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!

40 Comments

  1. colinc

    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

      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.

      • John

        Hey I have the same 4 cobs and driver, my questions are 1. where would you put the fuses and 2. where/which ones to buythank you

  2. Rob G

    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

      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

    Thank you. I understand cob and drivers now.

    • LEDGardener

      Glad to hear 🙂

  4. Trevor Walsh

    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

    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. Damian Eduardo

    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

      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.

      • Scott Goldie

        You are a electronics wizard. Math to!

  7. Andi

    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.

    • LEDGardener

      Good stuff! Thanks for the feedback 🙂

  8. BRYAN MCDERMOTT

    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

      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. David Moss

    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?

    • rob

      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

      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.

  10. Wazzup Dude ;)

    Is it possible to wire 36V cobs on HLG-320H-48B driver?

    • LEDGardener

      Technically, yes, you can, but it’s risky. You need enough of those 36V COBs wired in parallel to force the driver into constant current mode. You’d need about 5 of them wired up at minimum. If you ever had any less than that, you’d cook them all. Probably not worth the risk if you can afford to get the proper driver, but it would work.

  11. Anonymous

    Why when i put 2 warm white and 1 white light in parallel the white light does not light up?

    • LEDGardener

      Do you have model numbers?

  12. Dainius

    Hi,
    Can i connect 4 pcs CC LED drivers positive in one and use 4 channels negatives for RGBW hight power LEDs?

  13. Pfeffer Geist

    Hello and thank you for creating this page.

    Is there any other advantage to series parallel wiring other than saving on driver cost? Like system efficiency or temperatures?

    • LEDGardener

      Series is the easiest way to provide a specific current to your lights. You can really dial it in compared to parallel. It also completely eliminates the possibility of thermal runaway.

  14. Daryl Joseph

    Hi have a 3 led pool lights 50w .The cable from the leds didnt reach the control box in shed. I run one wire from the control box to the pool lights junction all 3 lights . Now realising I needed 3 individual wire runs.The leds are multi coloured. Is there any way of changing the resistor in control box in shed ,to run these leds. Other solution is a insurance claim the pool is tiled and junction to leds is hard to get to.Pool owner not happy.I appreciated any help.

  15. Isaac Grigg

    Hello. Your article has helped me understand the concepts behind these electronics, however, I am hung up on something you said about parallel wiring. Let me explain:

    I have some Vero 29s that I used in a project that went horribly wrong (don’t ask lol). Anyway, I still have the chips, but between them sitting around in the somewhat damp basement, and the events that put them out of commission, I am unsure if they are still working. Because of that, I don’t want to buy a cheap 50w driver from China, wait for it, test them out, then buy an HLG to run them.

    Where I am getting hung up is this: I was under the impression that an led can’t handle more current that it’s rated for, which is why I haven’t just hooked up four 9v’s in series (which I have on hand), and then wired my Veros up to that quickly, just to see if them illuminate. I have measured the amperage of the battery, and it’s about 6amps and 8.9v . Meaning, to my knowlege, when I hook the batteries up in series I will have nearly 36v at 6a.

    Would it be safe to test out each Vero individually, using this set up? I know it’s a bit dangerous to join 9vs like that, but I have a garage, and I’m not scared lol.

    Sorry if any of this is confusing, and thanks for any help.

  16. Ferran

    Hi thanks for the articles i learnt a lot! But i have a question.
    I’ll buy 2x Vero 18-c73 4000k 80 cri which can connect Pico EZmate instead of solding. And i want it to using the Wago connectors. But my question is the following… How i connect all in Serie?

    I understand the positive all in the same Wago Box, that should end in my case like (1 Wago with: 1 led driver, 1 Cob x1, 1 cob x2) and for the negative wire the same.. But that is not parallel connection?
    I got the idea but thinking if i connect like this will be Parallel instead of Serie.

    Sorry my unknowledge and my English.

    • ledgardener

      Sounds like what you’re describing is a parallel connection. You don’t want to put all your positive wires into a single Wago because that’d be parallel. Your driver positive should connect to your first Vero’s positive wire. Your driver negative should connect to your second Vero’s negative wire. Then connect the negative of the first Vero to the positive of the second Vero.

  17. Luis guerreiro

    Hey brother, so I am thinking about buying a cheap driver to connect some 5gen citizens, it’s 36v 10a, but some buyers said it doesn’t work well on 10a so I was thinking about using only 75% max of it and get 2 or 3,my question is, will it necessarily use the max current of the citizens? If so, won’t they get too hot as the citizens are suppose to be run on 1400mah for max efficiency?

    • Luis Guerreiro

      Found the answer to my question already, that made me decide to buy a 6a 36v cheap driver, that way 4 citizens (Gettin 6 gen now) will draw 1.5A each, now what I can’t seem to find anywhere is what resistor should I buy to limit the current to 1.5A, and how to install it, could you help me with that?

  18. michael

    Hello,
    what is not clear to me it’s if it’s possible to have different devices with different voltages feeded by the same driver. For example let’s says I have to run 2 smd LED running between 32-34 volt and PC fan to cool them down running at 12V.
    Another thing that is really fuzzy is that to avoid overheating most of DIY entusiasts run these chips at lower current, so avoiding the maximum power output. Let’s say a Cree is 137W max, but majority of people output 75w. So for example in my country is really hard to get Cree or Vero or Luminous, but I can get those 100W@3000mA chinese SMD chips. I assume to match efficiency I would have to run them @1800mA which is the 40% less than the maximum, as for Cree. So I would have to find – for example for 2 chips wired in serie system – a driver which is capable of 3.6A for 120W output, with 32-34 volt. Is it correct?
    Thank you for your assistance and patience.
    Regards

  19. Lucius

    Hi Ledgardener I’m having trouble understanding these led jobs so here is my question I have 4 cxb 1830 cob led max 53 wattage. I don’t want to run them at their max wattage I want to run them between 30 / 40 wattage at 800mA with 1 driver. I mean 1 driver for all 4 cob led, which meanwell driver do I need? sorry my english is not okay thank you.

  20. Ivan

    Hi my friend. Nice post!!! You help me a lot. I see this post a few month ago and then i could made DIY with 4 clu048 1212 connected in serie with ELG-240-C1400A. And perfect!!!! Now i want to do DIY with 100led strip lm301b and the alibaba strip seller tell me that the 100leds strip lm301b have 27v and 37w at 1400mA. And i dont understand. If 1led have 2,7-2,8v how the seller connect 100leds to be 27v????? I cannot understand. Becose if they put 100led in serie would be 270v. And if they put 10 paralel group of 10led in serie each group, then is not possible have 37w at 1400mA.

    Thanks.

    • Luis

      I’m not sure I would recommend those to you brother, seems like a rip-off, for Chinese LEDs, my go-to is buying multiple mingbens 50w driversless LEDs, they are cheap and can grow gold, they won’t last half what a citizen handles, but they’re cheap enough to substitute on a long basis, but I would much prefer getting citizens from that Estonia guy in eBay, they’re so cheap for what they give you, @ 1400w those clus are bloody monster of growing

      • Ivan

        Hi my friend. Thanks for the coment. The tell seller tell me 100% sure that all the led are original samsumg lm301b. And im paying with paypal what that means i dont be worry. And i allready know my doubt and how 100leds strip can be 27v at maxim forward current. Is easy, they do 10paralel group of 10led in serie each group. That would be 1 led is 2,7v and 10led in serie is 27v. X 10paralel groups = 100leds at 27v.

        The lm301b is the most eficient lm/w. For have the same umols with chinese led you have to spend a lot of more power. In a long time chinese led are to much expensive than lm301b.

        Now i have citizen, but with the same power used the lm301b give me 40% more umols. Thats money saved.

  21. Lam

    Most commercial LED lamps use a combination of series and parallel connections with constant current driver. However, it would first connect eash two LED in parallel, and then connect all the two LED groups in series. This way, when any LED will burn out, only the one connected in parallel to it will be affected. The method you described might burn out more than one LED in the other series since double the current would flow through this series.

  22. José Meirinhos

    Hello
    I have a single clu048 led and a mean well drive
    Can you tell me how to fix wiring to the holder?
    Thanks

  23. Valentin

    Hi,
    Thanks for your hard work! It’s been a while from your post and wanted to ask if the CXB3590 are still one of the best COB’s out there or you could recommend a better one. Also, when it comes to CXB3590 there are two options a 2-Step and a 3-Step version. Any idea what is the difference or which one to chose for a 6 piece setup on a HLG 320H C1400B?

    All the best

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