JBertok
Network Engineer
I've previously helped walk a few folks offline through setting up Flooded Lead-Acid batteries with their chargers and inverters to get the most possible functionality out of them. Although FLA is deservedly falling from favor and deployment, there will always be a small use-case for them as long as operating environment and cost remain factors, so I thought I'd post up the way I do it, in case it might be found useful.
The most important point gathered from the last 25 years of owning and maintaining FLA is that your chargers need to have temperate-based voltage compensation, and be configured to battery-manufacture voltage specifications exactly.
Other points:
- Different manufactures and types of FLA cells have published voltage specs with slightly varying voltages.
- FLA all have a sloping chart of Ah capacity inversely related to discharge amperage, and model and/or advertised capacity is sometimes greater than the 20-hour industry standard rate.
- U.S.-made battery specs for temperature compensation tend to be in Fahrenheit with a 80°F reference.
- Charger and Inverter specs for temperature compensation are generally in Celsius with a 25°C reference.
- Charger and Inverter presets for "FLA" battery type tend to be lower than optimal, to prevent liabilities related to overvoltage.
- Mixing of different types and manufactures of FLA in parallel will be compromised unless voltage and temp compensation specs match.
- Mixing of FLA of different vintages and internal resistances, although not dangerous, will not result in acceptable utilization of the older cells.
I'll use my gear as an example. Schneider MPPT 60 150, and U.S. Battery REL 16XC2 cells.
- The batteries have published specs at an 80°F reference, which isn't actually mentioned until you get to the part where it talks about voltage compensation vs. temperature, where it says that for every 10°F above 80 to reduce voltage by 0.028V per cell (0.672V for 48V string of 24 cells), or increase by the same voltage for every 10°F below 80. Problem: This spec is in Volts per 10°F with an 80°F starting reference, but Schneider needs Volts per 1°C with a 25°C reference. That latter number becomes the "Battery Temperature Coefficient" in mV/C in the Schneider setup, and since it's not listed it needs to be calculated manually.
- These batteries I've got are commonly marketed as "440Ah", but the actual 20-hour rate spec is 401Ah, and 401Ah should be used in configuration.
- These batteries have a higher than average specs for bulk, absorption, and float, but a lower than average voltage spec for equalization. Problem: all of these voltages are at 80°F reference and need to be adjusted for the 25°C (77°F) "warm" reference point of the Schneider equipment.
I begin by consolidating the published specs into a clear list with the number of cells in series already factored, in my case *24 cells for 48V nominal:
80°F/26.66°C REFERENCE PER U.S.BATTERY SPEC
Bulk Charge: 58.80V
Absorption Charge: 58.80V
Absorption Time: 2-3 Hours
Float Charge: 52.08V
Equalization Charge: 61.20V
Equalization Time: 1-3 Hours
Temp. Compensation: 0.672V/10°F, + for <80°F, - for >80°F
Then, I need to convert the compensation to V/1°C to determine the Temp Coefficient:
0.672V per 10°F = 0.0672V per 1°F, then 0.0672V/(5/9) = -120.96mV/1°C (quite different from Schneider's -104mV/1°C default!)
Also, whenever a voltage or time range is specified, I try to choose dead middle for settings.
Here are the setpoints entered into the MPPT, Inverters, and Battery Monitor: (some rounding is necessary, inverters only support tenths for example)
77°F/25°C REFERENCE PER SCHNEIDER
Bulk Charge: 59.00V
Absorption Charge: 59.00V
Absorption Time: 2.5 Hours (150 Min, 9000 Sec)
Float Charge: 52.28V
Equalization Charge: 61.40V
Equalization Time: 2 Hours (120 Min, 7200 Sec)
20-Hour Rating: 401Ah
Temp. Coefficient: -120.96 mV/C
Here are my MPPT settings, your "Recharge Voltage" will vary to your setup; I run in zero-sell mode with inverter charging disabled:
Hoping this might be useful to someone who's implementing the same obsolete battery technology I am!
The most important point gathered from the last 25 years of owning and maintaining FLA is that your chargers need to have temperate-based voltage compensation, and be configured to battery-manufacture voltage specifications exactly.
Other points:
- Different manufactures and types of FLA cells have published voltage specs with slightly varying voltages.
- FLA all have a sloping chart of Ah capacity inversely related to discharge amperage, and model and/or advertised capacity is sometimes greater than the 20-hour industry standard rate.
- U.S.-made battery specs for temperature compensation tend to be in Fahrenheit with a 80°F reference.
- Charger and Inverter specs for temperature compensation are generally in Celsius with a 25°C reference.
- Charger and Inverter presets for "FLA" battery type tend to be lower than optimal, to prevent liabilities related to overvoltage.
- Mixing of different types and manufactures of FLA in parallel will be compromised unless voltage and temp compensation specs match.
- Mixing of FLA of different vintages and internal resistances, although not dangerous, will not result in acceptable utilization of the older cells.
I'll use my gear as an example. Schneider MPPT 60 150, and U.S. Battery REL 16XC2 cells.
- The batteries have published specs at an 80°F reference, which isn't actually mentioned until you get to the part where it talks about voltage compensation vs. temperature, where it says that for every 10°F above 80 to reduce voltage by 0.028V per cell (0.672V for 48V string of 24 cells), or increase by the same voltage for every 10°F below 80. Problem: This spec is in Volts per 10°F with an 80°F starting reference, but Schneider needs Volts per 1°C with a 25°C reference. That latter number becomes the "Battery Temperature Coefficient" in mV/C in the Schneider setup, and since it's not listed it needs to be calculated manually.
- These batteries I've got are commonly marketed as "440Ah", but the actual 20-hour rate spec is 401Ah, and 401Ah should be used in configuration.
- These batteries have a higher than average specs for bulk, absorption, and float, but a lower than average voltage spec for equalization. Problem: all of these voltages are at 80°F reference and need to be adjusted for the 25°C (77°F) "warm" reference point of the Schneider equipment.
I begin by consolidating the published specs into a clear list with the number of cells in series already factored, in my case *24 cells for 48V nominal:
80°F/26.66°C REFERENCE PER U.S.BATTERY SPEC
Bulk Charge: 58.80V
Absorption Charge: 58.80V
Absorption Time: 2-3 Hours
Float Charge: 52.08V
Equalization Charge: 61.20V
Equalization Time: 1-3 Hours
Temp. Compensation: 0.672V/10°F, + for <80°F, - for >80°F
Then, I need to convert the compensation to V/1°C to determine the Temp Coefficient:
0.672V per 10°F = 0.0672V per 1°F, then 0.0672V/(5/9) = -120.96mV/1°C (quite different from Schneider's -104mV/1°C default!)
Also, whenever a voltage or time range is specified, I try to choose dead middle for settings.
Here are the setpoints entered into the MPPT, Inverters, and Battery Monitor: (some rounding is necessary, inverters only support tenths for example)
77°F/25°C REFERENCE PER SCHNEIDER
Bulk Charge: 59.00V
Absorption Charge: 59.00V
Absorption Time: 2.5 Hours (150 Min, 9000 Sec)
Float Charge: 52.28V
Equalization Charge: 61.40V
Equalization Time: 2 Hours (120 Min, 7200 Sec)
20-Hour Rating: 401Ah
Temp. Coefficient: -120.96 mV/C
Here are my MPPT settings, your "Recharge Voltage" will vary to your setup; I run in zero-sell mode with inverter charging disabled:
Hoping this might be useful to someone who's implementing the same obsolete battery technology I am!
