Adventure EV

Tag: Design

Weight Gain…

by on Nov.17, 2009, under Batteries, Battery Boxes, Design, EV Land Rover

Well, you can’t get something for nothing.  For now, the Rover remains on a strict diet.  But the plan for the not-so-distant-future involves bulking up a bit.  Actually, quite a bit.

I’ve got the motor.  I’ve got the motor controller.  You’ve seen those.  The last major bit of the equation is the batteries, and you havent’ seen those yet.  This is largely because they’re on their way to the USA by way of a large container ship from China.  At least, I hope they are.

While the engine in an ICE car is the heaviest, most expensive part of the drivetrain system, with an EV this task falls to the batteries.  In my case, about 790lbs worth of these:

Thundersky 160Ah LiFePO4 Cell

That is a 3.2v 160Ah LiFePO4 cell from Thundersky.  It’s about one quarter the size of a conventional, large lead acid battery, the kind you’d find in a pickup truck.  My conversion is using 64 of these battery cells, for a total nominal voltage of about 205v (240v peak charge).

I’ll try and give some perspective on the battery system.

Battery capacity is usually given in units of kilowatts (kW).  That’s 1000 watts.  If you were to burn ten 100 watt lightbulbs for one hour,  or one 100 watt lightbulb for 10 hours, you’d consume 1kW of energy.  If you had a battery that contained 1kW of energy… well you get the picture.  An average home in the US consumes about 30 kW of electricity a day.

One gallon of petrol (I use the word petrol because it’s petroleum, a liquid, while gas is… gaseous) contains about 36 kW of energy.  My battery system will contain about 33 kW of energy (3.2v x 160Ah x 64 cells = 32,768 watts).  Not even the equivalent of one gallon of petrol.  But, I’ve projected my EV’s range at between 50 and 75 miles utilizing a conservative 80% of the battery pack’s storage capacity, for cell longevity.  The low end of the range is calculated with the vehicle travelling at a constant 65 mph, while 75 miles is with the vehicle travelling 40 mph.

The Land Rover is horrendously, aerodynamically inefficient (there’s a tire on the bonnet… which is what I call the hood because, it’s British… the Rover, I mean), which explains the differences in range at the different speeds.  At speeds above 40mph most of the power used to move a vehicle goes into fighting the air, since drag goes up with the square of speed.  Every doubling of speed requires four times the power to counteract the atmospheric drag.  As a comparison, a Toyota Camry has a total drag index of 7.57, while my Land Rover comes in more like 18.  A Prius is a low 6.24, while GM’s electric car from the past, the EV1 was a very slick 3.95.

Rover Sunset

Since it takes more energy to push a boxy truck through the air, the Land Rover is at a disadvantage, but for speeds around 40mph drag becomes less of an issue.  And for its intended purpose, as a vehicle designed for local trips into town, 40mph is perfect… as is the range capability.  In fact, here in the Rockies the atmosphere is up to 20% thinner than at sea level, so that’s 20% less air to push.  With an ICE car, that means a corresponding loss of 20% power (20% less oxygen in which to mix and burn with petrol), but the electric motor doesn’t care.  Chalk up a bonus for EV power at altitude!

Imagine the numbers, though.  I’ll have less energy than a gallon of petrol onboard, and while counting on using only 80% of that, I’ll be able to travel 75 miles.  Astute math students will notice that’s more than 75 mpg (it’s actually more like 90 mpg)… in a 38 year old Land Rover!  That’s about five times more efficient than the 15-18 mpg the truck delivered with its internal combustion engine.

Throw the electric drivetrain in something lighter, smaller, more aerodynamic (pick any modern sedan or wagon), and you might see 125 miles of range, or 130 mpg.

In an ICE most of the energy extracted from the petrol is wasted as heat.  Only 20% makes its way into motion.  With an electric motor very little energy is wasted as heat meaning almost all of the power goes into turning the motor shaft.  Some are capable of being 98% efficient at turning electrical potential energy into kinetic energy.

But back to the batteries for second.  I mentioned in a previous post that I had managed to extract about 700 lbs of ICE related equipment that I wouldn’t need.  Well, with the batteries alone, it’s all coming back… and then some.  But the Rover will be faster, stronger than before.  So it’s more like 700+ pounds of muscle.  Beefcake!  Beefcaaaake!!!

Cartman from TV's South Park

Where to put 790 pounds of batteries?  The Land Rover, having a truck-based, ladder chassis, means that there’s a lot of space under the vehicle around the frame in which to hide stuff.  After taking lots of measurements and using Google’s free Sketchup program, I was able to find a very close-to-scale model of my Land Rover online.  This allowed me to mock-up component placement to give me an idea what I could fit where.  It’s been tremendously helpful, and Sketchup is pretty easy to use.

RoverEVConversion_HV

You can click on the same image in the gallery below to see a larger version.  The yellow boxes are the battery cells, and you can also see a rudimentary layout of the electrical runs.

I completed this mock-up several weeks before heading to Taos to work on the Rover… and it has proven to be very accurate.  There will be one modification to the rear cells, however.  The Sketchup model’s rear differential pumpkin isn’t fully realized.  On the real thing, it interferes with the rear battery box as laid out, so I’ll have to turn some cells sideways and figure out a location for two orphaned cells, to make room back there.  They’ll probably go up front somewhere.

The side fuel tank locations are being used as they exist on the truck.  I modified my truck for a rear fuel tank a long time ago, so there’s a position there.  The front is now bereft of engine and cooling radiator, so there’s plenty of space up there.

There are a couple of nice side-benefits to this setup.  For one, the cells sit low in the chassis which lowers the vehicle’s center of gravity.  This is a benefit to safety and capability.  Secondly, much more weight transitions from the front to the rear compared to the ICE layout.  This should improve weight distribution from the ICE’s 60/40 front rear split.  In fact, there will be about 300 lbs of batteries in the rear, 160lbs on either side, and 240lbs in the front.

Wait!  Said astute math students will note that, that is more than 790 pounds.  Indeed, all those battery cells must be contained within four separate battery boxes, which I will be constructing out of 1.5″ x 1.5″ x 1/8″ steel angle iron and some thin sheets of aluminum.

But before I can bust the metal out, I need to know for sure that the battery boxes will fit the truck.  Pre-visualizing the layout is great for a start, but as with the differential pumpkin, what you see in the virtual world is not always what you get.

So I spent a cold, snowy, windy Sunday building battery boxes out of cardboard… and then crawling around under the truck  discovering what would really fit.  This is when I was alerted to the differential clearance issue.

Battery Box Mock Up

Now that I have the actual dimensions I need, I can get started on building the real boxes.  It’s been over a decade since I last picked up a MIG gun, but it’s like riding a bike!  It comes back quickly.  This was my first weld on some practice pieces.  They can only get better.

First Weld

For those curious, I’m using a 110v Lincoln Electric Weldpak 100 MIG welder that I picked up at Home Depot in the mid-90s for about $300.  It’s got a gas conversion kit, and I’m running a 75%/25% Argon/CO2 mix.  I’m amazed that 12 years later there’s still a gas in the cylinder!  I’m probably running near the limits of what this particular model can handle, though it shouldn’t be a problem.

MIG welders make it really easy for the lay-person to weld.  I originally purchased the unit to make sheet-metal repairs to the Land Rover’s rusted steel bulkhead.  I self-taught myself, so just about anyone with any creative aptitude and desire should be able to pick it up.  And obviously, it’s been a handy skill to have.

Speaking of which, how did I do the performance projections on my Land Rover?  I used a performance analysis spreadsheet that I found at Brian Hughes’ MR2 EV Conversion site.  We’ll see how the real thing turns out.

The internet, in general, has been where I’ve learned most of what I think I know now.  Only finishing this project will answer whether I actually know anything useful, but for those wanting to learn more about EVs, conversion, batteries, motors, all this stuff… there are a couple of great web forums with people far more experienced than me giving their two cents.  One site in particular, the DIY Electric Car forums, has been where I spend most of my time learning.  Imagine that, an entire site dedicated to homebuilt EVs!

Another interesting resource to peruse is the EVAlbum, a web site dedicated to people’s DIY conversions.  Everything and anything has been converted, and you can find out what goodies were used and how well the resulting EV performs.  Fun for finding really weird stuff.

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Weight Loss!!!

by on Nov.16, 2009, under Design, EV Land Rover, ICE

Spent the last few days removing the last few bits of ICE related equipment from the Rover.  It’s almost all gone!  Let’s see how the weight loss tallies up…

Engine Radiator and Cooling Fan – 25 lbs

Side Fuel Tank (1/3 full) – 70 lbs

Rear Fuel Tank (2/3 full) – 105 lbs

Exhaust system – 20 lbs

Engine w/ancillaries but without clutch and flywheel/flywheel housing – 470 lbs

Total ICE weight loss = 690 lbs
Just short of my 700 lb goal.  But there’s some still left to go…  Fuel pump, fuel tubing, dual fuel tank solenoid switch, heater hoses to the rear…  And I never counted the weight of the anti-freeze and oil that came out of the ICE and cooling system.

If you recall, I was at 3116 pounds (or thereabouts)… with a little cheating, I think I’ve got the Rover down to 2400lbs pre-conversion weight.  Fantastic!  My Mini still only weighs, 1550 pounds with its ICE, though…

Before I mount the motor, I’ll try and four corner weigh the Rover again… if I have the patience…

Here’s a neat comparison:

EV vs ICE Comparison

192v 11" Kostov DC Traction Motor Land Rover 2.25L Petrol ICE
185 lbs 450lbs
165+ peak HP 72 peak HP
200+ lb/ft Torque 124 lb/ft Torque
11" x 11" x 17" (w/h/d) 25" x 18" x 26" (w/h/d)

The EV motor is significantly smaller, lighter, simpler, more powerful, and virtually maintenance free compared to the ICE.

EV vs ICE

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Weigh In

by on Nov.05, 2009, under Design, EV Land Rover, ICE

I need to figure out how much the Rover weighs prior to its conversion to electric power.  That way, I can know, roughly, how much it will weigh post conversion, which will give me some idea of its potential performance capability.  So it’s time for a weigh in!

I don’t have access to a truck scale, so I borrowed this idea for weighing a vehicle at home on a typical bathroom scale.  This method should be fairly accurate.  Even if it isn’t absolutely correct, if I use the same methodology for weighing the truck post-conversion, I will have a good idea of how things relatively compare.  But let’s see how I did.

I’ll be weighing each corner of the vehicle and then adding the results together.  This gives me the added benefit of seeing the weight differences on a per corner basis which can help guide battery placement to even things out, if necessary.

If I simply place a scale under one corner of a 3000lb vehicle, the scale would break trying to handle, potentially, 1000 lbs of weight.  So, I’ll use a lever system to scale the weight down to something reasonable.

How does it work?  A board, forming a bridge, acts as a lever between the scale and another anchor point on the ground.  The wheel sits on the board, and depending on the wheel’s location between the scale and anchor point, the weight measured at the scale changes.

Place the wheel at the scale end of the board and the weight of the truck sits almost entirely on the scale itself. The scale will reflect the entire weight of the corner.  Place the wheel at the other end of the board, at the anchor point, and the weight of the truck sits entirely over the anchor point, causing the scale to measure nothing.  Split the difference, positioning the wheel halfway between the scale and the anchor point, and half of the vehicle’s corner weight will transfer to the scale, while the other half goes to the anchor point.  In this case, multiplying the result measured by the scale by two will reflect the correct corner weight.

500 pounds is still too much for my cheap 300 pound-capacity bathroom scale, so I will use a 4x multiplier, by placing the Rover’s wheel 25% of the way from the anchor point.

Illustration of the weight theory

Illustration of the weight theory

First, I took a 2×6 piece of wood, four feet long, and marked it one foot from one end.  The board was suspended between the scale on one end and another piece of 2×6, my anchor point, at the other.  The setup was positioned so that each tire I measured would sit on the one foot marker near the anchor end.

Setup of the weighing rig

Setup of the weighing rig

For the measurement to be accurate the entire vehicle has to sit level with all four tire contact patches at the same height, otherwise the raised corner would receive more weight.  The discrepancy is not insignificant.  In my testing there was a 100 pound difference on one corner when I didn’t raised all the wheels to the same height.

All four tires raised to the same height

All four tires raised to the same height

When all measurements were taken I came up with the following (all measurements in lbs):

FL – 245  X 4 = 980 / FR – 184 x 4 = 736

RL – 176 x 4 = 704 / RR – 174 x 5 = 696

For a total weight of 3116 lbs and a 60/40 front/rear split.  Interesting to note the 250 lb heavier left front.  My only explanation is, the steering hardware, braking system, clutch, alternator, manifolds, exhaust system, and carburettor are all biased towards the left.  The suspension springs on the Land Rover are sided; the left side is stronger than the right.  Enthusiasts say this is to counteract the weight of the driver, and while that may be true, it may also be to counteract 250lbs more vehicle pounds on the left side!  The weight balance left to right at the rear is just about equal.

Multiply by four to get the real weight

Multiply by four to get the real weight

Not bad for a small SUV.  Of course, it does have an all aluminum body and not much in the way of creature comforts, carpeting, or insulation.  But it’s a good start.  That’s with two fuel tanks, as well.  Although they’re probably only about 1/4 full at the moment.  I wonder if I can get the rig down to 2400 lbs with all the ICE stuff gone?  More on that in  a different post.

How do my measurements compare to official published specs?  A stock 1971 Series 2A 88″ Station Wagon model is listed at 3281lbs, while a stock Base model lists at 2953lbs.  So I’m right in there.  My Rover is technically a Station Wagon, but I’ve added a larger rear fuel tank, stripped the rear of seats, and have a lighter than stock exhaust system.  I’m happy with 3116 lbs, at the minute.

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