the issue is that when a battery is disconnected from a BMS (ie, the BMS cuts power), and then reconnected, the JKBMS will default to Li-Ion settings. Is that the bulk of the issue?
This is correct.
While I do believe this is a fault. Shouldn't you catch this problem? First, If I'm going to disconnect or pull from service a battery, and plug it back in, you can be damn sure I'm going to immediately pull up my BMS data and triple check that everything is where I left it.
Having a battery in service is not really the issue here. Tho, that is definitely one of the use cases this could be an issue. Just because you take a battery out of service to work on it, why would you think to check all the nitty gritty settings of your BMS to make sure their settings are correct?? You don't do this when you turn your phone off for a day or so and then turn it back on. You don't do this with your computer when there's a power outage. You
expect the settings to be saved and restored upon power restoring.
The bigger issue here is not for those people who take a battery out of service for working on it. It's mostly an issue with people who shut the whole system down for Long Term Storage. When you leave a cabin, for example, that's built around battery power, you don't leave the BMS connected to the battery when you shut things down, otherwise you'd return to a dead battery. You disconnect
everything, including the BMS from the battery for Storage purposes.
Granted, when you return, you should double check the settings. I get that. But again, it is generally accepted and expected that the settings would be set and restored during power resupply.
Secondly, who is turning on a BMS after a time and just assuming everything is working?
The majority of users, to be completely honest. Think about this. Someone builds a battery pack for a scooter, or golf cart, or some other device, as a business model. They install one of these units and sell the whole thing to a customer. They tell the customer that when the cart is not going to be used for long periods of time (say for instance over the winter), to disconnect the whole the system by flipping that breaker on the side of the battery. Then the customer when they are ready to use the cart, or what ever device, flips the switch back on
expecting the device to work and function as expected. This isn't the fault of the customer to know the nitty gritty of the battery installed in their device. They expect the system to work as they purchased it.
You gotta remember that it's not just DIYers who rely on these things. Businesses do as well. Could you imagine the financial hurt a business could incur if this happened during
their warranty period?!? It could bankrupt someone who's totally innocent of the whole thing.
Thirdly, isn't the advice to only rely on BMS safeties as a final-defense? You should have external fuses in multiple places in your system for overcurrent protection, your charge controller should already be set to a proper max charge voltage that is under your BMS cutoff limit, if you use an inverter you can also set extra parameters on that side... and ultimately, batteries shouldn't be ignored if you're going to use them.
If the BMS resets to Li-Ion voltages, then what's the point of it being the last defense!? It's already failed and won't do any triggering to stop. Not all chargers are designed to stop at a specific voltage. And even
if they are designed, they wouldn't know the individual voltages of the cells in the battery pack. The charger wouldn't know if a cell was going high voltage while another was lagging behind, as it looks at the overall voltage instead.
Fuses wouldn't work in this situation. Breakers wouldn't work either. There isn't an
overcurrent situation. It's an
overvoltage situation, and according to the BMS that's defaulted to Li-Ion settings, it doesn't know any different. It'll continue to allow the cells to get more juice until they begin to swell. The
only thing that would hopefully save them at this point would be the temperature probe(s) as the cells would most definitely heat up. But again, if it's only a few cells and they happen to be the ones
without a temp probe, it'd be too late.
Again, I don't mean to argue that this isn't an issue (it is), nor do I think JKBSM shouldn't have to fix it (they should)
Just to play devil's advocate.
As you mention here, your being devils advocate. It's good to ask these questions for people who don't understand the severity of the situation and don't even know what to ask. They don't know what they don't know and don't know what to ask so as to know.
For example, on the Discord server I posted this video in there was a guy who didn't have the faintest idea why this was an issue. He has multiple LFP "12V" batteries in his various equipments. It took probably close to 10 minutes to fully explain (ya know, text and waiting for them to reply and such) what the problem was and why it was so severe. Afterwards, he was like "Oh damn! That's why! Yeah they need to fix that quick"
He was under the assumption it was a DIY only thing and was only used for huge battery packs.
Maybe I'm turning into a cranky old man
Meh, we all get that was as we get older. I'm seeing it even in myself. I have far less patience for certain things than I used to. Idiocy I can't stand.
