Adventure EV

Archive for December, 2009

Brrr, it’s cold. What to do?

by on Dec.08, 2009, under EV Land Rover, Heater

OK, back to the project…

It’s been unusually cold around these parts lately.  For a few days the daytime temperatures never raised above 20F.  The other day it looked like this:

Snow Panorama

Mmmm frosty…  If there was ever a reasonable need for 4WD, this might be convincing:

Snowy Road

Heater

This brings me the topic of today’s post, heat.

As we know by now, a conventional engine’s real party trick isn’t motivating a car down the road, it’s actually generating heat.  Since only 15-25% of the energy in petrol gets converted to kinetic energy, the rest goes into heat.  Most of the year, the heat is transferred into the atmosphere through the cooling system, but in the winter it gets used to heat the cabin through a little radiator (heater core) in the ventilation system.  An ICE is very effective at this, along the lines of producing 60,000 BTU.  For comparison, a 1500 watt room heater only produces around 5000 BTU.

We also know that an EV is far more efficient in converting potential energy into kinetic energy.  Not much heat is generated by the electric motor at all.  I don’t need a liquid cooling system.  I ripped the radiator and all the associated hoses out.  So, what to do in the winter?

I could do what I used to do when driving the Land Rover through the winter… bundle up like a spaceman…  Err, nah…  That was so 1996.  Let’s try something else this time.  In addition to adding an interior (carpeting, foam, rubber) and sealing all the air-gaps, I’m going to try an experiment.

There are a few options with heaters in an EV.  One method is to use a form of fuel burning device such as a kerosene or gasoline fired heater, the kind used in big trucks.  But I don’t like this idea because it just means another system to fill up.  I also wouldn’t exactly have a pure EV, either, though it would probably be the most powerful type of heating system.

Another idea is to use an electric boiler element to heat a liquid circuit that replaces the original car’s cooling system.  This is popular with some converters because it doesn’t require modifying the existing conventional heater core.  I’m going to stay away from this method because it means adding a liquid heating circuit with a pump, etc, and I just don’t have the room.

I could use a 12V 150 watt heater that can be found in automotive catalogs or Walmart.  Getting, err… warmer.

No, not powerful enough.  Instead, I’m going to try modifying a $20 120V ceramic room heater.  Actually, I’m going to use two ceramic heater elements, and instead of being a piddly 150 watts, they’ll be running about 1500 watts each, or around 10,000 BTU for the two.  It’s a far cry from the 60,000 BTU the ICE can put out, but how often do you run your car heater on full tilt?  I’ll bet not much.  Maybe to initially warm the car, but after a few minutes I end up turning it way down.

So I went to Big Lots and picked up two of these ceramic heaters.  The contents of these heaters will be used to replace the innards of my Land Rover’s heater box.

Ceramic Heater

First things first.  Grab a screwdriver and rip it apart.

Inside HeaterThe guts contain a bunch of things I don’t need; fan speed control, temperature control, crappy fan, casing.  That all gets chucked.  The parts I’m after are the ceramic heater core, the plastic core shroud, and the thermal cutout switch.

Heater PartsHere’s a closeup of the ceramic core with its original wiring compared with a quarter to give you an idea of element’s size.Ceramic Element

These should be plenty small to fit in the Rover’s heater box.  Here you can see the old radiator core in the box.

Old Heater CoreOne of the benefits of using a high-voltage, ceramic heater in an EV is that the EV is usually running at high voltage anyway.  I’ll be powering the cores directly off the 205V traction pack.

But wait, 205V is not 120V.  The ceramic elements will burn up!  This is true, so I’ve rewired them for 240V.  Each ceramic core actually contains four elements each rated to run at 120V.  Normally, you get two settings with these heaters, and this is accomplished by running the elements in parallel pairs.  Choose the ‘low’ setting and two elements heat up in parallel producing 750w of heat.  Select the ‘high’ setting and the other pair of elements join in to provide 1500 watts.

I’ll be running each of the two cores separately for two heat settings, and the individual elements have been rewired in series pairs.

Theory

According to Ohm’s Law, the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.

Huh?

I’m gonna have to get into some math here…

OK, I’ll simplify.  The key elements of basic electricity are Amps, Volts, and Watts.  Their relationship is expressed by the equation, Amps x Volts = Watts.  If you know any two values, you can derive the third.  Another handy piece of information is that wiring things in parallel doesn’t change the voltage, but changes the current draw (amps), whereas devices wired in series change the voltage, but not the current draw, the inverse.  Witness:

Series vs Parallel Wiring

Notice that the batteries wired in series in total have the same capacity (Ah) as a single cell, but multiply the voltage produced by the number of cells.  The parallel wired batteries retain the voltage of a single cell, but the capacity is multiplied by the number of cells.  Both circuits produce the same amount of power.  In the series case, 48V x 10Ah = 480 watt hours of energy.  In the parallel, 12V x 40Ah = 480 watt hours of energy.  It’s the same amount of power, just produced differently.  This also works for any device consuming power, like the ceramic heater elements.

In my case, I know that I’m using four elements rated for 120v and in total produce 1500 watts when all four elements are run in parallel.  I’ve split the four elements into two pairs, each pair wired in series.  This way the ceramic core will happily run at 240v but consume half the amperage.  The wattage will stay the same, and it’s the wattage that provides the heat.

Element Rewire

Here the two elements on the left are wired in series and run in parallel with the two elements run in series on the right.  It looks confusing because the elements are already connected to each other internally, so the bare tab (there are five tabs, three of which have wires running to them; left outer, middle, right outer) between the sets of wires is the connection between the two back-to-back elements.  Power for the two sets of elements comes in at the edges (red wires) and share a common ground in the middle (white wire) At least, I hope it’ll work that way…

I may not get the full amount of heat out of the setup since I’ll only have about 200 volts to feed it, but hopefully it should do.  Again, I’m running two of these cores in connection with the blower fan’s two different speeds.  Low speed will trigger only one core, while high speed will add the second core (in parallel, separately wired).

These ceramic cores are self regulating resistors.  As the cores temperature rises their resistance increases limiting the amount of electricity it consumes (inverse-resistance).  It’s a nice, safe design because the core can’t get too hot.  If it does, it just starts reducing the amount of electricity that flows through it.  Less electricity, less heat.

A side effect is that when air is run over the core (like the air from a blower fan) the core cools down, the resistance decreases and more electricity flows… more heat is generated until the core heats up more than the air can cool it, then resistance limits the current again.  Because of this inverse resistance behavior, within limits the more air available to cool the core will mean more heat output.

Enough theory, let’s get back to the heater box modification.  I was lucky.  Most people have to completely rip apart their dashboards to get to their heater boxes, a painful process that can take hours on some vehicles.  My Land Rover’s heater box sits in the engine bay attached to the firewall, fully expose.  It doesn’t get easier than disconnecting the blower hose and undoing six bolts!

I was also lucky because the heater box is plenty large enough to house the two ceramic heater cores.  And the dimensions of the box meant that I could bolt the ceramic cores in their original heat-proof, plastic shrouds directly to the box with the airflow having to pass through each core.  I didn’t have make any internal baffles or special mounts, I just used long #6 stainless screws to bolt the cores the box walls.  The lower core uses a set of stand off nuts to position the core one inch inside the output door.  Then I used some plastic, automotive wiring conduit to clean it all up.  That’s pretty tidy!

Final Heater Wiring

And the final result all buttoned up after repainting.  You can see one of the cores inside the blower hole.

Final Heater

AC vs DC and Safety

Controlling this whole process requires a few other goodies.  The major issue here is the use of DC (Direct Current) voltage in the EV traction pack.  Unlike the electricity coursing through the walls of your house, which is AC (Alternating Current) voltage, DC requires a whole different set of controls.

AC voltage turns on and off 60 times a second.  If you touch AC current you will get electrocuted, but your muscles will involuntary spasm in response.  This makes AC relatively safe because it tends to throw you away from the electric source.

High voltage DC is much more dangerous.  DC doesn’t alternate like AC, rather if you’re electrocuted by DC voltage your muscles will contract and stay contracted for as long as you’re touching the voltage source… or until you die.  Unfortunately, this also means that if you happen to grab a DC voltage source, your involuntarily contracted grip may not let you release the voltage source.  Bad news.

0511-0709-2016-1841_Careless_Electrician_clipart_image

For this reason, high current circuits are often remotely switched for safety.  You may operate a switch to turn a device on or off, but it’s only powered by a small amount of current.  The switch actually actuates another switching device designed to isolate the high current load from the switch you operate, keeping you safe.  These switching devices are known as relays.  It’s like those movies where the Captain of an ocean-liner uses a big brass throttle to signal the engine room.  The guys in the engine room actually operate the engine, while the Captain only operates a signal device.

A circuit is “under load” when a device uses electricity.  The higher the load, the more electrical current moves through the circuit.  Relays are used anywhere a high current load is used, whether the circuit is designed for AC or DC power.  But the two forms of power operate differently.  When a circuit is broken, like when a switch is used to break the power flow, a circuit under a heavy load can actually send power through the air between the switch contacts, or arc.

In the case of AC power, the alternating pulse of electricity minimizes the effect because the flow of electricity basically switches off for an instant, long enough to break the connection.

DC tends to hold on.  There’s no alternating break in the current flow, so as the circuit physically separates an arc of electricity forms in the air gap between contacts.  Welding equipment takes advantage of this behavior by sending high current DC power through the air to create an arc hot enough to melt metal.  If the air gap gets big enough, the current will be cut off, but because the tendency to arc with DC power is much greater and stronger than with AC, switchgear for DC has to be much more robust, with larger gaps between contacts, or devices like magnets that extinguish the arc.  It also means that DC switchgear for high-current use can get expensive.

Relays

To safely control my heater cores I have to use relays, and I have two choices here.  Electromechanical relays are the most common type of relay.  They’re used everywhere in cars.  Basically, a low current circuit connected to a switch operates a little electromagnet.  The electromagnet pulls a heavy duty circuit closed to complete the high load circuit.  Simple and cheap… usually.  An electromechanical relay capable of handling the voltages and current required by my heater cores requires the use of a “magnetic blow-out”, which makes them really expensive.Electromechanical Relay InnardsMy other choice is a Solid State Relay.  These are transistor devices that safely switch currents without using physical contacts.  No contacts means no air gap.  No air gap means no arc.  Being transistors, they consume more power than electromechanical relays, and this generates heat.  No much, but enough to need a heat sink to prevent device damage.  I ended up purchasing these Magnecraft (#6312AXXMDS-DC3) Solid State Relays from Newark, an online electronics vendor for about $30 with heat sinks.  These are rated for 200VDC and 12 amps, more than enough for my needs.  The equivalent electromechanical device would have been about $85.

Solid State Relays

Fuses

So, a two position heater switch on the dashboard will control low-current 12V power to signal the Solid State Relays to trigger which will safely control the 200V heater cores.  Meanwhile, the dash switch will also control the 12V blower motor.  Simple and safe.  To round out the circuit, the high voltage heater circuit passes through a fuse block with 12A time delay fuses rated for 600VDC.  Often a resistive-load circuit, like the heaters, can current spike when firs energized, so time-delay fuses were chosen to handle the initial current burst.

Fuses

And that’s about it for the cabin heater setup in my EV.  Only time will tell whether the two rewired cores will be enough to at least be reasonably comfortable in the winter.  I purchased three solid state relays in case I need to install a third core.

A nice aspect of this heater system is that it’s pretty much instantaneous.  No more waiting for the engine to heat up.   Sweet.

Those especially sharp in the audience, will note that any power used to heat the EV will reduce range.  Correct.  In this case, if I were to run the heaters for an our they’d consume 3 Kw power from the 33 Kw pack.  That’s about equivalent to five miles of range out of 50, a 10% hit.  Not too bad, especially considering the heater won’t need to be on full the whole time anyway… hopefully.

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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.

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Back To Our Regularly Scheduled Programming

by on Dec.01, 2009, under EV Land Rover, Fabrication, Motor Bracket

I hope everyone had a great Thanksgiving!  I know I did.  No snow this year, but it’s getting cold around here nonetheless.  It makes working outside less than enjoyable.  We’re projected for a high of 28F on Thursday… so yay.  Well, I better get a lot done on Wednesday.

Starting the post out with a picture

It seems like it has been awhile since I last updated this blog with actual project material, but rest assured I’ve been toiling away.

One of the tricky bits has always been the connecting of the motor to the Land Rover’s transmission.  In some cases electric motors can be strong enough, have enough torque, to power the EV through a direct-drive link to the differential.  With my project, I decided I wanted to retain the transmission for a few reasons.

For one, I wanted to retain the full capabilities of the Land Rover.  That meant retaining the four-wheel drive system.  Sure, it’s not the most efficient way to go, but keeping the Rover’s full off-road capability was one of my design mandates, and the easiest way to accomplish this was to utilize the existing transmission.

Secondly, the transmission allows me to change gear ratios in order to improve performance and efficiency.  The Land Rover isn’t the lightest conversion, so being able to downshift to climb a steep hill could help.  My projections indicate that I’ll be able to do most, if not all, of my driving in third gear up to 60mph.  Past 60mph I’ll need to grab fourth.  We’ll see if I have enough torque to start off comfortably in third.

Electric motors like to spin, they’re not happy poking around, so while I may have enough torque and power to single gear most of my driving, it may not be the most efficient at slower speeds and higher loads.  Again, the gearbox gives me flexibility.

Thirdly, the transmission’s clutch becomes a safety device.  In the event of a motor or controller failure which might result in the equivalent of a full-throttle situation I can easily disconnect the drive through the clutch.  Let’s hope this doesn’t happen.

Lastly, it’s just easier.  Connecting to an existing transmission is a common conversion technique, so many components already exist to facilitate this… like my adapter plate.

Motor with adapter plate.  Flywheel and clutch mounted.

I once considered going with a direct drive AC system designed to haul electric buses around, but in the end I didn’t like the performance specs, and while that system (Azure Dynamics’ AC-55) was designed to connect directly to a rear differential via a driveshaft and yolk, I would have needed to engineer a way of connecting it to my transfer case if I wanted to retain four-wheel drive.

You may have heard that a good conversion means lightweight and no four-wheel drive, two rules I’m somewhat breaking.  Maybe more like bending.  The Land Rover, as we’ve discovered isn’t terribly heavy for what it is.  I’ll keep telling myself that.  And the four-wheel drive system is unlike most modern setups.

The Rover’s four-wheel drive system is actually very basic.  It’s a manually selectable, part time four-wheel drive system.  That means most of the time I’m only in rear-wheel drive, with the front driveshafts disconnected by freewheeling hubs.  While there are still an additional set of gears to run through in the transfer case, it also means that there are no frictional losses running the front driveshafts and wheels when I’m in two-wheel drive mode, as you would find in most modern drivetrains.  Not so bad.  During the occasions I would need four-wheel drive, I shove down a lever and I’m in locked four-wheel drive.  True, I still have to lug around the weight of the additional four-wheel drive components, but that’s the way it is…  otherwise I would have converted something like a Civic.

Anyway, back on target.  While waiting for some additional components needed to mount the motor to the transmission, I test fitted the motor temporarily.  I needed to solve how I was going to mount the motor to the chassis.  The motor and transmission, when coupled together, act as one big unit, but the transmission’s mounts really only serve the rear of the unit.  The motor needs to have a front mount.

Here’s what I saw with the unit bolted together:

Conundrum_v01

The yellow circles are the two existing motor mounts.  The red arrow is pointing out the only position I can wrap my motor mount bracket around.  Big difference in location.  That flat black plate is the bottom of the motor mount bracket.

Mounting the very back of the motor would have been perfect, but that’s not a very structural part, and it’s where all the motor cooling happens with a fan back there.  Further forward and I run into a band of metal that covers the internal brushes, that’s a no go.  Further still and I hit the electrical connection block, that’s out.  So just in front of the block it is, then.

I have two options here, try and build some kind of bracketry to connect everything up, but I don’t like the idea of being levered out that far away from the chassis mounts… or build new mounting points into the chassis.  The latter idea isn’t attractive as it would mean designing new brackets and welding them to the chassis, but it’s the idea that won out in the end.

First I built a template out of cardboard and determined where on the frame I wanted the new mounts to go.  I soon discovered that I wouldn’t be able to put the new brackets directly under the mounting band because of front driveshaft clearance, so the mounts go a few inches to the side.

Template

The brackets are made from 2″x3″ – 1/8″ rectangular steel stock.  Initially, I wondered if the 1/8″ wall material would be strong enough, but the existing chassis used 1/8″ material that supported 490 lbs of engine and accessories instead of the motor’s 200 lbs.  Weight won’t be the issue, hopefully the increased torque from the electric motor won’t be, either.

After tracing the arc designed to allow driveshaft clearance on the steel stock, I used an angle-grinder and cut-off wheel to transfer the shape.  Came out kind of nice,  a relief after shattering a half dozen cut-off wheels with previous tasks.  Cut-off wheels are tricky, a slight grab or cut to deeply at the wrong angle, and they just blow apart.

Cutout

A smaller bracket was fabricated for the other side.  Both brackets have open bottoms to prevent them from collecting and holding debris.  Once welded to the frame, they should be very strong.

I decided to keep the existing mounts, in case.  In case of what?  I don’t know… returning the vehicle back to stock?  Doesn’t seem likely, but the stock mounts aren’t in the way, so for now they stay.

Here’s the longer bracket next to the stock bracket… you can see the driveshaft below it.  While nowhere near the bracket now, when the front axle is under articulation off-road, the driveshaft would have hit the new bracket if it had no arch.

Detail

Here are the two brackets welded into place, and you can see the arch in the original mount, as well.

New Mounts In Place

I’ve painted the brackets with POR-15, which works brilliantly for this stuff.  I coated the frame with POR-15 awhile back and the paint is tenacious!  You can’t scrape it off with a screwdriver.  Only an angle-grinder has succeeded in removing POR-15 from the well prepped chassis.

Hopefully, by the end of tomorrow you should see the painted result with the motor in place and mounted!


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