The motivation for this project is the need for light, light and more light when recording high speed film with my FPS1000HD camera. Something that resemaples the sun as close as possible and with low ripple voltage is preferable, to avoid flickering frames due to camera frame rate being faster than the switching current of the light source.
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I wanted to base the project on parts that I already had in stock, to keep overall cost down and to recycle parts instead of buying all new.
I had old Pentium 4 CPU coolers, HP server power supplies, metal parts for enclosure, plugs and switches at hand. I needed to buy LED COBs, lenses and fan controllers. Finding all the parts from different ebay sellers was not that bad and despite ordering the “same” part from different sellers it all turned out to be identical. Either pure luck or they all sell the same part out of China.
Normally a LED has to be fed from a continues current source to protect the LED from being damaged. I will run them at slightly lower voltage than their maximum rating and hopefully that is a safe enough way to drive them with power supplies I got available. The HP server power supplies should also have a high enough switching frequency and smoothing to avoid any visible flicker, even at 10.000 frame per second.
2nd April 2019
Gathering of materials and buying the rest from ebay. I wanted to make sure that the LEDs at least came from a seller that had tested them, so I bought those from a seller in Germany and the passive parts like lenses, collimators and fan controllers was bought from China.
I got no affiliation with these sellers, but it is where I bought my parts:
50W LED COB specifications
Light color: cool white approx. 6000-6500 K.
Luminous flux: approx. 4500 lm
Forward voltage: UF 31.0 – 38.5 V DC
Current: IF 1500 mA
Base plate: 1.0 mm copper
Chip size: 24 * 40 mil
120 ° beam angle
Lifespan: up to approx. 30,000 hours
Size: 42.0 x 52.0 mm
Hole spacing: 34 x 34 mm
Hole diameter: 3.5 mm
60 degree narrow beam lens and reflector seller 1: https://www.ebay.co.uk/itm/50W-70W-100W-120W-COB-Chip-LED-Lens-Fixed-Bracket-50mm-Reflector-Collimator/112785049513?ssPageName=STRK%3AMEBIDX%3AIT
60 degree narrow beam lens and reflector seller 2: https://www.ebay.co.uk/itm/50W-70W-100W-120W-50mm-Reflector-Collimator-COB-Chip-Fixed-Bracket-LED-Lens/263468105919?ssPageName=STRK%3AMEBIDX%3AIT
HP server power supplies can just as well be found on ebay at reasonable prices.
1st June 2019
I chose to use the internal soldering pads on the LED, as the outside flaps bend easily and I would have to add insulation to protect against short circuit against the heat sink. At first I ran into problems with short circuited LEDs that would draw too much power at low voltage when testing with a bench power supply. It turned out to be the silver paint on the reflectors that was conductive.
2nd February 2020
The enclosure is made from a discarded tool wall panel, that could just barely fit everything inside. I did originally want the LEDs to be adjustable on one axies to focus or spread the beam, but there was not enough room to have this feature. The handles come from base station amplifier teardowns that you can find elsewhere here on my website.
The fan controllers was mounted on one of the power supply enclosures with standoffs cut to flat surface. Input power plug and switches came from different salvaged equipment.
7th February 2020
Everything just barely fits inside the enclosure, especially when there also had to be space for switches, plugs and mounting hardware to put the enclosure together with lid and all.
The first test in a pitch dark night, it is like having your own sun!
5th March 2020
In this video the lux value is measured to 25000 at 1 square meter which corresponds to the given lumen value for the LED COBs.
The 36VDC power supply ripple is examined, the 50 Hz ripple is limited to around 1VDC and the high frequency 20-45 kHz switching noise is no apparent problem.
There is some flicker in the background when recording at 1000 and 4000 FPS, but once it gets up to 8000 and 20000 FPS, there is not enough light to even get the subject properly lit up.
The server power supplies provide a stable low noise voltage and the LED COBs regulate their current right about their specified consumption of 1.5A. The voltage should properly be adjusted down a bit to ensure that it always stay below 1.5A but that will also result in weakened light output.
The light intensity is good enough to film objects up to 20000 FPS at a close distance of up to 1 meter. Background surfaces do begin to get some flicker at 1000 and 4000 FPS, whereas the light source seems too weak to have this problem at higher frame rates.
Further improvements would be to add individuel fuses to each LED COB or even better to change to a constant-current power supply in order to prolong the expected life time of the LED COBs.
25th February 2020