LED Power Supplies — Frequently Asked Questions
60+ questions covering Class 2 requirements, sizing calculations, 12V vs 24V planning, IP ratings, installation, and TMT product specifics.
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General
What is a constant voltage LED power supply?
A constant voltage LED power supply maintains a fixed output voltage (12V or 24V) regardless of the connected load. This is the correct type for LED signage modules, which are designed to operate at a specific voltage. Constant current supplies are used for different LED configurations.
What is Class 2 for LED power supplies?
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). Larger TMT supplies provide multiple independent Class 2 circuits. This simplifies code compliance for LED sign lighting installations.
Electrical
What input voltage do TMT supplies accept?
100-277V AC per the product datasheets, covering standard commercial electrical environments without separate models.
What output voltages are available?
12V DC (LDM60-12, LDM60P-12, LDM150P-12, LDM240P-12) and 24V DC (LDM60P-24, LDM150P-24). Always match supply voltage to module voltage.
What is Active PFC?
Active Power Factor Correction aligns voltage and current phase, improving efficiency (TMT PFC models run 88-93%) and reducing harmonic distortion on the electrical system.
What protections are built in?
All TMT supplies include over-current (OCP), over-voltage (OVP), short-circuit (SCP), and over-temperature (OTP) protection.
Waterproof / IP
Are TMT power supplies waterproof?
Yes — IP67 rated: dust-tight and protected against temporary immersion, suitable for wet-location sign installations per UL8750.
What is the difference between IP67 and IP68?
IP67 covers temporary immersion (up to 1 m for 30 minutes); IP68 covers continuous immersion. TMT modules and supplies are IP67, which suits outdoor signage.
Can supplies be mounted inside a wet sign cabinet?
IP67-rated, UL8750-listed supplies can be installed in damp and wet locations; follow local code for mounting position, drainage, and serviceability.
Does IP67 cover the wiring connections?
The rating applies to the supply enclosure; field connections must be made with appropriately rated connectors and methods per local electrical code.
Sign Industry
Why do sign supplies emphasize Class 2?
Class 2 circuits (100 VA max) carry reduced fire and shock risk, simplifying code compliance, inspection, and wiring methods for sign installations.
What certifications matter for sign power supplies?
UL8750 listing for LED equipment, Class 2 output classification, and an IP rating appropriate for the install location — all TMT models covered on this site are UL8750 listed and IP67 rated.
How do multi-circuit supplies help sign builders?
One enclosure powers several independent Class 2 circuits (three on the LDM150P-12, four on the LDM240P-12), reducing supply count and mounting work on large signs.
Do LED supplies replace fluorescent ballasts directly?
No — ballasts are removed or bypassed during retrofit, and the LED supply connects to the line-voltage feed; see the Sign Cabinet Retrofit Guide.
Installation
Where should the power supply be mounted?
In a serviceable, code-compliant location — inside the sign, in a raceway, or remote — considering wire run length (voltage drop) and the supply's IP rating for the environment.
What causes voltage drop and how do I avoid it?
Wire resistance over long runs reduces voltage at the modules, dimming far ends. Use heavier gauge wire, shorter runs, or 24V systems for long-distance circuits.
Can I load a supply to its full rated wattage?
Use the official per-model module load limits, which build in the manufacturer's tested margin (typically 84-85% of nameplate). Use the 80% derating rule only when no official limit exists.
Who should wire the supply?
Line-voltage input wiring must follow local electrical code — generally a qualified electrician; low-voltage Class 2 output wiring is typically handled by the sign installer.
TMT Products
Which TMT supplies are covered on this site?
Six confirmed models: LDM60-12-C21, LDM60P-12-C21, LDM60P-24-C21, LDM150P-12-C23, LDM150P-24-C22, and LDM240P-12-C24 — 60W to 240W, 12V and 24V.
Which models include Active PFC?
All 'P' models: LDM60P-12, LDM60P-24, LDM150P-12, LDM150P-24, and LDM240P-12. The base LDM60-12 is the non-PFC entry model.
What warranties do TMT supplies carry?
5 years standard; the 60W PFC models (LDM60P-12-C21 and LDM60P-24-C21) carry 7-year warranties. Source: official datasheets.
Which supply pairs with 24V modules?
The LDM60P-24-C21 (60W, 2.5A) for smaller loads and the LDM150P-24-C22 (150W, 2×4A) for larger ones, driving the 24V Midi 4 and Midi Edge-lit variants.
Publishing note: this page currently publishes the verified question set below (organized to match the sidebar). Remaining questions from the 60+ source set are pending export from the React component and will be appended per section.