TILLUME LED Voltage Drop Calculator

Prototype tool for 24V TILLUME Spot planning: voltage drop, load-side voltage, wiring layout evaluation, and maximum recommended one-way cable length.

Trial version notice: This calculator is currently in pilot use. Parts of the product database are still being maintained, so the results are intended for planning reference only and should be checked against the final product datasheet and project installation requirements.

Input Parameters

Every 5 deg C.
Set this from the selected cable insulation rating.
This adjusts cable temperature rise only. Choose a worse condition for enclosed cavities, conduit, bundled wiring, or poor ventilation.
TILLUME 24V power supplies are adjustable from 23V to 27V. This setting changes voltage margin after cable drop; LED input current is calculated from nominal product power and does not change while the Spot remains above its minimum input voltage.
24V planning recommendation: Use 24V as the preferred calculation basis. Operation above 24V depends on actual cooling, mounting, ventilation, and ambient conditions. Better heat dissipation may allow a higher setting, but higher LED Spot input voltage can reduce service life. This calculator cannot evaluate the real installation thermal condition, so values above 24V are planning references only and must be verified for the project.
Copper conductor resistance uses a 0.0175 / mm2 reference value at 20 deg C, then applies the copper temperature coefficient during the thermal iteration. The iteration starts from the user-selected ambient temperature, estimates I2R heating, updates conductor resistance at the estimated conductor temperature, and repeats until stable or the iteration limit is reached. Production data should later be aligned with verified conductor resistance tables and installation rules.

Wiring Layout Selection

Cable temperature is a prototype iterative estimate. The calculator starts from ambient temperature, estimates I2R heating for each cable segment, updates copper resistance at the new conductor temperature, and repeats until stable or the capped iteration limit is reached. Risk is evaluated against the user-set cable insulation temperature limit: above the limit is marked risk, and within 10 deg C below the limit is marked borderline. Real cable temperature and permitted temperature depend on cable insulation rating, installation method, bundling, conduit, ventilation, and applicable electrical codes.
IEC 60364-5-52 voltage drop note: IEC 60364-5-52 includes voltage-drop planning values. For lighting circuits, this calculator uses 3% of supply voltage as a planning warning reference. Applicability to a specific 24V SELV LED installation, the installation origin, and project requirements must be confirmed by a qualified electrical professional.
Disclaimer: This calculator is intended only for preliminary evaluation. Real installation conditions, cable routing, heat dissipation, connectors, workmanship, and local electrical rules can differ from the theoretical model. The user is responsible for verifying the design and assumes all risk from using the calculator results.

⚡ How to use the TILLUME Voltage Drop Calculator

In 24V LED systems, voltage drop along the cable reduces the voltage reaching each Spot. This calculator estimates that drop, shows the resulting first and last Spot voltage, calculates cable power loss and temperature rise, recommends a power supply capacity, and compares single-run, split-run, and star wiring layouts side by side.

📋 The calculator is intended for planning reference only. Actual installation conditions — cable routing, terminals, connectors, workmanship, bundling, ventilation, ambient temperature, local electrical rules — can differ from the calculation. The final installation must be checked by a qualified electrical professional.

1

Input Guide

01

Product model

Select the TILLUME Spot model used in the project. Planning power, nominal voltage, minimum input voltage, and maximum input voltage are loaded from the product database. For dual-power product naming, 6+6W is calculated as 6W and 8+8W is calculated as 8W for one Spot.

02

Power supply output voltage

Enter the actual output voltage planned at the 24V power supply. TILLUME 24V power supplies are adjustable, but 24V is the recommended planning basis. Raising the output voltage adds voltage headroom after cable drop, but pushes LED input voltage higher — product lifetime depends on actual cooling and installation conditions.

💡 Recommendation: Use 24V as the preferred calculation basis. Operation above 24V depends on actual cooling, mounting, ventilation, and ambient conditions.
03

Voltage safety margin

Extra voltage reserve above the selected product minimum input voltage. A larger margin gives a more conservative result.

04

Power supply margin

Power supply capacity reserve. For example, if total LED load is 60W and the margin is 20%, the recommended power supply capacity is 72W.

05

Ambient temperature

Select the estimated surrounding temperature around the installed cable. This value sets the starting point for the cable temperature estimate.

06

Cable insulation temperature limit

Enter the temperature limit of the selected cable insulation. The calculator compares the estimated cable temperature against this limit. If the estimate exceeds the limit, the result is marked as a ⚠ high temperature risk.

07

Installation heat dissipation

Select the installation condition that best matches the real cable environment. This setting only changes the cable temperature-rise estimate. It does not change LED current.

Installation condition
Factor
🌿 Good ventilation / open mounting
0.7
🏠 Normal ventilation / standard cavity
1.0
📦 Limited airflow / enclosed cavity
1.3
🔧 Conduit or bundled cable
1.6
🧱 Insulated cavity / heat accumulation
2.0
08

Wiring layout

Choose the wiring method used in the installation. Single run, split runs, and star wiring produce different current distribution and cable length results.

⟶ Single Run
Spots are connected one after another on one cable path.
⎤ Split Runs
Spots are divided into multiple branches to reduce branch current and voltage drop.
✦ Star Wiring
Each Spot has an independent branch from the power supply or distribution point.
09

Distance inputs

Enter the distance from the power supply to the first Spot in metres. For single run and split run layouts, also enter the distance between Spots in centimetres. Star wiring uses one independent branch per Spot, so Spot-to-Spot spacing is not required for the star calculation.

2

Result Guide

●

Load-side voltage

Estimated voltage at the load after cable voltage drop. For single run and split run layouts, both first Spot voltage and last Spot voltage are shown.

●

Voltage drop

Maximum calculated voltage loss in the selected wiring layout. The percentage value refers to the power supply output voltage.

●

Estimated LED input current

TILLUME LED Spots behave as constant-current input loads while they remain above the product minimum input voltage. Changing the power supply output voltage does not increase the estimated LED input current.

●

Estimated cable temperature

A theoretical planning estimate. It adjusts copper resistance and flags a warning when the estimated cable temperature approaches or exceeds the user-selected insulation temperature limit.

●

Temperature iteration

Cable resistance rises with conductor temperature. The calculator repeats the temperature and resistance calculation until the result stabilises or the iteration cap is reached. The cap prevents extreme inputs from slowing the page.

●

Recommended PSU power

Total LED load plus the selected power supply margin.

3

Calculation Formula Summary

1

LED input current

Nominal product power divided by nominal product input voltage:

Ispot = Pspot / Vnominal

Itotal = Ispot × number of Spots

LED input is treated as constant-current within the valid input voltage range, so the current is not recalculated upward when the power supply voltage increases.

2

Copper conductor resistance

Base copper resistance at 20 °C uses 0.0175 ohm mm²/m:

Rm,20 = 0.0175 / A

where A is the cable cross-section in mm².

Temperature-adjusted resistance:

Rm,T = Rm,20 × [1 + 0.00393 × (T - 20)]

3

Segment loop resistance

Low-voltage circuits require both outgoing and return conductors, so each cable segment is calculated as a two-conductor loop:

Rsegment = Rm,T × L × 2

where L is the one-way segment length in metres.

4

Voltage drop

For each segment:

ΔVsegment = Isegment × Rsegment

For single run and split run layouts, downstream segments carry less current because fewer Spots remain after each load point. The last Spot voltage is calculated from the cumulative segment drops:

Vlast = Vsupply - sum(ΔVsegment)

5

Cable loss power

Cable loss is calculated with I²R loss for each segment:

Ploss = sum(Isegment2 × Rsegment)

6

Cable temperature estimate

Current density:

J = I / A

Temperature rise estimate:

ΔTbase = 3 × J2 × heat dissipation factor

Copper resistance is then updated at the new estimated conductor temperature and the process repeats until stable or the iteration limit is reached.

7

Maximum recommended one-way length

Maximum one-way cable length from the available voltage headroom:

Lmax = (Vsupply - Vmin - Vmargin) / [2 × I × Rm,T]

8

⚠ Voltage-drop planning warning

A 3% lighting-circuit voltage-drop planning reference based on IEC 60364-5-52. Applicability to a specific 24V SELV LED installation should be confirmed for the project.

📋 IEC 60364-5-52 note: The 3% reference is a planning guideline for lighting circuits. Confirm applicability for your specific 24V SELV LED project with a qualified electrical professional.

⚠

Important Limitations

  • The calculator is for preliminary planning and comparison only.
  • Actual temperature depends on cable type, insulation, conduit, bundling, ventilation, terminals, and installation quality.
  • The product database is still being maintained during the pilot stage.
  • Always confirm final product data with the latest TILLUME datasheet.
  • Final wiring, cable sizing, and power supply selection must be verified by a qualified electrical professional.

TILLUME Voltage Drop Calculator — Version 3.1 — June 2026