Lutron/ LED headache

Deleted member 9648 · Jan 10, 2012

I dont have much experience with this stuff but have recently completed an install and an issue has arisen. Maybe you guys can give me an answer.
The scenario is we installed cableing,LED lighting and connected all to drivers and PSU's supplied by the lighting designer,all of these are located on a central board in a roof void. Another company installed lutron control panels and commisioned the system.
Some of the lighting is dimmed and some are on straight switching outputs. Just after commisioning one of the PSU's supplying LED tapes failed,as there were no obvious issues I put it down to a dodgy unit and asked the lighting designer to supply another. Replaced the offending PSU today only for it to go up in smoke..(literally) within minutes of starting.
Too much of a coincidence, I checked the obvious connected load...no probs...and IR tested the cableing...no probs either.
It didnt take long to discover that the lutron comissioners had programmed this circuit as a dimmed output,and it was dimmed...it should have been a straight on/off. Now the PSU is a 60w 24v non dimmable unit,but it states on the case that the input voltage is 100-230v.
I called the manufacturers tech line to see if connecting this unit to a dimmed supply would cock it up,but couldnt get a definate answer...My problem is as follows,

As this is the only PSU to have failed on the system...(twice),and is the only circuit to have been incorrectly programmed....I blame the comissioners and have asked them to pay for the additional two PSU's..which are not cheap.....They are not having it and say they are not responsible.
They are going to reprogram the panel...but I need a definate answer on whether the PSU failure can be attributed to it being dimmed...as someone is having to pay,and it's not going to be us!

Rockingit · Jan 10, 2012

OK, this is nothing more than a guess based on experience, not a definitive answer, BUT.... I think what's probably happened is that the PSU hasn't enjoyed the chopped dimming output.

What most people tend to forget with thyristor dimming is that you aren't 'reducing the voltage'. What happens is that there's a timing circuit which fires the thyristor on/off and stops the waveform as a definition of TIME, not voltage. It's easier to explain with a drawing which I'll do in a minute! What you end up with is a waveform with all the smoothness of my chin after 2 days not shaving (hence why they interfere with things and buzz) and most things electronic won't like them. If you dim at 50%, you effectively create a voltage at 100Hz (kind of, it's a bit gappy).

Rockingit · Jan 10, 2012

This shows the cycle of dimming by firing a thyristor (although it's actually in reverse so you're turning it off) and the resultant choppy waveform. It's a bit simplified and it's not going to win any drawing awards, but hopefully may help to explain!

Deleted member 9648 · Jan 10, 2012

Big thanks matey....I can go back to then now with a bit more ammunition....It's a bit of an awkward one though,but I really think the commisioning guys are going to have to swallow it.

Rockingit · Jan 10, 2012

You're welcome - one of the many fringe benefits of a background in stage/theatre is to know a lot about how to dim lighting!!

davelerave · Jan 11, 2012

hi wirepuller
not too well upon this
the issue seems to be the dimming of the psu

the 100-230 is prob the input voltage range and you'd expect the psu to feature protection against issues such as overload sc surge etc

Deleted member 9648 · Feb 1, 2012

Update.....the lutron commisioners made said output a straight switching mode,and repalced the offending driver,and left all working. So I was somewhat peed to get a call to say the same lights have failed again.....went today and found the driver has failed yet again. Confirmed supply is not dimmed,and tested load cables to distruction.....meeting between myself,lutron commisioner,their spark..and lighting designer....we are all stumped. It has been suggested to try a different make of driver,so that is the next step,but given that there are identical strips running fine on the same make drivers I dont hold out much hope.........

Richard Burns · Feb 2, 2012

I do not really know but it seems like the load attached may be the problem, has the current limiting resistor partially shorted in the LED strip and it is drawing a large current that is burning out the driver, have you checked the current draw when in use, if there is enough time before it burns out!.

Deleted member 9648 · Feb 2, 2012

Well that was our thought....but the driver manufacturer has assured us that the driver has an automatic resetting overload cutout,so any load problems would result in the driver simply cycling on and off.....not ruling anything out at the moment though.