Voltage spike during periods of high charge current

[utkvols]

Equipment
16 EVE LiFePO4 304Ah
Victron MPPT 450/100
SmartShunt to measure current - 250A version
BMS is JK BMS - 150A max current model
Victron 48/5000

I am seeing my LiFePO4 bank voltage rise quickly with a charge current over about 40. I have MPPT absorption voltage at 55.3 with float 54.4. It happens regardless of the SOC - I first noticed it last week with a SOC of about 60. I experimented with it again today with a lower SOC (see graph below) and I am still seeing the voltage spike and then fall back to about previous as the cells "rest" for a minute or two.


The first (mobile) screenshot shows this phenomenon the best. The website screenshot was from today at the lower SOC- it is partly cloudy so I think it is a bit less clear on what is happening.
If you look closely you see amperage rise and shortly afterward voltage rises until the float voltage is reached. Float voltage on mobile screenshot I think may have been higher than the second screenshot - looks like its probably 55.4. (I know it is not any higher as I've never set it higher in the past)

Voltage reading reported correlates within a mV between inverter, bms, mppt etc - I don't think mppt is seeing an incorrect voltage.

I do feel the SOC is accurate as there is a constant load on the inverter and the consumption rate makes sense for the below SOC. It was recently "refreshed" with a full charge two days ago.

BMS is not hitting overvoltage or overcurrent cutoff - It is quite a bit higher for both.

I've noticed with a few tenths lower absorption voltage the bank will take a higher charge current but then things are cutting off before SOC is at 75% - I have node red reducing the charge rate when SOC hits 75%.

I don't think this is normal as this is less than 0.15C with these numbers. Any thoughts on what else to check?



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[Texas-Mark]

At quick glance it looks like the BMS is cutting off the charge for whatever reason (cell OV possibly) and the voltage spikes before the controller can react, then when the battery settles, the BMS resumes charging.

 

[utkvols]

Ahhhh facepalm. Thanks!! I have not paid attention to cell voltages, only the overall voltage. I will check that today and report back

 

[DIYrich]

The MPPT should not go over the 55.3v setting. What is the setting on the 48/5000?

 

[Texas-Mark]

The MPPT should not go over the 55.3v setting. What is the setting on the 48/5000?

It can if the BMS opens and there is no longer a load (assuming only one battery). It's not uncommon.

 

[DIYrich]

It can if the BMS opens and there is no longer a load (assuming only one battery). It's not uncommon.

If it was 56.0v at 0.1a, that would make sense. According to the graph, there is about 13 amps going into the battery at a voltage higher than the charge setting. Either the MPPT is exceeding its settings, or something else (the inverter) is supplying the higher voltage.

Not likely for the 56v going directly to the inverter. The shunt would show nominal 0 amps, and it still begs the question why the MPPT is exceeding the charge setting.

 

[Texas-Mark]

If a battery is actually still connected (meaning the BMS has not opened), it's pretty much impossible for the voltage to spike like that as the battery would load it down. A true voltage that high on a connected (closed BMS) battery would result in extremely high current. Something else may be drawing some current, but I doubt it's the battery.

 

[DIYrich]

If a battery is actually still connected (meaning the BMS has not opened), it's pretty much impossible for the voltage to spike like that as the battery would load it down. A true voltage that high on a connected (closed BMS) battery would result in extremely high current. Something else may be drawing some current, but I doubt it's the battery.

There shouldn't be anything between the shunt and the battery.

 

[Texas-Mark]

There shouldn't be anything between the shunt and the battery.

Regardless, the sudden drop in current and voltage spike is indicative of a BMS opening.
Lets wait to see what the OP'er says about cell voltages when it happens.