Solar MPPT and lithium batteries

[alpen1]

I switched my AGM batteries to lithium's. I can't get a definitive answer on MPPT charge parameters, except to "user define" which I have done. My question is: since MPPT chargers rely on voltage drop to start the charging process, and lithium batteries maintain a consistent voltage until depleted, how will the controller know when to charge?
The "user defined" parameter settings seem like a work around, but spending a week and watching the voltage stay the same, but capacity drop with minimal amperage charging from the solar panels, I wonder how long before they are depleted? Is there a solar charger that uses capacity drop to start the charging process?

[Itinerant1]

I'm in the boat as most charging lfp, mppt wakes up when the sun hits the front panels ( Bulk mode). Charges to 14.1v, absorbs for 6 minutes then floats at 13.6v till the sun goes down and the SCC goes into sleep mode. Rinse and repeated now for 6 years.

[3_tons]

LittleBill wrote:


the bms is safety system. its not suppose to engage unless there is an issue. that being overvoltage, undervoltage, temperature, cell voltage deviation and amperage.

the charger does all the charging. period.

Exactly, unlike PWM, MPPT is a more sophisticated dc-to-dc type charger (utilizing surplus voltage), but no need to be concerned by that - just set the charge voltage at 14.x volts, but not to exceed 14.6v… Float (say, 13.6v) is unnecessary but nor will it hurt, and forget equalizations…

3 tons

[vermilye]

My Victron 100/50 with parameters set for lithium also starts each morning in the bulk mode, charges until the charging voltage hits around 14.3V, switches to absorption and brings them up to 14.5V while balancing the battery cells. After absorption, it switches to float at 13.6V. Throughout a typical night, using 30 - 40 amp hours, the battery bank typically drops to 12.8V by morning. Bank is 3 100 amp hour Battleborns.

[time2roll]

alpen1 wrote:
I switched my AGM batteries to lithium's. I can't get a definitive answer on MPPT charge parameters, except to "user define" which I have done. My question is: since MPPT chargers rely on voltage drop to start the charging process, and lithium batteries maintain a consistent voltage until depleted, how will the controller know when to charge?
The "user defined" parameter settings seem like a work around, but spending a week and watching the voltage stay the same, but capacity drop with minimal amperage charging from the solar panels, I wonder how long before they are depleted? Is there a solar charger that uses capacity drop to start the charging process?

Might help to post the controller make and model.

Also post your user defined settings.

My Morningstar MPPT 60 wakes up with the sun every day and puts 13.8 volts into the battery and then drops to float at 13.0 volts. Yes the battery will rest at about 13.4 13.3 all day never getting power from float. Next day controller pushes the battery back up to 13.8 volts. No issues.

[LittleBill]

2oldman wrote:

LittleBill wrote:
lithium battery's drop voltage. not sure who told you they don't...

There seems to be this misconception they do not, but they do.

Actually I'm not sure if it's the BMS or the controller that's more in 'charge' of the charging. I set my Outback controller to the voltages specified, set Absorb to as near zero as possible, and it works fine.

The voltage will vary quite a bit when charging.. at least mine do.

the bms is safety system. its not suppose to engage unless there is an issue. that being overvoltage, undervoltage, temperature, cell voltage deviation and amperage.

the charger does all the charging. period.

[naturist]

It's not that lithium batteries' voltage doesn't drop, it's that it drops much more gradually until the battery is almost dead, when it drops like a rock.

[2oldman]

LittleBill wrote:
lithium battery's drop voltage. not sure who told you they don't...

There seems to be this misconception they do not, but they do.

Actually I'm not sure if it's the BMS or the controller that's more in 'charge' of the charging. I set my Outback controller to the voltages specified, set Absorb to as near zero as possible, and it works fine.

The voltage will vary quite a bit when charging.. at least mine do.

[LittleBill]

lithium battery's drop voltage. not sure who told you they don't... a standard 18650 cell is charged to 4.2 volts, it can drop all the way to 2.75 to be considered dead. thats over a volt difference.

there are multiple chargers that charge lithium, simply match one of them, lithium are some of the simplest batteries to charge.

[pianotuna]

Hi,

Find out the recommended charge voltage for the Li batteries. Set the charging voltage to that number, or slightly lower.