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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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#71 ·
I took similar measurements from my modules as far as these are the same. I have modified units to 12s37p so mine are a little higher.

In terms of width, this is 280 mm (or 279.80 mm actually, but I am using 280 as well). How tight would you fit these?
I am creating mounting rails to slide the modules using a distance of this 280mm.
 

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#72 · (Edited)
I would create alot more meat under those rail supports you have drawn, do not forget these things weigh 25kg.

Photo by Boekel shows roughly 28.5mm, if you can create clamps to secure the battery in the sliding direction (forward and back) as tesla do it in their packs.

Measured with my large calipers, the pinch ribs are 28.1mm so I would try and get the distance between rails to make 28.2-.5mm.

Also I would strongly advise anyone stacking them not to stack packs on one another as the do not have the "strong" plastic that makes up the frame protecting the bus bars.
 

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#73 ·
I would create alot more meat under those rail supports you have drawn, do not forget these things weigh 25kg.

Measured with my large calipers, the pinch ribs are 28.1mm so I would try and get the distance between rails to make 28.2-.5mm.
Thanks! 28.2mm sounds like a good idea.
Yes, good point, my box used to be less wide but I increased it in order to create room for the wiring. The support rails definitely need to become bigger.
Furthermore I will add micanite in between the modules. Have even considered (and am still considering) metal separation sheets.
I agree on not stacking them, each module should be supported and hanging on its own. Especially in my case with the studs to hook up the BMS wires sticking out.
 
#74 · (Edited)
Hi. We are on our second box now, a couple of thoughts:

We have a Solidworks model - I can share files, but won't post them directly on the website.

The spacing between sides we have found works best is 11.25 inches, which is 285.75mm. That leaves a little room for the plastic cover

The modules are alternately spaced vertically 1/2" and 1/4" apart. The former to allow room for connecting between the alternate modules which are facing one-another. The slot-width has been an issue: we now have a digital read-out on our table-saw and have made the slots (in multiple passes) to within 0.005". Also, believe it or not, the rails on either side of the modules are not the same thickness - beware.

We are making the box sides out of 1/2" PVC, and cutting 1/4" (deep) slots. The PVC has ample strength to hold-up the modules, and when the whole things is together (some parts glued, some bolted), it is rock-solid.

We love these boxes - no metal, cut threads with a drill-tap, easy to cut, glue, etc.... Our 5 module box is built; mounting contactors, shunt, fuse etc... all inside as well.

Edit: still experimenting with a few things bye-the way. Check-out the bulkhead terminals we built:
 

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#76 ·
Also, believe it or not, the rails on either side of the modules are not the same thickness - beware.
Thanks! Would have missed that otherwise. Just measured and you are right, one rails is 2,97 mm and the other is 2,91.
I was about to use 3,0 mm on each side.

The spacing between sides we have found works best is 11.25 inches, which is 285.75mm. That leaves a little room for the plastic cover
How do you "lock" the remaining 5 mm since the module itself is 279,80 / 280 mm wide. Is my understanding correct that in your case the module fixed and prevented from moving sideways by the 1/4" saw depth?
So the mounting fins of the module go all the way into this depth (and even leaving some room right, since the fin width is bigger dan this 1/4".

Looking forward to a photo and/or screenshot of you model!
 
#77 ·
Hi. Sure, will-do. Love to work with people and share ideas.

Here is an early version of a 3-box. Then there is the cooling manifold we had 3D printed. Spent tooooo long on that little project to give away the design, but we could make and ship them to those interested!

Interested in making double-voltage packs.....

Jim

Oops, took those right off my phone and they seem to upside-down. I'll see if I can re-post.
 

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#80 ·
Hi Lars. Yes there is very little wiggle-room, and with the weight of the batteries, friction and all that, I never thought about it, but I suppose they have 1mm each way they will move. End-wise, there are various ways of stopping the modules from sliding in and out.
 
#84 ·
Oh - cost. For the 5 pack, I think the plastic was around $CAN200, but it could be less. That is for 5 sides, the top will be 1/8" Lexan (clear plastic).

The box is 33" long x 18 7/8 high x 12.25 wide. It will all fit behind the back seat of a 58 VW. That's 27kWh - should have well over 100 miles range.

Oh - I should say "fits" as there will be some modifications of the back seat required where it sits against the top front edge of the box.

Jim
 
#88 ·
On another thread there is some discussion about the Tesla Pyro-fuses. Rather than hijack that thread, I thought I post some additional thoughts:

I've been staring at the big fuses in my battery packs and thinking how nearly useless the second one is. I've changed from one 5-pack to two packs, and now two fuses I guess. One yes, in case of - well, all kinds of things. But what do people think: are two fuses needed with two boxes? About all I can think of is that if the two HV lines between the boxes are shorted, one fuse would not cut the current from both boxes. If I ran the HV cables from the front on opposite sides of the tunnel, that would make such a situation much less likely. If there was an accident, the inertia switch would open the contactors, so there is that too.

The thing is, I don't think the fuse will blow right away anyway. One is a necessary (compromised) solution, and the second one is so close to unnecessary, I'm a bit resistant to putting it in.

Looking for a better solution and this cool Tesla fuse got me thinking. Anything-else out there??
 
#89 ·
I've been staring at the big fuses in my battery packs and thinking how nearly useless the second one is. I've changed from one 5-pack to two packs, and now two fuses I guess. One yes, in case of - well, all kinds of things. But what do people think: are two fuses needed with two boxes?
I hate repeating myself but if you would just add your location to your profile it would help greatly... in the UK you must have fuses per pack... consult with Mike at Indra if you need specifics :)

I'm not sure which country you are based in and therefore I can't really comment on the specifics of your battery box design in relation to local laws.
 
#91 ·
Always fuse per pack.

I have the rule, as soon as HV goes out of a sealed enclose it needs to have a switch (mechanical or contactor) and a fuse on one of the leads.

you would not want to be hooking up a "HV" pack/module with live connections ever. (some exemptions can be had but i prefer to make the high current connections when there is absolutely no way of shorting something out outside the pack.
 
#94 ·
I don't really understand your second-last sentence. My contactors and fuse are inside the box - If the contactors are open, then I'm not hooking-up a live pack??

Regardless, any suggestions for fuses? I don't think the one (or two) I have are going to blow fast enough to protect much, except maybe stop something from melting-down after the initial explosion.

(and just to be clear, that second fuse would only be required if there was a short between the two cables? Any other short would be taken care of by the other fuse, as the boxes are in series. Are we talking about an accident, or maybe during assembly, or?? I just can't imagine when that second fuse would be needed, except in a major crash. anyway, with a dead short, all of the internal fuses in the modules would blow?)

I'm playing a bit of the Devil's Advocate here - 'best' way to test an
assumption is to argue against it. The truth is, I mostly just don't like those fuses - back to why Tesla invented better ones....

Thanks. Will post more pics of boxes soon.

Jim
 
#95 ·
that second fuse would only be required if there was a short between the two cables?
Yes, I understand.
It depends a bit on the type of car and the routing of your cables.
But if you (like me) route the cables on the opposite sides of a tunnel in a RWD car there might be a risk.
What if the driveshaft or it's bearing breaks and start flying around (a shaft that snaps/twists while a car is running) and it hits the cables?
The inertia switch will not do anything about it and the BMS probably won't notice in time either.
Then a second fuse can add value.

But... in case these fuses are not fast enough they might not even blow before all the individual Tesla cell fuses have blown, right?
 
#96 ·
Yup. And thanks for chiming-in. Or I guess the inertia switch could fail to do its job.... Not so easy to test where it should go (?!!).

When I restored the Volvo, I used to tell myself every time a new thing was required (it was inevitably 500 dollars) "Its Art." In this case, it's a living "breathing" battery we are talking-about, and I guess the mantra should be "better safe than sorry." Gotta draw the line somewhere, or I would never step out of my house, but yeah. Will order another fuse of some kind.

Can you post a link to your car (again) - I'd like to see how you are going.

Jim
 
#97 ·
Yes, one fuse more probably disappears in the overall budget.
But still the question is, it is really protecting something?
I want it to protect the cell fuses as well so I don't have to buy new modules.
But if these go first, then I guess the big fuse won't blow anymore so why then add it in the first place?
Can speed be a reason for the new Tesla fuse? To protect the individual cell fuses? (Just guessing, do not know anything about these pyrofuses)

Thanks for asking: this is my English blog:
https://www.oudevolvo.nl/english/

I'm in the middle of designing the battery boxes and have just decided not to use a heat exchanger but I still need to translate that blogpost into English.
Will update my build topic soon again as well.
 
#99 · (Edited)
The individual cell fuses were tested by that whizkid Jason, and they could carry 25 Amps but blew at 26--another amazing tesla feat using 0.011" diameter aluminum wire.

The purpose of external fuses is to protect your external wiring from melting and shorting out the pack, not to save the cell fuses. There should be some control system monitoring the pack current and limiting it well before the cells and cell fuses are in danger, either from overcurrent or high temperatures.

Tesla went to the so-called smart pyro fuse in order to push the current up for ludicrous mode, 1520 Amps for a brief (~7s) period. The previous fuse was marked as 690 or 700 Amps, and looking at the datasheet it could carry 1500 A for ~20-30 seconds. But pushing the margins to the edge of datasheet overcurrent curves is not wise--so they designed their own device with an integrated current sensor to allow the higher currents without nuisance blows due to variations and tolerances in the standard fuses.

So in your case, you know the size of your pack and from that you can calculate the maximum current before the cell wires fuse. Hopefully your pack monitor or BMS has setpoints and limits below that point for pack charging and discharging currents. Also your motor controller would have current limits. Your external wiring would then be sized to carry the pack and motor currents with some margin factor, and that wire gauge would then be used to pick the fuse(s) to protect each branch of the wiring in the event of a controller fault or inverter or motor winding short-circuit.

i've seen classifieds on the tesla motors club forum selling the pyrofuses for $120.
 
#101 ·
Hey Kennybobby, nice post.

"The purpose of external fuses is to protect your external wiring from melting and shorting out the pack, not to save the cell fuses. There should be some control system monitoring the pack current and limiting it well before the cells and cell fuses are in danger, either from overcurrent or high temperatures."

I think what we are talking about then is a back-up for the BMS over-current shutdown, right? It may not be a dead-short, and therefore not blow cell-level fuses, but you are right: an inverter failure might make a pretty-good mess, and may take out the BMS with it.

A single fuse would solve that problem, but I guess it makes sense that a non-dead-short could happen somehow which a single fuse wouldn't catch.

I would like to find one of those pyrofuses from a Tesla - can you suggest a few links? Maybe the set-point can be adjusted. This would be a nice side-line for those wrecking Teslas: sell them pre-adjusted, or with instructions on how to do-so.
 
#102 ·
Thanks @kennybobby for your contribution and helicopter view.
You are completely right, for normal and expected operations my BMS will be in charge and protect the installation by monitoring max current out.

Like @SWF I will also have a contactor and fuse in each enclosure.

Nice to know that the cell fuses are capable of handling 25A. In my case (12s37p) that will be 925A and my normal peak will be around 300A. So I do feel comfortable having my BMS and two times a A50SQ400 in place.
 
#103 ·
Okay, I think we can all agree everything should have a backup failure-wise. A fuse is a back up for a failed inertia switch and other things, like a welded contactor. It would be interesting to have a truth-table with all of the components in it and how each is protected from the failure of another, (internally and externally). A suitable fuse between all components is a good method of protection, and that includes a somewhat unsuitable (slow), but still potentially useful big honking fuse in each battery box.

BTW, are you guys saying you only have a single contactor in each box? We use two. Tesla has contactors on both terminals of its packs, and we just adopted it without argument.

Jim
 
#105 ·
BTW, are you guys saying you only have a single contactor in each box? We use two. Tesla has contactors on both terminals of its packs, and we just adopted it without argument.

Jim
I was planning to use just a single contactor per enclosure. I assume two contactors are used to provide backup in case one contactor fails to open? I am trying to understand other failures that would be protected with two contactors. I don't recall seeing any other builds or circuit diagrams that have a contactor on both terminals of a pack.
 
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