Add multiple DC loads, get the exact PSU wattage you need, heat dissipation, topology recommendation, battery runtime, and solar panel sizing — all in one tool.
This free DC power supply calculator helps you size a power supply for any DC system. Unlike basic P = V × I calculators, this tool lets you add up to 10 loads with different current draws, load types, and duty cycles — then applies industry-standard derating to recommend the correct standard-rated power supply.
Whether you are building an Arduino project, designing a PLC control panel, sizing an off-grid solar system, or wiring a van conversion, this calculator gives you the recommended PSU wattage, heat dissipation in watts and BTU/hr, linear vs. switching topology guidance, battery backup runtime, and solar panel sizing.
Add up to 10 DC loads with individual current draw, quantity, load type, and duty cycle. The calculator sums everything and applies proper derating automatically.
Calculates heat output in watts and BTU/hr with specific cooling recommendations: passive heatsink, active fan, or forced-air ventilation based on heat load.
Converts any DC load into off-grid solar sizing: daily Wh consumption, number of solar panels needed, and battery bank for 1-day autonomy.
Any time you are powering multiple DC devices from a single supply, you need to calculate the total load, apply headroom, and select the correct standard-rated PSU. Here are the most common scenarios:
Arduino, Raspberry Pi, LED strips, servo motors — add all your components and get the right PSU size with proper motor surge warnings.
Size 24VDC supplies for PLC CPUs, I/O modules, HMIs, and field devices with industrial-grade 30% derating applied automatically.
Size your DC system for vans, RVs, and cabins. Enable solar bridge to get panel count and battery bank sizing for full off-grid autonomy.
Choose Electronics/DIY, Industrial/PLC, Solar/Off-Grid, or RV/Van. This sets sensible defaults for voltage, efficiency, and headroom.
Select your DC output voltage from 3.3V to 48V, or enter a custom value up to 1000V DC.
Enter each device with its current draw (amps), quantity, load type (resistive, inductive/motor, capacitive/SMPS, LED), and duty cycle. Add up to 10 loads.
Fine-tune efficiency rating, safety headroom (10–30%), ambient temperature, and topology preference if needed.
Open the Battery Backup accordion to see runtime at 100%, 50%, and 25% load for your chosen battery chemistry and capacity.
Open the Solar Bridge accordion to convert your DC load into solar panel count, daily Wh, and battery bank sizing for off-grid autonomy.
The next standard power supply wattage above your derated requirement. This is the size you should buy.
Sum of all your device power draws at rated current. This is your continuous DC power consumption.
Combined current draw of all loads at your supply voltage. Verify this does not exceed your wiring capacity.
Waste heat from the power supply in watts and BTU/hr, calculated from efficiency. Determines your cooling requirements.
Total power drawn from the AC outlet, accounting for the power supply's conversion efficiency losses.
Whether to use a switching (SMPS) or linear (LPS) supply, based on your power level and application requirements.
The calculator uses industry-standard formulas recommended by PSU manufacturers like Eaton, TDK Lambda, and Mean Well.
Total Power (W) = Supply Voltage × Σ(Current per load × Quantity)Safety Headroom: The PSU must be rated above Total Power / (1 − Headroom%). With 20% headroom, a 100W load requires a PSU rated at 125W minimum. We round up to the next standard rating.
Heat (W) = Total Power × (1 − Efficiency) / EfficiencyHeat (BTU/hr) = Heat (W) × 3.4192
Heat dissipation depends on efficiency. An 88% efficient supply converting 100W output generates 13.6W of heat (46.5 BTU/hr). Below 10W needs no heatsink; 10–30W needs passive cooling; 30–60W needs a small fan; above 60W requires forced-air ventilation.
Wall Power (W) = Total Power / EfficiencyTopology recommendation: Below 15W, a linear power supply (LPS) is suitable — ultra-low noise for audio and precision analog. At 15W and above, a switching supply (SMPS) is recommended for superior efficiency, smaller form factor, and lower heat output.
Battery Runtime (hrs) = (Battery V × Ah × DoD) / Total PowerSolar Panels = Daily Wh / (PSH × Panel kW × 0.80 × 1000)
Worked example: An off-grid cabin: lights (200W × 4hr = 800 Wh), refrigerator (150W × 24hr = 3,600 Wh), water pump (500W × 1hr = 500 Wh), laptop (65W × 6hr = 390 Wh). Daily load: 5,290 Wh. At 4.5 PSH with 80% system efficiency: solar array needed = 5,290 / (4.5 × 0.80) = 1,469W → 4 × 400W panels. Battery bank for 2 days autonomy at 80% DoD LFP: (5,290 × 2) / 0.80 = 13,225 Wh → 14 kWh bank.
Calculations sourced from SurgePV’s Power Supply Calculator — surgepv.com/tools/power-supply-calculator/
Common standard DC power supply wattage ratings and their typical applications.
| Wattage | Common Use Cases | Typical Applications |
|---|---|---|
| 5–15W | Single microcontrollers, sensors, small LED circuits | Arduino Uno, ESP32, small sensor nodes |
| 18–45W | Raspberry Pi setups, small Arduino projects with displays | Pi 4 + peripherals, 3D printer control boards |
| 60–100W | LED lighting strips, small motors, Pi clusters | 5m LED strips, small DC fans, multi-Pi stacks |
| 100–200W | PLC control panels, CCTV systems, network racks | S7-1200 + I/O, PoE switches, camera systems |
| 200–500W | Industrial automation, large off-grid DC loads | Motor drives, large LED arrays, telecom racks |
| 500W+ | High-power industrial systems, large off-grid cabins | Server rooms, industrial heating, large pumps |
Running a PSU at 100% capacity causes overheating and early failure. Always size for 70–80% load. Industry standard is 20–30% headroom.
Motors draw 3–10x rated current at startup. A 2A motor can surge to 10A+ briefly. Verify your PSU has peak current capability for inductive loads.
A 200W PSU at 88% efficiency generates 27W of heat. In an enclosed panel, this heat compounds. Plan ventilation for anything above 30W heat output.
Linear supplies are quiet but waste 40–50% as heat. Use switching (SMPS) for anything above 15W. Reserve linear for audio and precision analog circuits.
Sum the current draw (in amps) of all your devices, multiply by your supply voltage to get total watts, then add 20–30% safety headroom. Example: 3 devices drawing 2A, 1A, 0.5A at 12V = 3.5A × 12V = 42W + 20% = 50W minimum. Use this calculator to add all loads automatically.
Use a switching supply (SMPS) for most applications — it is more efficient, smaller, and produces less heat. Use a linear supply for audio equipment, precision analog circuits, or very low-power applications (under 15W) where electrical noise is a concern. SMPS is 85–93% efficient; linear is typically 50–65% efficient.
Industry standard is 20–30% headroom — size your supply so your load uses only 70–80% of its rated capacity. This improves reliability, efficiency (most supplies are most efficient at 50–80% load), and allows for load growth. Eaton, TDK Lambda, and XP Power all specify this in their application notes.
Yes, if all devices run at the same voltage and the combined current does not exceed 70–80% of the supply's rated output current. This calculator sums multiple loads automatically and recommends the correct supply size.
Motors (inductive loads) draw 3–10x their rated current at startup. Size your supply for continuous operation, but verify it has peak current output capability at least 5x the motor's rated current, or use a supply with adjustable current limiting to protect against startup spikes.
12V: small systems under 2kW, RVs, boats. 24V: 2–5kW systems, reduces wire sizing costs vs. 12V. 48V: standard for modern off-grid solar 5kW+, allows use of more efficient MPPT controllers and inverters, smallest wire sizes. Higher voltage = less current for the same power = smaller and cheaper wiring.
Runtime (hours) = [Battery Voltage × Ah × DoD] / Load Watts. Example: 100Ah LFP at 12V (80% DoD) = 960Wh usable. At 100W load: 960 / 100 = 9.6 hours. Use the Battery Backup accordion in this calculator for your specific setup.
Heat (watts) = Output Power × (1 − Efficiency) / Efficiency. Example: 100W output at 88% efficiency: 100 × 0.12 / 0.88 = 13.6W of heat. Convert to BTU/hr: 13.6 × 3.4192 = 46.5 BTU/hr. Under 30W needs passive cooling; over 60W needs forced air ventilation.
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