12V DC LED Dimmer

Question

I would like to fit dimmable LED lights in my new bathroom

Most solutions seem to involve a dimmer switch that chops a high-voltage AC supply, and a driver per light (often integrated into the bulb) that detects this effect and simulates it by flickering or current-limiting the LEDs. I can see this makes sense for retro-fitting into an old circuit, but seems overly complicated when starting from scratch

I'd prefer to have a single 100W transformer; a 12V DC dimmer switch that strobes the output or limits the current; and simple LED spots

• Does this approach make sense? Does anyone sell this kind of DC dimmer switch?
• Would I still need "dimmable" LED bulbs? Or would this approach confuse their drivers? Would I be better off with non-dimmable 12V MR16 bulbs?
• Would the current-limited approach result in some bulbs being bright and others dim (assuming they're wired in series and manufacturing differences cause some to have higher resistance than others)? If using the PWM approach, would the fact that the flickering in now syncronized make it more noticable?

Many thanks for any help!

Answer 1

It makes sense - look for "low voltage LED Lighting" to see what's available, or slide on over to Electronics to build your own.

Dimmable LED bulbs are those with drivers built-in that are "dimmable" - if just running controlled current to LEDs, they are all "Dimmable" (lower current, lower light) so, no, you don't want an LED described as "Dimmable" (nor one described as 12V, probably - a "bare" LED with no other parts attached is best when you are going to feed it controlled current.) If you purchase a "12V dimmer" pre-made, follow the dimmer-maker's suggestions on types of LEDs to attach to it.

LEDs are current devices, so controlling the current will give highly consistent light output (controlling the voltage, less so)

Answer 2

*Source

What you can use is a repeater connected to your original dimmer source and you can get them in various sizes. These are for RGB, Dimmers or just standard power supply.

Really, there is no such thing as dimmable or non dimmable LED's. The drivers are dimmable or not dimmable, like you mention with th the MR16. But that really depends how they are being dimmed.

LED dimmers work by PWM (Pulse Width MOdulation) instead of increasing or decreasing voltage. So the repeater listed above, recognised the frequencies, and applies them to the out put side with the wattage you need.This is why dimmers are expensive, because they are really micro circuits producing frequencies, instead of just limiting the voltage, which may damage some LED's (maybe this is the loosely coined 'non-dimmable' term we see) allot quicker than usual and causes uneven intensity shadows. But really, any LED can be "dimmed" using PWM.

But you can get something like this, which is fairly decent powered, LED dimming module.

*Source

• S : Goes to the V part of the repeaters or the LED itself (This is the PWM signal)
• Arrow and Wave - A analog potentiometer, that can be hooked up to any cheap 5USD wall "dimmer" knob. The device senses the analogue level, and produces a relative PWM, which can be adjusted with the dimming level control.
• L/N - Live Neutral.

Allot of these devices are difficult to find locally and if found locally have various names, and are usually highly overpriced. So always look on the internet before any salesman convincing you that you're paying 100$ for super quality... chinese junk, you can get yourself for 10USD from cheapBay

Answer 3

When starting from scratch, I recommend to look at

1. constant current LED's (350mA, 700mA hi-power), e.g. K3-572-622-70 using a chip from CREE
2. constant voltage LED's (24V, 12V) ... I'd prefer 24V over 12V because wire resistance is not so critical.

and as a very last resort at "retrofit" products. Even the ones calling themselves "dimmable" are very poor in dimming (large hysteresis, non-uniform behaviour when more bulbs used together)

For 1. and 2. OSRAM and ZUMTOBEL have good transformer and dimmer products, both stand-alone and DALI bus driven

Answer 4

I have now used this approach in my bathroom and can confirm it works very well. The "non-dimmable" bulbs dim perfectly well with no noticeable flicker or colour change. The transformer sometimes makes a high-pitched buzz but this isn't audible when the cupboard is closed. I found two commercially available 12V DC PWM dimmers - a basic one intended for boats/caravans and a very snazzy touch-screen one from China (making my own dimmer switch is a project for a later date)