LED PSU Calculator

Immediate symptoms:

• ▸LEDs appear dim or colors are incorrect (especially white appears yellow/orange)
• ▸Flickering or intermittent operation
• ▸Animations run slower than expected
• ▸Some LEDs don't light up at all

Long-term damage:

• ▸Power supply runs excessively hot and fails prematurely
• ▸Thermal shutdown protection activates, cutting power completely
• ▸Voltage sag damages LED driver circuits
• ▸Fire hazard in extreme cases

Always size your PSU at least 20% above your calculated maximum draw

to prevent these issues and ensure safe, reliable operation.

What the headroom buys:

• ▸Longer PSU lifespan due to cooler operation (less thermal stress)
• ▸Room for future expansion without replacing PSU
• ▸Better efficiency at typical load levels (most PSUs are most efficient at 50-80% load)
• ▸Reduced electrical noise and ripple
• ▸More stable voltage under varying loads

When oversizing becomes wasteful:

• ▸Only excessive oversizing (5x+ your needs) wastes money on upfront cost
• ▸Very low loads (<10% of PSU capacity) may reduce efficiency slightly
• ▸Larger physical size may not fit in your enclosure

The comfortable case:

a 100W PSU powering a 60W LED installation - plenty of headroom without waste.

Correct wiring method:

• ▸Run separate positive (+) and negative (-) wires from the PSU to each strip's input
• ▸Use a terminal block or distribution board to split PSU output to multiple strips
• ▸Never run power through one strip to feed another (daisy-chaining causes voltage drop)

Wire gauge considerations:

• ▸Calculate total current: sum of all strips
• ▸Use appropriate wire gauge based on total current and longest distance
• ▸Thicker wire for longer runs to minimize voltage drop

PSU sizing:

• ▸Total PSU wattage must cover the sum of ALL strips plus 20% safety margin
• ▸Example: Three 20W strips = 60W + 20% = 72W minimum PSU

For addressable LEDs:

• ▸Power in parallel (separate wires to each strip)
• ▸Data in series (DOUT of strip 1 connects to DIN of strip 2)

Inject power when:

• ▸5V strips exceed 2.5 meters - inject every 2.5m
• ▸12V strips exceed 5 meters - inject every 5m
• ▸24V strips exceed 10 meters - inject every 10m
• ▸Denser strips pull these distances in - the calculator accounts for it
• ▸You see visible dimming or color shift at the far end

How to inject power:

• ▸Connect additional power wires (+/-) to the strip's power pads at each point
• ▸Run these wires back to your PSU (or use a second PSU)
• ▸Use the same wire gauge as your main power connection
• ▸Only connect power (+/-), NOT data signal

Very long runs:

feed both ends as well as the points between them - the calculator marks every position for your own strip and length.

Yes, you should use a fuse for any installation over 60W.

Fuses protect against short circuits, wiring faults, and prevent fires.

Fuse sizing rule:

Choose a fuse rated at 125-150% of your expected maximum current.

Examples:

• ▸60W @ 5V (12A) → 15A fuse
• ▸100W @ 5V (20A) → 25A fuse
• ▸150W @ 12V (12.5A) → 15A fuse
• ▸300W @ 12V (25A) → 30A fuse

Fuse types for LED projects:

• ▸Automotive blade fuses: Cheap, easy to find, good for DC
• ▸Inline fuse holders: Mount on your positive wire between PSU and LEDs
• ▸Resettable fuses (polyfuses): Auto-reset after cooling

Important notes:

• ▸Fuse goes on the positive wire only
• ▸Place fuse as close to PSU as practical
• ▸A blown fuse indicates a problem to diagnose

5V strips (WS2812B, SK6812):

• ▸Individual LED control — best color effects and animations
• ▸Voltage drop limits one feed to about 2.5 meters without power injection
• ▸Higher current draw means thicker wires needed
• ▸Ideal for: short accent strips, TV backlights, small matrices, desk lighting

12V strips (WS2815, WS2811, GS8208):

• ▸Good balance between addressability and run length
• ▸3-LED segments reduce power wiring complexity
• ▸One feed covers about 5 meters before injection is needed
• ▸Ideal for: medium runs, staircases, under-cabinet, holiday displays

24V strips (COB, FCOB):

• ▸Lowest current for the same wattage — thinnest wires, least voltage drop
• ▸One feed covers about 10 meters
• ▸Mostly COB/FCOB for continuous, dot-free light
• ▸Ideal for: long runs, room perimeters, cove lighting, architectural

Rule of thumb:

Choose the highest voltage your controller and LED type support. Longer runs = higher voltage.

USB power limits:

• ▸USB 2.0: 2.5W (5V @ 500mA) — only a few LEDs
• ▸USB 3.0: 4.5W (5V @ 900mA) — about 15-20 WS2812B LEDs at full white
• ▸USB phone charger (5V/2A): 10W — about 30-50 LEDs at animation brightness
• ▸USB-C PD: up to 100W — viable for larger projects but needs a PD trigger board

When USB works:

• ▸Small accent strips under 30 LEDs
• ▸Low-brightness ambient effects (not full white)
• ▸Portable or temporary installations
• ▸Prototyping and testing

When you need a dedicated PSU:

• ▸More than 50 LEDs or over 10W total
• ▸Full-brightness white or sustained high output
• ▸Permanent installations that need reliability
• ▸Any 12V or 24V LED strips

Important:

Cheap USB chargers may not deliver their rated current reliably. For anything beyond a quick prototype, use a proper Mean Well or similar rated power supply.

How to set it:

• ▸Open WLED web interface → Config → LED Preferences
• ▸Find Maximum Current (in milliamps)
• ▸Set it to your PSU's rated output minus 20% headroom

Example calculations:

• ▸5V 10A PSU (50W): set to 8000 mA (80% of 10,000)
• ▸5V 20A PSU (100W): set to 16000 mA
• ▸12V 5A PSU (60W): set to 4000 mA

Why this matters:

• ▸WLED dims all LEDs proportionally when the limit would be exceeded
• ▸Prevents PSU overload, flickering, and brownouts
• ▸The dimming is proportional across channels, so the effect keeps its color balance
• ▸This is why our calculator's "Effects" mode is realistic: in practice, WLED rarely lets strips draw full power

Pro tip:

If your LEDs seem dimmer than expected, check this setting first. It may be set too low from a previous configuration.

When to use multiple PSUs:

• ▸Total power exceeds 300W (single PSUs get expensive and bulky above this)
• ▸LEDs are spread across different physical locations
• ▸You want redundancy in critical installations
• ▸Different voltage zones (e.g., 5V for short accents + 24V for long runs)

How to wire multiple PSUs safely:

• ▸Connect the negative/ground of all PSUs together — this is essential for data signals to work between segments
• ▸Each PSU powers its own section of LEDs on the positive wire
• ▸Never connect the positive outputs of two PSUs together
• ▸Data signal runs continuously across all segments

Wiring diagram concept:

• ▸PSU 1 (+) → LED segment 1 (+)
• ▸PSU 2 (+) → LED segment 2 (+)
• ▸PSU 1 (-) + PSU 2 (-) → common ground bus → all LED segments (-)
• ▸Data: Controller → DIN segment 1 → DOUT → DIN segment 2

Important safety notes:

• ▸All PSUs must output the same voltage for connected LED segments
• ▸Fuse each PSU's positive output independently
• ▸Use a ground bus bar or terminal block for clean common grounding

The two ways strip is rated:

• ▸Addressable strip is rated per LED. A WS2812B draws 0.202W at full white, so a 60/m reel is 12.1 W/m and a 5 meter reel of it is 60.6W
• ▸Continuous strip (SMD 5050, COB) is rated per meter directly, typically 14.4 W/m at 12V

The rated wattage is a ceiling, not a load.

Every figure above is full white on every LED at once, which is the one thing an effect never does. The calculator's Effects mode puts that same reel at 21.1W, and that is the number your PSU actually sees.

Watch the density.

Wattage per meter scales with LEDs per meter, so the same chip at 144/m is 29.1 W/m against 12.1 W/m at 60/m. Density also pulls in how far one feed reaches - 1.75m instead of 2.125m at 5V - so a denser strip is both more watts and more injection points.

To size from wattage:

total watts, add 20% headroom, then pick a supply at or above that. The calculator does this from your own strip and length.

The same 60.6W of strip, on three rails:

• ▸5V: 12.1A
• ▸12V: 5A
• ▸24V: 2.5A

What amp draw decides:

• ▸Wire gauge - the wire calculator picks the AWG from the current and the run length
• ▸Fuse rating - 125-150% of expected maximum current
• ▸PSU rating - supplies are sold in amps at a voltage, so a 5V 10A unit is 50W
• ▸WLED's current limit - set in milliamps, so 12.1A is 12100 mA

Measure at the feed, not the far end.

Amperage is highest where power enters the strip, and that first segment is the one carrying current for everything downstream of it.

The distinction matters because the parts are not interchangeable:

• ▸Constant voltage (what you want): holds 5V, 12V or 24V and lets the strip draw the current it needs. Sold as an LED power supply, LED driver, or just a 12V supply
• ▸Constant current: holds a fixed current in milliamps and varies its voltage. Used for COB modules, high-power emitters and downlights. Wiring one to addressable strip does not work

"LED driver" is used for both

, which is where the confusion starts. Read the output: a spec in volts and amps (12V 5A) is constant voltage; a spec in milliamps with a voltage range (700mA, 25-40V) is constant current. Only the first will run a strip.

"Transformer" is the analog-lighting word

and is not really accurate here - a transformer changes AC voltage, while everything in an LED strip build runs on DC from a switch-mode supply. If a product calls itself an LED transformer, check the output is DC at the voltage your strip wants.

Dimmable is a separate question.

A dimmable driver dims the whole output, which is not how addressable strip works - a WS2812B dims itself, per LED, in the controller.