I heard that most lifepo4 batteries will last much longer if not charged above 80% and not discharged below 20%. Is there a system or tool to do this automatically instead of manually shutting off the charger or inverter when these thresholds are reached?
System to stop charging over 80% soc and stop discharge below 20%?
- Thread starter bob1
- Start date
If you want to do that it is pretty simple. Example is a 12v system ..
After you have done an initial sanity-balance at higher CV's like 14.4v, you reset your CV to 13.5 or below for normal cycling. Maybe 13.45v for the CV. By staying under 3.4v / cell, this ensures you'll never reach a full capacity charge. This means you'll need an SCC capable of setting it to 13.5v for CV, AND 13.5v for float if that is not able to be disabled.
For a charger, you'll want to probably use a programmable bench charger - and KNOW how to use it. Or some other programmable charger that only allows for 13.5v CV. That means looking around a bit.
At the low end, you set your LVD to a higher value, like 12.8v. If you have a battery with an internal bms that doesn't allow for lvd adjustment, then you can purchase an external lvd like a Victron battery protect or similar.
After you have done an initial sanity-balance at higher CV's like 14.4v, you reset your CV to 13.5 or below for normal cycling. Maybe 13.45v for the CV. By staying under 3.4v / cell, this ensures you'll never reach a full capacity charge. This means you'll need an SCC capable of setting it to 13.5v for CV, AND 13.5v for float if that is not able to be disabled.
For a charger, you'll want to probably use a programmable bench charger - and KNOW how to use it. Or some other programmable charger that only allows for 13.5v CV. That means looking around a bit.
At the low end, you set your LVD to a higher value, like 12.8v. If you have a battery with an internal bms that doesn't allow for lvd adjustment, then you can purchase an external lvd like a Victron battery protect or similar.
Yeah I did some more research and it seems like only a few chargers may allow you to specify a particular voltage or change the charging profile. It seems quite hard to find and only on more expensive models. I'd probably save more money by using the battery at full charge and replacing it in 4-5 years.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
There are TWO points related to LFP which is often a source of confusion.
1) The Allowable Voltage Range which is 2.500-3.650 Volts per cell. This is the range where no harm or damage will come to the cells. New cells or those stored a long time should be charged to 3.600-3.650
2) The Working cell voltage which is 3.000-3.400 which is what delivers the actual Amp-hour rating, this is the operational & functional range. Even if you charge cells to 3.500 they will settle to the working range, this is perfectly normal.
You can consider that 2.500-3.000 is the Bottom 10% and that 3.450 is the top 10%. From 2.900 down it drops very fast and from 3.450 cells hit peak very quickly as well.
12V = 12.0V to 13.6V (Bulk to 13.8, Float @ 13.7)
24V = 24.0V to 27.2V (Bulk to 27.6 Float @ 27.5)
48V = 28.0V to 54.4V (Bulk at 55.2 Float @ 55.1)
EndAmps/Tailcurrent is calculated as (100AH x 0.05 = 5A)
Absorb/Bulk charge to the High Voltage above, reaching EndAmps then transition to Float (Constant Voltage/Variable Current @ designated Float Voltage, typically 0.1 volts lower than absorb.
Any decent Solar Charge Controller, All-In-One or Inverter/Charger will be programmable to these values.
Do not exceed 0.5C charge rate OR to the BMS Limit if lower.
1) The Allowable Voltage Range which is 2.500-3.650 Volts per cell. This is the range where no harm or damage will come to the cells. New cells or those stored a long time should be charged to 3.600-3.650
2) The Working cell voltage which is 3.000-3.400 which is what delivers the actual Amp-hour rating, this is the operational & functional range. Even if you charge cells to 3.500 they will settle to the working range, this is perfectly normal.
You can consider that 2.500-3.000 is the Bottom 10% and that 3.450 is the top 10%. From 2.900 down it drops very fast and from 3.450 cells hit peak very quickly as well.
12V = 12.0V to 13.6V (Bulk to 13.8, Float @ 13.7)
24V = 24.0V to 27.2V (Bulk to 27.6 Float @ 27.5)
48V = 28.0V to 54.4V (Bulk at 55.2 Float @ 55.1)
EndAmps/Tailcurrent is calculated as (100AH x 0.05 = 5A)
Absorb/Bulk charge to the High Voltage above, reaching EndAmps then transition to Float (Constant Voltage/Variable Current @ designated Float Voltage, typically 0.1 volts lower than absorb.
Any decent Solar Charge Controller, All-In-One or Inverter/Charger will be programmable to these values.
Do not exceed 0.5C charge rate OR to the BMS Limit if lower.
Steve S seems to hsve it right. Same situation here. Daytime they get too full, we just don’t use much power. Setting the max voltage at the charge controller for float and bulk and whatever the %#&* boost is on the Chinese stuff will keep you below that 80% staying above 20 involves either switching back to utility below that point of course, so that would be controlled by demand or system use, I often realize that while the expensive inverter has so many changing adjustments, the charge controller typically has less, yet the charge controller is the real link to the sun so to speak. I WONDER though if more cycles of less width end up using the same amount of battery life. Example If I carry 100 lbs of potatoes up the stairs in four 25 # bags will it use the same energy as carrying two 50# bags. I.e. no free lunch
12VoltInstalls
life passes by too quickly to not live in freedom
I think not overcharging is the primary thing to think about. The battery (s) should shut down reliably with the BMS but a properly sized battery bank is far more likely to be fully charged than fully discharged. Just by its nature since our goal is fully charged.
