DIY Electric Car Forums banner

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.
 

Attachments

See less See more
3
#34 ·
Someone wrote to ask how I was able to infer information about individual cells in a 74 or 37P group. I thought I would post my reasoning here for posterity...

The key to how I can say there are no damaged cells is that all six groups charged at the same rate with no balancing. Especially at over 4 volts, any mis-match in capacity between groups would have become evident. From this I can INFER all of the groups have the same number of functioning cells, and as a group at least, are matched.

To dig down a bit deeper, if the voltage of one group rose more quickly, that would be because it had a lower capacity. On a larger scale, if you charge - say - a 100Ah cell and a 160Ah cell, the smaller one would reach its max voltage more quickly - and reach its minimum voltage more quickly too. I watched particular cell-groups which were the highest/lowest, and they stayed in the same order. Since this crossover did not happen either, I am certain each group has an equal number of cells; it is unlikely all are missing one, two, etc....

Edit: hmmmm, I like that - the "crossover" may be a great way to pick up on cells/groups with lower capacity.
 
#35 · (Edited)
I'm posting a link here to a discussion which arose in the Classifieds section on a thermograph (?) of Tesla modules which seems to show them self-discharging/balancing after being removed from the car. Some discussion ensued regarding whether the Tesla modules balance themselves independent of the Master, or what was going on there.

http://www.diyelectriccar.com/forums/showthread.php/tesla-model-s-battery-modules-24v-165425p3.html

Let's keep this discussion going.

I have 10 modules, but they do not have boards on them, so I cannot verify any behavior. But even if they could, it seems odd to me they would be balancing themselves out of the car, does it not? One would expect they would only do this when charging. Might storage affect voltage to the point where they try to balance themselves out??

The final post on the thread above is useful - it seems to indicate the balance boards do not require a wake-up or some such thing from the Master.
 
#36 ·
@Jim: a question about your batterybox design.
From the cross-section drawing I tend to conclude that the length of your batterybox is 27.25 inch (69 cm), which is the same as the length of the battery modules.
How are you going to connect/route the cables?
My idea is to connect the modules in series within the box and have only two cables coming out. However I am trying to get an idea about how much space I need to take into account for that.
 
#39 ·
These modules can be potentially very dangerous. Have you read over and considered the Tesla battery box design information discussed in posts 4, 6 and others in this thread? The modules may work fine initially. But, as they age or if they're damaged, Tesla's safety features will limit the hazard and damage if there's a fire.
 
#41 ·
One could only hope you're right. But, if this was all that was necessary, you have to ask yourself: Why would Tesla go to all this trouble with the modules? This includes:

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

These modules have much more potentially dangerous cells than previously used cells. I have not seen any other OEM go to this level of hazard protection with their cells. I believe if these modules are to be used safely, an equal or better level of protection should be used by the DIY community. Rather than stick our heads in the sand here folks, let's come up with some workable solutions!
 
#48 ·
Only info I have found on these so far is by WK057 in
https://teslamotorsclub.com/tmc/posts/1149103/
The modules DO have two temperature sensors each. One is on a cell close to the inlet of the cooling loop, and the other is on a cell close to the outlet of the cooling loop. So, the temperature data is available to the car at least, and I'm going to use these sensors in my custom BMS (they're just 10k thermistors).
and in https://teslamotorsclub.com/tmc/posts/1398042/
temps in C. Temps are probably off, since I haven't done a calibration of one of Tesla's thermistors to see what the appropriate β coefficient is for them. I just guesstimated around 3.9k with a 25C center at 10kΩ for now.
 
#47 ·
Hi. Those numbers are conservative ones, but yes, or even more-so, as the range I will have is about 100 miles, but likely will only drive 10 or 20 miles a day. In general, the higher/lower the batteries go, the harder it is on them.

Another thing which can contribute to cell degradation is temperature (and time). I will not be cooling the batteries, as it never gets very hot up here and I won't be pushing them in terms of current draw, but I will be heating them. Since I have a fluid loop, I will be slowly running the fluid through them at ambient temperature whenever the car is moving. This is to keep all batteries at the same temperature so they at least degrade EVENLY. Also, I will reverse the flow on the loop every year, so the hot and cool ends get reversed to even-out differences there (I have found the pump I plan to use, which is good for 50,000 hours). I consider this a prudent way to keep them in balance, and my BMS will monitor cell voltage differences just to be sure.

When you charge the cells you will see just how little time it takes to get from 4.1 to 4.2V. Same for 2.5 to 3.0 That-said, I will be able to plug into the BMS and change the HVC and LVC for longer range if I think it is necessary. Much as Tesla does. I think this is a good compromise.
 
#51 · (Edited)
I will not be cooling the batteries, as it never gets very hot up here and I won't be pushing them in terms of current draw, but I will be heating them. Since I have a fluid loop, I will be slowly running the fluid through them at ambient temperature whenever the car is moving. This is to keep all batteries at the same temperature so they at least degrade EVENLY. Also, I will reverse the flow on the loop every year, so the hot and cool ends get reversed to even-out differences there
Based on your description, it sounds like you are planning to plumb the modules in series with respect to fluid flow. I am still trying to decide if I will plumb the modules off a header coolant circuit, so that each module receives the same temperature coolant like Tesla has them in their enclosure, or if I will just plumb them in series. Like you, I don't expect to require much if any cooling. I also don't plan to require much heating, since the car will not be driven in winter. So I am leaning towards just plumbing them in series and running the flow continuously. I will have 10 modules in two separate enclosures, so the longest fluid loop would be through 5 modules in series.
 
#50 ·
Ran across the 10K value too. Can someone tell me the pin out of the thermistor connector.

Working on getting a bms slave talking sense. Got a master and slave communicating now just need to get all the probable faults resolved with hardware. in order to get the slave to boot into its "normal" mode.
 
#61 ·
Working on getting a bms slave talking sense. Got a master and slave communicating now just need to get all the probable faults resolved with hardware. in order to get the slave to boot into its "normal" mode.
Forgive me, I'm just skimming this thread to see if it's appropriate to talk about the Tesla BMS firmware. Are the master and slave you refer to above Tesla master and slave BMS boards?

I have worked on TCCH/Elcon charger firmware (pre-2013 models), which use the same processor instruction set (basically Intel 8051 from the 1980s), and found a firmware file. I've had a go at disassembling it with Ida Pro. Disassembling firmware seems to be something few on here are familiar with, so I thought I might be able to offer some assistance if there is interest. I don't have a Tesla battery available, although I could probably get my hands on one for the occasional test if necessary.

It's been hard going so far, but these things often take time. Unfortunately I have quite a number of other projects going, so I can't invest much time right now. So I'm just looking for the level of interest at this stage.

It seems to me that the Tesla BMS is a quite well engineered product, but there is no information on how to talk to it, or how the modules talk to each other. It would be a shame if people had to throw away these BMS boards because there is no information on how to use them, and then have to adapt some other BMS and make all the connections.
 
#52 · (Edited)
Gen 2 board with respect to the temperature sensors.

J6 is the sensor jack on the board. Pin 1 is to the left when looking into the 4-pin male receptacle (pin1 is 'up' closest to the black 10-terminal J1 communications daisy connector).

pins wire color
1 ts1+ blue
2 ts2+ yellow
3 ts1- blue
4 ts2- yellow


The Gen 1 board that i have is (possibly mis-) labelled

1 ts1+
2 ts2+
3 ts2-
4 ts1-

although the temperature sensor pair that i got with it is wired exactly like the Gen2. The silkscreen labels are missing on the Gen 2, maybe removed due to the typo on the Gen1 boards?
 
#53 ·
Hi. We calibrated our tesla thermistor and it was bang-on! 10K@25C, 1/Beta=3380.

SWF, I am heating the batteries in parallel, three per box, two boxes, each with a separate temperature control system (working!).

We found our paltry 240W (12V) did not have much effect: about 0.1degrees celcius per minute.

We also have both Tesla boards and are hoping to harness them. Jack has figured some things out for the slave board, are you aware of this info?
 
#55 ·
Hi Stuart - thanks!

I like the 3-layer shell. Can you say a bit more about the aluminum honeycomb material?

This is quite similar to the front box in my build - I'll be interested to hear how it goes. One thing I'll mention is the wiring: Imagine flipping over alternate modules. Then you have + and - facing one-another and wiring is much simplified. This changes channel spacing (and hole placement) too, but nothing major.

You may be better at some things, but fabrication presented some issues - as you think things through, feel free to post your questions/solutions.

There are up and down sides to everything. I have a two-piece metal box in the front and a plastic one in the back - it would be good to discuss.

Insulation (thermal) is something I'd like to do a better job of next time.
 
#56 ·
This is quite similar to the front box in my build - I'll be interested to hear how it goes. One thing I'll mention is the wiring: Imagine flipping over alternate modules. Then you have + and - facing one-another and wiring is much simplified. This changes channel spacing (and hole placement) too, but nothing major.
I don't think flipping every other module is a good thing:

  • Half of the bus wires will be short, and you will have less room to move a module during wiring / mounting.
  • The + and - from two modules will be close to each-other (with an isolation shelve in between this won't matter btw)
  • depending on box design difficult access to bolts.

If you can use a 'flat' box, one of the best options might be to use part of the original Tesla box... You can easily cut them to the size you need, and you can re-use part of the original busbars:



 
#58 · (Edited)
ckidder sent me a copy of the cell board binary and i'm helping to disassemble that into the 8051 opcode source. This is for the chip between the cell monitoring chip and the daisy chain communication port. It appears to just be passing data thru, haven't discovered any secret commands of interest as yet...

edit: did find that the boards are uniquely coded with the information on the white QR label, e.g. model and serial number, at memory location x1D02.
And there is a tesla number, "T14C0618393" at x1D38, which may be their part number for the firmware load..?
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top