Tesla Batteries…Better to be Lucky than Good….

The heart of the issue of electric automobiles has always been the energy storage cell or battery and it remains ever so today and into the future. Moving from the crude lead acid batteries, the limitation on electric cars has always been the weight and size of the battery necessary to power it to any specific distance.

No, this is a new blog, not a repeat of the last one. But the battery thing remains true.

I am forced to recall a conversation from 2009. I was asked if the earlyish LiFePo4 cells of the day could be “improved”. There being some sense that we had reached some sort of limit. I know, sounds quaint. But the question was quite serious. Would batteries get better as we went forward with electric vehicles?

My reply was of course yes. I believe that ALL technological innovation is possible given a wide enough human desire for a particular result. But I was forced to point out that the desire wasn’t very wide. At the time, there were no OEM electric cars being built. Tesla was in the very early days of delivery of the Roadster. And so I posed the following question.

“If I had a battery the size of my pack of Camel Non-Filter cigarettes here, and it would power a car for a distance of 1000 miles, what do you imagine we would do with it?”

The answer was of course that we would sell it and people could make fantastic electric cars. Well let’s suppose it costs $27,000 each. Who are we going to sell it to?

And how do we make it? It will cost $40 million to outfit a fairly modest prototype production facility.

Well we could get some venture capitalists to back us? (This seems to be the answer to all problems in technology).

Ok. SO here’s our pitch: In a world where lead acid batteries are cheaply available with two main manufacturers splitting up an industry that enjoys margins of about 6%, we have an idea for a new battery that costs $22,000 to produce. And we need $40 million to build a pilot plant to run off a few to show around….

Since then one of the two manufacturers has actually gone bankrupt…(Exide).

The point being that in 2009, for all I knew there were dozens of battery technologies laying about in filing cabinets across the land. Who was going to productize them? For what demonstrated market? Literally if you had a battery the size of a pack of cigarettes that would power a car 1000 miles, WHO specifically are you going to SELL this thing to? Like ONE of them in a row?

And note that a central theme of EVTV from the beginning is that you don’t need a venture capitalist and you don’t need a government. One guy getting off his ass on the couch and going to work on something is an ENORMOUSLY powerful act that modifies the future for billions of other humanoids. I asked for 100,000 of you to do that, on the theory that in all that manure, bucking and whinnying and dust, there has to be a pony in there somewhere.

As it turns out, Elon Musk is a stallion. It amazes me to watch the world of trolls and haters and wannabe investor geniuses constantly harp on this guy. It’s not so much how WELL the bear dances, it’s that you taught a bear to dance at all.

His small team pretty much singlehandedly designed and built the best car in the world, and it is electric. It is a marvel. And all the Leaf’s and Volts and Bolts to kingdom come would not have been built at all were it not for the threat of the Tesla Electric Car.

But his vision quite exceeds that. He has purchased Solar City, a company he was allied with anyway, and raised billions to build a battery factory in the Nevada dessert that essentially doubles the worlds lithium battery production. And the significance of all that is that it removes the question of market and sales and potential. Battery researchers worldwide can now expend effort on battery improvements in the certain knowledge of untold riches for success. Investors are piled up ontop of themselves looking for the next breakthrough. The monster is off the chain. The outcome is now inevitable.

In this episode, we note the magic of Dr. John Goodenough and his development of the lithium anode solid state battery. Goodenough is the chair of the Cockrell School of Engineering at University of Texas at Austin. He also invented the lithium ion battery and more recently, the lithium iron phosphate LiFePO4 battery.

He had been threatening this for several years. Glass electrolyte/dialectric material seems to be the solution he was seeking. And I cannot persuade what an enormous breakthrough development this is. Only time will convince you. But the genie is out of the bottle.

As it turns out, he’s not alone. Plastic can ALSO be used as both an electrolyte and dialectric in a battery… Dr. Mike Zimmerman is a professor of materials science at Tufts University. He has been working on a plastic polymer electrolyte/dialectric and enduring some success as well.

Our previous episode announced that due to some unfortunate events among EV builders, our attention is rather forced to the Tesla Battery system. Individuals are turning to used batteries out of wrecked Tesla’s and as always, their sense of a value proposition is unerring. The individual battery cells, without the package, just the 18650 cells, currently go on eBay for about $5.60 in quantities of 100. That means that an 85kWh Tesla battery pack has $39,711.36 in battery cells alone. Yet you can pick these Tesla packs up for a scant $15,000. And if you remove the 16 modules and sell them on eBay at $1299 each, you can get about $20,784 for them. That’s a quick $5784 for about two hours work to disassemble the pack. If you do a lot of that, less than an hour.

Even then, the 444 cells per module would go for $2486.40 new – and that’s without the package holding them together rather nicely. Ok, so they are used. One guy wrecked a P100D less than an hour after picking up the car and it had 44 miles on it when it sold at salvage. Many wrecked Tesla’s have 50 to 100 cycles on them.

The problem is of course that the chemistry of the cells is a safety horror. They are basically firecrackers looking for a BIC lighter. They will burn your car/shop/house down in a New York Minute at the slightest provocation.

Tesla uses them because of very high energy density, the capacity to weight ratio. And the fact that they are manufactured in the brazillions and there is hope for economies of scale.

They survive this using extreme measures of battery management. They actively cool AND heat the battery packs with a 6kw system that circulates coolant past every single one of the 7,104 18650 cells in the pack.

They individually fuse link EACH and every cell in the pack so if it shorts, it will immediately remove itself electrically from the charge or discharge path.

They also carefully monitor the precise voltage of every 74 cell segment and monitor the temperature of BOTH ends of the 444 cell module. And they enclose all in a 250 lb hermetically sealed aluminum box and put a TITANIUM strike shield to guard THAT.

And if ANYTHING is in the slightest remiss, the system automatically and instantly opens two contactors disconnecting the pack from the car entirely and you roll to a stop. While charging, if ANY cell simply gets a tad higher than the others, it STOPS charging and opens the contactors automatically.

With THAT, they have still had explosive and incendiary fires while rolling and even while sitting still charging. But due to these extreme management measures, these incidents have been very very few given the number of cars out there.

The problem of course being that our erstwhile viewers, ever on the alert for a seam in the zone and a bargain, are buying these modules as is, and having no clue how the BMS works, they are using them without the cooling and heating and without the constant monitoring of voltage and temperature – to predictable results. Tragedy.

It’s true that some are attempting a homebrew battery management system. I can assure all of you that don’t know and don’t know you don’t know that EVTV’s stance against battery management systems derives from our early attempts to purchase one and later attempts to design one. And yes, I am aware that each of you is an undiscovered and poorly appreciated electronic engineering genius of the highest education and genetically disposed toward both brilliance and genius. And it IS further true that I am a doddering old man with early onset Alzheimers who has no clue what he’s talking about despite 40 years now of random tinkering and blowing shit up. But I would caution that BMS design is not precisely as it first appears, and there be dragons beyond these waters… We’ve actually seen more cars burned to the ground by well intended battery management systems than we have by batteries, and specifically in the LiFePo4 chemistries.

And the Tesla battery modules are very specifically NOT LiFePo4. They are VERY different. And as we learn more about them, a fright. For those with an ear to hear, these batteries WILL hurt you. It has nothing to do with whether. It’s all about when.

The cooling and heating is not very hard to reproduce, and probably not necessary. If you are willing to shut down the pack on a temperature anomaly, you don’t really need to cool and heat. But you do need to be aware that CHARGING of these cells below 0C freezing causes irreversible lithium plating of the anode and can result in destruction later when you charge normally.

And so the important part is to monitor both voltage and temperature every few milliseconds and DISCONNECT the pack from charging or discharging if anything is out of bounds. And that means relatively. It’s probably ok for these cells to be tiny bit over 4.2v as long as ALL of them are. The problem is if you have one at 4.25 while the rest are at 3.85. It’s ok for them to be warmish, say 45C as long as ALL of them are 45C. If you have one temp sensor at 45C and the rest at 33C it’s a problem. Potentially a big problem.

In the previous episode, I announced we were going to take a look at reverse engineering both the Tesla battery pack as a whole and the individual modules as well. I think most people focus on the individual modules. I feel safer treating it as the pack Tesla designed in the first place in its entirety. But we decided to attack both. The value proposition is an attractive nuisance and without action is going to hurt somebody. Actually, we’re too late. It already has.

We also created a blog entry with a general call for assistance on the topic of batteries. And we called out a moribund Hackaday project by Jarrod Tuma There had been no further postings on this since April 16 and Jarrod appeared stymied. But he had been doing some very interesting work on the little BMS boards on the individual modules and had identified the Texas Instruments BMS chip being used.

He also identified a fascinating RF isolator chip and a TTL serial bus operating at a very unusual 612.5 kbps that links all the individual modules to the battery pack master BMS board.
He was re-enthused by our video and blog and he, and Collin and a couple of others began the arduous task of disassembling the 8051 assembly language program that runs these boards to try to figure out how to communicate with it.

This microcontroller talks to the Texas Instruments BMS chip over a Serial Peripherals Interface (SPI) bus. All the commands to set configuration and read individual cell voltages and temperatures are defined in the Texas Instruments data sheet and so of course very public knowledge. But what did Tesla use to talk to the Microcontroller through this RF isolation chip and serial bus?

While they strove heroically to decipher the assembly language code, I offered a different approach. I could probably wire up to interface with the serial bus and capture some of that and maybe we would get lucky.
I never got around to it.

My next thought, which I shared with our by now ad hoc hack team, was that if I were designing it, I get the isolated serial bus concept. But why reinvent the wheel? I would have just used precisely the same register reads and commands that were defined for the Texas Instruments BLQ76 BMS chip in the data sheet over the isolated bus as well. The 8051 would just pass them on to the BLQ and then pass the replies back to the bus.

I was assured by all and by consensus that there was just far too much code in the 8051 firmware for it to be that simple. But Jarrod subsequently decided to try it anyway and wired up to a board and sent it a few trial commands.

Batta Boom Batta Bing. As we always say at EVTV, it is simply better to be lucky than good. Collin immediately sketched out some software to do this on an EVTVDue board as well as a Teensy 3.6. It takes a tiny bit of additional hardware with the EVTVDue but we are working on a shield that will let it control a couple of contactors as well. It does no good to monitor this thing if you can’t automatically and instantaneously disconnect it.

Here in the shop, we turned to the battery pack itself. A year ago I had written a program for our Tesla CAN monitor device to decode the 6F2 CAN messages from the battery pack. This message iterates in a sequence providing the cell voltages of each of the 96 cells, along with the temperatures of each of the 14 or 16 modules with two sensors in each module. So we figured out the pinout of the X035 and X036 connectors and could apply the 12v needed to power the contactors and get the pack talking CAN and giving us that data. But we were struggling to figure out the magic sequence to close the contactors. And without closing them, you can’t use the battery pack for much.

All suggestions centered on the High Voltage Interlock Loop. I checked it a dozen times. It can be 120 ohms or 180 ohms but those really are the two possibilities depending on the car. We were lucky to figure out that there was a loop in the high voltage connector to the pack and a single small pin in the connector is inserted into the pack bridging two contact rings that close that connection. But we still couldn’t seem to get it.

A helpful if expensive gentleman from Krasnau Lithuania offered some help. As it turns out, you have to have the output also connected – and it has to have a very specific amount of capacitance. This of course is because the battery pack does a precharge before actually closing the contactors.

We ourselves do this all the time on our vehicles. We put a 300 ohm 500 watt resistor across the terminals of the positive contatactor. Then we close the NEGATIVE contactor. This completes the circuit through the precharge resistor. After some brief time period, the capacitors in our chargers, dc-dc converters, and motor inverters charge to the pack value but the input current is limited by the 300 ohm resistor to an amp and a half or thereabouts. Then we close the POSITIVE contactor to allow full current flow.

Tesla does the same thing. But instead of a fixed time period, they measure the actual time it takes to reach full voltage, and if that time is not within a certain narrow window, it aborts the process. They aren’t doing ALL electric vehicles. They are just doing the Tesla Model S and so they know what the capacitance is of their system. So they time it.

Bottom line is that we can now close the contactors, charge the battery pack, use the pack to drive our UQM Powerphase 100 test bench which happens to be a few feet away, and generally use the entire Tesla battery pack as we will. But have also developed software to monitor the voltages and temperatures and operate two MORE contactors. You see, now that we know how to turn on the internal contactors, we are kidn of forced to simulate the Tesla with a capacitor, and then operate our own contactors and precharge resistor to do an effective precharge on OUR car or solar system. So we wind up with TWO sets of contactors. One inside the battery and one outside.

But if any voltage or temperature is noted outside our own selected range, we can disconnect the pack automatically and instantaneously.

The software will let you enter limits for high cell voltage, low cell voltage, high temperature, and low temperatures. As long as everything stays within the window you prescribe, good to go. Anything falls out of those limits, it disconnects the pack.

Bill Bayer is building me a prototype box. We are NOT going to sell the batteries but we will sell this controller. The issue is the high voltage connector. We don’t know where to get them. ANd if we did we would expect them to be prohibitively expensive. So using some 1/4 copper bar stock and some copper rod, Bill is incorporating the connector into the box itself so it plugs directly into the pack receptacle and eliminates the need to source the connector itself.

Collin Kidder is joining us with a trip down to Cape Girardeau from his home in Sparta Michigan next week. We will film both the module control and the pack control then and it promises to be a fascinating episode.
We had planned this trip to help me get some of this decoded. It is now shaping up as a victory lap on both the modules and pack. So it should make good video.

Meanwhile the full import of all of this had apparently escaped me. Robert Coyne of Colorado Springs called me with some excitement. He was actually a Boardwatch Magazine reader going back into the 1980’s and also a friend of my buddy Cowboy Dave Hughes of Colorado Springs. Dave was a big advocate for the Internet in the earliest days.

Robert called to assure me I have no clue of the import of what I am doing. He was quite excited. He noted there are MANY more people working on off-grid home solar than are working on electric vehicles and they are desperate for battery storage. They have already discovered the Tesla battery packs and are all too familiar with the shortcomings – numerous clumsy BMS design attempts in progress. So the idea of actually being able to use Tesla’s packs with Tesla’s BMS for DIY home powerwall designs is much more attractive than I know. Or so he assures me.

Actually I am not ENTIRELY clueless on the topic of home solar. I built a 15kw solar array at my home in Denver in 1998. 50kWh of batteries. At the time it was the largest residential photovoltaic array in the world at a cost of $270,000. Still operating. My son lives there now.

It also featured the TALLEST lighthouse in the world and it remains so today. It uses a five foot diameter four foot tall buoy light from the English channel in a sixteen foot diamater cab. . Brass, with bullet dents from the second world war. Clear polycarbonate floors on two levels and polycarbonate stairs look like crystal stairs. Quite a magic design if I do say so myself.

But he was correct in that I have heard from several DIY home powerwall guys. Most notably Joe Sidebottom. Joe’s dog doesn’t like shovels. And therein lies a tale.

Joe actually works for a solar installation company. He and three of his co-workers purchased a 20 acre piece of land ill served by a utility company. And they split it into four plots and are ALL doing off-grid home solar using left over bits and pieces and lightning strikes from work.

 

As our own Bill Bayer is currently shopping for 5 acres of dream homestead here in Missouri, with an eye toward off grid tiny house good eats combining everything he knows about cable tv, they hit it right off.

Joe has actually parted out SEVERAL Teslas in a quest for a whopping 140 kWh of solar battery. This will be enough to provide electricity until the Zombie Apocalypse. He’s following our progress rather closely.

He also has little use for drive units in his solar scheme. So we have hopefully scored some good ones. Thank you Joe.

He also notes that Outback has finally put together the solar guy’s dream box. It will do high voltage. It will both charge and invert. It will swing grid-tie. It will swing off-grid. It will use generators. And batteries. It appears they have finally pulled all the pieces together into a single unit that does what I’ve always wanted to do in solar. Of course, unobtainium but rumored to be available mid-year.

In any event, we are having a victory lap party next week with arrival of Collin Kidder. It is my intention to produce video of both a string of modules under full operational control as well as a Tesla battery pack charging and driving a UQM Powerphase 100.

Jack Rickard