I'm waiting on a handful of LED lights to come through for a project. The lights are the type of portable LEDs for lighting a video shoot - which is in fact the intended use. I've been asked to put together a "box with some sockets on the side" to power them all with some nicely coilable cables, rather than dick about with lots of extension cords and wallwarts hanging off the stands.





The only info I have about them at the moment is that they need between 7.2v - 12v and consume 18.24W each. I need to power 5 of them. My back-of-a-cigarette-box mathematics tells me that running them at 12v, they might draw up to 1.52A each, so I have to provide a minimum [email protected] supply (ie 91.2W)





In the interests of saving time and effort, there's a Switched Mode Power Supply that will give me [email protected] (ie 150W), which should do the job.





http://www.maplin.co.uk/p/power-pax-150w-switch-mode-acdc-multi-voltage-power-supply-n52kh





However, I've generally shied away from SMPS due to concerns over noise. More specifically, if LED lighting starts to flicker, than can completely fuck up a shoot in a way that you don't notice until after the event.





So, I have two questions that I'd like to offer up to the gurus of Arfcom.

1. Do you know if the type of noise from an SMPS is likely to influence or cause flickering in an LED light?



2. Is this something that could be addressed by introducing further smoothing caps or similar between the SMPS and the socket that will be used by the light?

Your thoughts and replies are, as always, appreciated
 

You might want to try ebay.  Look for an acopian 12v linear supply.  Linears usually have much less noise than switchers.  If you get the model number you can go to acopians website to make sure the PS is a linear....












----------------------------------------------------------------

Member, Friday the 13th
"Nothing tastes as good as skinny feels"  K. Moss
You can NEVER be too rich or too thin...
Life is not a journey, but a series of unplanned detours....
Perfection: is not a goal---it's a demanded expectation.

Do the LED lights themselves have some kind of built-in current limiting?

A very common setup is to use a SMPS, which is then connected through one or more linear LED controllers that have internal current regulation and supply power to the LEDs themselves.  This way no resistors or other external current limiting is required.  It also makes is easy to vary brightness, either with digital commands to the controllers or with external potentiometers.

A 12 V battery on the output is cheap insurance and adds a UPS capability to your lighting.

Caps on the output will also work, without the battery issues.

Thank you for your replies, it's appreciated.



While there may be better options with a bit more time to spare, this is partly a matter of expediency and the fact that I can (indeed, will) have the SMPS in my hands tomorrow.



I can use batteries with these lights, but (i) they eat batteries to the point that a mains PSU works out cheaper quite quickly, and (ii) we've been caught out in the past with the light levels gradually dropping as the batteries get eaten, because someone forgot to check the levels () and it was too subtle to notice until it was too late to fix it (). Generally they are being used somewhere with mains power, but I'll be keeping the supplied batteries charged and a few blocks of AA handy as well, as these lights can use either with an adapter.



After a bit of additional digging around, it seems that the amount of noise from the SMPS is unlikely to translate into detectable or recordable flicker. I'll find out tomorrow evening, hopefully, as I should be doing a test run providing I don't blow the test light up



The custom control panel is looking nice though. Priorities, etc

I believe so but have very little info on them to be honest.



They can take a 12V DC connection from a rather dubious-looking wall-wart, and have a dial on the back of the light itself to manage the brightness. This suggests some built-in current limiting capability.



The spiderweb of extension cords and wall-warts dangling off the back of lightstands is being replaced by some lovely 10m cables that coil beautifully (I have a thing about coiling and securing cables neatly instead of having the excess snake all over the place) all connecting back to my magic box - basically the SMPS splitting out to 5 quick connectors in the front of a project box from the UK equivalent of Radioshack.



Because the lights take a wide-enough range of V, I can get away with a bit more of a voltage drop than I would otherwise prefer. I forget the maths I did, but from memory it still fell close to 3% even over that extended cable length!



 

If you're still worried about output noise, you can always put a couple of ceramic caps across the output of the SMPS to help filter things.  It tends to be good for a SMPS anyway.  Luckily, the LEDs don't represent a rapidly-varying load, so the SMPS won't have to respond to wild swings in load impedance.

Polyester or other film caps are usually better than ceramic.

Sightly higher price, but much better performance.

You can also use some of the higher tempco ceramic caps.

I suggested the battery across the SMPS output because It acts like a HUGE capacitor and adds a capability (uninterruptable power supply)

I'd rather not turn it into a UPS, if I turn it off then I want to turn it off straight away, or near enough



I realised last night that I didn't have suitable switches (each line out will be individually switched with an illuminated switch, all the ones in the bits box want 240VAC) but testing from either side of where the switch should be has been successful. I mean, it's hardly a complicated or novel concept, but I always get nervous when I'm jury-rigging stuff out of random stuff lying around/under/stuck-between-the-wall-and-the workbench



My "power bus" (some strip board with wiring soldered along the tracks and lots of mismatched terminal blocks ) still has a bit of space to fit some caps, but looks like they may not be needed - which is a good thing because I can't figure out where I put my box of capacitors...



I really appreciate the input from everybody, though. Thank you



( is the official smiley that represents every project that starts life on my workbench; it is also applied to the rare projects that survive long enough to leave it!)