Quick BMS question

[Texas-Mark]

Do all BMSs have independent charge and discharge cutoffs? I ask because I had a "no-name" BMS that came with a complete battery that was cutting off early during charge (due to unbalanced cells) but appeared to be also cutting off the discharge circuit too (battery powers a router and I was seeing multiple reboots). Note: battery was always at 90% or more SOC so it was not rebooting due to low voltage.

I have since replaced the BMS (and all issues are resolved), but I was just curious if some of the cheap ones cut off both circuits at the same time, or if there was something else going on.

 

[12VoltInstalls]

came with a complete battery

What ‘brand’ are these batteries?

appeared to be also cutting off the discharge circuit too (battery powers a router and I was seeing multiple reboots)

hard to say.
It would seem that a bms is a fairly standard circuitry and the firmware applied to it determines characteristics. So one would expect it could decide what functions to switch for high voltage versus low voltage disconnects.

If using an inverter to power the router- one could guess that the inverter might either see a spike from the panels and shut down when the HVD initiated, or perhaps the router itself has native HV protection if running from DC? Alternatively, the SCC settings themselves could potentially suspend panel input at a high voltage spike when the BMS disconnected and that momentary sag at the cutout could knock out the router; that seems improbable.

or if there was something else going on.

what are you running for an SCC?

 

[Texas-Mark]

What ‘brand’ are these batteries?

This was a Lachy 12V 100AH that I previously posed only capacity tested at around 70%. After I ripped it apart, it turned out the cells were not balanced and one was reaching HVC well before the others. I have since balanced them and all is well on capacity. But I decided to install a smart BMS since all the rest of mine have BT capability.

If using an inverter to power the router- one could guess that the inverter might either see a spike from the panels and shut down when the HVD initiated,

This is possible. This battery is in a 'remote' locations, so I did not have eyes on it while all this was going on. All I know for sure is it was going into HVC at 14V (after further testing). I did lower the charge voltage to 13.8V just to get around the problem temporarily, but I was still seeing the router rebooting occasionally, so I suspect that one cell was still causing issues even at 13.8V . Since balancing and replacing the BMS, I have had zero issues.

what are you running for an SCC?

Renogy Voyager. This is for a remote trailer that has 4 100W panels. They are mounted flat on the roof, so I have not had any over-current issues with the controller (yet). Since they are all in parallel, I can always disconnect one in the summer when the sun gets higher if I have an over-current issue. The battery powers an inverter that runs the router and a wireless LAN bridge and a TV when I am out there.

 

[12VoltInstalls]

was just curious if some of the cheap ones cut off both circuits at the same time

but I was still seeing the router rebooting occasionally,

Thank you.

Since balancing and replacing the BMS, I have had zero issues.

So my questions were somewhat selfish as I have a mystery HVD I’m trying to solve.
I hate to cut open my batteries but they are cheap ones; I did charge each with a controlled 13.8V but considering your issues I’m unconvinced the cheap oem bms will balance their cells themselves

But thank you for the info. That was helpful.