Cant find information about the max forward voltage at 700mA and YES I've looked at the spec sheet from Cree. It only shows the minimum and max voltage at 350mA and then typical voltage from like 100mA to 1000mA. Just wondering if anyone has put 14 XT-Es on this driver? I've got 12 on it and want to add two more
How many Cree XT-E Royal Blues can you put on a meanwell 60-48
- Thread starter Nexenn
- Start date
der_wille_zur_macht
Team RC
Vf at 700mA is about 3.05v. Nominally, you have 48v to work with. If you allow one LED worth of "wiggle room" to accommodate how loose the spec is, you've got ~45v to work with. That puts you at 14.75 LEDs per driver.
When the ELN is pushed ABOVE its constant current range in terms of voltage, it just defaults to constant voltage mode instead of constant current mode and starts underdriving the LEDs. It'll do this happily without obvious malfunction. If you want 13 or 14 LEDs, you're probably fine. If you want 15 LEDs and you really care about making sure you are driving them at 700mA, I would suggest putting 15 LEDs on the driver, letting everything reach normal operating conditions (warm it up for an hour) and then measure current. If the current is LOWER than what you expect, you need to fiddle with the voltage limit trimpot (SVR1, NOT the current limit trimpot SVR2). Turn it up until the LEDs reach the desired operating current.
When the ELN is pushed ABOVE its constant current range in terms of voltage, it just defaults to constant voltage mode instead of constant current mode and starts underdriving the LEDs. It'll do this happily without obvious malfunction. If you want 13 or 14 LEDs, you're probably fine. If you want 15 LEDs and you really care about making sure you are driving them at 700mA, I would suggest putting 15 LEDs on the driver, letting everything reach normal operating conditions (warm it up for an hour) and then measure current. If the current is LOWER than what you expect, you need to fiddle with the voltage limit trimpot (SVR1, NOT the current limit trimpot SVR2). Turn it up until the LEDs reach the desired operating current.
der_wille_zur_macht
Team RC
The best royal blue XP-E bin is rated minimum of 500 mW at 350mA and drops 3.2v. The best XT-E bin is rated minimum of 550 mW and drops 2.85v.
So, effectively, at a given current the XT-E is about 10% better. But to get the real picture, you need to look at power levels, since as gpx mentioned the XT-E drops less voltage. The XP-E is doing ~446 mW/W while the XT-E is doing 551 mW/W. So it is roughly 20% more efficient.
The way this plays out in a build will depend on a few variables, but it basically means you can use 20% fewer LEDs at the same power level or you can use the same number of LEDs and run at 20% less power, etc.
Again though it's important to consider the power you're running at, not the current. If you try to do the math based on current (i.e. switch from 10 XP-E at 700mA to 8 XT-E at 700mA) then you'll get less light than you think, since XT-E drop less voltage and hence run at a lower power for a given current level.
Another inherent advantage of these LEDs is that you can fit more on a given driver, since they drop less voltage. Regardless of how you work out LED count and power level, this can mean you need fewer drivers and are hence saving on upfront cost and longterm efficiency losses.
der_wille_zur_macht
Team RC
Yeah, that should be fine. And it's a great way to optimize a single ELN-60-48. So many people who are using these drivers are running them well below their max power level, which is wasteful both upfront (you're buying more drivers than you need) and in the long run (the drivers are less efficient at lower power levels).
der_wille_zur_macht
Team RC
When figuring parallel strings, each string drops the drivers' voltage - current gets divided among the strings.
So when you're figuring how many LEDs to put in a string, you do the math the same way with 5 strings as with one string - so you just add up the Vfs of the LEDs in the string and see if it's in range for the driver.
When you're figuring current, you divide current among the number of strings. So if your driver does 1A and you have 3 strings, they each get 333mA.
The one thing to keep in mind - all the strings on a given driver MUST be balanced. They must consist of the same number of the same LEDs, i.e. if you have 10 of LED A and 10 of LED B, you can put 5 A's and 5 B's on each of two strings, but you can't have one string of 10 A's and one string of 10 B's. If you have 20 of one LED, you can't have one string of 12 and one or 8, you need two of 10.
And then once you get it all built, you need to determine through testing if the strings are actually balanced, and correct if they're not. Vf is a very loose spec, and if you end up with uneven strings you'll have issues.
So when you're figuring how many LEDs to put in a string, you do the math the same way with 5 strings as with one string - so you just add up the Vfs of the LEDs in the string and see if it's in range for the driver.
When you're figuring current, you divide current among the number of strings. So if your driver does 1A and you have 3 strings, they each get 333mA.
The one thing to keep in mind - all the strings on a given driver MUST be balanced. They must consist of the same number of the same LEDs, i.e. if you have 10 of LED A and 10 of LED B, you can put 5 A's and 5 B's on each of two strings, but you can't have one string of 10 A's and one string of 10 B's. If you have 20 of one LED, you can't have one string of 12 and one or 8, you need two of 10.
And then once you get it all built, you need to determine through testing if the strings are actually balanced, and correct if they're not. Vf is a very loose spec, and if you end up with uneven strings you'll have issues.
WickedBlue28
New member
I've been told you can run 16 XT-E RB on one MeanWell 60-48
der_wille_zur_macht
Team RC
I would not run 16 of these LEDs on an ELN without actively checking the current on the string and adjusting the voltage limit trimpot to compensate - otherwise it's likely you will be underdriving the LEDs.
WickedBlue28
New member
Where should the voltage be @ to run 16?
You will need to figure this out on your own. Adjusting the voltage trim pot as you are measuring the current.
