Adventure EV

Electrical

It Lives!!!!! (sort of…)

by on Dec.15, 2010, under Electrical, Motor

OK, so it’s been a while since my last post, a post which appeared to indicate that a full on road test of the EV Land Rover was imminent.  Here’s what happened…

It lives!  Though, maybe the above pic is false advertising.  That wasn’t quite taken from the EV Rover.  But it was taken nearby.

For about 12 miles, that’s what driving the EV Rover felt like.  Unfortunately, it was late in the day and I failed to record the moment on video.  Or in pictures.  So, you’ll just have to take my word for it.

Acceleration

Without any real quantitative measurements my seat-of-the-pants results feel as good or better than predicted.  The Rover will accelerate quickly to its top speed of about 55 mph all the while in 3rd gear, requiring no shifting.  I could, if desired, drive everywhere in this one gear as long as I don’t need to go faster then 55mph, at which time the rpm hits the motor’s limit.  That’s the weird/neat thing about electric drivetrains.  They have so much torque that first gear certainly becomes unnecessary, but in some cases the use of most gears becomes unnecessary.  And since the motor stops without power, I don’t even need to use neutral to come to a stop.  In this respect, driving a EV is like driving an automatic.

The truck will go faster…  shift into forth and I can easily hit 65mph while consuming a reasonable number of amps.  There’s easily more speed in it, but the road I tested on couldn’t support anything faster than a brief spurt to 65mph.

Slot the gearbox into second and the acceleration from a dead stop to the gear’s limit of about 40mph is electrifying (bad pun, sorry).  It’s hard to describe it.  The torque is ever present as soon as the accelerator is dropped, and the truck just goes!  While a conventional vehicle revs its engine, launches, and eases away, the EV just… goes.  No drama, just surfing a giant wave of intoxicating torque.  The lack of drama may seem uninteresting, but it’s anything but.  It’s a completely different experience that is no less exciting…  I mean, it just GOES!!! I’m guessing the acceleration in second gear would extrapolate to an 8 sec 0-60mph time if I could do it all in one gear.  At about three times quicker than normal, that’s essentially insane for a Series Land Rover.  It seems to pull about as strongly as my Callaway Range Rover, a 4.6L V8, in first!  I don’t know how much the gearbox will take… I imagine it’s not good to regularly practice that kind of performance with the stock box… or axles.

Running the same test in first gear would probably result in uncontrollable wheelspin and surely break driveline items.

With the weight of the batteries located so low in the vehicle, the Rover feels more planted than it did before.  It doesn’t roll as much.  I was lucky enough to have installed 109″ Station Wagon HD springs on the rear a long time ago.  While this choice resulted in a “rear up” attitude at the stock weight, the additional EV weight causes the rear to settle nicely, leveling the chassis.  The overall ride also becomes smoother, and traction over the rear has improved.  This is very noticeable when ascending the hills on our gravel/dirt road.  I have yet to determine the final conversion weight…

Range

What about range?  Hard to tell without some long-term testing.  The first thing I will upgrade is the tires.  I’m currently running really, really old off-road biased tires that are no doubt sapping large amounts of energy in the form of rolling resistance.  Over the 12 miles, I tested acceleration with average speeds around 45 mph I consumed 20 amp/hrs.  That’s about 1/6.5 of the pack’s storage capacity if discharged to 80% DOD, or a total range of 76.8 miles.  Discharge to 90% DOD (which is entirely acceptable with LiFePO4 cells) and I’m looking at around 86 miles of range.  Real-world testing will reveal more.  New lower rolling-resistance tires will increase that range figure.  And not trying to out-accelerate its big brother at every opportunity should lower the electrical consumption!

So the performance and range is bang onif not better than predicted and desired.

Having said all that, surely it’s been a couple of months since that last test drive?  Well, yes…  and here’s where I will reprise the phrase…

The Good, The Bad, and the Ugly

Keen followers will remember that I used this headline at the start of my conversion in reference to a leaking clutch.  Conveniently sandwiching the project, I use the headline again.

The Good… I just told you about the good.  The EV Rover works!

The Bad… More accurately, the EV Rover worked…  for 12 miles before it came to a dead stop on the side of the road.  On the way back to the house, under fading light, I witnessed some sparking through the engine-bay aperture that would normally be covered by the bonnet.  And then all was dead.  I rolled to a stop, pulled out my multimeter and started doing some rudimentary tests: Log in to motor controller via laptop…  controller seems to be working.  Check state of battery pack… battery pack is not shorted and outputting full system voltage.  Hmmm…  Feel HV wiring… room temperature.  Nothing out of the ordinary here.  Check the motor temp…  a few degrees above room temp.  No problem there…  Fuses… intact.  Puzzling.

With the help of a gracious neighbor (thanks Barb!) I retrieved the Range Rover and towed the EV back to the garage.  Further inspection revealed…

The Ugly…  Apparently one of the primary power cables inside the motor shorted apart by rubbing on the commutator!  Ironically, the most reliable part of the system failed.  And not because of anything I did!  That’s just weird.

Here's what the wire shorted on. The commutator.

That’s pretty ugly, isn’t it?  Fortunately, it doesn’t appear to be too bad.  Luckily the cable can be removed without disassembling the motor, and the commutator looks clean (aside from the carbon dust).  I removed the bad cable and jumped with another test lead, attached a 12v battery to the motor terminals, and thankfully saw the motor spin back to life!

This is definitely unusual.  Apparently someone at the factory may have forgotten to secure the cable with a simple wire tie.  Well, they say the devil’s-in-the-details, and this is certainly a prime example.  Kostov, the manufacturer, has been very easy to work with in this matter even though they’re located in Bulgaria.  They’ve already sent me a replacement cable!

But I’m not around right now… I’m back in California until the spring.  So there the EV Rover sits, its front up on jackstands, its motor awaiting a little surgery…

Projects never really end… do they?

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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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