LED Battens

[cedd]

I've been looking in to purchasing some 1m LED battens for general cyc/wall washing duties. The prices are, to be honest, more than I can currently afford - I'm going to need at least 6m of the things and can't find them for less than £70 per m, even taking China in to account.

 

I've been investigating building my own. Initially I'd thought about using a small Arduino with a DMX sketch and necessary hardware to drive it, but I've just found a 2W per channel (though looks to be 5A max across all 3), 3 channel DMX driver on eBay from China for a tenner - don't think I can do much better for that price, assuming 2A is enough. They make bigger versions too.

http://www.ebay.co.uk/itm/171551257150?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I'm not too precious about using this specific module, it just looked interesting.

 

I'm starting to think this might be a feasible project. I don't need segments to be individually addressable, simply all LED's in the batten the same colour.

They don't need to be too robust either. I'm thinking black plastic square conduit as the enclosure. Might have to have a slightly larger box on the end to house the driver and power supply.

 

My decision now is which LED's to use.

 

SO, has anybody got any recommendations for RGB Led's I can use? I'd considered buying ready made LED strip, but I'm not convinced about brightness VS the larger single LED's.

 

One option is to use the fancy addressable LED's such as these;

http://www.aliexpress.com/item/20x-Super-Bright-WS2811-3-Pcs-5050-RGB-LED-Pixel-Module-Light-Waterproof-12VDC/1462979736.html

 

They just need a power supply and then an arduino doing the DMX number crunching and then kicking out the data to the LED string - no external drivers to mess about with and they're nicely packaged for easy bolting in to the casing (whatever I decide to use).

 

Or I could use RGB LED's like these;

http://www.aliexpress.com/item/10PCSX3W-Super-bright-LED-Light-Cool-White-Warm-White-Red-Green-Blue-High-Power-Led-chip/1615267898.html

It's not very clear but I'm assuming the 700mA is per colour, so I could only run 5 LED's on the above driver (though larger ones are available), which would work well for a shorter 50cm batten. BUT there's a catch. All the single LED's I can find are common cathode. All the DMX RGB drivers I can find are common anode - am I missing something here? Why would all the drivers be made the opposite to all the common LED types?

 

If anybody out there has successfully done this, or has any thoughts on my above ideas then I'd love to hear from you. Has anybody used the WS2811 strings and if so, were they bright enough?

 

 

 

If successful then I could maybe make 0.5m battens for under £20 including cases and power supplies.

 

 

 

[timsabre]

I have made some battens to light up our church windows, using cheap RGB 5050 tape. (the same LEDs as in your first link, but not individually controlled - which would be unnecessary for your application)

Each window is approx 1.8m wide x 3m high. I used a whole 5m reel of tape for each window (4 strips side by side) and the brightness is just about enough. I don't think it would work for cyc washing over a larger height. The beam angle is very wide (almost 180 degrees) so a lot of light gets wasted.

 

The LED's in your 2nd link look more likely but you will need to drive them with a constant current DMX driver (plenty on ebay) and heatsink them properly. Rather than the ones you show, look for ones with 6 separate terminals so you can stack them up in series to avoid needing lots of drivers. You'll also need to put some lenses on them to control the light down to 20 degrees or something like that.

[smalljoshua]

Have you seen these? £61 Inc VAT.

 

http://www.thomann.de/gb/stairville_led_bar_2408_rgb_dmx_30.htm

 

They're pretty bright for what they are.

 

Josh

[timsabre]

Those look good at 30 deg beam angle. I tried some of the varytec ones like that and they are far too narrow beam. They aren't all that bright though - wouldn't compete with a stage wash.

[musht]

5050 based unless its really good quality or high density won`t really cut it.

 

Big LEDs 1W+ where you need to go, with optics, elliptical beam patterns are nice but may cost more than the LEDs.

 

http://www.ebay.co.uk/itm/10W-20W-30W-50W-High-Power-Super-Bright-Light-Lamp-LED-Chip-Cool-Warm-White-RGB-/201071607660?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item2ed0cd3f6c

 

http://www.ebay.co.uk/itm/1-Set-of-30W-50W-100W-LED-44mm-Lens-Reflector-Collimator-Fixed-Bracket-New-/371009496665?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5661e3a659

 

30W at 700mA drive will fit on range of DMX drivers with a high enough V PSU

 

Large chunk of alloy needed to keep `em cool.

[cedd]

Hi everyone

Thanks so much for the replies. They've been really helpful! I hadn't spotted those Thomann ones - they look much more affordable.

I never like to throw away the idea of a project once I've started thinking about it though! The addressable LED's may not be suitable for this job, but I still might invest in some to play with. In the past I've built a lit stage edge system that marked the edge of the stage in dim red, only seen from the stage, and also had some fixed coloured LED's to help the cast with key positioning in blackouts so they were dead on the money when the lights came up. It'd be really cool to be able to move multiple coloured dots back and forth scene by scene along the stage edge. Might give that a try.

 

Back to the battens though...

The beam angle is something I'd wondered about. If I'm mounting the LED's in the bottom of an aluminium U shaped extrusion, and if I leave the internal sides as bare aluminium, do we think that'll do the job of restricting the beam angle enough? I'd have to play a little with it. At the minute I'm wondering about using a larger number of smaller (1W ish) LED's arranged in short battens (short enough to only require one driver per batten, so the length is decided by my driver, but I'm thinking 0.5m. Then they're a useful device for things like lighting windows too.

 

Power supplies are probably my biggest expense. A higher voltage, lower current psu does sound attractive, and now I've done a bit more digging I think I understand a bit more about how the constant current source is behaving. I feed the device with as high-a supply voltage as it'll safely take ( to reduce psu size and cost) and the driver only provides the voltage to the LED's that it needs to maintain the current for that particular wattage LED('s). So it's basically a runway lighting regulator - now there's a beastie I do understand.

[musht]

Like runway lighting,but with my limited understanding, a lot lower voltage ;-) Interesting subject would like to know more about.

 

LEDs are in a series string, rule of thumb allow 4V an LED, 350mA is a 1W LED and 700mA is a 3W LED, total load on driver will be quoted in Watts.

 

Adavantage of big LEDs, selectable optics, these sort of things need holders glued on around the LED , and beware if mounting assembly in a U shape that can lever them back out the holder....

 

http://uk.farnell.com/l2-optics/op-520/lens-oval-20mm/dp/1242342

 

Dinnae cheap out on PSUs, seen some truly ferkin scary knock offs, genuine Meanwell/TDK Lambda etc. worth the peace of mind.

 

Because LEDs are current driven at higher voltage , V drop becomes less of a problem and can get away with remoting PSUs if necessary.

[DrV]

Because LEDs are current driven at higher voltage , V drop becomes less of a problem and can get away with remoting PSUs if necessary.

Whilst the voltage of the PSU is less important when using a constant current driver remember that all of the excess voltage will be dropped across the driver so keep an eye on the dissipation in that device.

 

And I'll be following this thread closely as I'd like to do something similar!

 

Dave

[musht]

 

And I'll be following this thread closely as I'd like to do something similar!

 

Dave

 

Do realise with Cedd involved the end result will have DMX pan , zoom and beam shaping ;-)

[timsabre]

Whilst the voltage of the PSU is less important when using a constant current driver remember that all of the excess voltage will be dropped across the driver so keep an eye on the dissipation in that device

 

Doesn't work like that, the driver adjusts its output voltage so that the correct current flows through the leds. Drivers are all switch mode so there's no power wasted when adjusting voltage.

 

Regarding putting leds in a channel for beam control, it works a bit but it's wasteful of light output as most of the light which hits the sides is lost. Lenses are a much better solution.

[DrV]

Whilst the voltage of the PSU is less important when using a constant current driver remember that all of the excess voltage will be dropped across the driver so keep an eye on the dissipation in that device

 

Doesn't work like that, the driver adjusts its output voltage so that the correct current flows through the leds. Drivers are all switch mode so there's no power wasted when adjusting voltage.

Doh! Yes, PWM of course. Although I must, therefore take issue with your assertion that the driver adjusts the voltage - as it is a switcher, it adjusts the average current through the string :P

 

Dave

[timsabre]

Doh! Yes, PWM of course. Although I must, therefore take issue with your assertion that the driver adjusts the voltage - as it is a switcher, it adjusts the average current through the string :P

 

I'm not quite sure what you mean, but the control loop in the power supply measures the current through the string, and adjusts the voltage of the output until the current is the desired value.

[DrV]

Doh! Yes, PWM of course. Although I must, therefore take issue with your assertion that the driver adjusts the voltage - as it is a switcher, it adjusts the average current through the string :P

 

I'm not quite sure what you mean, but the control loop in the power supply measures the current through the string, and adjusts the voltage of the output until the current is the desired value.

 

Hi Tim, I think we are probably talking about two different things. It's my fault because it was me who introduced PWM into the dialogue. What I mean is that a PWM LED driver can't directly control the voltage. By definition, it switches the current on and off. When it is on, the current is determined by the (fixed) output voltage of the PSU, minus the forward voltage of the LEDs divided by the total resistance of the string, which includes the forward resistance of the LEDs, the interconnects, the internal resistance of the PSU and driver etc. The average current is controlled, not by varying any voltages, but by varying the mark/space ratio of the ons and offs.

 

I accept that an LED driver might employ a standard switch-mode PSU which it then adjusts according to the measured/desired current in the string. However, in the fixtures I have investigated, there was always a conversion to a fixed voltage (12 or 24V) followed by a separate PWM driver to effect the current control.

 

Cheers

Dave

PS Why is it that the period between crashes of an internet browser is inversely proprtional to the time spent composing a reply... Grrrr

[timsabre]

I accept that an LED driver might employ a standard switch-mode PSU which it then adjusts according to the measured/desired current in the string. However, in the fixtures I have investigated, there was always a conversion to a fixed voltage (12 or 24V) followed by a separate PWM driver to effect the current control.

Um yes OK I think we are both talking about the same thing using different terminology. I wouldn't describe a switching power supply as PWM because the output is smoothed back to DC, but it does use PWM techniques internally to vary the duty cycle.

 

Anyway back to the original question, a DIY LED batten is an interesting project but I think there are several ready made options which will be cheaper.

[musht]

in the fixtures I have investigated, there was always a conversion to a fixed voltage (12 or 24V) followed by a separate PWM driver to effect the current control.

 

 

Current loop in the driver measures the V drop across a very low resistance and adjusts the output to keep voltage and hence current stable round the loop. Similar to a battery charger.

PWM is used internally to directly control the current loop. Some current driver devices will accept external PWM into KHz.

 

Constant Voltage drivers will use a mosfet on the output driven directly by PWM , closer to a D.C. motor controller.

 

Advantage of building them is with choice of premium LEDs and appropriate optics should be able to build something that punches above its weight price wise.

 

Like to learn more about runway current loops that can run into 000`s of volts in the loop with motorised autotransformers to control them.