Enter your ELK installation values
Enter normal device loads in milliamps. Add only extra active demand under alarm load.
Power supply and battery formulas
Complete each step carefully
- Enter the output voltage and rated current for the selected supply.
- Add normal current values from the labels or manuals of every connected device.
- Enter the separate current that runs only during alarms or active events.
- Choose a reserve margin that allows future equipment and normal variation.
- Enter the installed battery size, usable percentage, and required backup duration.
- Read both headroom values. Choose a larger supply or split loads when either value is negative.
Sample ELK load schedule
| Device group | Quantity | Current each | Subtotal | Condition |
|---|---|---|---|---|
| Controller | 1 | 250 mA | 250 mA | Standby |
| Keypads | 2 | 50 mA | 100 mA | Standby |
| Detectors | 8 | 20 mA | 160 mA | Standby |
| Auxiliary devices | 2 | 120 mA | 240 mA | Standby |
| Siren and strobe | 1 | 850 mA | 850 mA | Alarm only |
Why accurate supply sizing matters
An ELK power supply calculator helps plan dependable low-voltage systems. Alarm panels, keypads, sensors, cameras, and relays all consume current. Small values become important when devices share one supply. A proper calculation checks normal current, alarm current, available output, and battery support. It also leaves room for later additions. This reduces nuisance resets, weak batteries, and overloaded wiring.
Measure the standby load
Start with the controller’s normal current draw. Then add each connected keypad, detector, and auxiliary module. Use the manufacturer’s published current value for each item. Multiply that value by the number of matching devices. Add the separate results to find standby current. Standby current represents the normal condition. It should include components that remain powered during ordinary operation.
Allow for alarm demand
Next, estimate the alarm or active condition. A siren, relay, strobe, communicator, or powered lock may add substantial current. Enter the extra active load into the calculator. The calculator adds this value to standby current. The result is the peak demand. Peak demand matters because a supply can be acceptable during idle operation yet drop voltage when an alarm activates. Voltage drops can cause false troubles or poor device performance.
Keep practical reserve capacity
Reserve margin protects the installation from uncertainty. A 20 percent margin is common. It accounts for changing loads and future devices. The calculator applies this margin to standby demand. Compare the recommended continuous current with the supply rating. Compare peak demand with the rated output as well. A negative headroom value means the selected supply needs replacement or the load must be divided.
Size the backup battery
Battery sizing uses amp-hours and the expected standby time. First convert battery capacity into usable capacity. Lead-acid batteries are not fully usable during outages. A usable-capacity setting gives a practical adjustment. Divide usable amp-hours by standby current in amps. This estimates battery runtime. The reverse calculation estimates the minimum battery capacity for a chosen standby period.
Review power and wiring
Power calculations add useful check. Watts equal volts multiplied by amps. Standby watts describe the electrical burden. Peak watts describe the peak demand. These figures help compare transformers, power supplies, and cable heating limits. They do not replace checks. A device can fail from excessive current demand even when total wattage seems modest.
Use correct voltage values and observe polarity at every connection. Check cable length and conductor size before installation. Long runs create voltage drop, especially during siren operation. Place high-current devices near an appropriate supply when practical. Protect each branch with suitable fusing or resettable protection. Keep batteries, transformer terminals, and low voltage wiring inside approved enclosures.
This calculator provides planning estimates. It cannot replace equipment manuals, local codes, or a complete installation inspection. Review device labels and installation sheets before ordering equipment. Confirm battery charging limits for the selected supply. Test the finished system under normal and alarm conditions. Record the measured voltage at distant devices. A measured final check confirms that the calculated design works safely in the field.
ELK power supply questions
1. What does this calculator estimate?
It estimates standby current, alarm peak current, supply headroom, watts, backup runtime, and required battery capacity. It is intended for early design checks. Final selections should follow each device manual and the selected power supply documentation.
2. Should I use milliamps or amps?
Enter device loads in milliamps and supply rating in amps. The calculator converts between them automatically. One amp equals 1,000 milliamps. Check the unit printed on every data sheet before entering a value.
3. Why is reserve margin important?
Reserve margin creates room for tolerance, temperature, small load changes, and future equipment. It reduces the chance that normal operation reaches the supply limit. A margin does not correct an oversized alarm peak or poor wiring.
4. What belongs in standby current?
Include every device that remains powered during normal operation. Typical examples include controllers, keypads, sensors, access readers, communication modules, and powered interface boards. Do not omit a device simply because its normal current seems small.
5. What belongs in additional alarm current?
Include loads that become active only during alarm or special operation. Sirens, strobes, relays, door hardware, and high-brightness indicators often belong here. Use the highest expected combined current, not one device alone.
6. Why does the calculator show two headroom values?
Continuous headroom compares the supply to normal demand plus reserve. Peak headroom compares it to the alarm condition. Both matter. A supply can pass the normal check but still be unable to support a siren or strobe event.
7. How is battery runtime calculated?
The calculator multiplies battery amp-hours by the usable capacity percentage. It then divides that usable capacity by standby current in amps. The displayed runtime is an estimate. Age, temperature, charging condition, and discharge rate change actual performance.
8. What usable battery percentage should I enter?
Use a conservative planning value that reflects the battery type, expected condition, and your operating policy. Many designs avoid assuming full rated capacity. Follow the battery and system documentation when a specified test method or minimum runtime applies.
9. Does the calculator include cable voltage drop?
No. It calculates source loading only. Long cable runs can reduce voltage at distant devices, especially during alarms. Check conductor size, cable length, terminal quality, and peak load separately. Measure voltage at the device during final commissioning.
10. Can I use this for access control or CCTV loads?
Yes, as a general low-voltage planning tool. Enter their normal and active current values correctly. Locks, cameras, heaters, and infrared lighting can have significant peak demand. Confirm the required voltage and any inrush current with the equipment manufacturer.
11. What should I do when headroom is negative?
Choose a higher-rated compatible supply, reduce or redistribute the load, or add an approved auxiliary supply. Recalculate after every change. Verify transformer capacity, battery charging limits, fusing, and supervision requirements before putting the system into service.