Over/Under Voltage Lock Settings

[Dave McCampbell]

Hi Dacian.  Can you tell me why the Over Voltage Lock setting is at 3.75vpc instead of 3.65vpc?  My understanding is that 3.65vpc is the upper safe limit for modern LFP cells to avoid risk of damage.  The Under Voltage Lock is set at 2.5vpc which I understand is appropriate for the lower safe limit.  Just trying to make sure all my settings are correct before installing the SBMS0 unit on its mount.

[Dacian Todea]

The overvoltage lock is secondary limit and battery should never get there unless there is a fault. The normal limit is 3.55V (Over voltage) and there are some variations due to cell balancing current may be as much as 150mV during balancing so 3.7V is possible worse case thus 3.75V is just above that limit. There is no delay so even if a cell exceeds 3.75V for a few ms a fault condition will be set and everything will be turned OFF.

The 2.5V limit is the same way the normal limit is set at 2.8V.

[Casey]

Thank you for this information.  I would like to start writing up a detailed list of all the SBMS settings, note their default, and some explanation.  What exactly happens when a lock setting is reached?  Does the SBMS need reset and the individual battery cells tested?

[Center Right Proud American]

Casey,

May I suggest you contact @Oberon Robinson.    He has already started a guide with much of what you describe and is very open to taking additional information.   You may want to check out this thread:

https://groups.google.com/g/electrodacus/c/qorsBKh2HaQ/m/ekxp0vpdBwAJ

[Dacian Todea]

Casey,

No the SBMS0 will not require a reset the OVLK flag will reset as soon as the battery discharges below the 3.35V level tho due to OVLK flag both charge sources as well as all loads are disconnected so it may take some time to discharge with no load just self discharge and SBMS0 but you can force ON one of the loads for a much quicker discharge. In any case if this OVLK happens something will need to change either increase the OVLK limit or correct the battery connections and so you may need to power cycle the SBMS0 anyway to permanently fix the problem.

Cells are normally never the problem and the problem will be cell connections (high resistance connection) maybe long connections between cells (not allowed as that will act as an inductor and create this problem) or maybe to high charge rate more than battery can handle (should be below 0.3C ideally max 0.2C for most batteries) and noisy charge sources like most of the grid inverter/chargers especially when supplied from a generator that also struggles to provide a clean sine.

[Woodworks]

I am kind of having the same issue. I am  am using a rec bms pre charge relay to control a gigavac contactor for LVD. 

the relay is controlled by the xtio 3 set to 2, it works as it should for disconnecting the battery at low voltage. the issue 

I am having is when I charge the battery ( I am using a Pro Mariner 1230p charger, that is the same as a Sterling charger)

the chargers setting is a little high, it charges to 3.65v. There is no HVD,  I am just bench testing and cycling the pack to

try and get a battery capacity. I have one cell that runs at the top and causes the sbms to shut down OV and OVLK.

The first three or four times I cycled the pack I just put a jumper on the contactor and ran the inverter till it unlocked,

less than a minute at approx. 105a. the next time it would not reset till I ran about 50% out of the pack. I ran the pack to 3v today would not reconnect.

 I started playing with it today, 

 Repowered it then everything was back to normal.     

any help would be appreciated

Paul 

[Dacian Todea]

Paul,

You can not just use a charger without having SBMS0 controlling it and it is normal that one cell will be the first to be fully charged no matter how equal the cells are.

Not sure what other errors you had when you discharged the pack to 50% as that will not be normal so it is not related. The OVLK flag will be reset in about a few minutes at most of having a lod on the battery less than 1% DOD

You will just damage the battery if you use a charger that SBMS0 has no control over.  There is no such thing as setting the charger to 3.65V as charge can not measure each cell you likely set at 14.6V and then one of the cells most likely exceeded 4V and that will just damage your pack.  LiFePO4 are not increasing the voltage linearly with SOC when they are full they will increase the voltage almost instant as they can no longer accept electrons

[GLASHINC Developments]

Out of interest, UVLK flag sets at 2.5Vpc.  What is the voltage at which it resets?

[Plamen]

   Hi dev,

Page 31 of the manual - 3.20 V.

[GLASHINC Developments]

Thanks, knew that I had seen those settings somewhere :)

[Dacian Todea]

All cells need to be above 3.2V for things to be re enabled not just one of the cells same for Over voltage lock all cells will need to be below the overvoltage recovery level.