Working with Tesla Packs

GoElectric:

I hope you've read this thread:http://www.diyelectriccar.com/forums/showthread.php?t=175730

What's painfully apparent is that high output battery systems like the Tesla's are potentially more dangerous than other systems. Most failure up to now with less powerful, older battery systems usually involves cells swelling, off-gassing, and not too many fires. As seen in the above thread, the Tesla batteries can burn your house down.

I had a chance to look over a disassembled Tesla battery compartment for its safety features. These include:

1. The modules are isolated from each other by at least two layers of metal with an air gap between the layers of metal.

2. Each module is surrounded in their isolated compartment by a fire resistant material on all sides. It looks like the silicone mica sheets holding the heating elements in hair dryers and toasters. Something like this stuff: http://usamica.com/micapaper/

3. The sealed and isolated compartments that hold each module have vents that apparently pop open in the the event of a fire to direct gases and flames away from the passenger compartment. Here's the patent info on the vents:https://www.google.com/patents/US20120231306

My concern with your battery box design is that it does not have these safety features. It's good that you're using a BMS, unlike the unfortunate, ill advised person in the above thread. My concern is down the line, as the batteries age and/or systems fail, with the potential of a runaway cell(s) and a fire.

Good points on the safety aspects although it will be difficult and expensive to replicate the engineering that went into the tesla pack design--that's why they cost so much.

Looks like the cooling tube does have bends to contact each cell from the patent images.

Hi. I agree with Kenny - these features are excellent, but I don't know how to duplicate them (yet). Will ponder venting - burst valves come to mind.

I did not know that thread existed, so read it all now with interest. But I got a matter-of-fact email directly from StealthE including pictures, and they were chilling. He of-course was supporting my use of an Orion.

I have 1/2" between modules and will use the mica-like material between batteries, and then ceramic wool, which will help. And a BMS. The Orion has some great features which probably would have prevented this fire, like it will shut-down the system if cell voltages are too low, too high or differ by a user-defined amount. It also reduces/ceases charge/discharge currents at extremes of temperature according to a user defined scale.

Mis-handling is a definite issue/possibility as these bricks are not easy to manipulate.

I was not planning on using all of the thermistors, but will re-consider now.

It is of-course worth noting that EVWest does not use a BMS with any of their Telsa pack conversions. I put down their success to professional work and all-round solid design.

I have had thought of rigging-up a CO2 fire-extinguisher so it floods the battery compartment/box in case of a runaway - not sure why this product does not exist yet, but perhaps its time has come with Tesla cells likely to be more and more in use.

I wonder about regulations - in the face of over-regulation, perhaps it would be a good thing nonetheless. Lars: how are the EU regs??

Thanks for the input/warnings: well-meant and well-received.

Thanks for starting this thread, it will be useful to me to discuss since I am also using the Tesla modules.

GoElectric said:

I'm going to use two separate loops too - one for front and one for the back, which means quite a 12V current draw, so unless I think of something clever, will need a larger DC-DC converter (more $$$....).

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Another option to the 12V smart car heaters that I am considering is to use the HV water heaters that are normally used for interior space heating. It would likely need some form of thermostatic control to heat the water to the appropriate temperature to heat the modules.

GoElectric said:

One idea I'd like some feedback on is to keep all of the batteries at the same temperature by circulating fluid through them slowly.

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Not sure what you intend with slow fluid circulation. This may cause temperature gradients as you are increasing or decreasing the temperature of the modules, whereas a high fluid flow would minimize the temperature differences within and between modules.

GoElectric said:

We have a nice design for the battery boxes going. After building the front box out of metal using rails to support, we got the idea to use slots for the back - in 1/2" PVC. This is nice material to work with, as holes are easy to make, it takes a thread very well or you can use inserts if more strength is needed. We cut slots for the battery rails using a table-saw, and joining pieces was quite easy by cutting slots and using 1/8 x 1/2" aluminum bar (see sketch). All is tied-together with plastic banding - metal would be better, but the tooling is about $1,500 and that kind of strength is not needed. Then it sits in a steel frame. We built a box for three bricks, which weighs 37lbs and cost about $150. Half that price was the 1/2" clear acrylic top. If you screw something up, you only need to re-make that piece, not scrap the whole box. I'll attach some pics.

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I will be using all metal components in my battery box. I don't have a final design, but the exterior will have three layers: 18 or 20ga steel, 1/2" aluminum waferboard, and ceramic fiberboard all bonded together. Each module will be supported by rails and separated by ceramic fiberboard.

GoElectric said:

It would be nice to share ideas on cooling/heating, bulkhead connections (BMS anyone?) and...?

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I likely will be using the ZEVA BMS but have not ruled out the Orion.

Hi, SWF,

There is some info on using water heater elements on here, and maybe users can pipe-in and update us. In my mind, I just thought it was simpler to buy something designed for the task - the "build or buy" dilemma - and these heaters are a good price. I have a 750W 110V circulation heater which I was going to use for a single-loop design. It was at least designed for automotive use, but running pack voltage (120VDC) through it would have generated water well over 50C, and the high temperature shut-off is close to boiling-point (if it works at all), so that was worrying me.

I will be trying the Smart Car heater on the bench and hopefully the temps will not get too high as they were designed for these cells, otherwise I don't know what I will do.

I'm not an expert in reliability! I suggest the Orion though, as it does have temperature-sensing, and can limit current if the temp is too high or too low (eventually to zero if you set it that way). If you can control the temp, agreed, that is important, but a back-up is important too. I like the Orion for this, and other features, but the temperature-dependent output has only one thermistor input, is designed for cooling, not heating, and will require some screwing-around. A GEVCU is another option, but not plug-and-play, to say the least.

(BTW, I had an engineer calculate 5 modules would need about 900W to heat 5 modules by 10 degrees in 10 minutes. Heating protocol is a discussion which could be had)

On that note, as far as circulating fluid goes, the idea is to reduce temperature-differential between the cells - no heating - so the temperatures would equalize, and cells deteriorate equally over the long-term.

I suggest ceramic wool instead of fibreboard, as it will insulate as well as provide fire-proofing.

I have a metal box in the front which I built before the plastic idea came-about. I'd like to see pictures of your's, and I can post mine, but unfortunately, it will basically just be a metal box with not a lot of insulation or fire-proofing. This is why I think the CO2 fire-extinguisher flooding the box would be a good idea, but I haven't gone that far yet.

Electro Works: as far as venting gasses goes, if I decide I need to deal with that, I think the CO2 extinguisher with a manual as well as an automatic release would mitigate long enough to get out of the car. As far as I know, he just had his sitting in the back of an SUV. Figuring-out a system of valves and isolation is beyond me. Glad to have your input though and let's move-forward.

Aside from box construction and placement, another thing to learn from StealthE's failure is to have proper automated safety-protocols in place for these batteries, even though it will cost $$$ and time. This does not mean a cheap BMS which would work 'well' for LiPO4s, and imho does not mean top-balancing.

I like the theory that StealthE he had one or more cells short-circuit somehow; that seems to fit what we know about what happened. We will never know, but I think the root-cause of this failure is likely mis-handling, which can happen to any of us, or perhaps component failure. A discussion on bench-testing these modules would be a valuable one too.

All the best.

You've made the right decision- a BMS is minimally necessary safety equipment for a Li-ion pack, especially a Tesla pack with its high energy density chemistry.

Strongly recommending minimally necessary safety equipment is not" getting huffy"- it's merely providing responsible advice.

As to your pack enclosure and heating/cooling design, it seems reasonable to me.

I wouldn't try to provide explosion venting personally- I would provide an open vent in the safest location possible. Want an explosion vent? Tinfoil comes to mind... Lining the interior of the box with something like 1/4" ceramic fibre paper might give the box a bit longer survival time during a fire, directing the flames where you want for a while longer. CO2 will put a fire out, but once the cells are venting electrolyte it is probably not going to prevent a re-ignition- if you can't provide flood cooling, temporary fire suppression may allow enough electrolyte vapour to accumulate that re-ignition will be more violent when it happens than if you just let it burn, but that's a guess. The key is to not start the fire in the first place. For a pack made of cells with metal outer cans, to me that means providing good mechanical support, over current protection, a nonconductive durable inner surface, and a BMS with tested interlocks.

Hi. I know this is not my forum, but since I started this thread, I would like to keep the BMS debate out of it. Not that it isn't relevant, but the issue has been discussed elsewhere, and new information would be more valuable if it was added to those threads. I know it is tempting. I even let slip the word(s) top-balancing myself, and was pleased it did not elicit a debate on that particular topic.

That-said, if you are using Tesla modules, as part of the overall discussion I think it would be worthwhile to hear which side of the debate you stand on, and what you plan to do about it.

I myself am using the Orion. I mostly have the Orion to get a feel for how the cells operate for future projects. A simpler BMS might suffice. It does have the features mentioned previously for temperature-dependant operation, but these could better be managed with something like a GEVCU.

Right now I have no urgent need to get into BMS operation. What are you working on, or thinking-about?

As Jim mentioned I am also seriously considering using Tesla modules for my Volvo Amazon wagon (thanks Jim for the inspiration by the way).
I've done quite some research and am convinced I can do it in a safe enough way so I've nearly decided.
In terms of regulations (what you asked for earlier in a post). There are a lot of rules in general. Some info in English can be found here http://rebbl.com/approval-homologation/ and in the more info links.
There is noting specific about what cells you can or can't use. However the fact that there is no documentation or support from Tesla can be a challenge. I'm expecting to cope with this my using a robust design and implementation with a nice look and feel. What supports this is that the Tesla Smart EV modules are also feasible in terms of using them and having a DIY vehicle registered successfully.
My insights so far (and thanks again for the input in my cooling topic):

• I will be using the Lithium Balance BMS. Not only to be able to monitor the individual 3.6V parallel strings on voltage, but also for full thermal management (2 taps per module plus on the BMS modules themselves (1 per module).
• The BMS will help me in keeping the voltages and temperatures within certain bandwidths and both signal and intervene during both charge and discharge extremes
• Sorry for touching the BMS topic but it felt relevant (won't elaborate on why Lithium Balance)
• Next to the BMS I will also implement active cooling and heating of the modules. Active in this case is without AC but with radiator+fan. Heating is done both by 220V heating elements while plugged in and by using heat from the motor circuit while driving.
• My battery boxes will be made out of metal. Thanks to this post earlier in the topic by electro wrks I am also keen on trying to implement the vent valves and will add silicone mica sheets and will also try to implement individual compartments for the modules within my battery boxes while keeping it workable to install and connect them. At least every module will be mounted itself like Jim does
• To be continued

More to discover and to learn...

One question (at this point, probably many more) to GoElectric/Jim:
You mentioned something about CO2 to flood the battery boxes. What I've read on Lithium Ion fires so far is that the most effective way to stop the fire is to take the heat out. In that way the exothermic (runaway) chemical reaction stops (if you cool enough if you still can) and there will be no further propagation. What is the cooling capacity of CO2 while expanding?