It is springtime in Missouri. March rather carried a bit of late winter and so we’ve had a late bloom but a welcome one.
This week we talk a bit more about the VW Thing progress. This vehicle has turned into a pleasure to work with largely because everything has been so accessible. Rerant on the importance of component placement for maintenance purposes. But some vehicles just make this easier than others.
IN 1973 I was graduating high school and had pretty much decided to move on from my 1954 Dodge Coronet feeling I had gotten my money’s worth on the $60 purchase price. The VW SuperBeetle was kind of the craze and I recall spending some time at the local Wieser Motors looking at the shiny new SuperBeetle’s with what looked like enormous tail lights. I wanted one pretty badly. I recall they were about $3200 loaded. I rather purchased a brand new Ford Pinto, in all ways a better value at $2185 cash money hard come by. But not so much a better car.
That year VW introduced the Type 181 THING in the United States, Trekker Elsewhere and Safari in Mexico. It really was NOT a Type 82kubelwagen. The Kubelwagen was based on the original beetle pan and both the THING and the Karman Ghia shared a much larger pan. But at $3150 it was just a little too wierd for a little too much. Although 140,000 were manufactured between 1968 and 1980, only 25,000 entered the U.S. and in 1975 it failed to meet the new safety standards for windshield intrusion.
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With this build we are not necessarily striving for the best electric vehicle. We are using the THING as a platform to try a number of new things. Most notably of course is our AZD windfall of Siemens 1PV5135 liquid cooled AC induction motors and the AZD DMOC645 inverter. But the high voltage desired let’s us do more experimentation with the CA60FI cell from China Aviation Lithium Battery Company. We have never done a build with this SMALL a cell, either physically or with regards to AmpHour Capacity.
We get kind of a constant stream of inquiries about sizing battery packs and components. And it is always a wag without notice. But the process is pretty simple. First you start with the car. What kind of car do you want to convert? And it goes almost immediately to what kind of performance you want to achieve.
The car is mostly about weight. How heavy is it. In removing the motor and exhaust and tank etc. and replacing it with a controller and electric motor, you can expect to actually lighten the vehicle by 100 lbs or so. But you lose that gain when you add in the batteries and boxes. And the result is a car that is typically 400-500 lbs heavier than stock. So if you start with a 2600 lb car, you will normally be looking at 3100 or so.
We use a rule of 10:1 though it is admittedly very rough with regards to energy requirements. A 3100 lb car will nominally require 310 Watt-hours to move it a mile.
From there you go to range and performance. Now that you know you need 310 Wh per mile, if you want a max range of 100 miles that’s a 31 kWh pack. And at 80% DOD, you will get about 80 miles. So this is a consideration.
More difficult to define is performance. Acceleration. Not only is it difficult to calculate and define, but it is even difficult to compare in discussions. I have been astounded at the lack of performance of many builds that the owner found perfectly acceptable. Cars that wouldn’t get out of their own way were declared quite responsive in description. All things being a matter of feel.
I usually start with what is. The original thing had a 46 horsepower motor and accelerated from zero to 60 in a dizzying heart pounding 23 seconds. At a younger age, I needed two shaves in that kind of time. 46 horsepower is 46 x 746 watts very very roughly so a motor that peaks at 34kw would be sufficient. But it would not feel good.
The Siemens with DMOC645 peaks at about 118 kW. That’s a bit of an overkill. I don’t really need to hurtle down the ramp with a zero to 60 of 5 seconds in a THING. We chose the motor because we HAVE the motor and needed a vehicle to really test and improve Collin Kidder/Ed Clausen’s work on teh Generalized Electric Vehicle Control Unit.
But yes, that takes you to drive train selection. The other end of it is HPEVS claim that the AC-50 is good up to 3500 lbs. We are BIG fans of this Curtis 1238 HPEVS AC-50 drive train – up to about 2500 lbs. At that point our frenzied admiration begins to wane a bit. There are no hard and fast lines. It kind of goes to expectation. With enough gearing, certainly an AC-50 will drive a 3500 lb car and we would have no real concerns about longevity of the motor or overheating. But it might be a much more sedate driving experience than we like to enjoy.
One of our viewers contacted me this week about a conversion he was doing for a customer with a VW Vanagon Pritsche. This vehicle looks like a VW bus with a pickup truck bed and a crew cab and would actually make a GREAT electric vehicle. The conversion shop was trying to make the case to the customer that the AC-50 would be suboptimal in a vehicle that with battteries was just destined to breech the 4000 lb mark despite best efforts. I told him he was precisely correct and that I could not imagine delight and joy with an AC-50 in train. He bought one of our AC-75’s instead and his client is lucky to have him on the four function calculator. The AC-50 does about 110 ft-lbs of torque in the best case while the AC-75 is 180 ft lbs. Identical product with an extra 70% of torque and kind of focused on the low towing and tugging end of the rpm spectrum perfect for such a truck with a VW transmission.
So sizing a motor to a car is a bit of art, but you can’t go TOO wrong here. The AC/DC selection os always problematical. But your motor/drivetrain pretty much narrows your controller options rather sharply. And now we are getting down to cases.
A SOliton 1 has a hard limit at 350vdc as an upper limit as to pack size. If you pick the Soliton1, it can do up to 1000 amps battery or motor. So our pack MUST be less than 350vdc AND if we want to take full advantage of the motor and controller, we really need to be able to squirt 1000 amps without horrendous sag in our pack voltage.
In the case of the Siemens/DMOC645, the eTransit Connect is about 335 volts – almost exactly 100 LiFePo4 cells. And the charts we have show an upper range for this motor of 300-400 amps even for a few seconds. So we don’t need cabling or batteries beyond really 300 amps here.
100 cells is a LOT of cells. But 300 amps is really pretty tame with regards to current. THat points us to a smaller cell size, and a lot of them.
The CA60FI cells we have tested to 12C and are very comfortable that 10C regularly would not be at all damaging to the cell cycle life. Particularly for short durations. Hopefully less than 23 seconds in this case.
So our cells would do 600 Amps and indeed we could go to CA40FI cells and still run this vehicle.
320v x 40 AH is just over 12 kWh. We’re guessing at this point 2600 lbs and so 260 Wh per mile. That’s less than 50 miles. The CA60FI will give us 19kWh. 74 miles max range and probably a little under 60 miles at 80%. And we are at 5C to do the 300 amps. I like CA60FI for this application.
I share this so you can see the wag and figure tradeoffs as we actually do them. You start with car. Go to drive train. Then go to battery pack. Weight, performance, range.
So I get to play with 60 Ah cells. Unfortunately, we had already designed and purchased battery boxes for CA180FI cells which are MUCH larger. We planned 36 of these with an HPEVS system. But as you go down in cell size, they become more granular and easier to fit into spaces. So as it so happened, we were able to fit the CA60FI cells into the same boxes with very little excess space and get the full 100 in as well.
There are those who will tell you that you MUST constrain the cells to contain swelling otherwise your cells will go bad. Hogwash actually. Swelling means your cells HAVE gone bad. You need to constrain them to the degree they don’t fall out into your lap in the case of a rollover. ANd you don’t want them shifting around as you drive. A byte of foam rubber or styrofoam is actually quite useful to take up excess space.
We do reinstroduce the inertia switch. In an internal combustion engine vehicle, this unit shuts off the fuel pump in the event of a crash. Really any minor collision will trip it. This is actually a very key safety element, but also a bit problematical. If you are in a collision and incapacitated, you may wind up with a heavy foot on the accelerator but curiously unaware of it as you are UNCONSCIOUS. This could lead to the poor prospect that you are INJURED in the crash and KILLED in the aftermath as the vehicle tears itself up trying to accelerate to full speed AFTER the crash, and indeed maybe upside down. This little device has a magnetic ball in a cage that is for the most part stuck there, and the switch is normall closed applying either power or a ground to the electric fuel pump. A stiff whack and the ball breaks loose, triping a little mousetrap type device opening the switch. This cuts off the fuel to the engine. Accelerator position is largely moot when there is no fuel. The engine is cutoff.
The only problem with this is if you smack a shopping cart in the grocery store lot, or even hit a curb hard, you can trip it as well. And indeed, many parking lot fender benders you could drive home except the fuel pump is cutoff. If you KNOW about this, and know where the switch is located, it’s a simple matter to push the red button on top and reset it. If you do NOT know about it, you have to tow an otherwise perfectly operational car.
All that pretty much applies to electric cars as well. Perhaps more so. Electric motors spun up very high in RPM often explode in Claymore mine fashion – shrapnel akimbo. In any event, you don’t want your car jumping about after a collision. So we started including this switch in our builds with the Cadillac Escalade.
In this case, the DMOC likes to have power applied all the time. So we will put together a circuit with a Tyko Klovac Czonka EV200 contactor mid pack. We’ll run 12v through a slap switch on the dash to the contactor to keep it energized all the time. The inertia switch we connect between the contactor negative coil terminal and frame ground. If the inertia switch trips, the contactor looses ground and opens, disconnecting the pack circuit. Alternately, if you hit the slap switch, the 12v is removed from the contactor coil with identical effect.
At this point, I would recommend this setup for any build.
It does have a downside unless you run the contactor only with the key on. The coil is always drawing about 300 ma of current. Interesting aside here. Richard took the original speedster for a drive a month or so ago and failed to put the MAINTENANCE switch to off for storage when he got back. I didn’t notice. Yesterday, we had a visitor we were going to take for a spin in the car. It was strangely unresponsive.
The original Spededster has a stereo that hasn’t worked in a year. As I don’t really need music much in the Speedster, we haven’t done much about it. But it does draw current 24×7. We discovered our 57 cell pack of CALB SE180AH cells had incredibly drained to about 6.3v total. That’s a TOTALLY dead pack as best as I can tell and should have cost me 57 cells.
Young Hauber of course had almost pathologically balanced the cells at 2.75 volts. Our bottom balance trick. As I left the shop yesterday we appeared to be at about 183v with all cells very tightly grouped in voltage. I think we’ll get away with this with ZERO loss of cells, though undoubtedly we almost HAD to suffer some loss in capacity. But none evident at the moment.
Tesla actually ran into this problem with the Roadster. A couple of customers “bricked ” their Teslas this way. We did too. Without 12v, we couldn’t even plug in to J1772 to recharge it and indeed our charger would not charge the pack as it couldn’t detect its PRESENCE at that low a voltage. We connected two 12v batteries in series with the pack using a manual connection scheme. We quickly charged it up to about 40v and then removed the two 12v batteries and continued charging.
Meters, stereos, etc. We’ve encountered this before. No matter how SMALL the current drain is, or that it is only from the 12v side, doesn’t matter if you are parked for months. Eventually you will drain it.
It also points up the importance of bottom balancing. In truth, bottom balancing doesn’t really do much in normal operation. It is only important when you overdischarge your cells. The message is, sooner or later, you are GOING to overdischarge your cells. BMS as a solution? How do you power the BMS? It is more likely the CAUSE of this problem. You need a pack disconnect, and you need to disconnect it if the car is going to be parked more than a few days. And a few days can all too easily turn into a few months. WE are just not accustomed to doing regular checks on a car that hasn’t been used or moved in 17 weeks.
So there it is. Fearless leader and battery expert has hosed up ANOTHER electric car with a stupid mistake. My curious ability to fall on my own sword in public remains my most endearing feature. I guess I just don’t have a good “embarrassment” gene although this one does bring a little tingle.
The curious thing about the THING is that you have to have 12v from somewhere to START the pack so that the DC-DC converter can get power to make the 12v the first time. I haven’t worked out that part just yet. But probably a 12v battery you switch on and off.
I detest 12v batteries.