19 Aug 2026

How to Calculate Power Supply for DC24V Underwater Lights?

Choosing the correct power supply is an important step when installing DC24V underwater lights for fountains, pools, ponds and landscape water features.

A power supply that is too small may become overloaded, while an unnecessarily oversized power supply can increase system cost.

The basic calculation is simple:

Total Power = Number of Lights × Power per Light

Then, the power supply should normally be selected with an appropriate operating margin rather than being loaded continuously at its maximum rated capacity.

For example:

20 × 10W DC24V underwater lights = 200W total load

Instead of selecting a 200W power supply exactly, a designer may choose a higher-rated unit, depending on the manufacturer's recommendations and the actual installation conditions.

The correct selection should also consider current, voltage drop, cable length, ambient conditions, power-supply efficiency, control equipment and local electrical requirements.

IEC 60598-2-18:2022 covers fixed luminaires intended for use in or in contact with water, including swimming pools, fountains and garden pools.

What Is a DC24V Underwater Light Power Supply?

A DC24V underwater lighting system normally converts the available AC input into DC24V before supplying the underwater fixtures.

A typical system looks like:

AC Input

↓

DC24V Power Supply

↓

DC24V Underwater Lights

For an RGB or DMX512 project, the system may also include:

DMX512 Controller

↓

DMX512 Signal

↓

RGB/RGBW Underwater Lights

It is important to understand that:

Power supply = electrical power

DMX512 = lighting control signal

They perform different functions.

Step 1 — Calculate the Total Power of the Underwater Lights

The first step is to determine:

Number of underwater lights
Wattage of each light

The basic formula is:

Total Load Power = Number of Lights × Wattage per Light

Example 1

Suppose a fountain uses:

20 × 10W DC24V underwater lights

Calculation:

20 × 10W = 200W

Therefore:

Total lighting load = 200W

Example 2

A larger fountain uses:

30 × 18W underwater lights

Calculation:

30 × 18W = 540W

Therefore:

Total lighting load = 540W

This is the starting point for selecting the power supply.

Step 2 — Calculate the DC24V Current

Once you know the total power, you can calculate the approximate DC current.

The basic relationship is:

Current = Power ÷ Voltage

For a DC24V system:

I = P ÷ 24

Example

For a 200W lighting load:

200W ÷ 24V ≈ 8.33A

So the underwater lighting system requires approximately:

8.33A at 24V

This is useful when selecting both the power supply and the DC distribution cables.

Step 3 — Add a Power Supply Margin

It is generally better not to select a power supply whose rated output exactly matches the calculated lighting load.

For example:

Lighting Load = 200W

Instead of:

200W Power Supply

you might consider a higher-rated power supply, subject to the manufacturer's recommended loading and the actual system design.

A simple engineering example using a 20% design margin is:

200W × 1.20 = 240W

A practical selection could therefore be a:

24V 250W Power Supply

provided its specifications, environmental rating and installation method are appropriate.

The exact margin should be determined according to the power supply manufacturer, operating conditions and project requirements.

Why Should You Leave a Power Supply Margin?

A power supply may operate for long periods in outdoor environments.

Factors such as:

Ambient temperature
Enclosure temperature
Ventilation
Continuous operating time
Input voltage
Load characteristics
Power supply efficiency

can affect its performance.

Therefore, designing some capacity above the calculated lighting load can provide additional system flexibility.

For example:

Load

200W

Design Margin

20%

Target Capacity

240W

Possible Selection

250W

The final selection should always be based on the actual manufacturer's specifications.

Example: Calculate Power Supply for 10 DC24V Underwater Lights

Let's start with a small fountain.

Fixture

10W DC24V underwater light

Quantity

10 lights

Total Power

10 × 10W = 100W

Approximate Current

100W ÷ 24V = 4.17A

Using a 20% design margin:

100W × 1.20 = 120W

A suitable design might therefore consider a:

24V 120W or higher-rated power supply

depending on available standard models and the manufacturer's recommended loading.

Example: Calculate Power Supply for 20 Underwater Lights

Suppose a landscape fountain uses:

20 × 12W DC24V underwater lights

Total Power

20 × 12W = 240W

Approximate Current

240W ÷ 24V = 10A

Using a 20% design margin:

240W × 1.20 = 288W

A practical selection could be approximately:

24V 300W

subject to the power supply's actual continuous output rating and installation conditions.

Example: Calculate Power Supply for RGB Underwater Lights

RGB underwater lights require additional attention because the stated wattage should be understood correctly.

Suppose:

20 × 18W RGB underwater lights

Total:

20 × 18W = 360W

Approximate DC current:

360 ÷ 24 = 15A

Using a 20% design margin:

360 × 1.20 = 432W

A project could therefore consider a:

24V 450W power supply

if the fixture's rated power represents its maximum operating load and the power supply is suitable for the application.

Always verify the actual product specification before calculating.

Step 4 — Consider Voltage Drop

For DC24V underwater lighting, voltage drop is one of the most important considerations.

Why?

Because 24V is relatively low voltage.

For the same power:

Lower voltage → Higher current

Higher current makes cable resistance more important.

For example:

A 240W load at 24V requires:

240 ÷ 24 = 10A

If the cable run is long, the voltage at the far end can be lower than 24V.

This may result in:

Lower brightness
Uneven illumination
RGB color inconsistency
Reduced fixture performance

Therefore, selecting the power supply alone is not enough.

You also need to design the DC24V cable distribution system.

How Does Cable Length Affect DC24V Underwater Lights?

Consider two installations.

Installation A

Power supply → Light

5 meters

Installation B

Power supply → Light

50 meters

Even if both systems use the same 24V power supply, the second installation requires much more attention to:

Cable resistance
Cable cross-section
Current
Voltage drop
Circuit layout

For large fountains, it may be better to divide the lighting into multiple circuits rather than running one long DC24V circuit to every fixture.

How to Reduce Voltage Drop?

There are several approaches.

1. Use Larger Cable

A larger conductor generally has lower resistance.

2. Shorten the DC Cable Run

Place the power supply closer to the lighting area where practical.

3. Divide the Lights into Multiple Circuits

Instead of:

1 Power Supply → 30 Lights

consider:

Power Supply → Circuit A

Power Supply → Circuit B

Power Supply → Circuit C

depending on the project design.

4. Use Multiple Power Supplies

Large projects can use multiple appropriately sized power supplies.

5. Calculate Before Installation

Cable sizing should be completed during the design stage, not after the lights are installed.

Should One Power Supply Be Used for All Underwater Lights?

Not necessarily.

For a small fountain, one power supply may be practical.

For a larger project, multiple power supplies can simplify:

Cable distribution
Voltage-drop control
Circuit management
Maintenance
Load balancing

For example:

Small Fountain

10 × 10W

→ One suitable DC24V power supply

Medium Fountain

30 × 12W

→ One or multiple power supplies depending on cable layout

Large Fountain

100+ fixtures

→ Multiple power supplies and distributed circuits may be more practical

The correct configuration depends on the project layout.

Centralized vs Distributed DC24V Power Supplies

There are two common approaches.

Centralized Power Supply

All power supplies are installed in one electrical cabinet.

Advantages

Easy centralized management
Convenient maintenance
Simple control architecture

Considerations

Long DC cable runs
Greater voltage-drop concerns
Larger cable requirements

Distributed Power Supply

Power supplies are installed closer to different fountain zones.

Advantages

Shorter DC cable runs
Easier voltage-drop management
More flexible circuit design

Considerations

More power-supply locations
More installation planning
Environmental protection of each power-supply location

For large landscape projects, distributed power can sometimes be advantageous.

How to Calculate the Power Supply for a Fountain?

Let's consider a complete fountain project.

Project

40 × 15W DC24V underwater lights

Step 1 — Total Power

40 × 15W = 600W

Step 2 — Current

600W ÷ 24V = 25A

Step 3 — Add 20% Design Margin

600W × 1.20 = 720W

A designer could therefore consider:

24V 750W

or divide the system into multiple smaller power supplies.

For example:

2 × 24V 400W

could provide a distributed solution, provided the circuit layout and loads are correctly designed.

How to Calculate DC24V Power Supply for DMX512 Underwater Lights?

A common misunderstanding is that DMX512 changes the power calculation.

It does not.

The basic power calculation remains:

Total Light Power = Number × Fixture Wattage

DMX512 is the control signal.

For example:

30 × 18W RGB underwater lights

Total:

540W

The power supply needs to support the electrical load.

The DMX controller separately handles:

Color
Brightness
Scenes
Color changing
Dynamic effects

Therefore:

DC24V = Power

DMX512 = Control

This distinction is important when designing professional fountain lighting.

DC24V RGB Underwater Light Power Supply

RGB fixtures can have different power ratings depending on:

LED quantity
LED type
Optical design
Maximum output
RGB/RGBW configuration

For this reason, never estimate the power based only on the number of LEDs.

Use the manufacturer's rated input power.

For example:

If the specification says 18W input power, use 18W in the power-supply calculation.

Do not calculate based on the number of LED chips.

How to Calculate Power Supply for RGBW Underwater Lights?

RGBW fixtures can use more channels than basic RGB fixtures.

However, the power-supply calculation is still based primarily on the fixture's rated electrical input.

For example:

20 × 24W RGBW underwater lights

Total:

480W

Approximate current:

480 ÷ 24 = 20A

Using a 20% design margin:

480 × 1.20 = 576W

A project may therefore consider approximately:

24V 600W

subject to actual fixture and power-supply specifications.

What About Power Supply Efficiency?

A DC power supply converts electrical energy from the input side to the required DC output.

Therefore, when calculating the AC input requirement, the efficiency of the power supply should also be considered.

For example, if:

DC output load = 500W

and the power supply efficiency is:

90%

the approximate input power would be:

500 ÷ 0.90 ≈ 556W

This is different from calculating the required DC output capacity.

When selecting the power supply, first make sure the DC24V output rating is sufficient for the lighting load.

Where Should the DC24V Power Supply Be Installed?

The power supply should be installed according to its environmental and electrical specifications.

For outdoor fountain projects, consider:

Rain
Humidity
Temperature
Ventilation
Enclosure protection
Accessibility
Maintenance
Cable distance

Do not assume that a power supply is suitable for outdoor exposure simply because the underwater light itself is IP68.

The power supply and underwater fixture are separate components and may have different environmental ratings.

IP68 Underwater Light Does Not Mean the Power Supply Is Waterproof

This is an important point for project buyers.

You may have:

IP68 Underwater Light

but the power supply may be:

IP20 / IP65 / IP67

depending on the product.

Therefore, the power supply should be installed in an environment appropriate for its own rating.

The underwater fixture needs to be suitable for immersion, while the power supply needs suitable protection for its installation environment.

IEC 60598-2-18:2022 specifically addresses fixed luminaires used in or in contact with water, including fountains and garden pools.

Common Mistakes When Selecting a DC24V Power Supply

Mistake 1: Selecting Exactly the Same Wattage

Example:

300W lights → 300W power supply

This leaves little operating margin.

Mistake 2: Ignoring Cable Length

A correctly sized power supply cannot solve excessive voltage drop caused by an unsuitable cable design.

Mistake 3: Using One Long DC Circuit

Large fountain projects may require several circuits.

Mistake 4: Ignoring Maximum Fixture Power

RGB/RGBW fixtures may reach their highest load when all channels are fully driven.

Mistake 5: Calculating from LED Chip Quantity

Always use the manufacturer's rated input power.

Mistake 6: Ignoring Ambient Temperature

Power supplies can have reduced output capability under certain temperature conditions.

Always check the manufacturer's derating curve and installation instructions.

Mistake 7: Forgetting Local Electrical Requirements

Underwater lighting has specific safety requirements.

IEC 60598-2-18:2022 covers fixed underwater luminaires for applications including swimming pools, fountains and garden pools, while electrical installation rules may also apply depending on the location.

Quick DC24V Power Supply Calculation Table

Number of Lights	Light Wattage	Total Load	Approx. Current @ 24V	Example 20% Margin
10	6W	60W	2.50A	72W
10	10W	100W	4.17A	120W
20	10W	200W	8.33A	240W
20	12W	240W	10A	288W
20	18W	360W	15A	432W
30	18W	540W	22.5A	648W
40	15W	600W	25A	720W
50	20W	1000W	41.67A	1200W

Note: These are simplified calculations for the DC lighting load. Actual power-supply selection should consider the fixture's datasheet, power-supply characteristics, cable voltage drop, environmental conditions and local requirements.

A Simple Formula for Project Designers

For most DC24V underwater lighting projects, you can start with:

Step 1

Number of Lights × Wattage = Total Load

Step 2

Total Load ÷ 24V = Approximate Current

Step 3

Apply an appropriate design margin.

Step 4

Check:

Cable Size + Cable Length + Voltage Drop

Step 5

Confirm:

Power Supply Rating + Environment + Protection + Local Requirements

This gives you a much more reliable starting point for the project design.

Always Lighting DC24V Underwater Light Solutions

For professional fountain and water-feature projects, Always Lighting can provide DC24V LED underwater lighting solutions for applications such as:

Fountain Lighting
Landscape Water Features
Hotel Fountains
Resort Water Features
Garden Ponds
Swimming Pool Lighting
Architectural Water Features
RGB Underwater Lighting
DMX512 Fountain Lighting

Depending on project requirements, underwater lights can be specified with features such as:

DC24V

IP68

RGB / RGBW

DMX512

Stainless Steel Housing

Different Wattages

Different Beam Angles

Custom Cable Lengths

For a project quotation, provide:

Number of lights + wattage + cable length + water depth + beam angle + RGB/RGBW + DMX512 requirement.

This information allows the lighting supplier to help determine the appropriate power-supply and distribution configuration.

Conclusion

Calculating the power supply for DC24V underwater lights is not difficult, but professional projects require more than simply adding up the fixture wattages.

Start with:

Number of Lights × Wattage

Then calculate:

Total Power ÷ 24V = Current

After that, consider:

Power Supply Margin

Cable Length

Voltage Drop

Cable Size

Operating Temperature

Power Supply Environment

Local Electrical Requirements

For small fountains, one appropriately sized DC24V power supply may be sufficient.

For large commercial fountains, multiple power supplies and distributed circuits may provide better control over cable length, voltage drop and maintenance.

For RGB/RGBW + DMX512 underwater lighting, the power system and control system should also be designed together.

The goal is not simply to find a power supply with enough watts.

The goal is to create a stable, properly protected and correctly distributed DC24V underwater lighting system.

FAQ

How do I calculate the power supply for DC24V underwater lights?

Multiply the number of fixtures by the rated wattage of each fixture. Then calculate the required current using total power divided by 24V and select a power supply with an appropriate design margin.

How many 10W underwater lights can a 240W power supply support?

The theoretical load is:

240W ÷ 10W = 24 lights

However, the practical number should be lower if a design margin is required, and cable distribution must also be checked.

What size power supply do I need for 20 × 10W underwater lights?

The lighting load is 200W. A project might consider a 24V power supply around 240W or higher, depending on the manufacturer's loading recommendations and installation conditions.

Can I use a 24V 300W power supply for 20 × 10W lights?

The lighting load is 200W, so a 300W supply has additional capacity. The final selection should still confirm compatibility, environmental rating and the installation requirements.

How do I calculate current for DC24V underwater lights?

Use:

Current = Total Power ÷ 24V

For example, a 240W load requires approximately 10A at 24V.

Does cable length affect DC24V underwater lights?

Yes. Longer cable runs increase voltage drop. Cable cross-section, current and circuit layout should be considered during design.

Can one DC24V power supply control RGB underwater lights?

The power supply provides electrical power. RGB control normally requires an appropriate RGB controller or DMX512 system.

Can DMX512 and DC24V be used together?

Yes. DC24V supplies power while DMX512 provides control signals.

Does an IP68 underwater light need an IP68 power supply?

Not necessarily. The power supply has its own environmental requirements and should be installed according to its own protection rating.

How much power margin should I use?

There is no universal percentage for every project. A 20% example is useful for preliminary calculations, but the final margin should be based on the power-supply manufacturer's specifications, operating conditions and project requirements.

What information should I give an underwater light manufacturer?

Provide the number of lights, wattage, voltage, cable distance, water depth, beam angle, RGB/RGBW requirement and DMX512 requirement. This gives the manufacturer enough information to help evaluate the lighting and power-distribution system.