[RE-wrenches] Automatic Dark Start of Depleted Lithium Batteries

[Jason Szumlanski]

I have been thinking a lot recently about the reasons off-grid systems can
shut down, and working on strategies to prevent these nuisances that
require manual intervention.

Ideally, a BMS should never shut down due to low voltage/SOC because a
properly programmed inverter should reach it's cut off well before the BMS
decides it needs to protect the battery, especially where there is closed
loop communication. But let's say that happens, where the BMS does make the
DC battery output go to zero.

It seems to me like the inverter should be able to start a generator, and
then signal to the BMS that a charging source is available. But I'm not
aware of any system that actually does this. The inverter should be able to
wake up the battery. I can see this being particularly possible where one
manufacturer is writing the code (I'm thinking Midnite AIO/Powerflo).

Of course, the inverter would have to have power in order to do that, so if
it's nighttime and there is no PV, the inverter power would need to come
from somewhere. I have two thoughts. First, someone could manually start
the generator, waking up the inverter, but they would not have to reset the
BMS if the inverter told it to wake up. The second way would be for the
inverter to somehow close the 2-wire start circuit upon inverter shutdown,
restoring power to the inverter automatically.

If those are not options, an external NO relay powered by the inverter
output could be added to the 2-wire start circuit, perhaps with a time
delay to return to the NO position to allow the generator to remain powered
until the inverter does it's thing and starts charging the batteries.

Anyway, my question is whether any inverter/battery combination out there
works in a way that the inverter tells the battery there is a charging
source available to wake up the BMS and reconnect DC power. And if not, why?

Jason Szumlanski
Florida Solar Design Group
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