I have 4 of these Tuneable white Led’s wired In Parallel.
Im using Mean Well 37V Constant Voltage 12W 350mA Power Supply (Model APC-12-350 )
One of the Led’s is noticeably brighter than the other 3. I read it has to do with the unequal power distribution due to slight variations in manifacturing causing different current draw.
Is there a way to correct this problem other than changing the wiring layout? (its already installed above my ceiling. )
What is the correct Led driver for my setup?
To get the best equal brightness with multiple LEDs, they need to be connected in series and driven with a constant current power supply.
Constant voltage applied to parallel connected LEDs gives the worst brightness match.
To echo Paul’s advice, there’s no way to get perfect brightness matching with a simple driver swap. Running LEDs in parallel is always going to hit this issue. The only way to control brightness in this sort of set-up would be to install individual dimming circuitry on every LED and manually tune them until you get where you need to be. This doesn’t seem to be an option for an already-installed system where wiring can’t be changed. Apologies, Yuip.
Hello @yuip ,
Thanks for reaching TechForum. The incorrect LED driver you currently have is APC-12-350, which is only a 350mA ‘constant current’ driver, where the BXRV-TR-2750G-2000-A-15 led you have lists an individual test current of 700mA @ 36.3v. Since the LEDs are in parallel, they are looking for around 2800mA of current @ their individual rated voltage of 36.3V. The reason why the large brightness mismatch is because there is not enough current to power all 4 LEDs, and which ever one happens to get forward biased first is the one that remains brightest as it is the only one that is fully forward biased, allowing it to draw the most current.
-The good news is there shouldn’t be any damage done to the LEDs based on your current setup.
Parallel LEDs use singular LED rated voltage, but the individual LED current rating is additive:
For this circuit, 36.3v @ 2800mA
Series LEDs use singular LED rated current, but the individual LED voltage rating is additive:
For this circuit, 145.2v @ 700mA
For minimum LED driver power rating, multiply the output current and voltage:
=101.64W
It is common to add 10-15% on top of this for some headroom:
=112W-120W+
*Figures based on nominal values
This chart from the LED datasheet shows nominal CCT as defined by ANSI C78.377-2011:
This chart from the LED datasheet shows testing in pulsed conditions, Tc
= 25°C. Pulse width is 10ms while voltage minimum and maximum are provided for reference only and are not a guarantee of performance.
-You may have to factor the temperature of the environment for derating and also decide if you need a dimmable driver to allow various brightness.
Although not most ideal, you could keep your current parallel wiring, and use a driver like below and yield Much Better results.
Click here
Ideally, you could (re)wire the 4 LEDs into a series connection, and use a driver like below for BEST results:
Click here
Please review datasheet specifications prior to ordering to make sure one will work for your exact application and meet any environmental or safety classification.
Hi yuip,
There are several issues with your set-up.
As others have mentioned, your driver is under-powered, and running in parallel is sub-optimal. When running LEDs in parallel, you will always have a mismatch in brightness due to inconsistencies in Vf from one LED to the next. If they come from the same batch, this usually is not too significant, but running in series will always give better results, as they will always have exactly the same current through each module this way.
Additionally, in your case, using the BXRV-TR-2750G-2000-A-15 poses a greater challenge. That LED module is composed of two separate LED strings: one made up of warm Correlated Color Temperature (CCT) LED dies, and the other with cool CCT LED dies. If you want to be able to adjust the overall CCT, you will need two separate LED drivers to drive each circuit separately so you can blend them as desired. This means that at a minimum, if you want to control the CCT of all LED modules, you’ll need a minimum of two drivers, with cool LEDs connected in series on one driver, and the warm LEDs connected in series with the other driver.
Since the forward voltage (Vf) of each LED string in each module can range from about 31V to 43V, depending on forward current and die temperature, you’ll need a driver which can accommodate this range per module, or a multiple of these voltages if you connect more than one in series. The drivers @Ryan_2724 links should point you in the right direction.
THank YOu @Ryan_2724 for the detailed breakdown. You went into the level of depth that inspired me to read about how Pulsed Flux works and understanding signifance of ANSI C78.377-2011.
@David_1528 thank you for the explanation about slight variances of Led’s coming from the same batch, and seperate drivers recommendation for each CCT Color Circuit
I should have wired in Series from the start. Now I know better for future LED projects.
I have 2 questions
1- the LED is rated at 700mA for each Color. So that means it is 2800mA for WW and 2800mA for CW. Total power consumption for 4 LEDS with both colors running at rull power is 5600mA or ~220 Watts. is my calculations correct here?
2- If i Update the Power capacity of driver and individually control each LED downlight with a dedicated CCT controller. that will resolve the current misallocation issue because I can precisely control the color and intensity of each individual bulb:
ie:
Your math looks about right - a little above 200W at the nominal Vf of 36V and 700mA x 8 strings. Make note that if you go with this architecture, you may need a constant voltage a bit above 36V in order for the CCT controllers to properly feed each LED module.
Also, make note that you will need very good heat sinking, as you’ll be pumping as much as 50+ Watts through each module.
Hi @yuip ,
In reference to the schematic, do you have specific controllers in mind? The controllers will have their own electrical specification requirements and would most likely change the specification requirement of the driver. I am also not fully convinced you would need separate controllers just to level out the lighting intensity between each LED COB, but I could be mistaken.
From a hobby point of view, the parallel wired LED COB strips I’ve put together in the past using only one proper driver didn’t have any noticeable illumination differences between the LEDs from what I was able to tell. I believe having one driver to power all of these LED’s (8 all in parallel) without individual controllers would give you good results, but of course not a guarantee as that is up to the end user to decide what will work best for their exact application.
*If choosing an LED driver with voltage or current adjustment potentiometers on them, you will want to verify these are set to the correct or minimal value to prevent possible damage to the LEDs, and may be a good idea to perform LED voltage and current tests until you find an optimal setting.
As long as each of the COBs are well matched, it will probably function OK. However, with a single driver for all of them, there will be no ability to adjust color temperature, as both warm and cool will be driven with approximately the same current. With two drivers, one driving all of the warm LEDs and one driving all of the cool LEDs, you could have color temperature control.
The biggest risk in running COBs in parallel is if one or more of them go open circuit, either from a failure or from a faulty wiring/connection issue. In such a circumstance, a current controlled power source will force the fixed current into the fewer remaining COBs which are still connected. If this exceeds what they can handle, they will all be destroyed. Conversely, when connected in series, any open circuit fault will disconnect all of the COBs rather than over drive them. One can then fix the fault and all should be good – none of them should be damaged from the fault.
As David is suggesting, using a constant current driver for parallel LEDs can make for an expensive fix when any one LED issue arises, which is why some may prefer using a constant voltage driver over a constant current driver for parallel LEDs. Depending on what wiring design and color temperature control requirements you end up landing on, we can help narrow down a better list of potential drivers for you.
