Flickering downlights on dimmed L5508D1A

Hi all,

Hoping someone may have seen this before and has some suggestions, as I'm starting to run out of ideas.

I have a L5508D1A and, for one example, one channel connected to 4 x Atco Possums which connect to 4 x 50w downlights. At full ramp I see no problem at all. At a common dimming range of say ~40% to 60% I often, but not always, get a flickering and pulsing of the lights. I originally thought it was the cheap globes I was running, so purchased some Osrams. Unfortunately after installing these tonight the problem continues.

One interesting thing is that they will be fine for say 30 minutes (just an example - some nights I don't notice any flicker), then start flickering for say 10 minutes, then back to fine again. Also of interest is that all 4 lights in one group don't appear to flicker at once, but do tend to be effected on closer inspection - in that some in the group pulse of dim while others flicker. I originally thought it was just one in a group at any one time (not always the same light and not always the same channel on the dimmer) which pointed at a possible globe or transformer issue - hence why the globes were swapped out. Haven't touched the transformers yet as I was of the understanding they are highly regarded for this 4 x setup?

Anyway, just wanted to check with others running 4 x Atcos off one channel. I thought these were easily supported with their 33NF input capacitance?

Any thoughts or suggestions much appreciated!

Cheers,

Tom

 

Thanks for the reply Ashleigh, but unless I'm missing something major here I can't see that being the case. Each channel of the L5508D1A is rated to 1 amp as I'm sure you know and I'm running 4 x Atco Possums (rated at 33nF) each with a 12v 50W globe hanging off it = ~200W. Even with overheads I can't see this pushing 240W - saying that, this might be where I'm missing something

C-Bus documentation states running 4 x Atco Possums off a single 1A channel is ok and the wattage appears to be well within the limits - thus why I'm stumped. I'm happy to swap out the globes for a lower wattage alternative, but then again don't want to throw unnecessary money at this if that isn't likely to be the issue.

Any further views or opinions might help sway me one way or the other, so please let me know your thoughts

Cheers

 

Maybe 4xPossums plus cabling has pushed it over the limit?

You could try installing a 32EIND on the circuit or temporarily remove one transformer and see if the problem goes away.

 

I too see this with four atco's on a 1 amp dimmer circuit - mainly one of them.

When dimmed low (18%) it seems to change ever so slightly. The one I notice is above the couch where I sit and it appears to be the one only and not the others on the channel. I put it down to the transformer.

The thing is when I am watching it, it is hard to see the change, it seems to be only noticeable when not looking at it.

The first thing to try would be swapping transformers around to see if the problem lies there or at the dimmer itself.

Cant help more than that as I just left mine and live with it.

Mick

 

Thanks for the replies guys. Good to know I'm not alone and think I have some methods to start narrowing down the issue. The load theory sounds right, but the sums just don't add up on paper - but I guess only one way to find out The only reason I didn't think the transformers were at fault was due to them being held in high regard by most - I guess it's always possible though.

Cheers

 

I was facing problem similiar with you before
L5104D5A was trying to solve this problem together with 32EIND inductor ...
Transfomer is OSRAM ET-Z

 

I have exactly the same issue, yet I couldn't possibly be overloading my dimmer channel. I have 2 x 12v 50 watt halogen's running off each 1A dimmer channel and I get the flickering whenever the light is other than full bright. I like to have these lights on dim when watching TV and the flickering is annoying and gives me eye strain. I really would like a fix for this problem.

 

Sorry, are you saying you were able to solve the issue with a 32EIND? or did it not help?

Cheers

 

32EIND is an Inductive Filter, rated at 250V~ 2A. By installing
it between the dimmer and the load, it will eliminate the necessity to derate to compensate for the input capacitance of electronic transformers.

Therefore I don't see what it would help in your case....

There are many issues when you have flickering, especially it is random and at such high brightness (40-60%).

Possible cause; the neutral cable of that lighting is shared between other loadings in the room. So, it may be affected if the other loads are (1) connected to a different phase source; (2) connected to some cheap Fluorescent ballast; (3) the neutral cable is too thin to cover the whole area...maybe there are cause 4, 5, 6...

Or the transformers are faulty, or universal transformers that may switched itself to trailing edge mode, or simply faulty dimmer channel.

And yes, cheap bulbs (normally come with the lightings) would have problem, but mainly breezing noise because of the cheap material...

So, normally you can try a few things for a few days: check the current value at 100%; or use another dimmer channel; or disconnect the last bulb; or write down what is on when flickering occurs and try to see if there is other possible cause; or change transformers....

A quick fix would be replacing the transformers with mechanical transformers if there is enough space. The problem may still be there but the mechanical transformers may be too "slow" to response...

 

Check all dimmer mains connections for a loose terminal. Also make sure the neutral is clean and is a true 0 volts or the dimmer may have issues with finding a 0v ref. point to chop up sine wave.
Input capacitance should be OK with 4 x Possums. I have had a couple of situations where the loads flickered a bit where 'dirty power' was present usually in rural area's or near sub stations and only could eliminate with a UPS or a line filter (noise choke) before the dimmer.

 

Thanks for your input guys.

Some more things to think about there and I hope to have this nutted out before too long. Not a paid job (at home) so just putting up with it until I get time to have a play. I'll let you know when I get it sorted just in case anyone else is suffering the same issue.

Cheers