Recent content by jmole

  1. J

    The secret to compression

    Both - typically it’s thermal runaway, which causes, and is exacerbated by swelling. And another good reason to use compression pads between cells, since it will thermally isolate them to some degree. This is a big deal in vehicle applications where you don’t want a single hot cell to destroy...
  2. J

    The secret to compression

    Characterization is not the same thing as application. The issue is that prismatic and pouch cells can't self-compress like cylindrical cells do (I.e. when they expand, all that energy is spread equally around the circumference, like an arch.). what we're doing is supporting the long side of the...
  3. J

    The secret to compression

    I wish I had access to some of the high resolution 3D scanners I had before the pandemic started. Take one of those to the side of an EVE cell and you’ll see that the “flat” sides are really very hilly when you look microscopically. When discharged, the highest ridges are probably at the edges...
  4. J

    The secret to compression

    IMO, if you're going to compress the cells, you want to have foam in between them. All these fancy spring rigs would be much safer with foam compression pads. When in doubt, look at what the pros are doing: https://www.altenergymag.com/article/2013/04/lithium-ion-energy-storage-safety/1226...
  5. J

    The secret to compression

    Polyurethane is an insulator unless you add something like Carbon to make it conductive. When compressed, there’s a lot of friction between the cell and the foam, I don’t think you’d be able to displace the cells in any significant way.
  6. J

    The secret to compression

    4p4s, using REC BMS. Each busbar has its own cell balance wire. The busbars are tapered to distribute current equally to all cells even at max load.
  7. J

    The secret to compression

    Yep, your post from the other thread nails it here: I physically cringe when I see that people are just compressing raw cells together with no foam or anything. You can’t stop the swell, or contain it with a hard flat surface. If you try, your cells are going to rupture. Even with the perfect...
  8. J

    The secret to compression

    Shouldn't have said that - Tesla was the wrong EV manufacturer to pick. Rogers recommends these for use with pouch cells that *do* expand, not cylindrical cells which mostly don't.
  9. J

    The secret to compression

    Poron is spec'd at 5% max compression set when tested w ASTM D 3574-95. Don't know the details of the test TBH, but if it's good enough for EV manufacturers it's good enough for me. Edit: not Tesla, they use cylindrical cells which have different constraints.
  10. J

    The secret to compression

    I don't, in this case datasheet + manufacturer reputation was good enough for me. I thought about incorporating a calibrated force sensor in the stack (pressure = force/area), but ultimately decided that I didn't care *that* much. Dimensional stability WRT the busbars was the most important to...
  11. J

    The secret to compression

    https://www.mcmaster.com/86375k64/ Also known as Poron: https://rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes/poron-evextend Foam compresses 25% at 11psi. If you buy 1/4" foam, then plan for 3/16" between your cells when you design your busbars and your box, and...
  12. J

    3P8S 840 AH build

    I’d be reasonably skeptical of those numbers without doing a test with a real load of 100A or more and measuring the dV between 0A and 100A with a multimeter. The connections do look good though, I’m about to a second pass on mine with a little more NoAlOx on one side of the connection that I...
  13. J

    3P8S 840 AH build

    Nice write up, thanks. Have you done any measurement of internal resistance (and busbar connection resistance)? I would be curious to hear how much your voltage changes under load given all the work you did there. great choice on the terminals BTW - I got welded studs without really thinking...
  14. J

    REC ACTIVE BMS vs Orion Jr for 4S4P 280Ah LiFePO4 system

    Maybe some DC ripple from the inverter itself, but the AC loads I was testing with were a hairdryer and a space heater so no ripple there AFAIK. I could feel the 4/0 battery cables pulsing though, so it's clear there is some serious EM energy moving around when the inverter is pulling 250A. But...
  15. J

    REC ACTIVE BMS vs Orion Jr for 4S4P 280Ah LiFePO4 system

    Yes, I realized that today after finally fully charging the battery and seeing that the contactor indeed stayed closed. The BMS reduced it's Charge Current Limit (CCL) as the voltage increased, and finally set it to zero when I topped the battery off this morning from the Victron inverter. That...
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