4 ms·
In theory they should be good for several thousand cycles, so -- a long time. As long as you don't overcharge them, drain them too low, or try to charge them i
by elihu 3y ago
In theory they should be good for several thousand cycles, so -- a long time. As long as you don't overcharge them, drain them too low, or try to charge them in below freezing temperatures.
Also, they say that usually LFPs will last a bit longer if they're installed such that they're under a bit of sideways compression. I don't know why that is.
- jacquesm 3y agoThat only goes for prismatic cells (boxes rather than cylinders). The reason is that they tend to swell up while charging if you don't compress them so manufacturers will specify a clamping force required for the cells to keep their shape. If they change shape in such a way that you can observe it then your cells are toast so better stick to that mfg indicated compression. There are a number of articles out there that show how to do this the right way and also some that get it hilariously wrong. The direction to compress the cells in is in such a way that the electrodes remain under compression perpendicular to their surface. So compressing from the top and compressing from the front will do absolutely nothing.
- kragen 3y agothank you very much for explaining it makes sense that cylinders would be immune to swelling
- jacquesm 3y agoYou're welcome. I've been working for more than a year on a blog post about the various safety aspects of building battery packs but it's a never ending rabbithole of stuff to research and learn about so I haven't gotten around to publishing it.
- ilyt 3y agoMaybe multi-part series would fit it better ? Probably better SEO for one-subtopic-per-article if you care about that.
- jacquesm 3y agoNo, I don't care about SEO at all. I just would like this info to be out there for hobbyists and tinkerers as well as people that are contemplating designing something with Lithium Ion based batteries in it. But because it is safety related I really want to get it all right and with little room for error I get a lot more careful about what I publish. It will happen.
- T3OU-736 3y agoHah. Post it on HN, and let Cunningham's law help you :) Snark aside, I feel that on HN, there are enough actual proper experts who will point out avenues of research and gotchas that a single person chasing down rabbitholes on their own is unlikely to discover.
- kragen 3y agoyou might be surprised what this particular single person is likely to discover on their own one of jacquesm's previous personal rabbitholes was designing and building a wind turbine from scratch, down to cutting out the stator and rotor windings for the generator from sheet metal
- T3OU-736 3y agoFair point. Either way, my ulterior motive was to be able to read what they have, and learn vicariously that way :)
- jacquesm 3y agoIf you drop me a line I can share the google doc with you so you can comment on it. Email in profile. And if you google my name + long range e-bike you get an article about a pack that I laid out (170 cells, 2.2 KWh).
- louwrentius 3y agoIt feels to me that the battery compression discussion is a bit of a game of telephone. I think this video by off-grid-solar explains it quite well. https://www.youtube.com/watch?v=63-Nx75_xXM https://www.youtube.com/watch?v=63-Nx75_xXM