Wiring LEDs in Series and Parallel

There are 2 ways to go about wiring LEDs: series and parallel. In most cases, if you have a constant current driver, you’re going to want to wire them in series. If you’re using a constant voltage driver, chances are, you’ll be wiring in parallel. You may even need to combine both methods in order to hit a certain voltage or current to match to a particular driver (see my post on matching COBs to drivers for more info on this). This information applies to LEDs of all types, whether they’re COBs, boards, strips, or whatever.

Wiring LEDs in Series

Series wiring is used most often with constant current drivers. When you wire in series, you add the forward voltages of each LED in the circuit but the current fed to each LED remains the same. If you have 3 LED COBs, each with a forward voltage of 36V at a given current, when you wire them in series, the total voltage drop of the circuit becomes 108 Volts. If, for example, your LED driver produces 1400mA of current within a voltage range of 100-150V, then as long as your total voltage drop of your circuit is within  the 100-150V range (our circuit of 108V would work), then all 3 of these COBs will receive the full 1400mA.

Here’s what 3 COBs wired in series looks like:

If you look closely, you can see that each COB has 2 contacts; one has a “+” sign to indicate it is the positive side, and the other is unmarked, which is negative. To wire in series:

  • Take one of the leads from your LED driver (it doesn’t matter which polarity) and wire it to the corresponding input of your first COB (e.g. – positive lead to positive input OR negative to negative input).
  • Take the other LED driver lead and wire it to the corresponding input on the last COB in the chain.
    • In my example above, the 2 white wires are the leads from my LED driver. I have wired the positive driver lead to the positive input on the left COB, and wired the negative driver lead to the negative input on the right COB.
  • Now, all you need to do is connect the first LED in the chain to the last LED in the chain, by interconnecting the positive and negative terminals of each LED in between. If you started by connecting the positive side of the LED driver to the first COB like me, then you will wire the negative side of the first COB to the positive side of the second COB. It seems counter-intuitive to wire a negative to a positive, but this is how series wiring works. Once this is complete, continue wiring the negative of one COB to the positive of the next, until you reach the end of the line, where your other LED driver lead is connected.

    A series circuit. The COBs are interconnected by wiring positives to negatives.

Wiring LEDs in Parallel

Parallel wiring is most often used when working with constant voltage drivers. A lot of people are now using constant voltage drivers and wiring up their COBs in parallel, since the drivers are usually cheaper and people are more comfortable working with low voltages like 36V, as opposed to high-voltage series circuits that can be 200V+. One drawback is the fact that wiring COBs in parallel does make them vulnerable to thermal runaway.

Thermal runaway refers to the process that occurs when a COB heats up, causing it to draw more current, which heats it up further, drawing even more current, and this loop continues until it destroys itself. Unless you implement something like a resistor to limit the maximum current, there’s nothing stopping the COBs from pulling as much current as the driver will provide if the COBs go into thermal runaway, or the voltage output of the driver rises. That being said, in my own testing, current levels have always stabilized at reasonable drive currents and I have only seen thermal runaway occur at very high currents that nobody is going to run at (3+ amps per COB!).

Now, when you wire in parallel, the forward voltages of each LED no longer add together like they do in series. If your driver outputs 36V, then every single COB that you have hooked up to it in parallel will have that same 36V across it. Instead, the current is what becomes split among the LEDs in a parallel circuit.

For example, your COB data sheet may tell you that when you apply 36V, each of your COBs will pull about 2,400mA of current. So, if you have 2 of these COBs on a 36V constant voltage system, your driver would need to be able to supply at least 4.8A of current. If it can do more, that’s fine – the COBs will only pull what their particular unique current-voltage curve dictates, depending on what voltage you run them at. They may each pull 2,400mA when you put 36V across them, but jump to 2,700mA each when you put 36.5V across them.

You can also wire COBs in parallel on a constant current driver. When you wire in parallel on a constant current driver, you don’t have to worry about the COBs pulling any more current than the driver is rated for, but the current will not necessarily be evenly split among the COBs. You could have 2 identical COBs in parallel on a 700mA constant current driver, and one COB could be pulling 500mA while the other only pulls 200mA, due to small differences in the composition of the LEDs in each COB. See my post on constant current vs. constant voltage for a more in depth look at this.

To wire in parallel:

  • Instead of creating a long single chain of COBs, you simply wire all the positive sides together, and all the negative sides together.
  • In the picture above, I’ve wired the positive and negative leads of the driver to the first COB on the left, and then connected them to their respective polarity down the line to the last COB.
  • Below is a paint schematic of a parallel COB circuit. I won’t be doing graphic design anytime soon.

A parallel circuit. The COBs are interconnected by wiring all positives to positives, and negatives to negatives.

Combining Series and Parallel Wiring

There may be instances where you need to combine series and parallel in order to match a certain number of LEDs to a driver properly. Generally, it’s better to just add more drivers to keep things simple and in series, but if need be, you can work some magic to make what you’ve got work.

If, for example, I wanted to run 8x CXB3590s (36V) on my driver that’s rated to do 1400mA between a voltage range of 71V and 143V, I could not hook them up in serial. Hooking all 8 up in serial would give me a total voltage of 288V, which is way out of range. What I could do, though, is wire 2 strings of 4 series-connected COBs in parallel. Each string would have a voltage of ~144V (a little less due to the low current) and would draw 1400mA of current. If these 2 strings were then wired together in parallel, the voltage of 144V would remain the same, but the current of 1400mA would be divided among them, giving each COB in each string 700mA.  Check out my miserable paint depiction of this type of circuit below:

series-parallel

And that’s the basics of wiring LEDs. As always, if you’ve got any questions or comments, please share them!

17 Comments

  1. Hi led gardener.

    I will be wiring x4 cobs in parallel (50v, max 2.88a) with an hlg240h 48a (max 50.5v, 5.2 amp approx)

    I want to include 2.5amp inline fuses to protect each cob. Should i use quick blow or slow blow fuses?

    ColinC

    • LEDGardener

      April 4, 2017 at 10:55 pm

      Hey! I would use a fast blow fuse. If you have any one of the 4 COBs getting all the way up to 2.5A and hogging almost half the power supply, you’d want that fuse to blow right away without giving the system anymore time to dump more current into it. I highly doubt you’ll ever run into this problem but fuses are a great idea to protect your gear just in case.

      If your power source had a big current surge on startup, a slow blow fuse might make sense, but in this case I think a fast blow is the way to go.

  2. any wiring instructions using vero 29’s with the Ledil reflector holder a pinned heatsink with the molex connectors in series?

    i have 4 pinned heatsinks and 4 vero 29’s gen 7 with molex connectors

    • LEDGardener

      June 21, 2017 at 12:28 pm

      Same principle. Positive of driver goes into positive of first COB, negative of driver goes into negative of last COB, then connect negative to positive for every COB in between.

  3. Jeffrey Pinson

    August 8, 2017 at 2:36 pm

    Thank you. I understand cob and drivers now.

  4. In your last example with the 4×2 series/parallel setup you wind up having 8 powered at 700mA/~36V, doesn’t that give you a similar efficiency as 4 at 1,400mA? Is the upside to this setup more light distribution per watt without having to buy a second driver?

    If you added a second driver and made it two separate 4 COB series circuits, wouldn’t you double the output instead at a pretty good efficiency? It just seems like running 8 lights at 25% power instead of 4 lights at 50%. Maybe I’m missing something?

  5. LEDGardener

    September 5, 2017 at 4:15 pm

    Hey Trevor. The efficiency of each LED at 700mA vs 1400mA will be considerably better (in terms of what percentage of input power is converted to photons vs the percentage converted to waste heat) but it comes at the cost of double the gear. In practice, I would rarely run at 700mA on a 36V COB because it’d be so expensive and I mainly drew this out as an example to demonstrate how series-parallel worked. Wiring like I showed might make more sense in an instance where you had something like a 2800mA driver and you were looking for 1400mA per COB though.

  6. Hi Led Gardener, do you think its possible to combine 2 700mA drivers to run the cobs at 1400ma? Do you have any idea or info about that? Thanks in advance, this is my first question but i have been here for loing time!

    • LEDGardener

      October 11, 2017 at 4:05 pm

      Hey Damian, good question. I’ve done a little research on wiring power supplies in series like this, and most of the information I’ve found suggests that unfortunately it won’t work and will cause problems. If I was an electronics wizard, I’d tell you exactly why, but alas – all I can say is that you should just grab a 1400mA driver.

  7. Hey mate,
    thanks a lot for this!
    Got really confused between those two when I just read on how to do the DIY LM561C.

    Awesome work.

  8. BRYAN MCDERMOTT

    November 3, 2017 at 5:22 pm

    Little help needed….

    Got a Mean Well 320H-36b driver. currently NO potentiometer hooked up to it.

    Have 2 cobs, Citizen CLU048-1212 properly hooked up to their heatsink.

    When wiring just one cob from the driver, brown driver lead to positive, negative to blue driver lead, the cob powers up brightly.

    When wiring BOTH cobs in parallel, both cobs power up.

    When trying to wire both cobs up in series, ie. Brown driver lead to positive cob 1, negative cob 1 to positive cob 2, negative cob 2 to blue lead on driver, neither powers up.

    Any ideas?

    • LEDGardener

      November 7, 2017 at 2:12 am

      Hey Bryan. That driver is designed to run those COBs in parallel. It doesn’t have the voltage to run them in series so just wire them up parallel and you’re good to go – they should pull around 1750mA at 36V.

  9. I read in another forum that if using Cree CXB3590 72v chips you need to wire them in parallel, it can’t be done in series. Is this true?

    • i wired mine in series but only 3 of my 5 3590’s are 72v. the other 2 are 36v running off a 400 watt meanwell driver with dimmer.

    • LEDGardener

      November 15, 2017 at 3:23 pm

      The problem with wiring them in series is that the voltage adds up so fast that you can only do 3 of them before you exceed the max voltage ratings of the connectors/COB holders. That’s why the 36V models are more popular.

Leave a Reply. For help with your own build, please make a thread in the Forum

© 2017 LED Gardener

Theme by Anders NorenUp ↑