Our charger is set for a 40 amp charge rate and continues that until battery is full, then drops immediately to nothing. BMS and charger are set to 14.6 v. Battery is 280 ah lithium, charged voltage set 14.1 v, tail current set 4%, charged detection time 1 minute. Why won’t our 712 BMV auto sync?
Our charger is set for a 40 amp charge rate and continues that until battery is full
When exactly is that?
That's not a fully charged battery (altough 14.6 - 14.7V is a too high voltage; reduce it to 14.4V or less).
With the Renogy charger there is only the bulk charge stage- once the battery reaches 14.7 volts the charger stops.
CV/CC is constant voltage constant current. It will provide a constant current (in your case 40 amps) until it reaches the charge voltage setting and then simply stop charging. The problem with this is that when the charge voltage is reached the batteries are still absorbing a large amount of current, they are not fully charged (which really isn't an issue for LifePo4), but most importantly the tail current will never be reached, resulting in no synchronization of the SOC.
I would set the bulk/absorption voltage to 14.2 - 14.4, float voltage 13.2 - 13.5, charged voltage setting in the 712-BMV to 0.1 volts below the bulk/absorption setting, tail current at 1 to 2% with a detection time of 3 minutes. Tail current and detection time might need some adjusting depending on what type of balancing the BMS is doing and if you have solar. This should give you a good baseline to start from.
As for your question about my business, I own/operate an RV service and repair business with about 25 years in the industry. And no, I am not affiliated with any stealership. I take pride in workmanship and customer service.
Edit: oops I accidently dropped some 24v values in there. Not good for 12v systems lol.
“If the battery voltage has dropped more than a certain value, a new charging cycle will begin (Bulk - Absorption - Float) if there is still Sun to power the PV panels.”
I have read your posts, perhaps not completely understanding. The information above is what I think you are referencing and the “certain value” is what I’m asking about. I don’t have any way to set that in a custom profile with my charger.
The SOC calculated by the BMV can reach 100% just by charging the battery with enough energy, without synchronization to 100%. This does not happen in your case because the charger stops when Bulk stage ends.
The synchronization to 100% is the other way the BMV SOC gets to 100%. In order for the synchronization to happen, during battery charging the voltage must reach the "charged voltage" set in BMV (14.1V in your case), while the charging current is less than the "Tail current" set in BMV (4%, corresponding to 11.2A in your case), and maintain these conditions for the time set in BMV (1 minute in your case). I suspect that this does not happen in your case because the charging current is still too high.
Yes. The BMS in the battery controls when the charging stops actually- once 14.6 volts is hit, the BMS stops the charging. There is no tail current. As I understand it this is a characteristic with all lithium batteries, not just ours (is this understanding correct?). It seems to me- unless our system is somehow different- the charge voltage and tail current will never be reached for the set time with our set up. And isn’t this how all lithium systems work??
LiFePO4 charging should be like this:
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LiFePO4 cells should not be charged more than 3.6V (but they can be charged to a lower voltage than 3.6V). So for a 4-cell battery, the maximum value for the Absorption voltage is 14.4V.
Float voltage for a LiFePO4 cell is around 3.35V. So for a 4-cell battery Float voltage is 13.4V.
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If your charger has adjustable Absorption voltage value, then reduce it from 14.6V to 14.4V (or even lower if the cells are not well balanced).
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Also, a LiFePO4 cell should not be discharged below 3.0V. Even if the manufacturer lists a lower limit, don't push it. You gain almost nothing, with high risk to damage the cells or shortening their life span.
Of course, no problem if you limit the discharge at higher cell voltage value (losing some usable capacity, but gaining aa longer cell life).
Our charger is a Renogy 2000 w inverter charger, and in the lithium setting as I understand it there is only one stage- the bulk. According to the Renogy manual it charges to 14.7 volts, then is off until the voltage drops to 12.4.
I found a manual (hopefully for the model you have).
https://www.renogy.com/content/R-INVT-PCL1-20111S/R-INVT-PCL1-20111S%20Manual.pdf
In that manual they also call the "Absorption stage" and "Absorption voltage" as "Boost stage" and "Boost voltage" respectively.
If you stick with the "Lithium" charging profile, at least use the custom one, which allows to modify the voltages.
All of your posts have been very helpful. I’m a student with these things and appreciate guys with experience helping. Interesting that I’ve stumbled on something that is controversial: there is a lot of information I’ve found through further researching saying lithium batteries do not need a float charge stage. Clearly Renogy is in that camp. Clearly Victron is not. So for me the jury is still out. One thing I’ve learned is that the Victron BMV needs a certain charge profile to auto-sync. For the short term I’m going to manually sync and stay with the Renogy charge profile for lithium batteries- I have an indicator on our batteries in the BMS that shows when the batteries are fully charged. Simple to sync then. Again: thank you very much.
Interesting that I’ve stumbled on something that is controversial: there is a lot of information I’ve found through further researching saying lithium batteries do not need a float charge stage.
In my post above I wrote this:
Float stage. After the absorption stage ends, the charger maintains a voltage lower than the Absorption voltage and no current enters the battery anymore (assuming it is not being discharged by powering some loads).
The LiFePO4 battery is (should be) fully charged at the end of the Absorption stage.
The Float stage is very important when using MPPT chargers (which charge the battery but also power the loads - such as an inverter). By maintaining the Float voltage, the MPPT charger can power the loads and the LiFePO4 battery should not discharge (if the MPPT can provide all the required power for the loads).
If you have a load bigger than what the MPPT can provide, the battery will start to discharge, to cover the difference. The battery voltage will drop. Once the big load is turned off, the battery will be charged even in Float stage.
If the battery voltage has dropped more than a certain value, a new charging cycle will begin (Bulk - Absorption - Float) if there is still Sun to power the PV panels.
