Moore from the Land of Harsh 12v busses and Itty Bitty Batteries: Unraveling the World of Electric Car Battery Systems

In this week's underdog adventure, we retrace our steps on the Aux battery and the 12volt subsystem.

We have a number of loads that need to be on all the time - parked or running. In fact, the number of these is reaching kind of alarming proportions.

We are powering our Xantrex AH meter also with 12vdc. We've tried a number of near disastrous ways of powering this little device and the best seems to be to use an inexpensive (usually $10-$12) DC-DC converter module to take 12vdc from the car, isolate it through the 12v/12v converter, and power the Xantrex with it. Of course, if we are to account for IN amp hours while charging, we have to have it on all the time. Since I can't read it without the backlight, that's on all the time as well. It's a bit of a 24x7 load on the 12v system.

But, it is ON for 24x7. So we tried using an aux battery to the ignition switch, and that voltage to in turn run a contactor that turned on our main DC-DC converter. This quelled the complaints from the Netgain Controls Warp Drive Industrial, but caused endless other problems. Most notably, we kept running down the battery when we charged overnight.

We added a manual bypass switch to bring up the DC-DC converter and recharge our dead battery. But the whole thing was a nightmare and we were going to have a totally destroyed battery within days.

We have tried an aux battery in the past - always to some bad end or other. We've had numerous people point out that if we lose our DC-DC converter, our car won't operate. Duh. What we've found is if we lose our DC to DC converter, we don't know it at first because we have an aux battery. But within a few minutes, the battery runs down anyway and our car won't operate. Plenty of weight, an inherent maintenance item, and same effect.

We're also warned of dire safety issues as a sudden shut down will cause us to lose power brakes and power steering and all manner of ills suddenly while hurtling down the freeway. Same answer really. But most of our cars don't have power steering, power brakes and so forth anyway. For the ones that do, for example the 2009 Mini Cooper Clubman Electric, we have a different solution - redundant DC-DC converters. Indeed the design of the Mini's startup sequence requires 12v of course, and we use one converter to bring it up, and when up it engages a second converter as well. When we shut down, we disconnect the big one, but leave the small one running.

The original problem on the eCobra had to do with the Warp Drive Industrial controller. It threw a series of errors when we shut OFF the controller at the end of the drive. This was very peculiar. But the controller stored the errors and so wouldn't operate the next time we fired it up. We learned to clear the errors with the Interface Module, but once we have all this working, we don't see really using this Interface Module day to day. A great troubleshooting device, it can't count Amp hours and doesn't really add much operationally. Certainly having to clear these errors prior to driving wasn't happening.

Ryan Bohm insisted this was caused by noise on the 12v system and wanted us to scope it. I have a problem with all that. What noise are we looking for? There is noise. And there is noise. And in fact, we find the 12v system in a car a very noisy place, and one of the primary culprits is in rather circular fashion - the controller. So I'm vaguely disinterested in noise in general. Assume we are going to have it in an automotive environment.

In this case, I had another problem with the concept. The controller worked fine - ONCE we had cleared the errors. Indeed, the errors only occurred when we were shutting DOWN the system. If the controller has an issue with "noise' in general on the 12v system, why didn't it throw errors while I'm driving down the street?

Our 12v system does have an unusual number of inductive loads on it. We have a prius pump, for the controller cooling system, a Derale heat exchanger fan of actually some size, again for controller cooling, and an XSTurbos turbocharger we are using as a cooling blower for the 11HV motor. At 435 cubic feet per minute, this fan draws 4.6 amps at 12v.

The windings of a motor are an inductor. An inductor resists changes in current. Current through the windings causes the expansion of a magnetic field around the windings. This field stores energy. When you cut off the current, the field collapses. This collapse induces a current in the same direction. And this can cause relatively huge voltage spikes. The spikes are hard to see on an oscilloscope because while they can be surprisingly high in amplitude, they are very transient. They only appear for a handful of milliseconds. I happened to have a very cool very fast 600v 100 amp diode laying around - about 10,000 X overkill for this test. But we hooked it up between our 12v bus and ground.

It had NO effect.

Ryan Bohm was able to duplicate the problem as he had a Derale heat exchanger as well. What he found was something very different. The fans have a bit of inertia in them. When you shut them off, they keep spinning for a second or two. And when they do, they act as generators. They were maintaining 4-5 volts, quickly decaying of course, on the 12 volt line.

The problem is that the ON digital input to the controller uses this 12v to signal the controller that we are indeed on. So we have shut DOWN our 12v supply to the controller, but the fan is producing sufficient voltage that the ON input is high - for a second or two. This causes the errors to be noted and stored.

We tested this by putting a diode in series with the fan. When it is shut off, the fan does generate, but the diode blocks the feedback into the line.

That pretty much fixes the problem, but as the Derale uses six or seven amps of current, I did not want a semiconductor in that line heating up and inevitably becoming a failure item.

As a workaround, we connected the fans with a relay and used the ignition voltage to energize the relay. In this way, when we turn the ignition off, the fans are simply disconnected physically fro the system. The 3-5v cannot reach the ON input, and the errors do not occur.

This was an interesting problem. But it had us running in circles for days. And it is probably beyond our concept that ANYONE can convert a car to electric drive. in this case, anyone can't, and indeed Jack could not for some period of time. So the "fix" is for the controller to be fixed where this is not an issue.

It does bring up the concept that all such loads ought to be on separate relays with separate fuses. Not a bad practice actually, and you will see this in most modern automotive fuse blocks. Lots of fuses, and lots of relays. There's a reason. But the controller should not depend on that to operate. Put a relay inside the controller if you like.

We also devoted a bit of time to a discussion of the Tesla/Panasonic connection. Tesla makes all this needlessly secretive and confusing with their constant claims of proprietary madness. But that's mostly illusion and press puffery. Panasonic did invest $30 million in Tesla and owns 2% of the stock in the company. And they are working together. But the original concept was for Tesla to use off the shelf cells that are produced in the millions for laptops, cell phones, and flashlights. With the acquisition of Sanyo, Panasonic is the largest manufacturer of those in the world, BYD perhaps excepted. on raw numbers.

In March of 2012, Panasonic begins the production run of a brazillion of their new NNP 3.4Ah cell. This is there New Nickel Platform. It's actually a Lithium Nickel Cobalt Aluminum Oxide cathode material with a carbon anode. And the thing carries 12.24 wH of energy in a 46 gram package. This is something like 266 wH per kilogram. By contrast, the CALB or Winston type cells are more like 109 wH/kg in their optimum size.

This is very nearly two and a half times the energy by weight. And if our 444 lbs of CALB cells were these new Panasonic's instead, we'd be seeing 266 miles instead of 109 in Speedster Duh. As I've actually driven Duh pretty flat at 110 miles, I'm onboard.

Ergo the 300 mile Tesla Model S.

We also learned a bit about cycle life in these cells which is very encouraging.

Cycle life to the industry "traditional" 80% of original capacity is somewhere in the 500-800 cycle range. Not good. But if you look to 70% as the mark, it gets much better as the deterioration curve flattens out in a very unusual fashion. You're looking at well over 2000 cycles to that level. And 70% of 300 is still 210 miles.

These are not here yet. But I do not classify them as unobtanium per se. They have good prospects for being available subsequent to March 2012. Tesla has contracted for enough of these cells to do 80,000 cars over four years. That's 640 million cells. As it will also be the highest energy density of any 18650 form factor cell, it will undoubtedly be popular in a number of other applications - flashlights if no where else. And so we have a truly MASS market battery cell here. That brings in economies of scale. That's the game we need.

I don't relish making modules of all these little cells. But 2.5x energy at potentially a LOWER price within a few years from what we're now paying for CALB/Winsston cells could be a play.

In a much larger sense, there is a perception, espoused by Elon Musk himself, that the Moore's law of PC speed and bandwidth only applies to batteries in a rather sedate form of 8% per year or so. I've never completely bought into this. The creeping advance were in a product that had zero market and no cash flow. As soon as you add oxygen in the form of ducats coming in the door in substantial numbers, innovation in batteries is not that hard. There is tons of cool science laying around with the usual problems of engineering to a product level, but there simply has been no oxygen (money) to drive the productization. Panasonic has already announced plans for 2013 to bump this very 3.4Ah cell to 4.0Ah by using a silicon alloy anode in place of the carbon anode in this cell, for example. But if a fire ensued in the battery market, there are plenty of players and plenty of advances to come. I think Moore's law is alive an dwell in Batteryville. And a car with a 1000 mile range is not inherently a preposterous notion.