Adventure EV

Design

Wiring It All Up

by on Nov.09, 2010, under Design, Electrical, EV Land Rover

HV Circuit Control Box

The main battery pack powers more than just the motor, it also provides electricity for the ceramic-element, cabin heaters, as well as feeding a DC-DC converter (replacing the role of the original alternator) that transforms the 200+ volts to a more conventional 12 volts for the rest of the vehicle’s accessories (headlights, turn signals, etc).

All of these individual circuits need switching and fuse protection.  I created a custom, water-tight box full of these odds and ends;  main switch contactor, fuse blocks, and solid-state relays.

AccessoryControlBox_v02

Watertight NEMA-rated cable glands used for all cable transfers. GM Weatherpack and Anderson Power Pole connectors used for all connections

Accessory Control Box

High Voltage circuits. Clockwise from top left; power distribution blocks, heater element solid-state relays with heatsinks, blue Belktronix voltage prescaler for LinkPRO battery monitor gauge, fuses, Kilovac EV200 contactor

A contactor is essentially a giant relay designed to switch high-power circuits through the use of a safer, low power circuit.  Normally, special circuitry is needed to protect the motor controller circuit from an in-rush of high current when switching it on and off.  The Soliton-1 motor controller comes with a contactor and pre-charge resistor circuit built in, so I don’t have to worry about it.  Handy.

The Kilovac EV200 contactor pictured in the lower left of the box is designed to switch the HV accessory circuits.  Power from the main battery pack comes into the control box, is controlled by the contactor, and then goes to a set of distribution blocks.  Power is split to individual high-voltage rated fuses which then feed the particular accessory circuit:

2 x 12 amp fuses for the two solid-state relays (SSR) controlling the two ceramic heater matrixes for cabin heat.

1 x 30 amp fuse for the DC-DC converter

1 x 1 amp fuse for the HV ammeter wiring

1 x 2 amp fuse for the HV voltmeter wiring

Battery Pack Monitoring

While I can’t monitor individual battery cells without an advanced battery management system (BMS), I can keep track of the entire pack relatively easily with a battery monitor such as the Xantrex Link PRO.  Normally used for monitoring the state of batteries used for marine applications, the LinkPRO seems to work quite well for EV use.  It comes in a handy gauge form-factor, monitors voltage, and the flow of current (amps).

Xantrex Link PRO Battery Monitor

Keeping track of current flow is particularly useful.  Lithium chemistries have a very flat discharge curve.  That is, the voltage when a cell is full doesn’t differ greatly from an empty one.  This is great for performance as the power out of a lithium cell won’t seem to reduce very much as the battery drains.  Conventional lead-acid batteries have a steeper discharge curve.  It’s pretty easy to tell the charge state just by reading the voltage output.  Concurrently, the performance of the vehicle will diminish over time.

While the performance benefits tilt in favor of lithium, the danger is not knowing where empty really is.  When the cell actually hits empty, the voltage will drop off very rapidly, possibly rendering the cell dead.  A more reliable way of measuring the amount of electricity left in a lithium cell is to track the amount that was extracted from it.  The LinkPRO  keeps track of amp usage over time (amp-hours) which gives me a pretty good “fuel-gauge”.  A side-benefit to measuring the amount of current flowing is that it works both ways.  When I charge the battery pack the gauge runs in “reverse” to fill up.  If there was ever an error in the charging process, the gauge would reflect the true amount of charge in the cells.

The LinkPRO is not designed for high-voltage battery systems.  It works to a maximum of 35 vdc, so also located in the accessory box is a Belktronix voltage pre-scaler.  This device takes the high voltage from the main battery pack and scales it down by 10x to match the 0-35 vdc input range of the monitor, 205 volts becomes 20.5 volts, for example.  Software within the gauge multiplies the result by 10 to display the correct battery voltage.  The gauge itself is powered by a small 12v DC-DC converter that takes its power from the 12v accessory side.  Its presence is merely to isolate the gauge from the 200+ volt traction pack for safety.

Current measurement is handled by a big, beefy 1000 amp shunt inline with the main battery pack.

Deltec 1000 amp / 50mV Shunt

Finalizing Installation

The main power cables transferring power amongst the four battery boxes and the motor controller are made up of flexible, orange 2/0 gauge welding cable.  Welding cable is ideal due to the large number of fine strands of copper.  It remains very flexible while allowing great current load.

Two giant Ferraz-Shawmut 500A/300vdc fuses protect the HV circuit.  One is mounted on the rear battery box, the other in the front bay.  While an essential safety element, hopefully these never see use.

Ferraz-Shawmut 500 amp / 300vdc Fuse - Image courtesy KTA-EV

A large, Anderson-style disconnect ensures that the HV electrical path can be easily broken for safety and maintenance.  Clear-acrylic is used to cover the engine-bay battery box and to offer spectators a peek of what the battery system looks like.

FinalBayTop_v01

An Elcon PFC-5000 5kw charger sits onboard under the motor controller (hard to see).  The charger is very flexible, capable of working with 220v or 110v input, and since it’s onboard I can charge anywhere I can get power.  220v circuits, such as those found at home or in RV parks will produce 5kw of charging power capable of filling a completely depleted pack (32.8 kwh) in about 7 hours.  If used on a smaller 110v circuit, output is reduced to 2kw, which would take 16 hours to charge.  However, the pack should never really be taken below 80% usage, and I predict that regular, predicted use will be more in the realm of 50-60% making for very reasonable charge times of only a handful of hours.

Elcon PFC 5000 Charger

Since the 12v accessory circuit is mostly powered by the DC-DC converter (currently an Iota, but will probably change to a  sealed Chennic converter… if they ever get back to me), a smaller than normal accessory battery can be used to provide backup power.  An Odyssey PC625 AGM normally used in powersports applications (snowmobile, jetski,etc) is mounted in front of the main battery box.

Final Motor Bay Side View

Here it is, mostly finished.  I’ve run out of time this round, but I discovered late in the installation that the white control box needs to be re-mounted lower to provide enough room for the bonnet.  This should also help clean up the wiring a bit.

Final Bay Top View

Unfortunately, I don’t have a picture of what it all looks like with the side wings and grille on.  Testing is done with the bonnet off.

Next up… first drive impressions!

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Carb(on) Loading.

by on Nov.25, 2009, under Design, EV Land Rover

Let’s take a minute to look at some basic environmental ramifications of an EV conversion.  Everyone wants to know what their carbon footprint is these days.   Is an EV superior in this regard?

I’ve heard the argument by fans of oil that, “pluging in an EV just moves the emissions from the tailpipe to the powerplant.”  The phrase is absolutely correct.  All pollution generated by running an EV happens at the electricity generation plant.  But not all methods of generating electricity produce the same amount of CO2.  In the case of renewable generation sources such as solar or wind the “tailpipe” emissions from an EV are zero.

Power and communication lines in Bangkok, Thailand

Power and communication lines in Bangkok, Thailand

So if you’re charging your EV with your own PV (PhotoVoltaic solar panel) setup you aren’t contributing a whole lot of CO2 into the atmosphere.  But most people don’t have their own little power plant at home.  They rely on the electrical grid to charge up the batteries on their EVs.  How much CO2 does that electricity generation really produce?  How does it compare to burning petrol in a conventional car?

It’s hard to say without knowing the makeup of energy producing fuel sources in your area, because as we’ve seen with renewables, not every fuel produces the same amount of CO2 per kWh.  Let’s look at the CO2 emission rates of various types of fuels when generating a common amount of energy, 100,000 BTU.

Electricity Generation CO2 Emissions by Fuel Type

Fuel Type Pounds of CO2 per 100,000 BTU
Coal 21.52 (avg)
Liquified Petroleum Gas 13.90
Natural Gas 11.71
PV (Solar Electric) 0
Wind 0
Nuclear 0
Hydroelectric 0

Data from the Department of Energy

Coal is the gross polluter while hydroelectric, PV, wind, and nuclear get a clean bill of health.  Keep in mind that this is the CO2 rate for electricity generation.

The EPA estimates the amount of CO2 produced by burning a gallon of gasoline (petrol) in a car is 19.4 lbs/gallon of CO2, and a gallon contains 114,100 BTUs of energy.

To compare these figures with EV energy consumption and emissions we can convert kWH, the most common method of working with energy when talking about EVs, to BTUs; one kilowatt hour is equivalent to 3413 BTUs, so corrected that would be 33.40 kWh per 114,100 BTU or one gallon of gasoline (114100 / 3413 = 33.40).

Lots of numbers swimming around, but bear with me.  I’m going to use my conservative projections for the Land Rover’s EV performance to see how it all relates.  I’m projecting a 90 mile range @40mph if I were to deplete all the energy stored in my 32.77 kWh battery pack.  The pack contains just under a gallon’s worth of energy so that equals 91.73 mpg ( (33.40 / 32.77)*90=91.73) when corrected to a full gallon.

Now let’s pick a fuel, the dirtiest fuel… coal.  If 100% of my EV’s electrical generation were attributed to coal I’d generate 21.52 lbs of CO2 everytime I drove 91.74 miles (the distance equivalent to a gallon of petrol).  That’s 0.235 lbs/mile of CO2.

When it had an ICE the Land Rover would get about 18 mpg @ 40mph.  Remember, the EPA estimates 19.40 lbs of CO2 per gallon, so that works out to 1.078 lbs/mile of CO2 when burning petrol (19.40/18=1.078).

With the worst fuel source, coal, the EV is still 4.587 times (1.078/0.235=4.587) cleaner than its ICE counterpart when “burning” the dirtiest fuel.  Keep in mind that the relationship between the ICE and EV would remain the same, more or less, regardless of the speed traveled or the type of vehicle, providing the comparison is between the EV and ICE versions of the same vehicle.  This relationship is a reflection of the efficiency of the chassis and powertrain.  If were to drive faster my mpg would go down in both the electric and the ICE.  Compare a lighter, sleeker car and the EV version would benefit from the same attributes that the ICE version benefits from.

Cholla Coal Power Plant in Arizona

Cholla Coal Power Plant in Arizona

The reason the EV is more efficient is due to the efficiency of its drivetrain.  ICE engines waste 70-80% of the energy they consume by generating heat, and any energy used to create heat doesn’t get translated into useful motion.  Electric motors generate very little heat.  Almost all the energy they consume is translated into rotational motion.  The best brushless AC motors have efficiency ratings of around 98%.  EVs are simply more efficient, therefore they go farther on less energy, and they generate less CO2.

In the Northeast, around 50% of the power generated is from Nuclear or Natural Gas, which emits 54% of the CO2 that coal does.  Charging in the Northeast would make my EV Land Rover 849% cleaner in CO2 emissions compared to it’s ICE counterpart.

And it can only get better from there.  If you live in Vermont, 79.7 percent of your power comes from nuclear generation, so your CO2 emissions would drop to… well, a very low number indeed.

And therein lies one of the beauties of the EV, it adapts very well.  If you charge your EV from solar panels, you generate no CO2 emissions regardless of how far you drive.  No matter what you do, an ICE car will always generate 19.40 lbs of CO2 per gallon of petrol.

And there are the numbers…  One version of them, anyway.

See how your state generates its electricity in this handy Excel document:

http://www.nei.org/resourcesandstats/documentlibrary/reliableandaffordableenergy/graphicsandcharts/stateelectricitygenerationfuelshares/

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EV Design Considerations. So you want to build an EV?

by on Nov.24, 2009, under Design, EV Land Rover

I’ve been asked to comment on what makes a good donor vehicle for an EV conversion.  There are a couple of books on the subject of EV conversions, but I mean that literally.  Perusing Amazon, you can find loads of books on other alternative energy projects; solar hot water heating, wind turbine power,  solar photovoltaic, etc…  But converting a car to electric power, that’s a tricky one.

The most well known book on conversions is probably Bob Brandt’s, “Build Your Own Electric Vehicle”.  Another is Michael P Brown’s, “Convert It!”.  Both were originally written in the mid-90s, so while the theory found within is as relevant today as it was in 20th century, some of the technology is different.  If I had to recommend only one, it would be “Build Your Own Electric Vehicle” because it’s quite a good reference tome with lots of charts and graphs, equations and examples.

At the heart of it, EV conversions still remain the pervue of hobbyists and hackers,  environmentalists and gearheads.  And thankfully the internet exists, because its probably the best place to gain insight into building your own EV.

Let me start with a fundamental rule of EVs.  EVs cannot replace a conventional car 100% of the time for 100% of the people.  But an EV could play the role of a second vehicle perfectly, even if it’s the vehicle you do 90% of you driving in.  The simple reason is range.  The batteries just can’t practically store enough potential energy for  significant range.  You won’t take your EV on a long driving vacation, but depending on your commuting habits it could be a winning solution.  GM thinks that 75% of Americans commute an average of 33 miles a day.  It’s why they’ve designed their upcoming Chevy Volt to run 40 miles on a single battery charge.  How far do you drive a day?

GM's Chevy Volt plug-in hybrid.  Will do 40 miles on electric power alone.

GM's Chevy Volt plug-in hybrid. Will do 40 miles on electric power alone.

This kind of subjective thinking becomes the driving force behind choosing a donor vehicle for EV conversion.  What do you want out of it?  Do you need ultimate range because of a long commute, or will 20-40 miles be enough?  Do you mind spending lots of money on state-of-the-art lightweight, high capacity battery technology, or is budget more of a consideration?  Do you need to dust everyone in the vicinity away from a stoplight, or is more leisurely performance acceptable?  Do you need the utility of a large vehicle, or will a compact suffice?  Do you need the latest automotive gadgets at your disposal, or will the technology from a decade do the job?  Homebuilt EVs become a very personal decision and design, but findamentally they all come back to one imporant factor.

Designing an EV centers around efficiency.  Since the battery technology is limited in this regard, everything about designing an EV takes efficiency into consideration.  Sometimes, ultimate efficiency isn’t the desired goal or even necessary,  but efficiency is what ties everything together; it dictates the design, component selection, packaging, range, performance, and cost.  At the end of the day, choice of donor vehicle often comes down to availability and desireability.

Tesla Roadster EV can do 250 miles on charge and 0-60 in under four seconds. Costs $109,000!

Tesla Roadster EV can do 250 miles on charge and 0-60 in under four seconds. Costs $109,000!

There are a few basic tenets of EV design.  Weight is bad.  Friction is bad.  Both of these things will sap the energy out of batteries in short order.  And, I’ve chosen to convert a heavy, 4wd, aerodynamic brick of a vehicle!  Well, that’s not entirely true… except the aerodynamics part.  Let me explain my reasoning.

Let’s look at weight first.  The less weight, or mass, you have to move the less energy is required to move it. Keeping a heavy mass moving at a constant speed doesn’t really use much more energy than a light mass, but accelerating the heavy mass to speed will consume more power.  The trick is finding a vehicle chassis (or “sled”) that manages to be lightweight yet strong enough to carry the EV power system and have the utility you desire.  Geo Metro’s make great conversion candidates because they weigh very little, but they may not be practical from other standpoints, such as some of the ones that didn’t make them very attractive as conventional vehicles.  I really dig that this particular Metro has a scoop on the hood.  I don’t know why (I don’t know I dig it or why it has a scoop on the hood.)

It's a Geo Metro!  With a hood scoop!  Why?!?  Why not!  Awsome...  Sadly, this particular car isn't an EV, but if it was it would have made the hood scoop that much better.

It's a Geo Metro! With a hood scoop! Why?!? Why not! Awsome... Sadly, this particular car isn't an EV, but if it was it would have made the hood scoop that much better.

My Land Rover is actually fairly light for the type of vehicle it is.  Most modern cars have bloated in recent years due to the addition of safety equipment and amenities; things like soundproofing and complex electronic systems.  Today’s Toyota Camry weighs close to 3400 lbs.  My Land Rover, a 4wd truck that stands 6-1/2 feet tall with a boxed-steel ladder chassis, weighs a little over 3100 lbs.  This is mainly due to its short length and weight saving aluminum body panels… and zero sound insulation or amenities.

Back in 1999, the Toyota Camry weighed about 3100 lbs, as well.  In 1986, the last of the first generation models, it weighed a scant 2300 lbs!  Now of course, it has grown dimensionally over the years, it’s gotten more powerful,  and it has, no doubt, become safer and more comfortable.  But the Toyota Camry remains a perfect example of where cars have come over the past 20 years.  The current hybrid version of the Camry weighs in a 3700 pounds.  What a porker!

Weighs a ton... or two.  But I still managed 45 mpg in one.

Weighs a ton... or two. But I still managed 45 mpg in one.

I mention it because it’s something to think about when choosing a donor car.  Do you want all the amenities and luxuries of a modern car?  Or can you live with something a bit older?  Certainly, going with the older vehicle is a more efficient option.  Using older vehicles as donor platforms for an EV conversion not only becomes a less expensive option, but the lack of electronic doo-dads in the older models makes a conversion much easier.

VW Beetle is a popular EV conversion, with kits supplied by several companies

VW Beetle is a popular EV conversion, with kits supplied by several companies

That covers weight.  What about friction?  There are a couple of things which contribute to friction.

One is the drivetrain layout.  A four wheel drive system will be less efficient than a front-wheel drive layout due to the increased number of moving parts.  The same thing is true, but to a lesser degree, with rear wheel drive vehicles… unless they’re rear or mid engine designs, like VW Bugs or Porsches (or Lotus Elises or Toyota MR2s… or Lamborghinis.) Every time power has to make a turn, such as with a direction changing differential, the system loses power to friction.   Front wheel drive transmissions do have differentials, but most designs are transversly mounted, which leads to no directional change in the differential… more efficient.

My Land Rover is indeed a 4wd vehicle capable of wasting useful power, but it’s not full-time 4wd.  Unlike most modern 4wd systems, I can choose to run the vehicle in 2wd with power going to the rear.  I can also unlock the front hubs which disconnects the front driveshafts and differential from creating parasitic drag, so it essentially becomes a rear-wheel drive car.  Not the most efficient, but not terrible either.

Ford Ranger EV, popular with converters due to its high load capacity, its relatively light weight, and good utility

Ford Ranger EV, popular with converters due to its high load capacity, its relatively light weight, and good utility

Second on the friction list is aerodynamic drag.  The more sleek a vehicle is, the more efficient a path it can carve out of the atmosphere.  Modern vehicles are pretty good in this regard.  38 year old tractors aren’t.  I have no design excuse here except that,  aerodynamics don’t really play a part unil faster speeds since aerodynamic drag increases squared to speed.  I takes substantially more energy to push through air at 55 mph than 35 mph, and exponentially more to go 65 or 75 mph.  If I needed an EV that could do highway speeds, I wouldn’t choose the Land Rover.

Mercedes-Benz SLS AMG in the wind tunnel.  An EV version is planned for 2015.

Mercedes-Benz SLS AMG in the wind tunnel. An EV version is planned for 2015.

That’s not to say that my projections for my Land Rover’s performance don’t include highway speeds.  On the countrary, I should be able to hit very illegal speed limits with ease… but I’ll burn through juice doing it for too long.  My design considerations only required an average of about 40mph and for that, while slightly bloated, the Land Rover should do fine.

While not the most ideal EV candidate for efficiency reasons, the Land Rover becomes moderately reasonable.  It more that makes up for it with its classic appeal, the fact that I already owned one, its ability to soak up EV components with ease, and utility.

As with most other products that can be represented by a triangle of competing attributes, the three points on the EV triangle are cost, performance, and range.  You can have amazing range and performance, but it will cost you.  Or you can have a low cost conversion with decent performance but low range.  The trick is finding out a middle ground that works for your situation.  Start with one point on the triangle and work from there.

So what makes a practical EV?  It all depends on how much work you want to do, how involved you want to be in the building and designing of your EV.

The easiest way is to purchase someone else’s EV, or find a factory built EV.  There aren’t a lot.  Many of you may know the demise of the GM Impact (as documented in the film “Who Killed The Electric Car”), but another factory built EV that continues to survive to day is the Toyota Rav-4 EV.  They’re hard to find, but by all accounts are great EVs.  You can also find Ford Range EVs, which was actually produced by FoMoCo for four years.  Most were sold to fleets.

Toyota RAV-4 EV.  Look Ma! No Engine!

Toyota RAV-4 EV. Look Ma! No Engine!

But where’s the fun in that?  This is about building an electric car!  For those that want the excitement of building their own, but without the stress of figuring it all out, you may opt for an EV kit.  Several EV companies produce plug-and-play kits for a few platforms; the VW Beetle, Porsche 914, and some universal small car or small truck kits.

Rebirth Auto's VW Beetle EV Conversion kit.

Rebirth Auto's VW Beetle EV Conversion kit.

By far the most challenging and satisfying method has to be building your own, from scratch.  At least I hope so.  We’ll see when I get to the end.  For the most part, though, pick any smaller car from around the late 80s to the late 90s.  Those seem to be cars that aren’t necessarily too old, but still maintain a reasonable weight, degree of safety, and functionality.  The slipperier the better!

You can certainly choose a late-model car, but the conversion will probably be more expensive and more difficult, namely due to weight gain and the complex electronics of today’s cars.  Things like older Honda Civics, VW Rabbits, Passats, Jettas, Toyota Tercels, Corollas, Geo Metros, Ford Rangers, GM S-10 small pickups, Miatas, Toyota MR2s, all would fit the bill.  I like the idea of converting a mid-90s Subaru Impreza or Legacy Wagon if you live in the snowbelt.  They suffer from a full-time 4wd drivetrain, but the losses may not be too bad.

It all comes down to what you desire… and how much you desire it.

More on how I came up with the component selection for my conversion in a later post…

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