Dimmable LEDs

Ok, so I have been experimenting with dimmable leds and have found what I think is a good solution.

When I was doing my bench tests I found that if I connect only Leds to a dimmer circuit they would tend to flicker slightly only when they are ramping up and down, but then stop flickering when they you stop ramping the circuit and then remain stable.

I then decided to replace one of the LEDs in the circuit with a halogen lamp, therefore I had 4 LED globes and 1 halogen globe on a dimmer circuit, this seemed to sort out the flickering of the leds when ramping.

Is this due to the resistance of the fillament of the halogen globe causing the triac in the dimmer to function correctly?

If so, is there a way that I could put a resistor in-line with my dimmers outgoing channel to mimic the halogen globes resistance, then I could have only LED globes on a dimmer circuit?

I would appreciate any advice here?

 

What I have done in the past with LED's is put a C bus relay in series with the dimmer. Have the relay channel set as the same group address as the dimmer, and set the relay (Turn On Threshold) to 5%. This way the dimmer still dims the load and when it's turn off, The relay cuts the power to the LED's, but the dimmer will still dim them. Reason for setting the Turn On Threshold to 5% is that LED's wont dim much lower than 5%, they normally just drop out anyway. Hope this helps.

Cheers
Daniel

 

Minimum Load

Dear,

Please check the minimum load, by using 4 LED's it may not be having 20W minimum load.

The solution given by Daniel is good if there is already minimum load and makes flickering in the minimum end, it happens even in 0-10V analogue dimmer which we have to set the minimum level as per the flickering of the circuit.

 

It sounds to me like the kind of LEDs you are talking about are retro-fit LED lamps that connect to the existing low voltage transformer. Is that correct?

Are you able to say which LEDs you have got? That may help in understanding how they're behaving.

These types of replacement lamps are a complete minefield in terms of compatibility and dimming performance. As Ashleigh says, all you can really do is test what you have.

Most of the electronic-type LV transformers have a 20W minimum load and LED replacement MR16's are not more than about 6.5W, well below this minimum. If they are more than this then they are either physically larger than an MR16 or they are lying (very common). This means that the transformer is typically not in a stable region of operation causing flickering and dimming issues.

If replacing one of the LED lamps with a halogen solved the dimming issue then it's doing this by either increasing the minimum load on the dimmer or changing the ratio of the input capacitance c.f. the actual real load power. Throwing away some power in a resistor may seem like a reasonable way to stabilise the dimmer channel, but you may find that the size of the resistor and heatsink you'd need may be unacceptable, even dangerous if it gets too hot.

The proper way to do it is to replace the lamp and transformer with a unit that is designed for dimming and long life from the beginning. These cost more, obviously, but the good ones just work.

 

Philips have a 10W MR16 replacement (Master LED MR16LV 10W), just fits in the holder though. Have replaced a few halogens around the house with them. They work with my old 5104D750 box dimmers, two use iron core trannies and 1 uses an electronic trannie. None of them cause any problems and work fine.

Only thing I don't like is the light spread is quite narrow, which is fine where I have used them, but no good in more open parts of the house.

 

I have experimented with a single Philips 10W MR16 on a Crompton transformer off a L5504D2U without success as either on or off. I am wondering if an LED Dimming transformer would solve the issue as I quite like the globe output.

 

These lamps reach 10W of power by including a small fan inside the lamp to circulate air. They're still only 10W so whether they work with your transformers will still be a bit hit-and-miss depending upon the particular transformers used. I know of people who have ripped these out because the vibration of the fan has made the ceiling panel hum. When the fan fails, the lamps will start to flicker and flash. The protruding front surface also interferes with some fittings.

 

The most likely issue here is that you are not meeting the minimum load requirement for the dimmer channel. I suggest you try 2 x transformers, each with a lamp, and see if that solves the problem.

If you really only need 1 lamp in your application then I'd move the transformer over to a relay channel.

 

I thought that LED's ran a lot cooler than halogens! Why the need for fan?

 

For current LED efficacies, the most power you can put into an true MR16 form-factor replacement LED lamp and keep temperatures down to levels that won't cook the LEDs is roughly 6W. Beyond this the junction temperature of the LEDs exceeds their designed ratings and the LEDs may be damaged. The problem with this is that this amount of power simply doesn't put out the equivalent light of a 50W halogen lamp. It is theoretically possible that one day this will be achievable, but that day is not today.

To increase the amount of LED power, and therefore light, Philips have opted to include a small fan inside the lamp. The fan is the most likely point of failure with these lamps.

50W halogen lamps operate with a reflector surface temperature of 300 - 350 degrees. At this temperature, LEDs would be severely damaged. Typical LED bulb heatsink temperatures are about 80 - 90 degrees, a significantly lower operating temperature than the halogens, but lower power and less light too.

 

Well said ... If only the general public/bureaucrats understood this ... Y2K comes to mind as being a similar issue that the general public/bureaucrats got sucked into what they thought was simplistic ...

 

Don't take this as a contradiction, I believe 100% what your saying and have experienced first hand the clearly different lighting profile of these "10W" Philips lamps. But why if the lamp cannot put out the equivalent light as a 50W halogen can Philips sell and market this lamp as being equivalent to a 50w halogen?

Also agree the fan will be the first thing to go, wonder how this will effect the warranty which oddly enough doesn't seem to appear in any literature that I've seen.

Attached is an info sheet on these 'globes'.

http://www.ledlightingaust.com.au/wp-content/themes/classictone/pdf/MR16-10W-Data-Sheet-2.pdf

 

Philips are quite open about the lamp being a 50W halogen replacement but they are a lot more coy about calling it a 50W halogen equivalent. On the box for the lamps there's some fine print that states "Actual light output not equivalent." On the other side of the box they say "Light intensity is similar to standard 50W LV MR16 halogen lamps." In other places they use the "10-50W" nomenclature, inferring that they're equivalent without explicitly stating that they are.

Regarding the lifetime, it's stated as 25,000 hours in both the literature and on the box. There's a difference in definition between a lifetime and a warranty though.

I think these lamps still do have a place in the market. In fittings where the LED replacement lamp simply must be the same form-factor as the halogen MR16, or when the halogen transformer is "built in" or otherwise inaccessible then these lamps offer an alternative. The 10W ones put out about 65% of the light of basic halogen MR16's (but in a narrower beam angle which artificially inflates the figure a little), they are dimmable on some transformers and in some applications that may be good enough. When halogen MR16's become effectively banned (coming soon) then people will be clamouring for DIY replacements and the 10W Philips LED MR16's are the highest output true retrofit lamps available. I guess Philips are banking on the fact that by the time the fan fails the purchase price has probably been forgotten.

 

I'm in the process of changing over from 12V halogen to dimmable LED's.

I tried the Eco Light UP 6W MR16 dimmable but they would only go dim or full bright and wouldn't switch off (using D5504D1A dimmer). Next I tried the Superlight ECO-12 and they seem to be working fine with CBUS, so far, so I'll stick with these. I'm covering about double the floor area compared with my previous halogens, so the economics worked out quite good. They've only been in for a day now and they were an instant hit with my wife - she likes the "characteristic" of the LED light, the halogen light was "yellowish" in comparison.

We had over 60 people in the house yesterday and many of them commented on the LED lighting, and of course CBUS generally!!

 

I've had a chance to play with the Ekolights. specifically the 12W ones, and they have very good dimming compatibility. The minimum brightness was a little high; that's about the only criticism on the dimming. They work on both the leading edge and universal C-Bus dimmers. Just don't expect them to get near their claim of 130/140 lumens per LED for 4 LEDs. The actual light output of the complete unit is just over half that of a 50W halogen downlight. They also fall into the category of being an integrated replacement fitting, not just a replacement lamp.

 

So it was these you are referring to?

http://ekolight.com.au/products/product-range/12w-warm

I think my halogen lighting was configured by the installer to ramp to 90% maximum brightness level. When changing over to LED's, should this level be tweaked back up to 100%?

 

That's the ones, although the one I had was white.

The reason your installer would have done this would be to extend the life of the lamps. The same mechanism is not present in LED lamps so you might as well put the maximum level back to 100% as this will guarantee that you are getting the maximum possible light output.