Seplos Reducing Current Toward Full Charge

[Tulex]

When looking at my setting for an issue I had with my Sol-Ark 15K, the tech commented that I'm charging my batteries at full current right up to full charge.
I've looked at my settings on my Seplos BMS, I don't understand which is the parameter to change that. I already know that I'm going to reduce my peak charge, as it seems pointless to charge to 57.2 volts if it's just going to drop right back down. Below is what it's doing now, and my settings. Also, SA shows battery got down to 65%, but shows 53V at that point. Does that seem right? Apologize for the large images, thought they would resize. Should also note that I'm running closed loop, so can't do it via inverter settings.

 

[Tulex]

Today I reduced the maximum charge current to only 50 amps when it got to around 97%, and while it still dropped, it resumed and slowly climbed to around 55.5V, about a volt higher than when I let it charge to full at 200 amps.

I've got to believe this is easier on the battery, so there must be a way to control this.

 

[houseofancients]

It you are charging full current till full, you must have some protections disabled..
Normally the seplos will start limiting the charge current around 98% full or as a cell hits alarm status

 

[Checkthisout]

It you are charging full current till full, you must have some protections disabled..
Normally the seplos will start limiting the charge current around 98% full or as a cell hits alarm status

So the charger lowers it output voltage so the amperage drops as the battery nears full?

That's a weird feature.

I'm still learning or always learning but what purpose does that serve?

 

[houseofancients]

So the charger lowers it output voltage so the amperage drops as the battery nears full?

That's a weird feature.

I'm still learning or always learning but what purpose does that serve?

The BMS sends a signal to the charger to lower it's amps .
If the charger doesn't respond it will hard limit it to 10a on the BMS itself

And that certainly isn't a weird feature

 

[Brucey]

Today I reduced the maximum charge current to only 50 amps when it got to around 97%, and while it still dropped, it resumed and slowly climbed to around 55.5V, about a volt higher than when I let it charge to full at 200 amps.

I've got to believe this is easier on the battery, so there must be a way to control this.

What batteries are you using? General rule of thumb is to charge at 0.5C i.e. 50A for a 100Ah battery, to maximize lifecycle count.

 

[Tulex]

What batteries are you using? General rule of thumb is to charge at 0.5C i.e. 50A for a 100Ah battery, to maximize lifecycle count.

I've got 3 304ah batteries.

 

[Checkthisout]

The BMS sends a signal to the charger to lower it's amps .
If the charger doesn't respond it will hard limit it to 10a on the BMS itself

Interesting. Ok

So if you have absorb voltage to say 3.5 volts per cell, as the battery approaches fully charged, the charger will lower it's output voltage in order to limit the amps flowing into the battery or the BMS itself begins to throttle the current down by duty-cycling the fets to control the amperage flowing in?

So if the charging voltage was set to say 3.6 volts per cell, as the cell reached 100% charge, we would see the BMS begin to make a voltage difference between the cell terminals and the BMS negative terminal? (duty cycling the fets)

That is weird. I didn't know they did that.

I just thought amps reduced on their as battery voltage and charger voltage reached unity and the ending amperage or tail current was just a user setting that decided at what amperage to turn charging off or change to float voltage.

 

[houseofancients]

Interesting. Ok

So if you have absorb voltage to say 3.5 volts per cell, as the battery approaches fully charged, the charger will lower it's output voltage in order to limit the amps flowing into the battery or the BMS itself begins to throttle the current down by duty-cycling the fets to control the amperage flowing in?

So if the charging voltage was set to say 3.6 volts per cell, as the cell reached 100% charge, we would see the BMS begin to make a voltage difference between the cell terminals and the BMS negative terminal? (duty cycling the fets)

That is weird. I didn't know they did that.

I just thought amps reduced on their as battery voltage and charger voltage reached unity and the ending amperage or tail current was just a user setting that decided at what amperage to turn charging off or change to float voltage.

Where are you getting the notion it is dropping the voltage ?
It is dropping the amps, not the voltage, nor did I ever mention a lowering of voltage

 

[Checkthisout]

Where are you getting the notion it is dropping the voltage ?
It is dropping the amps, not the voltage, nor did I ever mention a lowering of voltage

The only way it can drop amps is by dropping the voltage.

If battery voltage and charger voltage are equal, no current will flow.

 

[doityourself2021]

So the charger lowers it output voltage so the amperage drops as the battery nears full?

That's a weird feature.

I'm still learning or always learning but what purpose does that serve?

Depending on battery types, controller charger, etc.. BMS typically associated with LifePo4 Lithium Phosp types and if they are Seplos board(s), as the battery(s) reach up around 98% SOC between the BMS and Charge controller if the BMS board(s) are in communication with the Charge controller.. It is typically that two things be done when charging, not only is the Amps/Current flow need to be reduced when getting close to Full charge, but the Voltage Balance level also needs control. All of which for the benefit of Longivity of the Battery(s) I'm not familar with all the different type of charge controllers however, the settings limits of the Charge Controller interact with the BMS battery boards.. One needs to follow Mfg. guidelines both for the Controller and BMS.

 

[Checkthisout]

Depending on battery types, controller charger, etc.. BMS typically associated with LifePo4 Lithium Phosp types and if they are Seplos board(s), as the battery(s) reach up around 98% SOC between the BMS and Charge controller if the BMS board(s) are in communication with the Charge controller.. It is typically that two things be done when charging, not only is the Amps/Current flow need to be reduced when getting close to Full charge, but the Voltage Balance level also needs control. All of which for the benefit of Longivity of the Battery(s) I'm not familar with all the different type of charge controllers however, the settings limits of the Charge Controller interact with the BMS battery boards.. One needs to follow Mfg. guidelines both for the Controller and BMS.

I didn't know there were BMS that could throttle current and did so based on state of charge.

That's news to me. I didn't realize BMS had the ability to duty cycle the fets and could gradually lower the voltage present at the cell terminals.

I always thought "tail current" or whatever setting that people talk about on charge controllers just controlled at what amperage the charge controller switched to float. I didn't know it was actually backing voltage down to lower the amount of current flowing into the battery as it got full.

 

[houseofancients]

I didn't know there were BMS that could throttle current and did so based on state of charge.

That's news to me. I didn't realize BMS had the ability to duty cycle the fets and could gradually lower the voltage present at the cell terminals.

I always thought "tail current" or whatever setting that people talk about on charge controllers just controlled at what amperage the charge controller switched to float. I didn't know it was actually backing voltage down to lower the amount of current flowing into the battery as it got full.

Pace BMS ( sok , jakiper and others)
Jk BMS ( server rack)
Seplos
EG4
And others

Almost all BMS's that have inverter communications do this, as it helps with cell balancing ( both passive and active) , life of the MOSFET'S, and inverter circuitry and it is a safety feature

 

[Checkthisout]

Pace BMS ( sok , jakiper and others)
Jk BMS ( server rack)
Seplos
EG4
And others

Almost all BMS's that have inverter communications do this, as it helps with cell balancing ( both passive and active) , life of the MOSFET'S, and inverter circuitry and it is a safety feature

I know that BMS can communicate with inverters and charge controllers.

What you said is the bms itself can control the amount of charging current using its own internal circuitry which implies it does standalone without the need for inverter communications unless what you meant is the inverter can monitor state of charge using the bms?

In which case you stated the inverter/charger/mpppt or whatever can reduced the current as the battery nears full.

I didn't know they could do that. The only way to control current flow into the battery is by changing the voltage present at the cell terminals so this implies these particular chargers work differently than other chargers in the past which just held voltage steady and let the current naturally reduce as the battery comes up to full charge.

With of course the user being able to set what that output voltage is, among other things.

I thought the tail current was just for setting when the charger switched from bulk or absorb to float based on the natural current taper that occurs as charger voltage and battery voltage reach unity, not that the charger was actually tapering current

 

[houseofancients]

Just a random image of a pace BMS ,
But what would you guess these are for ?
Arrow is not pointing to those capacitors

 

[Checkthisout]

View attachment 214400
Just a random image of a pace BMS ,
But what would you guess these are for ?
Arrow is not pointing to those capacitors

I don't know.

 

[houseofancients]

I don't know.

Current limiting and/or in/out rush limiting

 

[Checkthisout]

Current limiting and/or in/out rush limiting

When do they come into play?

Edit:

So as the battery comes to full charge, the fets disconnect the main charging path and charging is completed through those coils?