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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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#104 ·
High voltage: two contactors.

For a household battery on a boat (24 or 48 volts) I was considering using only a fuse on the output, but a contactor to create a short circuit when cell voltages go outside spec.
This way there isn't a constant current draw on a contactor, and in normal circumstances all connected devices would listen to the bms or not operate above and below set voltages...

A pyrofuse would be able to get the same result, but with a bang just in the fuse and not on all connected devices...
 
#106 ·
Same here, I will also use one main contactor per enclosure.
More contactors is also more contacts so possible points of failure / resistance. So my aim is to use as less contactors as safely possible. Therefore I add the main + and precharge contactor to the rear box and the main - and charger relay to the front box. In that way I don’t need a midpack contactor.
Indeed curious why you have chosen 2 per exclosure Jim.

Furthermore I am interested to hear why you will use the EVTV main BMS board instead of the Orion setup.
 
#107 ·
Here's a description from the Miev manual on HV control using + and - contactors, and precharge contactor.

When the electric motor switch is turned to the START position or when the charger is connected, the EV-ECU enters the high voltage start mode. At this time, the main contactor (-) is turned ON, and the charging contactor is turned ON. Then, the smoothing condenser is charged while the current is being restricted by the resistance. Subsequently, when the smoothing condenser voltage exceeds a predetermined value, the main contactor (+) turns ON, and the charging contactor turns OFF. Under the above condition, the main battery becomes ready for use. When in the high voltage termination mode, the main contactor (+) turns OFF, then MCU is instructed via CAN communication to discharge the smoothing condenser. Subsequently, when the smoothing condenser voltage becomes less than the predetermined value, the main contactor (-) turns OFF.

 
#109 ·
I think I will start by saying one can go overboard on safety - one might never get the car built.

I don't know The Answer to using two contactors per box but yes, in our case it is in case one contactor fails. It is not that expensive or time-consuming. It would be ideal to have some way of determining the actual state of a contactor, but you would still need two: if a contactor does not open, you need to have another one which does.... EVTV sells contactors with a status output and uses them in their Tesla battery BMS. This output feeds back to the ECU (which presumably checks them) and Jack uses two.

In my case, the Curtis controller does its own pre-charge. I can see if the pre-charge (or lack thereof) caused some failure which fused the positive contactor, two contactors would be good. Jack does not monitor precharge per se - the second contactor closes after a predetermined time, regardless of the outcome of the pre-charge. We don't like this - it seems reckless (and he will probably change this). Also, I believe it is Zeva which makes a pre-charge device with closed-loop feedback, which I would use if the Controller did not do-so itself. Not sure what voltages it is rated for.

Further to the topic of battery isolation and safety, we are thinking about having an illuminated manual switch on the box which opens the circuit to the contactors. And/or a light which turns on/off on the outside of the box whenever the terminals are live (or not); this would be helpful when handling the box,and again, simple to do. One of those plasma bulbs (?) which you find in testing equipment.

In general, I think something rigorous to keep track of protection would be useful, but rules of thumb honed by experience are good too. I've been scratching some things down and perhaps a truth table is too complicated. Perhaps one table for each component, or failure-mode? This may go nowhere, but if there is a reliability engineer out there somewhere, I'd bet he has a rigorous method of tracking protection from cascading failures.

You really need to read-up on Jack's Tesla battery BMS, but at the very least, we prefer to have the cell-taps terminate inside the modules themselves, with voltages and temperatures reported by isolated CAN, rather than running 7 tiny little wires per module (ready to vapourize if they are shorted) some distance to the Orion. The Orion has features Jack does not have in his software, so in the end it is what you are comfortable with. Heck, what can I say: I'm an early-adopter.
 
#110 ·
I guess I will rethink the option of using one or two contactors per enclosure. Safety is top of the priorities list, so even if it also introduces another failure point I will have to consider it.

The controller I am using (Soliton 1) has built in precharging, but the chargers (Brusa 513) will require precharging since I don't plan to have the chargers permanently connected to the battery. So I will need to work up the proper control of the contactors/precharging for charging vs driving.

With respect to BMS, I agonized over using the Orion vs distributed ZEVA BMS setup and decided on the ZEVA. The Orion had greater flexibility with respect to programming, but I did not like the idea of running cell tap wires all the way to the Orion, since at least one battery enclosure would be some distance to the Orion. Also, the Orion is not a sealed unit, so would either need to be put in one of the battery enclosures, put in its own enclosure, or put in the passenger compartment. None of these were ideal for my build. Folks that are not in a hurry will also have the option of the Lithiumate Vinci EV BMS which is supposed to be available sometime next year. It is a distributed BMS system that would probably also work well with the Tesla modules.
 
#112 · (Edited)
for safety reasons such as containing a fire, would a metal box not be necessary?
Many engineers would argue that a 'fire proof' battery box is required, not only for safety reasons but also to protect the engineer from legal liability when something goes wrong. In the UK (and I suspect in many countries) the insurers will undoubtably hold the engineer liable when shit happens :(

My advice is to follow the Tesla battery box design as closely as possible. It's fully documented in patents, online posts, and YouTube videos. It will make the design heavier and more expensive but IMO that's the price we pay for using cutting edge technology in our cars. If you're unwilling to do this then I believe you really should use safer cells like those from CALB or Nissan. Note 'safer' not 'safe' as EVTV discovered.

Don't get me wrong, I'm absolutely prepared to fight for the rights to undertake DIY (see here) but good engineers prepare for worst case scenarios :eek:
 
#114 ·
Hi SolarSail et al. Yes a flame-proof box would be nice. We made one and found lots of reasons to go to plastic, but flame-proofness went with it. One question I would have for the steel box guys is: how do you attach the modules to the rails? We ended-up drill-tapping small holes through both, and this was really tricky.

I'll attach a few pics taken the other night of the sides of a two-pack. If there was some kind of fireproof material we could use instead.... I suppose one could cut slots in aluminum, although it would be tough, to say nothing of deafening?

I haven't been willing to, but is anyone trying to mount them on their sides?

Sorry, phone not connecting - no pics.
 
#120 ·
One question I would have for the steel box guys is: how do you attach the modules to the rails?
For my front box I add stops at the end of my rails. I plan to slide the modules in as a tight fit.
Not sure yet how to secure them at the front. Current ideas are a bolt though the alignment hole and/or a stop screw all the way through in front of it or some kind of spanner screw/block.
This is my current design. Am still working on the rails and in doubt whether I will ad steel in between the modules or just micanite.
@SWF Thanks for your take, I think I'll decide similar.
Currently I anticipate on using 1,5 mm steel for the body of the box. The highlighted part in yellow and that weighs 11 kg excluding front and top cover.
 
#115 ·
Oh - I forgot to answer the question about sourcing the plastic. We bought from a local plastics supplier, Industrial Plastics and Paints - no biggie to find something local. I just called and they charge $CAN13/ft2 for 1/2" pvc. For a 5-pack that would be about 6 sq ft. Cheep! A 1/8 clear plastic cover will be about the same/ft2. We put together a 2-pack last night and it weighs about 20 lbs, and will mount it with metal tabs (angle-iron) screwed onto the sides with 1/4"-20tpi bolts, and another brace. The bolts will bend before the plastic gives-way, we tried that last night too....

You need a saw which can make accurate cuts. A DRO (digital read-out) will help a lot. They are easily installed and only a couple hundred bucks. We made one without and wouldn't do it again....
 
#116 · (Edited)
Heh - a fellow Canuck - am in Vancouver. I am buying new 18650 Panasonic (Sanyo) 'B' cells 3.4Ah (or LG cells) from a reputable supplier to build 12 kWh for a Leaf and maybe 100 kWh for a sailboat. I plan to spotweld 1.5 kWh (sub)modules - 13s10p and make that a building block for the projects. For the larger project I plan to go 8s2p(4p13s10p) (a module is made of 4p 13s10p sub-modules in parallel - 6 kWh - then two modules in parallel to make a bank, and then 8 banks in series). Each 13s10p sub-module comes with one micro-fuse per cell, its own balancer, multi-way protector board, and one CCCV 1 kW step-up charger per module. I don't plan to have an intelligent BMS for the 12 kWh, but will have it for the 100 kWh. Charge/discharge is low-C so no heating/cooling. Of course this is all on paper and in practice it will be very different as I hit the realities. If Tesla T3 2170 modules of 15 kWh each become available, then that would be the way to go.

I reckon in the marine environment I have the option to detect a thermal condition, via the BMS, and flood the module with a pump and seawater.

What kind of safety boxing would you recommend for each module (1.5 kWh and 6 kWh)? 20 gauge sheet metal, or aluminum or plastic? Multiple layers? Insulation? Big vent or small vent? I don't plan to stack the modules.
 
#118 ·
Thanks Go-Electric. I will wait till I have built a sub-module so I know what I am talking about, and have something to report in the thread. One thing I noticed is that few DIY people build modules from scratch. This is a bit of a mystery for me. The Chinese are just putting e-bike 13s10p 1 kWh modules together (using 2.2 Ah cells) and dumping the market, and they seem to work. How many e-bikes have caught on fire? The hoverboard fires are I believe due to the use of LiPoly, or faulty electronics. Out of millions of hoverboards shipped, many via air, how many have caught fire?
 
#123 · (Edited)
I like that idea / approach, thanks!
That triggers an idea I have been playing around with in my head of using the separator sheet as a mount flange.
Have you explored that?
I tried to think of different ways to isolate the modules when they are stacked on top of each other, rather than just a single layer side-by-side like in the Tesla enclosure. Bending an alloy or steel sheet like in your diagram so that it acts as both a separator between modules and as a top clamp for the side rails would provide some separation. I had similar ideas, but I could not think of a way to extend this type of separation all the way past the ends of the module to the sides of the enclosure. At the terminal end there will be the heavy gauge cables connecting the modules and the BMS cell tap wiring, and at the other end there will be the hoses for the cooling/heating system. So these cables and hoses prevent a complete isolation between the modules when they are stacked vertically, unless you somehow have separate compartments for the hoses and wiring. However, I still think having a sheet between the modules like in your diagram would be helpful. I myself decided to just use a 1/16" thick sheet of the fire resistant UTR composite material I described above between each module.
 
#124 ·
Nice ideas. I can appreciate the level of accuracy involved in lining-up the modules with the holes in the U-channel. On the box I did build out of steel, we welded angle-iron onto the side, with pre-tapped holes in it match with holes in the flanges. Rather drill our own holes rather than have spacers, but similar. It worked, but there was a lot of checking. To assemble, the angle iron had to be ground-off in places to be able to install the threaded screws. This messy, and your approach of building it up as you go has that advantage.

What is this UTR like? I found this:
https://www.electro-wind.com/500-1-...minate-sheet-130-c-red-48-w-x-96-l-sheet.html

Aad wonder if I could cut slots in it for the batteries?

Jim
 
#126 · (Edited)
I can appreciate the level of accuracy involved in lining-up the modules with the holes in the U-channel.
It actually was fairly straight forward. A hole drilled right in the center of the 3/4" u channel also lines up perfectly for the depth of the notches in the sides of the module rails. It was also nice that 5/16" nuts fit snug up inside the u channel. See 3 photos below that show the channel held up under the a module rail, one of the spacers I made that have the same thickness as the rail, and a 5/16" locking nut up inside the u channel. Bar stock with matching holes is laid over the rail and then bolted down sandwiching the rail to the u channel.

Rim Hardware accessory
Latch Metal
Rim


What is this UTR like? I found this:
https://www.electro-wind.com/500-1-...minate-sheet-130-c-red-48-w-x-96-l-sheet.html

Aad wonder if I could cut slots in it for the batteries?

Jim
Yes, that is the material. I ordered from a local supplier. The total cost for all the 1/4" material I used to line the inside of the enclosures plus the 1/16" material for between each module was ~$350, so not too expensive.
 
#125 ·
Some solutions make things very expensive and a lot of work.

Tesla uses a steel lid with an insulation blanket on top (not sure if it's fire retarded btw), and a thick aluminium base (about 1/4"). In case of fire in a module it would not spread quickly, as there are vents in every module bay.

Also there are the mica sheets, these will help slow down the melting of the case, but are probably also used to give some thermal insulation in normal use.

So it would slow down the fire, but not stop it.

I'd say you can use about any material for the pack, preferably one that has minimal toxic gas release in a fire (pvc is not one of them thus). Ad a thin layer of stainless steel to the outside, with a vent (plugged with something to keep the weather out) to a location where fire can do the least damage.

If you use aluminium, please realize this melts at a low temperature and is not a fireproof material. normal steel would also work but stainless steel is much more suitable for high temperatures.

All the fancy expensive materials might slow down the heat transfer, but it has to be able to get out somewhere because pressure inside the pack will rise until something blows.

Probably simplest solution: make a wooden box, 1mm thick stainless steel cover, vent, done.
 
#127 ·
The modules are designed to vent the hot gasses, if the module catches on fire. However, if you put an enclosure around several modules, and stack the modules on top of another as in an oven, would that not cook the modules above and below the fire module? Are you providing vents in the enclosure to vent the gasses and fire? If the enclosure has vents, then would the gasses by any chance pass by other modules to get to that vent?

The module vents allows for the release of the hot gasses. On the other hand, they also allow oxygen to enter and sustain the fire. Would it not be a better idea to have smaller vents or maybe tubed vents so that oxygen cannot enter the enclosure?

When an 18650 pops with flames (and often they pop without a flame), would it not require oxygen to maintain the fire? So maybe funnel all the hot gasses through a metal tube drain vent to outside, and this will prevent oxygen from getting in?
 
#128 ·
Well, you've hit the nail on the head, safety wise. Tesla keeps the modules separate, except for the stacked front two. And, all modules are surrounded by silicon mica sheets good for ~ 1000F (540C). BTW this is quite a bit higher than the UTR stuff @270F (135C).

On the venting issue, each module in the Tesla in its separate space(again, except for the front two) has 6 one-way/pop-off valves exiting into a plenum running along or into the rocker panels under the doors. I don't know the exact plumbing here, but it looks like it's designed to direct hot gasses and flames away from the cabin.

If I were buying these modules, I would make sure they came with these valves and the silicon mica sheets. At least this would allow a DIYer to try to replicate the Tesla safety features in a battery box design.
 
#133 ·
We finally glued together our battery boxes this week - meaning we think they are good! Contactors and fuses were mounted and bus bars made-up. Jack's BMS fits inside one box. We just need a couple of amphenol connectors, a push-button illuminated switch and will also install a little plasma/neon bulb across the terminals to give final warning if there is pack voltage across them (contactors welded).

Somebody asked about the weight of the boxes, and a 2-pack weighs about 15lbs empty. Not including the bracketry to mount it to the car, which is mainly a 34" piece of angle-iron.
 

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#134 ·
I mentioned awhile ago that the rails on either side of the modules are not the same thickness. The rail on the LHS (facing the terminals) is thicker. Well, it turns-out we have found TWO thicknesses on that side, so beware when cutting your slots (and in general, check your assumptions!).
 
#138 ·
Yes, indeed. Right around 108 I can see them. Since we are at it now, are the plastic rails also different thicknesses on either side? Maybe you don't care, but we made our slots JUST wide enough (for what we thought were two different rail thicknesses), and it mattered.

It looks thicker too.
 
#140 ·
Using a rail that is different in thickness left and right and even on one rail does not make sense to me. Looking at the teardown pictures I'd say they use a n shape to press down the modules. Furthermore the edge on the mounting material for the stacked modules is the same over the whole lenght.
I just measured two of my modules (plastic rail type) and did not find any significant differences within a rail or left versus right.
All within 2,87 and 3,02 mm
Product Technology Machine Electronic device Steel
 
#141 ·
Hi Lars,

Yes, you make some good points. I think we are probably talking about quality control issues, not design. I have not seen a pack come apart myself yet, so was just reporting.

I like the nice, tight-ish slots, and we are tooled-up to cut exactly what we want, but perhaps for most it is not important.

I really must post some pics of our 2-pack and 3-pack. I just have to go out and buy a nice LED bezel, then we can wire the whole thing up. Lots of trial and error bending bus-bars - and always room for improvement - but we like them, and like to swap 'n share.
 
#142 ·
Yes, I agree, probably quality control issues. Perhaps that's why they also used metal rails.
I like the tight slots too. My idea is to use a steel frame which supports the modules and build a skin around it.
I used my mill to cut a slot of 3 mm in a 15x15x2 tube.
Steel Metal Cutting tool Bumper

My idea was to use these on the outside frames and bolt the modules onto the shared center frame.
Line Parallel Triangle

Nice idea, but in practice it turned out that there is not enough room to tilt it in.
Machine Metal

At least not when I want the space between the frames to be max 280mm.
Now I'm switching to a design where I bolt them down on all sides.
 
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