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Working with Tesla Packs

53K views 248 replies 25 participants last post by  brian_ 
#1 ·
Hi. Okay, this is a spin-off of Lars` thread on cooling Tesla packs.

The last post brought up heating the packs using the heaters from EV West, which I am also going to use. I have a Tesla water pump too, but cannot make it spin - it looks like an AC motor (5 wires - 3 phases, plus encoder?). I have bought some pumps for circulating hot water for solar-heating applications, but will instead try the EV West pumps from a Smart Car, as they are not diaphragm pumps, probably quieter, and a good price. We will see how hard they are to mount - on order.

I had an Engineer calculate that to heat 5 modules by 10C in 10 minutes would take about 900Watts. Two of these heaters will be less than that, and I now have six modules, but I still like them.

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 $$$....).

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. My thinking is: over time it is temperature differences which will cause them to drift. I am not a fan of top-balancing, but will monitor everything using an Orion - so I could top-balance if I want, or found I needed to.

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.

In the end we went with continuous sides rather than the modular idea, but the slots as shown worked perfectly.

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

We will be receiving our first 3D printed manifold today - only $80 - and yes, we will share.
 

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#3 ·
Hi. Of-course I have not taken a module apart, but have seen pictures, and the coolant tube snakes around between the cells - I imagine they press the curves into it before assembly.

And you are correct about the white ribbed material - it is for heat transfer (somehow).
 
#4 ·
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.
 
#6 ·
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.
 
#7 ·
It looks like EVWest is a resident of the Jack Rickard fool's paradise of anti-BMS people. They don't even sell a BMS, as far as I can tell. Although, the Enerdel battery packs they sell have a built-in BMS. Go figure. I hope they have good insurance!

I think these are the safety valves: http://files.wizkid057.com/teslapack/update3/2014-09-09 21.21.31.jpg It looks like they just pop into round holes in the bottom, outside edge of the battery box. Also notice the silicone mica sheet in the foreground of the photo. The sheets I saw were lightly held in place with double-sided tape. You might be able to request the mica sheets and valves from module suppliers. I'm guessing they would otherwise just throw them out. The custom battery box with separated modules would be a lot of work-but doable. It probably should be made of metal.
 
#8 · (Edited)
It looks like EVWest is a resident of the Jack Rickard fool's paradise of anti-BMS people.
In recent videos Jack has recommended that a BMS is used with the Model S packs and said several times that EVTV hope to reverse engineer the Tesla BMS.

I believe Jack's 'no BMS' policy is battery chemistry dependent (i.e. he would argue that CALB's are more tolerant of abuse than OEM battery's).
 
#12 ·
Fair enough! I think SWF's design with metal, fire resistant componants, and separated modules is a safe way to go. If anything can be learned from StealthE's experience, it's that some kind of pop-off valves or blow-out bulkheads (or maybe a plenum or ductwork) that direct hot gases and flames away from the passenger area would be a real safety benefit. Separated modules might have also limited the fire. As it was, he had no chance of backing or pushing his vehicle out of his garage because of the location and intensity of the flames.

In a driving situation, all you're doing with these safety features is buying some time to safely park and exit the vehicle.
 
#11 ·
Thanks for starting this thread, it will be useful to me to discuss since I am also using the Tesla modules.

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 $$$....).
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.

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.
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.

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.
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.

It would be nice to share ideas on cooling/heating, bulkhead connections (BMS anyone?) and...?
I likely will be using the ZEVA BMS but have not ruled out the Orion.
 
#13 ·
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.
 
#14 ·
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.
 
#15 ·
"The key is to not start the fire in the first place."

And the rest sounds good to me too. No hard feelings about rants/strong opinions.

Now, the devil is in the detail. I think there at least 3 more conversations worth having, although the heating stuff is limited to us Northerners:

1) Heating system hardware and protocol - when to heat, and related issues such as controlling charger;
2) Bench testing batteries
3) BMS.


All the parts are getting close to the battery box, and then I will be doing some bench-testing.
 
#17 ·
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?
 
#19 ·
I would like to keep the BMS debate out of it.
Ok, I'll finish by saying I think Jack's reversal from anti- to pro-BMS (for OEM based packs) is extremely relevant when "working with Tesla packs" :)

It's also worth remembering that Jack kindly demonstrated what happens if you ignore 'battery management' ;)

 
#18 ·
GoElectric: do the Tesla modules contain any intumescent goo (caulking) between the cells themselves? I thought I read about their use of intumescent materials which are an effective way to reduce fire spread, but I don't recall where in specific it is being used.

If you want to force heat transfer to/from the liquid in the tube, gooing up the gap between cells shouldn't hurt and might help.

Personally I've only seen the intumescent materials as a spray or a caulking- imagine it could be provided in a trowelable consistency material too. But if it were available in sheets, it might be an effective part of an anti-firespread design, helping to reduce the risk of a fire in one module spreading to its neighbours.
 
#20 ·
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?
 
#21 · (Edited)
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?
I do not believe any transportable extinguisher will help in something as large as a fire in a traction battery. In the UK the fire service is instructed to allow electric cars to burn themselves out whenever possible (and that's despite them having access to thousands of gallons of water and fire suppressants).

I recommend reviewing the FAA guidance on laptop battery fires to better understand what we are up against;



In the lab it might be worth considering a purpose built extinguisher (see link below for specialist product from EVTV) but the best precaution IMO is keeping packs mobile so they can be moved into the open air at the first sign of trouble.

http://store.evtv.me/proddetail.php?prod=firebane&cat=23

afaik no OEM packs have fire extinguishers, they all use BMS to prevent fires in the first place :)
 
#23 ·
GoElectric:

It looks like your thread has been semi-hijacked with this important safety discussion. I just completely read through the patent info on Tesla's battery safety venting system: https://www.google.com/patents/US20120231306 . Talk about a tale of potential doom and gloom! And this is their own battery system!

Because of the increased hazard with using the Tesla batteries, and others like them, I think it's important to have this discussion in the DIY community.

When we tried to express our safety concerns with StealthE before his Tesla battery fire, he pretty much ignored us. Even his Tesla module supplier pleaded with him to be safe, and use a BMS-which he ignored. You, at least, are responding and thinking about the concerns. Thank you.
 
#24 ·
Good stuff, especially the video.

I like the idea of picking-up on the "intumescent goo." Any leads would be appreciated. I haven't disassembled a pack, but yeah, it is in there somewhere. The Tesla packs come with a layer of 1/2" ceramic insulation, so anyone who purchases modules should ask for some, as well as the mica (I have both) and the valves.

More research would be necessary to assess the heat-sinking capacity of a CO2 extinguisher vs. potential heat released in the event of "rapid disassembly (an anachronism I ran-across for batteries exploding). Getting the stuff around the modules would be another challenge.

Anyone want to start a business building Tesla battery boxes? There is a lot to it, what with heating/cooling and BMS wiring. I'd be willing to build boxes - I have a good (cheap, light, fast to make) design with plastic, am building my own high-current bulkhead terminals and have a design for a 3-D printed manifold which is inexpensive and economical with space. In my design, each box has its own self-contained heating system. I also know someone who is building a wireless BMS which could go in there(!), but cannot say more.

I think most of us are believers in a BMS, so let's just leave it at that. What kind of BMS etc... is absolutely fair-game!
 
#25 · (Edited)
At Lars' request, I did the calculations for temperature change of a single module charging at 3 amps/cell for 15 minutes. I used the number quoted on his thread of 0.83J/gK.

Given a pack weighs 45 lbs (I've never weighed one, but 45 is the number I usually see), the temperature increase was almost exactly 5 degrees C!

This is assuming even distribution of heat, no losses, constant resistance with temperature, no other significant resistances, and neglects any part of that 45lbs which is not a lithium cell. There may be other errors but as stated, I'd be pretty certain that number is accurate to +/-20%.

CONCLUSION: Charging a 12S37P Tesla pack at 100 amps fo 15 minutes should present no heating issues.
 
#26 · (Edited)
I looked-up the heat of sublimation and specific heat of CO2. Discharging 2kg (5lbs) of CO2 into a box and then converting most of it to a gas would take about 1.1MJ of heat. Assuming most of the solid CO2 stays in the box, this would cool a 3-module pack by about 22 degrees C, or 40F.

Thinking about the effect of a blast from a fire extinguisher on those cells in the video, this seems at least promising in terms of slowing down a fire. Plus getting rid of any oxygen should prevent it re-igniting for awhile.

How 'fun' would experimenting with this be???
 
#29 ·
I looked-up the heat of sublimation and specific heat of CO2. Discharging 2kg (5lbs) of CO2 into a box and then converting most of it to a gas would take about 1.1MJ of heat. Assuming most of the solid CO2 stays in the box, this would cool a 3-module pack by about 22 degrees C, or 40F.
??
How would you store 2 kg of dry ice until it was needed in the pack ?.?
 
#28 ·
Hahahahaahah.

I think the CO2 would work if the manifold was designed to shoot it in-between the modules, don't you?

I don't imagine I will do it, but I actually posted this idea in the Spring. There was someone who designed a simple set-up some years ago, but it never caught-on with the DIY crowd.

Anyway, let's not get too far off topic.
 
#31 ·
I'll throw out what I have done so far to test my packs.

I measured all voltages/cell. I have an RC balance charger from Progressive, so it can display all cell voltages at once. All were within 0.02V. I then bulk-charged them (no balancing) and when they reached 4.1V all were still within the same range. I then discharged them to 3V (still monitoring the voltage) and they were still the same. Then charged them all again and as they were still within 0.02V I concluded there were no damaged cells within the 74P groups since they charged evenly, and that all of the groups were still matched.

There was a bit of bounce after charging, but did not quantify it.

That was a far as I got. Not sure yet what else to do.

I used a giant resistor wire in a ceramic jig from an electric fireplace to discharge them, tapping it at different places to get a healthy current but not melt my wires too badly.
 
#45 ·
Hi GoElectric. Is the 3 - 4.1V range what you are planning to use for a LV and HV cutoff for the charger and BMS? It will still be a while before I set these parameters, but I have read that Tesla uses a HV cutoff of 4.15V which is about 95% SOC. However, charging only to 90% SOC (~4.05V) apparently will extend battery life.
 
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