# Use AC to illuminate DC LED's

I need guidance in the explanation of utilizing LED light bars for a different function then designed. I do stage production, sound and lights for concerts and would like to adapt these LED light bars to "blind" to crowd.

My issue is that each light bar operates 12-30 Volts DC @ 300 Watts. In order to power and control with our DMX software (standard lighting control language/interface for stage production) I would need to build a more complicated device for each light bar. Meaning I would need DMX control PC board, relay to handle high wattage, power source, XLR in/out jack for communication, IEC jack, fuses, housing etc... Multiply by 4 costs add up FAST.

My thoughts include:

A single high wattage (24volt @1500watt) DC power supply to power all.

Then I thought, can I wire in series to 120AC, this would put me at 30volts AC for each fixture. This would make controlling ALOT easier and cheaper because I could use an off the shelf DMX relay switch to control the bars.

I hope I explained well...

I am looking for any suggestions.

• You can't use AC directly to power the light bars, it must first be rectified and, possibly smoothed, but what do you mean by "control"? Is it 1. a simple ON-OFF function, 2. do you want/need to be able to control the intensity of the lamps, or 3. something else? Can you post a copy of the lamp's data sheet or a link to it, please? – EM Fields Nov 4 '16 at 8:43
• Aside from @EMFields question and Neil's answer. Do I read correctly, that the fixture has no control input itself? I.e. no 1-10V, DMX or whatsoever input? – Ariser Nov 4 '16 at 9:07
• Why can't you wire them in parallel to one DC relay and the normal power supply? – user253751 Nov 4 '16 at 9:16
• I can help you power them in series if I have the datasheet on the power bar But 100Wac powered utility lamps are pretty cheap these days $0.3/W and DIY$0.1/W in volume – Tony Stewart EE75 Nov 4 '16 at 14:16
• cost of power supplies is about same as LEDs depending on consumer \industrial type unless mass produced with LED – Tony Stewart EE75 Nov 4 '16 at 14:43

From your description of what you do, it sounds like you interact with the paying public, so are subject to the full force of public safety, liability, elf'n'safety etc.

From a safety point of view ...

A LED bar that is specified to operate off 12v to 30v DC is probably not rated to operate at other potentials. If you connect several in series, then some will be at around mains live. I can see local authority inspectors and insurance companies coming down on you like a tonne of bricks for bodging 'low voltage' things into series and running off mains.

From an operating point of view ...

The 12-30v input spec sounds like it has electronics in it to operate from a range of voltages. That sort of range is common when the intention is to use one or two automotive batteries in series. This might, or might not, get upset if fed with rough DC, say from a simple bridge rectifier. It would certainly get upset if fed with AC. How clean the DC would need to be to operate properly, how much reservoir C on the bridge rectifier could only be guessed at.

You might want to consider a PC power supply with its 12v output. They are relatively inexpensive, and are rated to be connected to the mains safely. There is an issue over how much 5v you would have to draw to get the 12v output regulated, so maybe that's not such a good idea.

A single 24v supply for the whole lot sounds the best route. Given the wide input voltage specification of the bars, you might be able to tolerate poor voltage regulation, and possibly much ripple, so do not need one with gold-plated specifications.

Now the question is, where does the DMX relay go? Ideally on the mains side, lowest current, and where it is 'rated'. However, that needs a power supply capable of powering up quickly (and repeatedly?), you would need to check. If on the DC side, you have 60Amps at 24v, not a trivial current, so you would need a suitably rated, and rated for DC, relay.

If you already have, or have paid for, these low voltage bars, then you're stuck with finding a way to power them. If you haven't yet invested in them, you might want to see whether a mains input type is available, that you can use directly, or ones with a standard control input exist.

Using high power LED light bars to "blind" the crowd in a concert is not a harmless joke, it may be dangerous to the eyes. Carefully read the datasheets and application notes of high power LEDs.

I developed an array of intense LEDs some years ago. When I looked into a LED for a short moment, I got a partially blind spot in my eye, no permanent damage, but for some minutes, the acuteness of vision was substantially reduced.

If somebody gets a permanent damage to his eyes in the concert, you will need a good lawyer and a liability insurance.

• Nonsense! Even with a stack of high powered xenon strobes, you will never match the intensity of the sun, save for lasers. Also, your eyes are self-regulating. They have a DC servo called an iris for long term adjustment and a shutter called an eye-lid for short term step responses. – winny Nov 4 '16 at 12:45
• Incident radiance ( what they see) is measured in Candella and reflected radiance ( what you see) is measured in Lumens. ( sorta.) Candella depends on density or watt/sqmm so smaller appears brighter but not necessary high lumens ( what you see) Both drop inverse squared with distance. I have several 100mW lasers with rotating beams split into hundreds of spots in different patterns. Each spot is < 0.5mW and safe at a distance but if you looked directly at really short range to capture all the spots, your eye would burn goo.gl/updk3H so common sense prevails in locating the source. – Tony Stewart EE75 Nov 4 '16 at 15:12