Shoot I missed the point again.
In the above scenario the charger will likely prime the caps before the battery is reconnected.
As
@FilterGuy had already explained.
Actually, with a seperate port BMS, it seems like the charger may not prime the caps.
Even with a common port BMS, there are BMS cut-out scenarios that make me wonder about potential problems:
In particular, if the BMS cuts off discharge due to low temp, it is likely the charger is also turned off so when the temp rises enough for discharge to turn back on there is a potential for a surge. (The same scenario could apply to recovery from an Over-temp shutdown) .
Having said all of that.... I have not experienced any problems like this..... but I have never let my cells get too cold or too hot. I don't know how large of a worry this really is.
I would expect the series resistance of BMS MOSFET's, battery line resistance, DC breaker resistance, and any current shunt resistance is normally enough to prevent popping circuit breaker.
As I mentioned above, I agree that a typical DC circuit breaker will not pop (assuming it is properly sized in the first place)
The two concerns I have are 1) the BMS Over-current sense poping and 2) stress from the surge on the FETs and other components.
It is a good point that the parasitic resistance of the circuit will cut the peak surge. It does not take very much resistance to knock down the peak. The first-approximation for the surge is that there is zero resistance and the surge is initially infinite. However, that is
not real life. There is always resistance. I just don't know what a good 'total system resistance' estimate would be.
In
@Will Prowse demonstration videos he typically has an absolute bare bones set-up. When he hooks up the inverter without pre-charging, it pops the over-current in the BMS. However, in my real-life set ups I have at least a fuse a shunt and a buss bar (or two) in the circuit. I work hard to minimize the resistance in all the connections.... but each one of these things will add resistance.....and reduce the peak surge current.
Note: I can't bring myself to purposfully create surge scenarios to test all of this.... I am too cheap to endanger my equipment.
So, is there a 'real' problem or am I just worrying too much? I don't know. However, if the problem is real, I would expect to hear stories from folks that experienced it.... but so far all of the discussion has been about a theoretical problem. Consequently, I suspect it is not a huge problem.
Note: In Will's videos and on this forum there is a recent trend to design systems where the BMS turns off the charger or inverter rather than directly cut the current. With this type of design the caps stay charged all the time.... even when the BMS shuts down the inverter or charger.