I am setting up a mutiplus to charge my Renogy lithium batteries and I am not sure about what to do for the float voltage. According to Renogy my charge voltage is 14.4, cut off is 14.6 but it doesn't say if you should have a float voltage.
asked
Charging parameters for multiplus 3k and Renogy RNG-BATT-LFP-12-170
I think you should go back to Renogy and ask what there float voltage is I would think it would be around 13.6
Bulk/Absorption 14.2 to 14.4
Length of time for absorption 1 hr
Float 13.6
The above are mostly generic values so you need to find the correct ones from your battery suppler or take a guess
Renogy didn't really give me a good answer to the float voltage question, they said
"We are in the process of investigating whether float is indifferent or has an effect on our particular battery"
This is what Renogy told me:
We recommend using the following setting
- absorption voltage: 14.4V or 14.6V
- absorption time: depending on the Li charging profile in the controller
- float voltage: off
- equalization: off
The ideal charging profile for lithium battery is keeping the constant current stage (fast charge) until the battery is reaching 100%, which means when the battery charging voltage reaches the absorption (boost) voltage set point, the battery is almost fully charged. Then the duration of constant voltage stage (absorption time) will be minimized before the charging is terminated.
Please contact Victron and ask for their recommendation on the absorption time based on the their controller model. 6 hours is way too long.
Renogy LFP batteries don't need top up charge when the battery is kept connected to charger without any load running, since the self-consumption is very low. If you can't get rid of the float stage, please track the float charging current and make sure it's small enough to not over charge the battery.
Renogy gives a cut-off current, so to stop charging after that. Lithium doesn't like to be trickle charged.
But..as most systems have loads attached to the batteries, you want a voltage to use to prevent discharge of the batteries. That's where the 'float' voltage comes in: configure it to the value the batteries aren't loaded, for LiFePO4 about 3,35V per cell = 13,4V
This can provide another problem: in an ESS system the system will actually discharge the battery to reach this float-voltage. As you didn't tell what kind of system you have, I don't know if this is an issue for you.
This is for an RV, so essentially a backup system with solar, an ESS with the intent to keep the batteries 100% charged until the shore power (grid power) goes away.
I have two concerns at this point, first is the Renogy battery doesn't have output contacts from the BMS so I do not know how to trigger the Multiplus to turn the charger off after the battery is fully charged if I don't want to use a float voltage such as when in storage and what triggers the charger to charge again if the battery does need "topped off". My second concern is If I am connected to shore power and using the RV 12v system for lighting, fans and so on how do I keep the battery from cycling unnecessarily (I assume this is when I want a float voltage). I assume I need to program the Multiplus for each situation but perhaps there is a profile that works in both cases?
I am sure it is something I have missed in the manual but for the life of me I re-read it and I have not figured it out so any help would be appreciated.
