I´ve done some research but not clear solutions are given to this problem, so I will post my case here in case somebody can help. Thanks in advance.
I want to use a DC power supply to power up 121 LEDs. Each of these LEDs is taking 460 mA, so, mounted in parallel, I need an outcome of 55A for the complete LED series.
The problem comes now, the DC power supply that I have found most suitable (RSP 2000-24) can be configured at 21V minimum, and these LEDS need something in between 19V and 20V, so I need to drop the voltage from 21V to 19.5V with the 55A current flow. (They could probable work with the 21V but these LEDs are expensive and I dont want to screw it up)
I´ve found some resistors which can support up to 250W, so I could use several of them I guess… I suspect is not a good solution. I have also found some voltage regulators but none of them seem to stand the 1000W that I need..
Any ideas would be really appreciated!
EDIT: Thanks for your replies first of all. I will answer here the questions mentioned by Russell McMahon so we can tackle the problem better.
Why are you using those particular LEDs?
The set of LEDs working togheter will be used as a flash light for camera shooting. There will be 6 camera shots delayed 500ms among them. So the LEDs will be turned on 6 times each 500ms for a duration of just 1ms when the flash signal closes the circuit formed by the PSU and the LEDs. That is why I´m not regarding heat sinking, because they will only be shining for 1 ms.
Since the duration of the pulse of just 1ms, I think we may have problems with the Rise up Time & Setup time of the PSU, I´ve thought about using a capacitor so the current can flow immediately after closing the circuit´s switch and the LED´s can light up sincronized with the camera shot. Any suggestions on this issue are appreciated as well.
Do you need a high CRI?
Yes. Otherwise object colours will appear distorted in relation to reality.
How long do you want these LEDs to last?
As much as possible. They will only be flashing 6 times for 1ms each time the camera shoots.
Do you care or know anything about this manufacturer?
For the specifications I need, this manufacturer resulted to be the cheapest and fastest in delivery. Cree was more expensive and takes longer time.
Best Answer
Edits to this answer have subtly but significantly changed things I was trying to say. I've changed some back, but it gets hard and time consuming and it's easy to make a mess unawares. I could have just done a "revert" but that would be a sad thing to do as there were numerous worthwhile changes.
If editing please try to retain the sense of each point being edited. Fixing typos and spill chucking is fine. Adding poncy formula renderings is fine. If you feel you wish to change phraseology or grammar rather than technical content I'll hazard that you'll find that there are many more worthy candidates which warrant prior attention.
A major problem is that you have not told us what you are trying to achieve but rather how you are hoping to achieve whatever it is that you are doing. A good overall description is liable to result in a superior solution.
Things to consider:
Why are you using those particular LEDs?
Do you need a high CRI?
How long do you want these LEDs to last?
Do you care or know anything about this manufacturer?
These LEDs MAY be extremely good and have a long lifetime.
The webpage and site look good and the published specifications are good...
However, experience has shown that for other than well known manufacturers, it is highly likely that the LEDs will be be sub-standard, having a short lifetime and low efficiency.
LEDs of this power level and this cost essentially must be driven with constant current(CC). While it is possible to get CC power supplies which control a resistive pass element these dissipate excessive energy in high power applications. What you want is a CC power supply that adjusts adjusts its voltage as required to control current so that energy dissipation in the driver is minimised. What the LED manufacturer terms the "largest value" in his spec sheet (which is why I used the term here but it was edited out) = 20 V is the maximum value = Vf, max that may appear across the LED at rated current, but usually actual values will usually be lower and will vary between devices.
If you parallel LEDs the differences in Vf will at best result in different light output from each LED, and at worst may cause a cascade of failures over time. (Some LEDs having low Vf hog the current and starve high Vf LEDs. The low Vf LEDs dissipate excessive power and die early leaving fewer LEDs to carry the same current and the process accelerates. )
It is not obvious that you have considered LED heat sinking or other thermal management. [My reference to LED heatsinking was edited out but I was specifically meaning that as other heat dissipatioon had been mentioned, making the LED aspect more noticeable by its ommission. /. Most of the almost 2000 W input will be dissipated in the LEDs as heat and will require substantial heat sinks.
The LEDs are specified as having 100-120 lumens per watt (l/W) or thereabouts. If they achieve this then about 25% of the input power is converted to light and 75% as heat you must deal with. Cree is selling 200 l/W LEDs and they have achieved 350 l/W the lab. However, most LEDs are far lower. You can buy 120-150 l/W LEDs from top manufacturers, but many lesser-known manufacturers claim much but deliver less. High CRI will likely reduce l/W. Looking at their graphs the methods they use to (claim to) achieve include bandwidth notching (where part of the spectrum is suppressed) which reduces l/W if it is done by adsorbing emitted light. Even Cree appear to do this rather than solely using phosphor spectrum tailoring.
Anyways, if you budget for about 1500 W of heat dissipation and say 80 °C their Topr,max) LED at the manufacturer's external measurement point, and keep an ambient temperature of 30 °C (optimistic) you need a 0.03 degree C per Watt heatsink [just try and buy one!]. This requires an extremely good (or large) heat sink.
Liquid cooling or well-designed fan cooling in conjunction with large heat sinks is required for such power levels. If you were to pack the 13.5 mm square LEDs at, say, 20 mm centres (6.5 mm = 1/4" between each LED) they would occupy about 220 mm square (~9" square). Evacuating 1.5 kW of heat with a lower than 50 °C rise (given no hot spots) will be "interesting".
Simple test:
Success?
OK. Try 1.5 kW.