Help me understand running LEDs strings in parallel

[NirvanaFan]

Help me understand running LEDs strings in parallel off the same driver.

I'm using a MeanWell ELN-60-48D driver. If I run 12 LEDs per string, and run 2 strings from the same driver in parallel, the max mA I can run each string is 650 mA right (since the drivers output 1300mA max).

So, if I want to run any LEDs over 650mA, I need to run one string. Is that correct?

[der_wille_zur_macht]

Yup, that's correct. When you put (identical) strings in parallel, you divide the total current by the number of strings. Each string still gets the driver's full voltage.

In practice the ELN drivers can go over 1.3A output, but your mileage may vary.

The catch is getting fully identical strings. HP LEDs tend to have very poor voltage tolerances. It's fairly common that people need to swap LEDs from one string to another to get balanced strings. You also need to implement a protection mechanism if the driver's nominal current would be damaging to a single string of LEDs - typically a fuse is placed in series with each string, along with a 1 ohm resistor which allows for easy current measurement (check for voltage drop) without having to break the string to put a multimeter in series with the LEDs.

[NirvanaFan]

I know you can't answer this question for me, but...

Is it worth it to run them in parallel? I could see if you were to have 10 or 12 drivers, but if you just have 3 or 5, is it worth it?

[der_wille_zur_macht]

It really depends on the way the specific build is planned out. You have to consider the current you need in an LED, the current a given driver can provide, and other factors.

The ELN drivers are very popular. They are typically used in a way that takes poor advantage of their capabilities and results in wasted capacity and lower efficiency overall.

For instance, consider if you wanted 24 XP-E royal blue running at 700mA. A "typical" approach would be to use two ELN drivers, each adjusted to provide 700mA. The ELN 60-48 is capable of 1.3A and 48v (52 if you tweak the voltage limit trimpot). Running 12 XP-E at 700mA means you're barely over half the total wattage the unit can deliver, and it happens that the ELN's efficiency gets poor as the current is adjusted down that far. So you're paying for twice the capacity you need and you're using that capacity in an inefficient way.

An alternative would be to just buy one ELN and run two parallel strings. This way, you're using all the capacity you paid for, you're operating the driver at it's most efficient point, and you're spending less since you only bought one driver. The only real drawback is that you have to "deal" with parallel strings (fuse protection, current balancing). Another possible drawback depending on your desired dimming/control method is that you've now got 24 LEDs on one driver instead of two drivers with 12 each, so you're losing control resolution.

You're right, on smaller builds these things aren't a huge deal, but on larger builds parallel strings are practically a way of life with commercial drivers, especially if you start getting in to some of the high-wattage products like the HLG.

[NirvanaFan]

Makes sense.

I don't think using an ELN-60-48 driver makes sense to run two strings then. Unless you know that you'll never want to go above the 650mA mark. It doesn't make sense to limit yourself. So my options are to go with a different (more mA) driver and deal with running strings in parallel or just go with the more inefficient (space, plugs and efficiency wise) ELN-60-48 drivers.

Decisions... decisions...

[der_wille_zur_macht]

I'd look at the inventronics drivers that some vendors are starting to carry. At the very least, they are typically available in slightly different current/voltage configurations than the Meanwell drivers so you might find something more suited to your build.

Running the ELNs at less than fully loaded might not be ideal from a purist standpoint but it is certainly not the end of the world, and is an extremely common thing these days.

[thor109]

If you run strings of 10 you can get more ma per bulb. I've read when it comes to par readings leds are not linear. I mean if you get 80 par at 500 ma you won't get 160 par at 1000 ma. Some say the sweet spot of par to watts is around 800.

[ctreefer]

As DWZM mentioned some drivers have a much higher output than others. I bought 2 units for my build and one of them was outputting 1900ma. So half gets you 950 per string. Not sure if you can somehow see if they can test one for you before they send it out.

[kcress]

You SHOULD run two strings on an ELN60. It makes way more sense than buying extra ELNs "just in case" you 'might' want to run the LEDs a little harder. You can hardly see the difference between 650mA and 700mA.

I suggest you go read this entire thread:
http://www.reefcentral.com/forums/showthread.php?t=1973462

[NirvanaFan]

What about if I want to push them to 750mA, or 800mA? Then what? I've never seen what the 3w LEDs even look like all together (just one at a time). For the cost of a driver or two, doesn't it make sense to have the flexibility? I'll start looking at that thread now.