Why correct driver sizing improves crop consistency
Grow lights run long hours, so an undersized driver can overheat, flicker, or hit protection limits. That reduces photon output and can create uneven canopy response. Aim to operate around 60–85% of rated watts after heat effects. Slight oversizing lowers driver temperature and can extend capacitor life. This calculator turns your real load into a recommended driver class using margin, future growth, and derating.
Match the driver type to your fixture design
Constant voltage drivers suit 12V/24V strips and bars, where long cable runs and parallel branches increase voltage drop. Constant current drivers suit COBs and series strings, where current sets brightness and voltage shifts with temperature. Selecting the correct mode helps estimate CV output current or confirm that CC strings stay within the driver’s voltage window.
Use temperature derating to avoid nuisance shutdowns
Many drivers are rated at a specific ambient temperature and may lose output above that point. The calculator applies a per‑°C derating rate above the rated ambient, then increases required watts to compensate. Example: a 200W design load with 30% margin at 45°C can land in a 320–350W class if derating is strong and airflow is poor in humid tents.
Plan the AC side using efficiency and power factor
AC circuit loading depends on efficiency and power factor, not just DC watts. Input VA is estimated as (DC load ÷ efficiency) ÷ power factor, then divided by supply voltage for input amps. Use the VA and amp estimates to distribute drivers across breakers, choose safe extension cords, and size backup power for small gardens.
Choose the next standard size and wire with intent
Driver lines come in standard watt ratings, so buying the next size above the calculated requirement improves reliability. For multiple fixtures, splitting load across two drivers can reduce heat concentration and simplify future replacement. Confirm output voltage range, dimming method, connector ratings, and inrush behavior, then follow local electrical codes for final installation.
| Scenario | Mode | Load | Key settings | Suggested driver |
|---|---|---|---|---|
| Seedling rack strips | CV 24V | 6 modules × 18W = 108W | Headroom 25%, Ambient 30°C | 150W class |
| Veg shelf bars | CV 48V | Total 240W | Headroom 20%, Future 10% | 320W class |
| COB flower array | CC 1.4A | 2S × 2P, 36V each ≈ 202W | Headroom 20%, Ambient 35°C | 250W class |
| Warm grow tent | CV 24V | Total 180W | Headroom 30%, Ambient 45°C | 300W class |
Example suggestions depend on temperature and margins. Always verify driver specifications and local electrical codes.
Why correct driver sizing improves crop consistency
In indoor gardens, LEDs run for long photoperiods, so an undersized driver can overheat, flicker, or hit protection limits. A practical target is to keep steady-state loading near 60–85% of the driver’s rated wattage after temperature effects. This calculator converts your real load into a recommended watt class using margin, future expansion, and derating.
Match the driver type to your fixture design
Constant voltage drivers are common for 12V/24V strips and bars, where wiring length and voltage drop matter. Constant current drivers are used for COBs and series strings, where current sets light output and voltage varies with temperature. Entering the correct mode helps estimate both output current (CV) and the required string headroom (CC).
Use temperature derating to avoid nuisance shutdowns
Drivers are often rated at a specific ambient temperature; above that point, available output power may reduce. The calculator applies a derating rate per °C above the rated ambient, then increases the required wattage accordingly. For example, a 200W design load with 30% margin at 45°C can push selection into a 320–350W class if derating is significant.
Plan the AC side using efficiency and power factor
Two drivers with the same DC rating can draw different AC current depending on efficiency and power factor. Input VA is estimated as (DC load ÷ efficiency) ÷ power factor, then divided by supply voltage for input amps. These values help compare breaker loading, extension cord limits, and generator sizing for mobile grow setups.
Choose the next standard size and wire with intent
Driver families come in standard ratings, so selecting the next size above the calculated requirement improves reliability. When using multiple fixtures, splitting loads across two smaller drivers can reduce heat concentration and simplify replacement. Confirm output voltage range, dimming method, and inrush current, then follow local electrical codes for final installation.
1) Should I size a driver exactly to the LED wattage?
It’s better to add headroom. Continuous operation in warm grow spaces benefits from a margin, often 20–35%, plus any temperature derating. This reduces thermal stress and avoids protection trips.
2) Why does the calculator ask for “real watts” instead of “equivalent watts”?
Driver sizing must use actual electrical power draw. Marketing “equivalent” ratings do not reflect consumption. Use fixture labels, a watt meter, or the manufacturer’s datasheet for accurate input.
3) When do I pick constant current mode?
Choose constant current for series LED strings or COB modules where current regulates brightness. You’ll specify target current and the string voltage range. The driver must support that current across the full voltage window.
4) What happens if ambient temperature is higher than the driver rating?
Many drivers reduce available output or run hotter, shortening life. The calculator increases required wattage by dividing by a derating factor, helping you select a driver that stays within limits at your ambient temperature.
5) How do efficiency and power factor affect my breaker load?
Lower efficiency increases watts drawn from AC, and lower power factor increases VA. Both raise input current. The calculator estimates VA and amps so you can distribute drivers safely across circuits.
6) Can I run multiple LED fixtures from one driver?
Yes, if wiring and ratings match. In constant voltage, total watts and current must stay within the driver limits. In constant current, fixtures must be compatible in series and within the driver’s voltage range.