hbpowerwall
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- Oct 7, 2016
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Video says it all - but short story - I think two cells were beside each other keeping each other warm
Yeah, kind of my position on all the balancing issue. A BMS which cannot tell you how much energy was transferred from where to where is pretty much useless in terms of balancing. Spending a lot of money in active balancers which at the end only light up some LEDs are just dangerous.I think the takeaway from this is that 1Amp balancing current is great at masking problems.
For now, it should be significantly dialed back (50mA?) for regular use, so that faulty cells cause an imbalance in short order and trip the low voltage triggers.
Long term, agree with Korishan re need for the BMS to monitor abnormal balancing and sound alerts, and eventual shutdown.
Yes, I would say the warning signs were ignored.. perhaps the train of thought was its just the bms doing what it should do.Based on seeing the videos, pictures, and chatter over in the other thread (https://secondlifestorage.com/index.php?threads/when-things-go-wrong-it-can-go-really-wrong.10317/), I will have to agree.
There should of been warning signs evident that were ignored, or misunderstood. A rise in balancing of the other packs should have triggered an alert to check the "non-balancing" pack(s) as to why it didn't need balancing as much as the others, or why the others have increased so much.
That's an interesting take on it..that said the longmons are easily turned down or up as needed with in the software.I think the takeaway from this is that 1Amp balancing current is great at masking problems.
For now, it should be significantly dialed back (50mA?) for regular use, so that faulty cells cause an imbalance in short order and trip the low voltage triggers.
Long term, agree with Korishan re need for the BMS to monitor abnormal balancing and sound alerts, and eventual shutdown.
BMS well at least the WM4 and later all have years and years of loging also shows how much each cell has bypassed.Yeah, kind of my position on all the balancing issue. A BMS which cannot tell you how much energy was transferred from where to where is pretty much useless in terms of balancing. Spending a lot of money in active balancers which at the end only light up some LEDs are just dangerous.
Let cells go out of balance! It is just indicating that there is a problem or a design flaw. Of course that is not a convenient situation. We tend to throw electronic solutions on every problem just so it manages itself away. But in DIY that might be the wrong approach. We need to stay in touch with what we have built. Don't get lazy or complacent...
A well build battery Tesla for example what do they have 0.01amp balance current.. Also home energy storage are often smaller batteries, and cycle more hence drift further.. the bigger the battery the less drift.Taking this a bit further... I don't need/have-balance turned off for regular operation. My 84 (healthy) packs slowly drift from a daily 40mv-60mv max difference to a 40mv-90mv max difference after 5 months. At that point, I do some touch-up balancing for a few days to bring it back to 40mv-60mv and they are good again for another several months. So far, my oldest 14packs are nearing 900 cycles but show no trouble staying in balance with the newest packs. I take all this as a criteria of health packs.
So healthy packs shouldn't need much balance. My plan is to aggressively fix (retest/rebuild/discard) packs that will no longer run for ... at least a month? ... without balance. By keeping on it I hope to avoid serious problems. It will be interesting to diagnose a pack that won't run without balance when I get one.
Just FYI, the ones with massive bypass numbers are most likely the good packs. They are dumping energy (bypassing) on purpose to match the leaky packs with lower SoC.[...] Some of those have massive bypass numbers
This is my point. Once a balance has been done (for a few days) then balance can be turned off - no balance at all for months. In my case, I can go 5 months before a max difference of 60mv creeps to 90mv among 84 packs - e.g. healthy packs don't need daily balance. Then, a few days of auto-level bring it back to 60mv max difference.Question with heaters, I understand that when charged they will immediately self-discharge, by shorting out and generating heat. Now the question is does it also continue to take the energy from the other cells, therefore depleting the entire pack?
If so, then it's probably a good idea to routinely take packs out of service (especially during summers when there's plenty of sun), then let it sit idle for a week to see if any of the packs starts to drain. There should never be any drain in a week, so any drop in voltage would be suspect.