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.
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…
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 on… if 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.
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?
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.
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).
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.
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.
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.
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.
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.
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.
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!
And we’re back… Are you? Drop me a comment or a pm if you’re still following the build!
Is everyone psyched? I am… After a more than half year diversion (isn’t it just like paying gigs to get in the way?) I’m back in the southwest, back in the garage, and back to work on my Land Rover EV conversion.
When last we met I had just received four crates of lithium battery cells. The final part of the Rover build is to get the cells from the crates onto the truck. Here’s what they all look like splayed out on the floor in roughly the configuration of the four battery boxes.
There’s something missing from these groups of cells… the aluminum end-plates that sandwich cells together. Unfortunately, I designed my boxes around the dimensions of the cells themselves. I hadn’t accounted for extra width of the end-plates. Some allowance for extra space was made, but not enough. The stock end-plates add at least another inch to the totals which in some locations couldn’t be spared.
That’s OK. While the cells should be strapped together to prevent side-wall swelling the tight fit into the metal battery boxes should be adequate containment. Besides, technically the cells don’t start to swell until they’re over-charged, and I don’t anticipate putting them through that kind of abuse.
In the meantime, I’ve procured a set of polyester-strapping tools, from an EBay seller, to bundle easy-to-handle groups of cells together. It’s the same stuff used for package shipping. Unlike steel or plastic, polyester strapping retains its elasticity/tension while remaining very strong. This means that the cells will always be under positive compression. The polyester straps are quite easy to work with, as well. Will the strapping alone prevent swelling? Not sure, but in this case the battery boxes themselves will provide that duty.
The strapping kit consists of a roll of polyester strapping, a tensioner/cutter tool, a crimper, and crimps.
Final Box Construction
Once all the cells are strapped together they are placed in their appropriate battery boxes. As mentioned in a previous post regarding heating during winter, each box contains a battery heater designed to keep the cells at room temperature. Batteries tend to lose their ability to pump out power at cold temperatures. Keeping them at room temperature ensures that the EV’s performance during the winter doesn’t suffer. The heaters are designed to be plugged into a standard 120v circuit while the EV is charging. They don’t leach power from the battery pack. As the EV is driven, the cells will naturally heat up due to internal resistance negating a need for active heating during discharge.
Each box is lined with layer of Ionomer foam (purchased from the ever helpful McMaster-Carr). The battery pads are secured to pieces of aluminum sheet which act as a second floor. The heat from the pads diffuses through the aluminum plate allowing an even heating of the cells sitting above. Each heater pad is designed to work at 120v and output 35 watts. Every heater is wired in parallel to create one large 120v, 420 watt load.
Before everything can be buttoned up the cells need initial balancing. This is a crucial step. It’s impossible to know the charge state of each cell as they come from the factory. There’s a good chance that they’re all near the same level of charge, but initial balancing is the only way to be sure. Forgoing this procedure could result in the destruction of individual cells.
Imagine each cell is like a bottle of water. When they’re all linked together in series their energy levels increase at the same time when charged. If one were half full, at the start of the procedure while another 3/4 full their levels wouldn’t arrive at the top at the same time. Balancing makes sure that the levels are all equalized before-hand. Overfilling would be disastrous.
This procedure should only really need to be done once, for all intents and purposes. There’s a caveat to that which I’ll get into later.
The best way to make sure all the cells are filled the same amount is to connect them all in parallel. All the positive terminals get connected together and all the negative terminals get connected together. This allows the cells with more energy to drain into the cells with less, and vice versa. It creates one giant battery pack that delivers 3.2v at a capacity of 10,240 amp-hours. That’s equivalent to a REALLY BIG pair of AA batteries or a battery pack that could power a 4G iPhone for nine years.
14 gauge wire from a 50′ extension cord was used to tie all the cells together temporarily. There are better ways to do this. Line all the cells up in a line with all the positive terminals on one side and all the negative terminals on the other bridged with two pieces of angle iron, for one. But all my cells were already configured for an alternating-connecting, series configuration, hence the crisscrossing maze of wires.
In addition to wiring all the cells in parallel I used a Mastech, adjustable, regulated power supply to charge the batteries to 3.8 volts which is essentially the top of the LiFePO4 chemistry charge curve for these Thundersky cells. This insures that not only are all the cells balanced, but they’re balanced when full making it very difficult to over-fill a individual cell when charging in series.
The way to the power supply works is simple. You wire it in parallel with the cells, and set it to output a set voltage (in the case of the picture 3.6v). The batteries all fill identically until they reach the set voltage. My Mastech can output a maximum of 20 amps. The battery pack I’m trying to balance is 10,240 amp-hours in capacity. If the cells started off empty it would take at least 21 days to fully charge the pack.
Luckily, they weren’t empty… and I cheated a bit and first wired them in series so I could use my big EV charger, an Elcon PFC-5000. Rather than the pidly 76 watts I was limited to with the Mastech, the Elcon could charge at 5000 watts, but I had to make sure to monitor the individual cells with a voltmeter to ensure a cell didn’t go above 3.8v. Once the first cell hit 3.8v, I wired the pack in parallel and finished off the balancing with the Mastech for about three days.
Once the balancing was complete, I rewired for the final series configuration using the supplied copper bus-bars and stainless steel hardware provided with the cells. Not liking the standard lockwashers that came with the cells, I went to my local Fastenal and picked up some toothed washers (also known as star washers) which do a better job of holding hardware together especially when heat-cycled. If you can get your hands on Belleville spring washers, that’s another good choice. I also picked up larger washers to better spread the clamping forces. After the battery terminal was cleaned up with a red Scotchbright pad, a very slight amount of NoAlOx anti-oxident paste was used between junctions to ensure clean connections.
My boxes are designed to be sealed against the elements, which I can do quite easily with lithium since it doesn’t vent gas like standard lead-acid cells. I use marine power pass-throughs to transfer the high voltage between boxes and to the motor contoller.
Wood blocks wedged under the frame tops prevent the cells from moving vertically. Once everything is in place, the cells can’t budge… yet removal for maintenance remains relatively easy. Of course, one of the reasons to go with lithium cells is to negate the need for maintenance like having to add water to the cells of a lead-acid battery.
What!?! No BMS????? (Opinion follows… )
EV affecionados will notice that there doesn’t appear to be a Battery Management System (BMS) in place. And they’d be right.
To use a BMS or not use a BMS? It’s a hotly contested debate within the DIY EV community with opinions and tempers raging on both sides.
Basically, a BMS is used to insure that each cell within a battery pack doesn’t become over-charged or over-discharged since these two events are more or less catastrophic with lithium chemistries.
Active battery managment is much more important for chemistries like Lithium-Cobalt. These are lighter-weight cells similar to the type used in laptop batteries. Allow them to over-charge and they have a tendency to catch fire or explode.
Thankfully LiFePO4 is much more inert. However, a very expensive cell can be rendered dead-as-a-door-nail if either end of the charge spectrum is breached. While it’s relatively simple to tell the voltage of an entire battery pack, it’s much more difficult to drill down to the individual cell level. It requires a lot more circuitry. Enter the BMS.
Many designs exist, from those that monitor cell voltages and report them to a user-interface, to solutions that actively try and balance the cells by shifting charge levels around, to simple management that just employs bleeding excess charge away from a particular cell. All the systems, however are designed to deal with over-discharge by throwing up an alarm, or over-charge by limiting charge current to a cell.
Some question whether management is even necessary. Through a combination of anecodotal and emperical evidence it’s been found that once a set of battery cells is balanced it tends to stay balanced as long as it isn’t pushed to extremes. As long as the user isn’t attempting to drain all of the energy from the battery pack as well as charge it to its absolute limits, all should be well.
I’ve designed my EV to be somewhat over-engineered. While it should have a range of over 80 miles, I don’t intend on every using more than 50 miles. And chances are, 35 miles may be a good average. That could be considered a waste of battery storage capability and efficiency, but regardless it puts a lot less stress on the pack negating a need for a BMS.
I am a tech-nerd, however, and in the future I may install a BMS just to learn more about what actually goes on with the battery cells… in which case I might install an Elithion BMS system.
Next is wiring it all up.