Adventure EV

The Knowledge: Battery Tech. What’s on everyone’s mind… range.

by on Dec.05, 2009, under Batteries, EV Land Rover, The Knowledge

In an, apparently, ongoing series of articles, not directly involving my build, that I will now categorize under the title, “The Knowledge”, I present to you… Battery Tech.  Yes, it’s another boring theory post, but hey, you might learn something.

I’ll cover a bit about the types of batteries that go into your average DIY EV, address the issue of hybrids, and quickly shut down the perpetual motion and over-unity fans.

I wish I could show you pictures of my batteries, but I don’t have any yet… so for now, you’ll have to stare at random stuff I found across the interwebs.

Batteries

Range anxiety.  It’s the EV’s skeleton-in-the-closet.  Everyone seems to preoccupied with how far you can go on a charge, and that comes down to the batteries.

Battery technology is evolving quite rapidly these days.  The key to energy storage is how much energy you can cram into a given amount of weight.  Obviously, the higher the energy density the longer the range.  Here’s a breakdown of the most mainstream battery types for EV use in order of their energy densities:

Energy Densities of Different Battery Chemistries

Battery Type Energy Density (Wh/kg) Cycle Life
Lead Acid (Pb) 30-50 100-300
Nickel Cadmium (NiCd) 45-80 500-1500
Nickel Metal Hydride (NiMH) 60-120 500-1000
Lithium Polymer (LiPo) 100-130 2000-7000
Lithium Ion (LiIon) 110-160 1200
Alkaline (non-rechargable) 110 NA

It’s amazing what we can develop when we put resources behind it.  Some of it isn’t as new as you might think.  Lithium battery chemistries have been around for a few decades, now.  Lithium Ion first saw commercial use in the early 90s.  I always thought they were a relatively new development.  And Lead has been around since the middle of the 1800s.  Battery tech isn’t new, it’s older than the internal combustion car.  EVs aren’t just the future, they were the past.

Lead Acid, the very same battery that powers the 12v electronics in your conventional car, is the cheapest way to provide energy storage for an EV, but as you can see from the chart it’s also the least energy dense.  Lead is one of the heaviest metals on the periodic table, hence it makes for some of the heaviest batteries.  Typical Lead EVs have ranges between 10 and 40 miles per charge.

Lead Acid Batteries

While “Lead Sleds” may initially be inexpensive to get into, Lead has some serious disadvantages over the long haul.  Their limited cycle life means they need to be replaced every couple of years.  They also don’t like being drained of all their energy.  Sapping more than about 50% of the storage capacity of a Lead battery severely shortens its cycle life.  So, not only do you get the least amount of energy storage, with Lead, but you can really only use about half of it… and they don’t last as long.  But they’re cheap.  A conventional set of Lead batteries for an EV can go for $1000-2000.  If you’re on a tight budget and your range needs aren’t extravagent, Lead can make sense.

The middle technologies, NiCd and NiMH really don’t get much play in the homebuilt EV world.  NiCd has about the same storage capacity as Lead but benefits from a much greater cycle life and durability.  The problem is, it’s ten times more expensive.  So it really doen’t make much sense for the home EV builder.

Nickel Cadmium Battery Pack

NiMH is also expensive, but it’s the battery of choice for today’s production hybrid car producers.  The technology has been proven to be quite safe and reliable, if not the highest performing.  This has probably more to do with the way the OEMs utilize the cells.  The Toyota Prius uses a NiMH battery pack, but it’s rumoured the electronics only allow the pack to be charged to about 50% capacity and then only allowed to discharge about 7% before being charged back up to 50% again.  It makes for an extremely long lasting battery since it’s never pushed, but that’s carrying around an awful lot of unused battery.

Nickel Metal Hydride Battery Pack

Then we come to the high rollers of the battery world, the Lithium chemistries.  Lithium Ion has the highest energy density of all the mainstream commercial battery chemistries.  Lithium Cobalt (LiCoO2), a form of LiIon technology is the same stuff that powers your cell phone, laptop, or even the Tesla Roadster (powered with 6831 AA-sized cells) .  It’s expensive stuff, but since Lithium is the lightest metal on the periodic table it makes for the lightest batteries.

The biggest problem with a battery like Lithium Cobalt, apart from cost, is safety.  These are the same cells that were seen catching fire in laptops.  If something goes wrong with one of these, they go into a thermal-runaway chemical reaction, and poof… there goes whatever you were powering.  They’re getting safer every day, but the explosive potential is always there.

I’m using Lithium cells in my conversion, but I’m using a Lithium Polymer cell, a variant of the Lithium Ion technology.  Lithium Polymers were the most recently developed type of cells, first seeing use in the early part of the decade.  The most popular format for EV converters has become the Lithium Iron Phophate cell (LiFePO4).  In recent years they’ve really become a real game changer.

Thundersky LiFePO4 Battery CellLiFePO4 cells aren’t as energy dense as a Lithium Cobalt battery, but they also don’t do the whole blow-up-if-there’s-trouble thing.  They’re also cheaper to manufacture and have very long cycle lives.  While Lead gives up the ghost after only 300 charge cycles, LiFePO4 cells might see upwards of 3000 cycles while using 80% of the capacity of the cell!  If you drove 50 miles per charge that’s 150,000 miles.

LiFePO4 cells being studied at the US Department of EnergyLabratories in New Mexico have hit 7000 cycles and are still going.  This kind of cycle life surpasses even traditional Lithium Ion technology (~1200 cycles), making the Lithium Polymer cell one of the most economical chemistries over the long run.

LiFePO4 is also completely non-toxic and recyclable.  Even at the end of their useful lives in EVs, the cells can be reapportioned for use in solar power installations as storage, since weight isn’t an issue in this capacity.

Faster, lighter, farther, longer, safer…  Sounds too good to be true.  Well it could be but for the hard initial pill to swallow.  The price of admission to the LiFePO4 party isn’t exactly cheap.  A typical EV battery pack that would provide between 50 and 150 miles of range could cost between $6000 and $20,000.  When considered over the life of the pack, though, LiFePO4 becomes about as economical as Lead.  It’s just a very large initial investment.  While Lead will have to be replaced every couple of years, the LiFePO4 pack should last over ten… and you get the added benefits of better range, lighter weight, and higher performance.

As automakers scramble to offer pure EV cars to the public, many are planning on using LiFePO4 technology.  This will surely drive the cost done for the future.

And the future is bright.  New chemistries continue to crop up all the time.  Companies are trying to develop ultra-capacitors, lightweight electronic storage devices that are capable of storing energy and releasing it very quickly.  While capacitors traditionally don’t have anywhere near the storage density of even the lowliest battery, a company, EEStor, is claiming that their ultra-capacitor design will be capable of storing close to 700 Wh/kg, some six times greater density than Lithium Ion, and that the technology will cost $40 per kWh, compared with LiFePO4’s $350 per kWh.  So far it’s just vapourware.

Ultracapacitors

Researchers at the University of Dayton Research Institute are developing Lithium-Air cells that could be capable of storing 1000 Wh per kg, or ten times the density of today’s Lithium Polymer cells.  Imagine that, my 33 kWh, 780 lb battery pack reduced to the weight of just 73 pounds!

That’s the future… and it may not be that far away.  That kind of technology would give my Land Rover a 900 mile range.  A more efficient vehicle would be able to drive across the country on a single charge with a battery the weight of just one conventional Lead-Acid car battery.  It’ll be a trick trying to find enough energy to fill the things, but that’s a problem for another day…

Hybrids

On the topic of range, a couple of people have asked me whether you can use a small generator to power the EV, and the answer is yes.  What you will have built is a “Series Hybrid”, one in which the engine generates electricity to fill the batteries which power the motor to move the car.  This is different from the parallel hybrids, such as the Toyota Prius and Honda Insight, which use the engine primarily to motivate the car while the motor acts as a booster.

Honda Insight Hybrid

The upcoming Chevy Volt is an example of a series hybrid.  The car is always powered by the electric motor and battery system.  When the batteries run out of the juice, the ICE starts up and charges them.  In this configuration, the car has about a 40 miles range on pure electric before the engine kicks in.  The ICE is never mechanically connected to the wheels.

The problem with the current crop of hybrids is that since they use the ICE for primary motivation the engine has to be large enough to do all the cruising and accelerating, so it’s heavy.  You end up carrying a large engine and a large motor around, both doing their jobs more efficiently as a team, but still leaving a lot on the table.  Think about the last time you utilized the full potential of your ICE, and for how long.

The same thing could be said for an electric motor that has more than “enough” power, but the motor is so darned efficient, it’s less of an issue.  Besides, electric motors work differently in their ability to generate power compared to an ICE.  I’ll explain more in a bit.

An ideal series hybrid uses an engine only big enough to provide an amount of power slightly greater than the car’s demand at cruising speeds on the highway.

2010 Fisker Karma Series Hybrid

Upcoming Fisker Karma, a series hybrid, has twin 201hp electric motors for a 0-60 time of less than six seconds. Batteries are charged with a turbocharged 2.0L GM Ecotec Direct Injection engine. Only $87,000... gulp.

Acceleration requires a lot of power.  The only reason to buy a 200hp vehicle (about what a Camry Hybrid has) is for acceleration, because most vehicles only use a fraction of their total power to sustain highway speeds.  Even my brick of a truck only requires a projected 32 hp to maintain 60mph (at 7000 ft ASL).  That’s the power needed to overcome the aerodynamic drag, rolling resistance of the tires, and drivetrain friction.  But a 32 hp engine would mean extremely slow acceleration.

Here’s where the series hybrid concept comes in.  The electric motor provides a large amount of power for acceleration, while the ICE charges the battery at a rate only needed to sustain a moderate constant speed.  For example, 200 hp out of the electric motor for acceleration, but only 30 hp out of the ICE for cruising.   That way, the ICE can spin at its most efficient, constant speed, sized just large enough to provide 90% of the driving needs, and the electric motor and battery system can take care of the muscle.  Since our driving usually only involves short bursts of acceleration, the battery system will always be replenished by the relatively small ICE.

Let’s take the Chevy Volt, again, as an example.  It has a 160 hp electric motor, but only a 71 hp ICE.  If it were a conventional car, trust me, the 71 hp would be marginal for today’s perceived needs.  At around 3500 lbs it would take around 18 seconds to accelerate from 0-60 (funny, my Land Rover had a very similar power to weight ratio and far worse aerodynamics…)

But with 160 hp on tap from the electric motor, the Volt could do the same run in about 9 seconds.  Much more reasonable performance.  Then when it’s on the highway using a whopping 30 hp to maintain 70 mph, the 71 hp ICE would have more than enough power to sustain the speed and give the batteries a little charge.

2011 Chevy Volt Hybrid Layout

I’ll get back to the issue of how electric motors produce power, now.  One key difference between an ICE and electric motor is that an ICE can produce its peak amount of power continuously.  An electric motor is typically rated for its ability to provide power on a continuous basis, but beyond that it may have the ability to produce three, or more, times its rated power for brief spurts.  That means that my Kostov, rated at 52 hp, can make 52 hp all day, but it can also do 160+ hp for shorter periods of time.  Perfect for acceleration,and perfect for the way we drive.  Unlike the ICE, the electric motor can be smaller because its power can be overrated for a bit.  It’s like having a that 71 hp-sized ICE that can do 160 hp for acceleration in a pinch.

So, yes, it’s possible to use a small engine or generator teamed up with the EV power system.  Another term for this setup is a “Range-Extended Electric Vehicle”.  Because of the public’s increasing interest in hybrids, and automakers’ need to build more efficient vehicles in order to satisfy government efficiency mandates, companies are starting to develop range-extender engines, small engines designed to power generators to charge batteries.

Lotus, one of my favourite auto and engineering companies, has developed a little 1.2 liter, 3 cylinder engine that can produce about 45 hp.  It has an integrated generator and the whole setup weighs a paltry 123 pounds.  Perfect for a lightweight, series hybrid.

Lotus Range Extender

But implementing this idea isn’t so easy, so it really isn’t done much in the DIY world.  People have towed little generator trailers for extended range, but integrating an engine system on-board… that’s tricky.  For one, the electronics required to manage the whole affair are over most peoples’ heads.  And fitting an engine in with the already crammed electronics needs of the EV is another hurdle.  Remember, with most EV conversions, a lot of space is used by the batteries.  While I’m lucky enough to be able to carry all of my cells outside of the passenger compartment, a quick look at BMW’s EV Mini proves the point… the entire rear seat is consumed by batteries.

You could use less batteries (the Volt uses about half the batteries I’m using) to have more room and less EV range, but you’re really not building an EV anymore… and efficiency will lie somewhere between the conventional and EV version of the vehicle, probably more towards the conventional side.

This is why it all comes down to your particularly needs.  If 90% of your driving can be accomplished with the range of a pure EV then a pure EV makes sense.  If half of your driving involves greater distances, then an EV may not be the right choice.

At the end of the day from a DIY standpoint, it’s just not as practical… and certainly not as efficient.  But that won’t stop me dreaming about one day building my turbine-hybrid powered supercar…

I have heard instances of people using little generators to give their packs an emergency charge just to get the last few miles to home in the event of range miscalculation, shall we say.

Perpetual Motion and Over-unity

This one is easy to get, but difficult to fully understand.  If you take it on rote that the laws of physics actually apply to our reality then you will have no problems.

1920-10-Popular-Science-Norman-Rockwell-cover-Perpetual-Motion-400-Digimarc

Someone asked me once, why not stick a wind-turbine on the car to generate electricity to fill the batteries while moving?

The brief answer is that for it to work, you’d be defying the laws of physics.  People forget that a wind-turbine creates drag.  It’s what happens whenever any object obstructs a flow of air.  In the case of a wind turbine, the flow of air spins the blades which generates electricity, but the amount of energy produced is far smaller than the amount of energy that goes into moving the blades through the air in the first place, because wind turbines aren’t very efficient.  Only 30%, or less, of the available energy used to spin the turbine blades gets converted to electricity.  Stick one on a car, and you’ve successfully created an airbrake.

Same thing with putting a generator (or alternator) onto the driveshaft to recapture energy while driving.  There’s no doubt that you will recapture some energy, but you’ll be recapturing less of the energy you put into moving the vehicle, to drive the generator, in the first place.  Much less.

This is true of every technology.  There is nothing out there that will produce more energy than is put into it.  Some things get close… AC electric motors by themselves for example, are theoretically capable of converting 98% of the potential energy feeding them to kinetic energy.  But “close” is still a literally, impossibly far cry for “more than 100%”.

Wind-Turbine-Car-and-Truck

Adding things like wind-turbines or alternators to capture energy just increases the overall energy consumption via drag.

That’s not to say that these device can’t be useful… well, maybe not the wind-turbine on a car.   Some people have used modified alternators to slow the vehicle when braking.  Instead of the energy of the moving car being converted to useless heat by the friction of the brakes when stopping, the energy is recaptured and stored in the batteries for later use.  Certain motors have this “regen” capability, as well.  The key is that, the devices are only used when energy would normally be bled off as something useless, like heat.  And it still ain’t over 100%…

I’ve seen some ingenious devices out there, but all of them will eventually slow and stop when not supplied with energy.

And if you’re still hanging on at this point… congratulations!  And goodnight.


1 Comment for this entry

  • Gabriel

    One day ill invent a car that can recharge itself whilst it moves….one day….i still have hope that theres a way…even if the laws of physics make it impossible:)

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