hbpowerwall said:
any updates on this project ?
thanks for the interest/query. : ) ... but no, ... not a whole lot of updates. I've been busy harvesting cellsand enjoying my new electric skateboard. I made a battery for it that has ten ~99Wh packs, which can be unclipped from each other for air travel ... which is more than even a
Zillboard battery has.. lol. Here's a 'bits and pieces' update on the powercase, and my recent advances:
-- I finally had the courage to drill some holes in this otherwise waterproof case. *gasp* ... the need to pull/push power in and out of it WITHOUT opening the lid made this unavoidable. So I now have two external XT60's, with 10 gauge cable and separate fusing on each port. Yahoo.
-- I have reloaded the powercase with an updated set of cells. still all pairs, but this time I have TRIPLE tested all the cell (pair) capacities. This caught out MANY cells that had deteriorated, or ... been mis-measured originally?? In any case I am much happier with the 'balance' of this battery now.
Finding some 10-20% of the cells to be up to 50% different capacities after such a relatively short period of time/use got me wondering ... so I started retesting both my stockpile of tested cells (waiting for BIG pack making) and ALSO retesting (3x) the latest cells Ive harvested ... which has been a very slow process as I only have four Opus's ... has shown me that it is very unwise to assume that the first test is accurate. I'm far from reaching any firm conclusions, IE is it that the harvested cells need a few cycles after a long 'sleep'? is my testing/charging/precharging methods damaging cells? Are the cells I'm getting so very well used that they truely have little life left in them?
At first I thought that my very initial handling of cells might be the problem -- IE I used to store them at 4.20V, long ago. Now I store all cells at 3.92V. BUT, I have found similar problems with cells harvested a few months ago, which I never left sitting this high. So then I was worried that my use of them in batteries without BMS, that I had overdischarged them, somehow. BUT, then I found similar issues with cells that I had never even repacked, just tested and stored. So now I'm left without a clue. DOH!
I have also modded all my Opus testers ... basic stuff, but worthwhile for me. 1/
fan mods were needed for two reasons. Thermal shutdown is wasted time for the Opus's. I test cells in pairs, at 1A discharge -- so the Opus gets a major workout (read: hot). Also, noise has become an issue for me in my workshop area, and having this mod done allows me to put them (mostly!) in a drawer, with only the screen bit sticking out, and despite the confined space, they run smooth and cool, and the noise is both quieter and less 'whiney'. 2/ joined J1 on all of them. inside the Opus is a labelled solder bridge on the PCB which substantially (60-70mV?) alters the voltage sense on allslots. If it is open, it reads low[er] which is optimal if you want the tested cells to be recharged AND topped off by the Opus. If it is closed, it reads lower on all slots, which is optimal for testing cells, as it doesn't 'hang' on (try to top off) cells which are 'only' 4.16-4.19V, it just gets started testing (discharging), as it thinks they are 4.22V etc. FYI I do NOT recommend the Opus AS A charger ... just saying. GREAT capacity tester though. If only it had a 'dump' port (like the antimatter dose?) instead of dumping energy to heat, it might be the 'perfect' cheap tester.. oh, and lastly 3/ I put some silicone wires in between sliders and PCB. This should mitigate any wear and tear on them as I thrash them to death. These Opus testers are much more rugged than my old Nitecore D4 charger, which had sliders made out of butter. But even with stronger sliders, my Opus's run 24x7 at 1A mainly ... and they don't skip a beat now.
One totally brilliant thing I have figured out, is how to get zero heaters -- thats right folks 0% !! -- is a much gentler precharge, and 'first charge'. Sure, some cells still test with very low capacity (fail) but they just don't get hot anymore. And no more bump charging. The advantage for me is not so much in getting a larger number of cells passing the capacity test, but rather ---> I now do not fear leaving the precharging cells unattended. I just stick them in a big bunch, eg 4s40p and let them go for a week or so, at like C50 charge rate. IE VERY SLOW. And I do that now on a basic (ruideng?) CC/CV buck converter. Im not even [pre]charging on a balance charger now, like I used to. Although I do top them all off with balance chargers, for sure.
I'm very much looking forwards to getting a
Batrium WatchMon5, hopefully in the next few months. I think I've pretty much hit the wall in terms of what I can do (safely?) without a BMS. In the meantime ... harvest harvest harvest. ; ) The cells that I am sourcing here in NZ are absolutely terrible. But that's ok, I test them all, and the piles are stacking up.
I'm SUPER glad that I have learnt so much with this 'little' battery, before getting in the deep end and making 100p packs. The powercase is relatively easy to service and has taught me a lot about building/assembly techniques, as well as the whole cell deterioration thing etc. Thanks again all of you for inspiration, teachings, sharings, and entertainment too.
PS sorry that was quite a rant, eh? thanks for reading to the end. NB please do NOT quote my whole post in any replies. pick the bit you need to quote, if you need to ... lets keep this forum clean/readable. cheers.
