LED Power Supply Buyers Guide
Complete guide to selecting LED power supplies for sign lighting. Covers Class 2 requirements, 12V vs 24V planning, sizing calculations, voltage drop, and installation best practices.
Use the ROI CalculatorWhat is Class 2?
Class 2 is a UL safety classification limiting each low-voltage output circuit to a maximum of 100 VA (60W at 12V via the 5A limit). Class 2 power supplies are required for most LED sign lighting installations in the United States. They simplify code compliance by reducing wiring and protection requirements compared to Class 1 circuits.
Larger TMT supplies provide multiple independent Class 2 circuits. The 240W model, for example, provides four independent 5A Class 2 circuits. Each circuit is independently protected and can power a separate zone of LED modules.
12V vs 24V: Which to Choose?
12V Systems
- Most common for channel letter applications
- Widest range of compatible modules
- More susceptible to voltage drop on long runs
- Maximum wire run: approximately 50 feet at 12V before significant drop
24V Systems
- Preferred for larger sign cabinets and longer wire runs
- Half the current of 12V at the same wattage
- Less voltage drop over long distances
- Required for 24V LED modules (Midi 4 24V, Midi Edge 24V)
Sizing Your Power Supply
Step 1
Count your LED modules and identify the wattage per module from the TMT datasheet.
Step 2
Use the official per-model 60W load limit from the TMT datasheet. Divide module count by this limit and round up to get supply count.
Step 3
Verify wire run length for voltage drop. For runs over 50 feet at 12V, consider 24V modules or larger wire gauge.
Use the LED ROI Calculator for automated power supply count estimates using official TMT load limits. Read the calculator methodology for the full formula.
Frequently Asked Questions
What is the 80% derating rule?
The 80% derating rule is a conservative planning guideline: do not load a power supply beyond 80% of its rated capacity. For a 60W supply, this means a maximum of 48W of connected load. TMT's official per-model load limits typically land at 84-85% of rated wattage, which is the manufacturer's tested safe operating point. Use the official limit first; use 80% only when no official limit is published.
What is voltage drop and why does it matter?
Voltage drop is the reduction in voltage along a wire run due to wire resistance. In LED sign lighting, excessive voltage drop can cause uneven brightness or module failure. At 12V, voltage drop is more significant than at 24V for the same wattage. Use larger wire gauge or 24V systems for long runs.
Can I use one large supply instead of multiple small ones?
TMT offers multi-circuit supplies (120W, 180W, 240W, 300W) that provide multiple independent Class 2 circuits in one enclosure. This simplifies installation while maintaining Class 2 compliance. Each circuit is independently protected.
What is the difference between IP67 and IP68?
IP67 means dust-tight and protected against temporary immersion in water (up to 1 meter for 30 minutes). IP68 means dust-tight and protected against continuous immersion. TMT LED modules are IP67 rated. TMT power supplies are IP67 rated. Both ratings are suitable for outdoor sign applications.