Series V. Paralell wiring for Meanwell 60-48D

[Mike]

Hey Evil,

What are the pro's and con's of a Paralell circuit set up for my DIY LED. Total LED's came out to 210 (in a 50/50 mix). In a series wiring scheme I will need 16 drivers (assuming 13 CREE XRE on each driver). What are the numbers with the paralell scheme?????

[evilc66]

Any time you wire in parallel, you divide the total current by the number of strings. You can wire in as many as you like, but the current seen by each LED drops. You can wire 26 LEDs in two strings of 13, but your max current is ~750mA.

I really don't recommend wiring in parallel though. There are many issues with this scheme that can actually damage more LEDs if a single one fails. There are far more cons than pros. The only pro is that you can run more LEDs on a single driver.

First problem comes during operation. Voltage differences between LEDs create imballances that can put undue stress on the LEDs. Lets say you do two strings 13. Both strings have to be equal in size, and will see the same total voltage. If the total voltage drop of one string is lower than the other, it will be forced to run at a higher voltage, and as a result, a higher current. The imbalance doesn't create issues short term, but can cause a reduction in life long term. The increased voltage can also cause a spectral shift in the whites.

The next issue shows up during failure events. The normal failure mode of an LED is to fail open. If that occurs, it will take out the string it's connected to. When that happens, the total current isn't divided anymore by all the strings. This can create problems depending on how hight the total current is. With the ELN-60-48D, it's not too bad, but the current is still beyond the spec limits of the LED and can shorten the life of the LED. If the current is too high, the LED can be severely damaged quickly.

If in the event of the LED shorting (rare, but it happens), the voltage imbalance that I mentioned earlier gets worse in the string that has the dead LED. With the loss of an LED, damage tot he remaining LEDs can happen very quickly.

There have been some attempts at reducing the damaging effects from running in parallel, but none of them cover all of the problems at once. There is a simple circuit called a current mirror that can help with imabalances between strings, but won't protect from LED failures. Meanwell documents a method of parallel wiring where all the LEDs are wired in a grid. This will help with the majority of issues, as there is always a current path if an LED fails. The effects of a voltage imbalance are less with this method. The drawbacks to this method is that you need a minimum of three strings, and it's a ton more wiring.

I know this was kind of a long answer, but it covers all the issues with parallel wiring.

[Mike]

Thanks for the thoughtful answer. I am going to be ordering heat sinks and thermal pads to get started in a couple weeks on this. I was looking for a way to minimized the number of drivers given the size of the build. I think I will stick to my original thought of building the array in 30" sections lined up together instead of a cumbersome 60" section. I think the 30" sections will be far easier to manipulate where wiring is concerned.

[evilc66]

I wish there was a better way to do it, but right now running strictly in series is the safest and most reliable way to run LEDs. The Meanwells are the highest output drivers we have available to us in the DIY market.

[Mike]

I got my multimeter yesterday so I can set the drivers properly. I guess in series it is then ;)