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I'm looking to buy a LRS-350-36 for my project to feed 5x50W LED at 30-34v Vf 1750mA (https://www.aliexpress.com/item/32867490711.html). This PS use a 1U form factor that I must have due space constraints. My question is: can I drop 4V using the adj. pot and have a output of 32V without problem or affect PS performance? Is there any downside of such drop? Another thing that datasheet is lacking is that ajustment range, anyone know the up/down limits?

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  • \$\begingroup\$ Slightly unrelated, but maybe get a Constant Current PSU instead of a Constant Voltage one if you are driving High Power LEDs directly. \$\endgroup\$ – Wesley Lee Apr 1 at 1:46
  • \$\begingroup\$ which LED are you using? \$\endgroup\$ – Jasen Apr 1 at 1:47
  • \$\begingroup\$ @WesleyLee That can be a route, better use one driver per LED right? And not share, like lets say 100W for two LED? Jasen LEDs are: aliexpress.com/item/32867490711.html \$\endgroup\$ – Tiago Conceição Apr 1 at 1:51
  • \$\begingroup\$ You can find LED drivers that would be able to drive some of those LEDs in series. There are also LED drivers with multiple channels, so you could get 2 RGB drivers and only use 5 channels. It depends on what you want and the specs of what you find. \$\endgroup\$ – Wesley Lee Apr 1 at 2:15
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I was able to adjust such 12V supplies down to about 10.5V, which means that you are likely to get as low as 31.5V or 32V minimum.
Here is an actual datasheet for your supply:
https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF
It states that you can adjust the 36V version from 32.4V to 39.6V, but I think that the actual range is just a little bit wider (because the range they specify is guaranteed, but the actual one is usually beyond that).
Lowering this power supply's voltage to its minimum adjustable value should have no negative consequences because it was designed for that.
However, I would recommend that you use a constant current source instead of a constant voltage, since an LED current varies greatly over a very small voltage change. You need to somehow protect the LEDs from too much current. It is better to under-power them instead of over-powering.
Personally, I tend to drive LEDs at no more than half of their rated power; the lower the power applied, the longer they last, which is especially true with cheap Chinese LEDs. Most LED lights manufacturers do the opposite and drive LEDs with 2-3 times their rated power (to save money on LEDs), and that's why they don't last that long. Heat is another issue, as most LED lights have too much heat produced in too little space with no means of dissipating it sufficiently.

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  • \$\begingroup\$ Dam i inpect datasheet three times and i miss that line, how i!? Thank you for pointing out. A question about LED drivers - constant current, should i opt for it rating 50W, or a bit lower to protect the LEDs? I edited main question with LED link. \$\endgroup\$ – Tiago Conceição Apr 1 at 1:57
  • \$\begingroup\$ Personally, I wouldn't go "a bit lower", I would actually drive a 50W COB LED with no more than 30W. I would even go to 10-20W if the LEDs are cheap, and rather use an additional 1, 2 or even 3 COBs in order to spread the current and heat around. Your LEDs will thank you with a much longer lifetime (and a slightly higher efficiency). \$\endgroup\$ – Edin Fifić Apr 1 at 7:53
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  1. Forward Voltage: 30-35V
  2. Forward Current: 30W:1050mA,50W:1750mA 100W:3500mA

Note: voltage is given as a range while current is a fixed value.

These LEDs need a fixed current (or current limited supply) attempting to use them with a fixed voltage supply will not work well.

get a LED power supply.

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  • \$\begingroup\$ Are these a good choise? aliexpress.com/item/32832717948.html Looking at table, 50W have 30-34V 600mA, that's only 20.4W, whats wrong? \$\endgroup\$ – Tiago Conceição Apr 1 at 2:19
  • \$\begingroup\$ I think i found a proper one (1500mA 24-34V 50W): aliexpress.com/item/32756673848.html more expensive but look the spec i need \$\endgroup\$ – Tiago Conceição Apr 1 at 2:29
  • \$\begingroup\$ @TiagoConceição: Most of the cheap Chinese LED drivers are of low quality and overheating, not to mention their poor Power Factor (PF). The second one you picked says they have 0.95 PF which is very good, but the Chinese manufacturers and sellers often put false information on their labels. You can only know for sure when you measure their PF. \$\endgroup\$ – Edin Fifić Apr 1 at 8:01
  • \$\begingroup\$ Speaking of Power Factor (PF): if a mains power supply/adapter doesn't specify he PF, chances are it is fairly low (bad) and the build quality of the supply is not that great. Even when a high PF is specified, you just can't be sure unless it's from a reputable manufacturer or you measure it yourself (but that means you would have to buy it first). \$\endgroup\$ – Edin Fifić Apr 1 at 13:08
  • \$\begingroup\$ @EdinFifić Thanks for point this, i know most of them will lie, even if you conact it about the specs, if you know any reputable seller on aliexpress please share a link \$\endgroup\$ – Tiago Conceição Apr 1 at 13:58

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