Understanding LSP's FlexCalculator Suite - Part 4: Standby Time
In the first three posts in this series, we learned about the Voltage Drop, Wire Size, and Battery Size calculators in LifeSafety Power's Excel-based FlexCalculator Suite . If you missed them, those posts can be found here:
n this part, we will cover the Standby Time calculator. This calculator will tell you the estimated standby time with a given battery size, current, and alarm time. Note that this calculator is only for lead-acid/gel cell type batteries. The FlexCalculator Suite can be found on Calculators page of our webiste.
Once the suite is downloaded, open the file. A main menu will appear with buttons for each of the calculator pages. For this exercise, click the "Standby Time" button. The Standby Time Calculator page will open.
The interface for the Standby Time calculator is very similar to the Battery Size calculator, with some minor differences.
About The Calculation
Like the Battery Size Calculator, the Standby Time calculator uses Peukert's Equation to accurately calculate the standby time based on rate of discharge. This gives a slightly different, but more accurate, results than the Amps x Hours calculation used in typical battery calculations. This is because a battery's amphour capacity is rated at a 20 hour discharge rate. If you discharge an 8AH battery over 20 hours, it will give you 8AH. If you discharge that same 8AH battery over 48 hours it will give you MORE than 8AH. Conversely, if you discharge the battery faster than 20 hours, it will give you far LESS than 8AH. For more information on this, see our in-depth white paper on backup batteries.
Standby Load
Like the battery size calculator, this is where the standby load currents are entered.
DC1 - This is the total standby load connected to DC1 output terminals on the FPO Power Supply. In this example, the load connected to the DC1 terminals of the FPO power supply is 500mA, so 0.5 is entered.
DC2 - This is the total standby load connected to the DC2 output terminals on the FPO Power Supply. In this example, we have no load on DC2 during standby.
Accessory Boards - The total standby load connected to any accessory boards connected to the FPO Power Supply. In this example the total load on the accessory boards is 2.1 amps.
Total Standby Load - This is a calculated field giving the sum of the DC1, DC2, and Accessory Board currents. This value cannot be changed. In this example, the total is 2.6 amps.
Note that breaking the currents out into the individual fields is not required. If you know your total standby load is 2.6A, you may simply enter 2.6A into the DC1 field and leave the others blank.
Alarm Load
This is where the alarm load currents are entered. If there is no alarm time, leave these fields blank or zero.
DC1 - This is the total alarm load connected to DC1 output terminals on the FPO Power Supply. In this example, there is still a 0.5 amp load on DC1 during alarm.
DC2 - This is the total alarm load connected to the DC2 output terminals on the FPO Power Supply. In this example, a 6 amp load is on the DC2 terminals during the alarm period.
Accessory Boards - The total alarm load connected to any accessory boards connected to the FPO Power Supply. In this example, the same 2.1 amp load is on the accessory boards during alarm.
Total Alarm Load - This is a calculated field giving the sum of the DC1, DC2, and Accessory Board currents. This value cannot be changed. In this example, the total alarm current is 8.6 amps.
Note that breaking the currents out into the individual fields is not required. If you know your total alarm load is 8.6A, you may simply enter 8.6A into the DC1 field and leave the others blank.
Battery Size and Required Alarm Time
These fields are where the battery size and alarm times are entered.
Installed Battery Size - This field is where the battery size is entered in amphours. In this example, the installed battery is 40AH
Alarm (Hours/Minutes/Total) - These fields are where the total alarm time is entered. Enter the requirements into the Hours and Minutes fields. If there is no alarm time, leave these fields blank or zero. In this example, the alarm time is 15 minutes.
Results
The results for the calculation appear in the Result section. To get the results, click outside of the last field you entered information into, or click the "Calculate" button.
Alarm AH Required - This is the calculated number of AH used to cover the alarm portion of the requirement. If there is no alarm requirement, this field will be zero. This is a calculation and cannot be changed. In our example, 4AH of the 40AH battery is required to supply the 8.6A alarm current for 15 minutes.
Standby AH Remaining - This field is the remaining battery AH after subtracting the Alarm AH requirement. In our example, 40AH minus the 4AH required for the alarm period gives 36AH remaining.
Expected Standby Time - This is the estimated standby time factoring in the alarm period. This is a calculation and cannot be changed. In our example, a 40AH battery will allow a 2.6A standby for 12.67 hours and then still be able to supply 8.6A for the 15 minute alarm period.
The final part in this series will cover the Ohms Law and Miscellaneous Calculations. These include power, resistance, temperature conversions, power factor, and many other calculations. As always, if you need assistance our Technical Support department is always here to help.