Newb charge controller “pass through” safety question

[Burton4290]

Okay guys, my overthinking brain is getting the best of me and I need an explanation of whether this thought is right or wrong.

Let’s go with a standard diy setup hypothetical situation here. You have a solar array connected to a charge controller, and CC is connected to 48v lithium battery, and then battery connected to an inverter.

If the battery is hypothetically COMPLETELY full, but solar array is still producing, and inverter is still feeding a load, how would this not cause metallic lithium plating within the battery as the battery is full but CC is still supplying current as some sort of “pass through” to the inverter? Would this not essentially act as a trickle charge as current is still going through the full battery to feed the inverter?

I’m sure this might be the dumbest question ever asked on this forum, but this crazy thought popped into my head and won’t leave now.

For those wondering why I’m thinking along these lines, I’m trying to see if there is a way to extend the capacity of an eco flow delta. My thoughts would be to have solar feed CC, CC would feed standalone battery, and that battery would then be plugged into the back of the eco flow solar input which accepts 12-55v. If the standalone lithium battery’s are full but eco flow is not, would the current passing through the full lithium pack to get to the eco flow not cause issues?

 

[BentleyJ]

While its true that Li chemistry does not need or desire a constant trickle charge while sitting idle. The situation you are describing is called Float and the voltage used is low enough that the battery is not being damaged by overcharging but the CC is still producing power at a rate consistent with what is consumed by the Inverter.

 

[Burton4290]

While it’s true that Li chemistry does not need or desire a constant trickle charge while sitting idle. The situation you are describing is called Float and the voltage used is low enough that the battery is not being damaged by overcharging but the CC is still producing power at a rate consistent with what is consumed by the Inverter.

Okay so let’s take it one step further. Let’s say somebody is using a variable bench-top power supply set to 48v that is feeding the battery instead of the charge controller in the above scenario. The bench top power supply will cut current when set voltage is reached. So the battery is now full, current is cut from power supply, but suddenly the load turns back on of exactly 48v. Now the power supply kicks back on and is supplying the load THROUGH the lithium battery that is full, essentially providing a constant current situation passing through into the load. (Hopefully this is obvious that this is strictly a hypothetical scenario just to confirm or deny my thinking is correct)

 

[FLD]

Hi. I see you're also in Michigan. I'm near the lakeshore, west of Grand Rapids. Great weather we're having, isn't it?
My charge controller voltages are set for bulk charge voltage of 14.2 with the float voltage set at 13.2. When my lifepo4 battery bank reaches 14.2 volts, the charge controller basically shuts off until the battery voltage drops to 13.2, at which time the charge controller will start recharging the battery if the panels have sunlight.
If my inverter is running equipment in our camper and it's consuming 100 amps from the battery bank, the panels and charge controller will contribute whatever amp rate is possible as soon as the battery bank voltage drops to below 13.2 volts.
Let's say it's a bright sunny day and my system is generating upwards of 50 amps. The 50 amps being generated by the solar charge system will contribute that 50 amps towards the 100 amps the inverter is drawing, and the batteries are contributing the other 50 amps. When the load on the inverter drops, like if the microwave oven turns off, the solar charge system will continue to replenish the battery bank until the battery bank's voltage again reaches 14.2 volts. The charge controller then "turns off" and waits for the battery bank voltage to drop to 13.2 volts.
You have a 48 volt system, right? Multiply my numbers by 4.
I'm no expert on this stuff so don't take my word for it.

 

[BentleyJ]

Okay so let’s take it one step further. Let’s say somebody is using a variable bench-top power supply set to 48v that is feeding the battery instead of the charge controller in the above scenario. The bench top power supply will cut current when set voltage is reached. So the battery is now full, current is cut from power supply, but suddenly the load turns back on of exactly 48v. Now the power supply kicks back on and is supplying the load THROUGH the lithium battery that is full, essentially providing a constant current situation passing through into the load. (Hopefully this is obvious that this is strictly a hypothetical scenario just to confirm or deny my thinking is correct)

Yes, that is essentially how a charge controller or inverter-charger works when in Float mode. Its a Constant Voltage Power Supply.

 

[Burton4290]

Hi. I see you're also in Michigan. I'm near the lakeshore, west of Grand Rapids. Great weather we're having, isn't it?
My charge controller voltages are set for bulk charge voltage of 14.2 with the float voltage set at 13.2. When my lifepo4 battery bank reaches 14.2 volts, the charge controller basically shuts off until the battery voltage drops to 13.2, at which time the charge controller will start recharging the battery if the panels have sunlight.
If my inverter is running equipment in our camper and it's consuming 100 amps from the battery bank, the panels and charge controller will contribute whatever amp rate is possible as soon as the battery bank voltage drops to below 13.2 volts.
Let's say it's a bright sunny day and my system is generating upwards of 50 amps. The 50 amps being generated by the solar charge system will contribute that 50 amps towards the 100 amps the inverter is drawing, and the batteries are contributing the other 50 amps. When the load on the inverter drops, like if the microwave oven turns off, the solar charge system will continue to replenish the battery bank until the battery bank's voltage again reaches 14.2 volts. The charge controller then "turns off" and waits for the battery bank voltage to drop to 13.2 volts.
You have a 48 volt system, right? Multiply my numbers by 4.
I'm no expert on this stuff so don't take my word for it.

That makes perfect sense and is exactly what I was looking for. Setting the float LOWER than bulk allows a safety buffer where the inverter is only pulling from battery and doesn’t allow my concern above to take place. What charge controller are you using? Feel free to dm me any pictures of your setup as I’d love to take a look.

I am also on the west coast. I’m down in Fennville near the little store. I usually love this weather but right now it is killing me! Been waiting for my eco flow to be delivered and it’s been 3 days of “weather delay” ?

 

[Burton4290]

Yes, that is essentially how a charge controller or inverter-charger works when in Float mode. It’s a Constant Voltage Power Supply.

Okay that makes sense! So when the controller switches to float or “constant voltage”, it will maintain the batteries 48v, but allow the actual current to the load to be fed from only the battery’s? Does the above post from FLD make sense with having the float voltage set to lower than bulk to allow that safety buffer? Thanks for your help

 

[BentleyJ]

Yes, but of course the voltage would probably not be 48 exactly. For a 16 cell LFP it would be 53.6V - 54.4V. A 15 cell LFP or a battery with Li-NMC cells would all have their own specific float voltage.

 

[Burton4290]

Yes, but of course the voltage would probably not be 48 exactly. For a 16 cell LFP it would be 53.6V - 54.4V. A 15 cell LFP or a battery with Li-NMC cells would all have their own specific float voltage.

i have a 12s 44.4v battery actually, I was just using the arbitrary 48v value for conversation. My 44.4 has a max SoC of 49.8, however I am only charging it to 80% or 47.1v to extend cell life and safety.

 

[FLD]

Ok, don't laugh or make jokes about how much of a cheapskate I am. I have a MakeSkyBlue 60-amp charge controller.
I'm old and retired. So I'd rather fry an inexpensive controller ($90) than fry a nice one when I make the inevitable mistakes rookies make. And actually, my controller has been doing an admirable job for two years. Like the wristwatch commercial from a lifetime ago, it takes a licking and keeps on ticking. Was it Marlin Perkins that did those ads?
The controller is slightly over-panelled but my solar panels are mounted flat on our camper's roof, so the panels are never at an ideal angle toward the sun. That said, I've seen the controller's display hit 58 amps a few times.