When an LED driver is described as “non-dimmable”, does this mean that only the input power must be constant, or that both input and output power must be constant?
Disclaimer: I’m not an electrical engineer and I’m probably not using the correct terms for everything—but I’m willing to learn.
Background
-
I have some pre-installed LED strip lighting installations set up as on/off only.
-
These installations have their own separate non-dimmable 24V/48W LED drivers.
-
I want to make them dimmable using Shelly RGBW2 Wi-Fi-operated
relayscontrollers, which operate on the output side of the driver (and which means I don’t need or want a physical dimmer input). -
I’m confused about whether or not my existing non-dimmable LED drivers will suffice.
Analysis
The word “non-dimmable” should say it all, right? What is stopping me from heading out and purchasing replacement “dimmable” drivers?
-
Most information I’ve found paraphrases to:
If you want dimming, you need a dimmable LED driver.
This advice seems oversimplified: it doesn’t explicitly acknowledge the possibility of the dimming occurring on the output side of the driver. Since dimmable LED drivers all appear to expect variations on the input side, it is almost certainly not being made with any consideration for output-side dimming at all.
-
I can find only one source (on Reddit) acknowledging the variation on the output side, and it goes on to state that a non-dimmable driver is okay in this situation:
Dimmer compatible power supplies refer to their ability to take a dimmed input. In this case, the input to the driver is never dimmed so no need for it to be compatible with a dimmer input.
However, this truly is the only source I’ve been able to find in support of using a non-dimmable LED driver in this way. Going off numbers, the odds are (sadly) in favour of this being bad advice.
-
One of my non-dimmable LED drivers starts making noises as soon as the lights are either switched off or dimmed to around 40% or less, and I’m unsure whether this is caused by the driver being non-dimmable, or by an unrelated issue.
Questions
- What exactly does “non-dimmable” mean (and not mean) in the context of LED drivers?
- Can a non-dimmable LED driver be used to dim LED lighting if the dimming occurs on only the output side of the driver?
- Do (or can) non-dimmable LED drivers have any minimum output load requirements—and if so, what happens if those requirements are not met (such as a light being switched off)?
Best Answer
Yes.
Based on the problem description and linked parts, and assuming your existing installation is sized correctly (not too many LED's/fixtures for the chosen power supply/driver), you can use that "relay" to control your existing LED fixture(s) with your existing "driver".
You install the Shelly controller between the "driver" and the LED fixture(s). Everything should work per the Shelly's user manual.
As to your questions in detail...
What exactly does “non-dimmable” mean (and not mean) in the context of LED drivers?
There is no standard definition, but, typically, dimmable drivers offer an electrical (or mechanical) control port to adjust the output of the driven LED fixtures. Electrical ports can be wire terminals or wireless interfaces, while mechanical ports are things like knobs and switches.
Non-dimmable drivers output either a constant current (meaning, they try to always output a constant current, this isn't always possible) or a constant voltage. In your case, your driver is the constant voltage type.
You can determine this from (A) the specification is for a constant 24V DC output -- a single number is specified here, and (B) the specification is for a range of output currents 0 to 2 Amps.
Constant voltage sources vary the current to make sure the voltage stays constant and constant current sources do the opposite (vary the voltage to keep the current constant).
Most low-cost constant voltage LED drivers are indistinguishable from a "normal" power supply. They're branded as LED drivers to appeal to buyers looking for LED applications, but the electronics aren't any different from any other voltage-mode power supply (the most common type).
Can a non-dimmable LED driver be used to dim LED lighting if the dimming occurs on only the output side of the driver?
If you implement the dimming with Pulse-Width-Modulation ("PWM") then this works perfectly fine in theory. The Shelly website doesn't say how they implemented the dimming function, but PWM is the most cost effective and common way of doing it. I'm pretty sure that's how it works in their device.
PWM is about varying the amount of time the LED is on vs. off over a given interval. The driver doesn't really know (or care) how long the LED is off and the driver is capable of handling the LED when it is either on or off.
Keep in mind, that no one here has complete access to the schematics and internal design of the devices you are asking about and there are some esoteric failure modes for rapidly switching a load on the output of a power supply. That said, be careful (keep an eye on things for a while in the beginning), but I wouldn't worry too much about problems that are unlikely to affect you in this scenario.
Do (or can) non-dimmable LED drivers have any minimum output load requirements
Practically, no. All feedback-based power supplies (meaning anything that specifies, and therefore "guarantees" a stable output) have a minimum output requirement in order to ensure stability, but this requirement will be handled inside the power supply/driver itself.
—and if so, what happens if those requirements are not met (such as a light being switched off)?
This isn't how the minimum load requirement works. Minimum load is about the light fixture when it is on.
If you violate the minimum load of a constant voltage driver, you are providing it a fixture whose voltage requirements are below that of the driver -- and if you do that (say connect a 12VDC LED string to a 24VDC driver) the LED's will be destroyed by the excessive current that will flow through them.
If you violate the minimum load of a constant current driver, you are providing it a fixture whose maximum safe operation current is less than the driver wants to provide. Exactly what results in this case depends on the internal details of the LED fixture and driver architecture. Either the result is that the driver will output a voltage that is too high and cause more than the intended current to flow damaging the LED's, or the driver will be unable to operate resulting in the LED's being off (without damage to either component).