. Also, check wheel bearings for signs of wear; if you have any doubts about them, replace them.

BATTERY PLACEMENT

Try to distribute battery weight throughout the vehicle for better handling as much as possible. Too much weight in the back of the car can cause over-steer with a sensation that the vehicle is too responsive to any change of steering wheel position. If there's too much weight over the front wheels, the under-steer created will make you feel like you're driving a snow plow. Also, try to place batteries as close as possible in the center of the car at a low position to lower the vehicle's center of gravity and to avoid the 'dumbbell' effect whereby the vehicle will yaw with each change of steering wheel position.

A vehicle is safer if batteries are kept out of the passenger compartment. If placement outside of the passenger compartment isn't possible, be sure to enclose and secure the batteries inside of a box structure.

SAFETY COMPONENTS AND SAFE TECHNIQUES

The power components in an electric vehicle propulsion system can be as simple as a motor, a motor controller, a set of batteries, and some cable to interconnect them. Using only these basic ingredients in the vehicle propulsion system will work. If you're lucky, you may never need additional components for safety.

This reminds me of the time a fellow was proof-testing components in a 2-seater dune buggy with no body. The propulsion system had no safe means of disconnecting battery power from the motor if a problem ever occurred. Sure enough, as Mr. Murphy might have it, the controller shorted out during a test run and the 'test mule' began to run away. Good thing that this fellow had a tool box sitting in the passenger's seat next to him. He was able to retrieve a hammer from the tool box, and after two well-placed swings he succeeded in knocking the post off of a nearby battery. This maneuver (at 50 MPH and climbing) interrupted power to the motor, and the vehicle was then brought to a stop. Brakes alone were not enough to stop the vehicle, and depressing the clutch would have caused the motor to blow. Fortunately, in this case, the only casualties were a battery with a broken-off post and some underwear that was badly in need of changing! The vehicle could have crashed or some part of the system could have caught fire.

This incident points to the fact that the more safety components you have in a propulsion system, the safer your vehicle will be in the event of some emergency condition, even if some seem redundant.

(1) FUSES. Fuses provide an instantaneous automatic interruption of power in event of a malfunction or short-circuit. No fuse is any good unless it is rated at the voltage/current/time characteristics appropriate to its application. Use at least one safety fuse in the main battery pack to protect system power components. An enclosed safety fuse such as the Ferraz-Shawmut is best because the fuse element is enclosed in a fire-retardant powder. A fuse link is usable, but with its open construction it can spew molten balls of metal when it blows. If a fuse link is mounted in the open over the top of a battery and it blows, molten balls of metal can burn through a battery case--causing a potential fire or explosion--or, at the minimum, a ruined battery. If using a fuse link, please enclose it in a piece of high temperature insulated tubing such as phenolic. Also, for maximum safety, any instrumentation line that ties into any part of the propulsion system should be protected with a small fuse of 1-amp or less that is mounted close to the propulsion system tie-in point. This will protect small gauge wiring from catching on fire if a short ever occurs within the instrumentation circuit.

(2) CIRCUIT BREAKERS. Whereas a safety fuse provides instantaneous automatic interruption of propulsion battery power in event of a malfunction, optional use of a circuit breaker can provide a fail-safe manual and/or automatic interruption of battery power in the event of a drive system malfunction. It also can be used to shut-off battery power during routine servicing of the system. A circuit breaker is no good unless it is rated at the voltage/current/time characteristics appropriate to its application. Use of a double-pole circuit breaker offers an advantage over a single pole unit by allowing both sides of a battery pack to be interrupted instead of just one. The circuit breaker should be mounted within easy reach of the EV driver for maximum safety.

(3) CONTACTORS. A contactor is used to switch high power remotely by means of a low-level control voltage--such as 12-volts DC supplied from a key-switch. In an EV propulsion system, high voltage, inductive loads, and extremely high current levels are encountered. A contactor should be correctly rated for the high voltage and current characteristics appropriate to its application. Even though a contactor's primary function in most EV systems is to carry current, the type used should be capable of breaking current to an inductive load (motor) In case of a shorted controller condition. This means that the contactor used should be fitted with magnetic blowouts which extinguish arcing--otherwise, a contactor could weld into a shorted condition if it can't break the arc. Magnetic blowouts work on the principle of Fleming's Left-Hand Rule. At least one main contactor should be used in a propulsion system to apply and remove main battery power to the motor and controller. Contactors used for electrical reversing should be fitted with magnetic blowouts as well.

(4) WIRE, CABLE, AND TERMINALS. Wire and cable used in an EV should be sized to safely handle the current being carried without overheating. Undersized wire can get hot or even catch fire. Manufacturers' amp capacity tables should be referred to when deciding which size wire to use. Use wire that has thicker insulation to maximize abrasion resistance in EV applications. When running heavy-duty cable underneath a vehicle, add abrasion resistance to the cable by enclosing it in PVC conduit or rubber heater hose. Put extra covering on wires that are routed through sheet metal with potentially sharp edges. Use copper wire, never aluminum. The debate on whether to crimp or solder terminal lugs onto heavy-duty cable ends may go on forever. Basically speaking, all lugs should be crimped onto wire ends using a proper crimping tool. Solder them too, if you like, but do crimp them. If a cable lug secured to a battery terminal ever becomes loose, it can become hot enough to melt the solder and separate. A crimped lug will hold to the cable because of its mechanical bond. Check all battery terminal hardware at least once per month and retighten as required.

(5) BATTERIES. Batteries, of course, should be securely fastened from moving around in an EV. The most common type used today for EV applications is the flooded-cell lead-acid battery. These have a liquid electrolyte and are unsealed. During approximately the last 20% of their recharge cycle they will produce a significant amount of hydrogen gas. Allow adequate ventilation for the hydrogen so that it doesn't collect and present an explosion hazard. Hydrogen ventilation can be assisted by using small fans. Never use a DC brush type fan in this application because commutation sparks can ignite the hydrogen. Always use brushless DC or AC fans. Also, when handling or working around batteries, always: (a) wear heavy-duty shoes to protect your feet and heavy-duty gloves to protect your hands and fingers (b) wear a face shield to protect your face and eyes in the event of an explosion (c) tape the unused ends of wrenches which are to be used for removing, installing, and/or tightening battery terminal bolts and nuts (d) place an insulating cover over all batteries which are adjacent to others being installed, removed, or serviced. A sheet of plywood will work fine.

(6) MOTORS AND MOTOR INSULATION. Use motors that are heavy-duty enough for your application. Don't try to use a 4 HP motor when a 10 HP unit is required, Motors that are undersized for an application will overheat and can eventually burn-up. Never use a motor that has an inferior insulation system or is constructed from inferior materials. Insulation systems are rated by 'letter' according to their temperature value. Use motors that are rated class 'F' (155 deg. C), or 'H' (180 deg. C). Better materials may cost more money but the added price is worth it.

One formerly-popular motor manufacturer used class 'B' (130 deg. C) insulation in his motors to save money. Because of inferior insulation, the armatures in nearly all of his motors eventually overheated and shorted out in electric car applications.

(7) FLOATING GROUND SYSTEM. For maximum safety, no part of the propulsion system should be connected to any part of the vehicle frame. Isolating the propulsion system from the frame will minimize the possibility of being shocked when touching a connection point such as a battery terminal and any part of the body or frame. It also minimizes the chance of having a short circuit to the frame if wire insulation becomes frayed and touches metal.

(8) FRAME GROUNDING AND BATTERY CHARGERS. In most EV-conversions, the frame and metallic body structure of the vehicle will carry the circuit return path for the 12-volt auxiliary power system (for lights, horn, radio, etc.). As mentioned in step (7) above, the frame shouldn't be connected to the propulsion system--but it can and should be used as part of the 12-volt auxiliary system. However, the frame and body should also be connected to the third-wire mechanical ground of the AC input power (green wire) whenever battery charger power is connected to the vehicle. Battery charger power connected to the vehicle can be DC, in the case of off-board chargers, or it can be AC, as in the case of on-board chargers. Making this third-wire mechanical ground connection will prevent potential shock hazards when the vehicle frame or body are touching and while the batteries are being charged. Transformer-type chargers, in and of themselves, do not always insure against frame and body shock hazards. Chargers without transformers should always have a ground fault interrupter (GFI) installed on their AC inputs, preferably ones that are UL listed or approved.