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I doubt a local fire department has the ability to educate such a large international group of enquiring minds. The willingness of wk to share his experiences and knowledge is really about as philanthropic as science gets. We aren't getting the abridged edition, we are getting the moment by moment update. He is giving us the nitty gritty details just because he wants to, I think he can handle his project without giving cells to the fire department. obviously any fire department could benefit from the knowledge obtained from testing, but when was the last time you followed a fire department blog
Doubtful--anthing harsh enough to weaken the epoxy is going to have a laundry list of associated problems.
wk057--are the cells potted, or just bonded at the base? If they're potted, how is the negative connection made?
I thought about a solvent then immediately rejected the idea since I have no idea what the insulator partitioning the positive and negative electrodes is made out of and how it would react to such a solvent.
As for how the cells are held in place, here is a pic of a shard from the edge of the framework that holds them that didn't have much if any glue on it.
This is the inside side where the cells sit. The cells sit in their own little recessed spots with a cutout on the end for the cell level fuse connection. On most of the module the glue is all inside this recessed spot and excess around the edges on the inside part. Very little, if any, excess adhesive on the terminal side. But they're glued all around the casing in that ~1/4" recess.
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As for donating some cells or the module to a fire department, probably not as useful as it would seem. I may contact the NFPA about it and see if they want to do some testing/experiments with it if I can't find anything else to do with it.
I'm not the person to ask that question and expect the answer you're getting. I'm regularly speaking to various first responder communities on how to deal with these situations, especially local volunteer fire departments.
The point wasn't that he needs to give them to fire departments, but rather if he's given up on extracting cells and has a damaged module, he has an option to donate it to a local fire department that can do training (similar to how we use dilapidated homes for training exercises). Of course, if there are better uses, then he does have a right to put them to use. I was thinking they could create true runaway by purposely damaging some cells and applying flame-o-matic.
mitch672
Active Member
I work at BatteryMarch Park in Quincy, which is a complex of buildings where the NFPA's headquarters are located.
One day, the head of the NFPA's Head of the "Electric vehicle safety program" was waiting for me by my Model S, he wanted to use my car for a photo op at their onsite EVSE... since then, they've also shot some promotional video of my car driving around in the parking lot. At any rate, I can put you in contact with him, if you'd like to see if they have any interest in examining/testing the remains of your module. let me know, thanks.
Definitely going to investigate possibly uses for the module. If there is something that can be gained from it via local training or otherwise, I'll look into it.
After having some time to mull on yesterday's event, I may try extracting more cells in a different way. But with even more precautions. Mainly, I want enough cells to run some meaningful tests of capacity at different discharge rates along with some cycle life tests as well as some to share with some others who would do similar testing to confirm.
JRP3
Hyperactive Member
Apologies if I missed it, but did you ever confirm a definitive total cell count of 7104 cells for the total pack? Also, have you done an actual capacity test of an individual cell?
I live pretty close to the the Massachusetts Firefighting Academy: The Massachusetts Firefighting Academy (MFA)
If the NFPA doesn't pan out, I could try to head over there on a work from home day and see if they want them. Although I'm not sure how easy it would be to ship from NC to MA.
Edit: Now that I think about it, all states probably have a similar training program to the MFA - you could probably find NC's equivalent.
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bluenation
Member
you were very very VERY lucky none of your loved ones were standing in the way of that stray batt.
that said
+1
you are doing it for science, wk. Thx a ton.
that said
+1
you are doing it for science, wk. Thx a ton.
I finally got around to doing some testing of the cell level fuses using a power supply and my DC electronic load.
I was able to get them to carry 24A for 60 seconds+ and they would consistently pop within a second or two at 25-25.5A.
Honestly, that's more power than I had figured they were able to handle. Assuming they're sized for 25A, that's 90W per cell, almost 40kW per module, or close to 8C max before consistent popping.
Using an NEC-style 25% margin gives me a constant current draw of about 19A possible before popping fuses. That'd be about 6C, or about 485kW nominal for an 85kWh pack.
This could explain the reason the P85D doesn't show 691 HP (515kW) under full acceleration. However, that's speculation since the D variants have a different battery pack part number which may or may not have larger fuses. No way to know for sure until someone tests the fuses in one. I believe the full 515kW+efficiency losses could be pulled from a fully charged pack for a very short burst, though.
Edit: It's worth noting that the primary goal of these fuses is likely simply to prevent a single cell with an internal issue from destroying the rest of the cells, not to protect against module max current draw. Let's say a single cell developed an internal short. The other 73 cells in that set would then be sending all of their power through that cell, since they're in parallel. With the fuses, the fuse would just pop under the hundreds of amps available, and barring any thermal issues related to the bad cell, would save the rest of the cells.
I was able to get them to carry 24A for 60 seconds+ and they would consistently pop within a second or two at 25-25.5A.
Honestly, that's more power than I had figured they were able to handle. Assuming they're sized for 25A, that's 90W per cell, almost 40kW per module, or close to 8C max before consistent popping.
Using an NEC-style 25% margin gives me a constant current draw of about 19A possible before popping fuses. That'd be about 6C, or about 485kW nominal for an 85kWh pack.
This could explain the reason the P85D doesn't show 691 HP (515kW) under full acceleration. However, that's speculation since the D variants have a different battery pack part number which may or may not have larger fuses. No way to know for sure until someone tests the fuses in one. I believe the full 515kW+efficiency losses could be pulled from a fully charged pack for a very short burst, though.
Edit: It's worth noting that the primary goal of these fuses is likely simply to prevent a single cell with an internal issue from destroying the rest of the cells, not to protect against module max current draw. Let's say a single cell developed an internal short. The other 73 cells in that set would then be sending all of their power through that cell, since they're in parallel. With the fuses, the fuse would just pop under the hundreds of amps available, and barring any thermal issues related to the bad cell, would save the rest of the cells.
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Did you test the fuse while still attached to the bus bar?
Ie, one lead attached to the end you cut carefully from a cell
the other lead clipped to the bus bar
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I don't agree with this assessment. In fact, my analysis of the P85D performance and charging shows almost no difference in charging, voltage drop, and only ~390kW peak draw from the pack, for only a very short period (at full charge) [~370kW at 70% charge]
That's only ~16A per cell for ~5 seconds, and it quickly tapers to half that, and even lower. This is easily sustainable by the existing cells.
If anything the only difference between a D and an E is the wiring for the front motor, perhaps upgraded connections.
Basically. I left one end attached to the bus bar, and the other end I pulled from the cells to keep the length correct. A few I snipped. Didn't change the result for either method. I fed power into the bus bar and to a tight clip on the very end of the fuse with my electronic load setting the current.
I'm not sure I agree with either assessment.
The part description for the P85D pack is "ASY,HV BATTERY,S3,DUAL MTR,MDLS". The S3 I think is the important part. The modules themselves have the S3 label on them. I see no real indication that they are difference cells, although they likely have heavier internal wiring.
Also, as for power draw, at full throttle the P85D kW meter lands just below the 480kW mark. I'm not sure where the 390/370kW numbers come from...
There is no front motor wiring related to the pack itself. The wiring for the front motor comes from the rear seat area and is routed via the driver side to the front motor.
Edit: Maybe I'm crazy, but I can't find any pics showing these points on the taper for my P85 showing power at these levels during a supercharge at these SoC.
Edit: Actually, I found a fuzzy pic from my P85 showing 257 out of 264 rated miles, which would be ~97% showing only 6kW vs 18kW on the P85D. *shrugs*
Looking through my pics I seem to snap them to show the peak output and not the taper. Maybe I'll try to do a side by side next time I have both cars at a supercharger.
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Johan
Ex got M3 in the divorce, waiting for EU Model Y!
llavalle
Member
Not sure I'm following you here. Did I miss something about the tapers?
I just did a 15->90 SOC supercharge on my E Pack and I've got a video of it (sent it to okashira). What were you looking for?
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