# Thread: Can someone explain the difference in series/paralell leds.

1. ## Can someone explain the difference in series/paralell leds.

Can someone explain the series/paralell differences in leds.

It has been mentioned that wiring them in paralell will split the amp to each led. How do they react in series? If a 1 amp driver is used and 2 leds wired in series, will they both see 1amp? And how is battery life affected?

Planing out a 2 xml bar light with taskled driver. I get 3.5h on high with a sinle xml at 2.2ish amps.

2. In series, all leds in the string would see 1amp current. (or whatever current your driver is set to output)

In series, their Vf is summed, so, the driver is seeing (N)*(vf) - where "N" is the number of Leds.

Since the vf increases, that means the driver is having to supply more voltage to the LED string. That voltage has to come out of your battery, so battery life decreases.

also what TaskLED driver are you using - that will make a difference in the answer.

3. In a parallel rig, assuming you don't change your output current, the driver sees the same Vf, so the current is split between the parallel LED's. Essentially, in a 2 led parallel string, each would get half the output current - thus about half the light output. a 3-led parallel string would each see 1/3 the output current, and so on.

All things equal, you wouldn't see a ton of difference in output.

In series, all leds in the string would see 1amp current. (or whatever current your driver is set to output)

In series, their Vf is summed, so, the driver is seeing (N)*(vf) - where "N" is the number of Leds.

Since the vf increases, that means the driver is having to supply more voltage to the LED string. That voltage has to come out of your battery, so battery life decreases.

also what TaskLED driver are you using - that will make a difference in the answer.
Havent picked the driver yet. The pack I use now is 4x18650 running in series.
I know task has a 6amp driver and a 3amp.

I was curious if its more efficent to run the 6 amp with 2 in parallel or run 3 amp in series. Or it might not even matter.

The 4 18650s I use on the bar now will go tonthe 2 xml set up. To keep run time up I would get more to add to the pack but i seem to remember reading that using to many cells is bad. Not sure if its a voltage thing or what.

Thanks

5. Generally speaking, it's better to run LEDs in series rather than in parallel. That's because the current doesn't necessarily split exactly evenly for LEDs in parallel. For the current to split evenly, a number of things have to be true. The LEDs have to be the same temperature, the LEDs have to have closely matched Vf's, the temperature coefficient of Vf needs to be similar. If you are using LEDs from the same or similar manufacturing batches and you're attaching them to the same heatsink, you typically won't have any problems. But you don't have to worry about any of that with LEDs in series.

A real world example of where you could run into trouble, is if you have an LED burn out after a couple of years and you want to replace just the faulty LED. If it's in parallel with another LED, you may run into problems. That's because even the same type of LED may have different Vf characteristics due to improvements in the manufacturing process over time.

So if you have control over all the design variables for a project, it's almost always a better choice to go with a series configuration. If you have certain design constraints, such as the battery voltage has to be something specific, then it may be worth considering parallel LEDs.

6. Won't matter in that situation - you're referring to the H6Flex buck driver that is 6A capable. You're running a 14.8v pack to drive a pair of XM-L that is going to present about 3.3vf @ the 3A current they would see each if you wired them parallel and ran the H6flex @ 6A. So think of it this way - you're splitting half your battery to one LED, and the other half to the other.

I don't know what your cells capacity is, but let's assume 2400ma just for examples-sake.

you're presenting half the voltage per parallel circuit, with plenty of capacity overhead in the battery pack.

wired in series you're presenting the same requirement to the bFlex running at 3A. both drivers run about 90% efficient, so there's no efficiency gain really.

the big difference is the H6flex is 1.3" in diameter and a lot taller. that's a lot of real-estate in a light housing. It is also \$40 the bflex is smaller, and \$35

7. Oh - and either way - running either config, with my assumed 2400ma batteries, you'd get about 1.3hours of runtime @ high

8. Thanks. What said makes sense to me. I also just read some info on the b3flex and it is most efficient with 3 leds. It was a good read.

So if running 2xml on the 3amp task driver the 14.8v would be plenty of headroom.
If I wanted mor run time would another 4x18650 at 14.8 parallel with the first pack be ok? Total voltage would remain the same.

When my riding partner go out at night we tend to explore alot of of the beaten path trails and never know how long we will be out for. I dont mind the weightas it sits on the bike.

Oh - and either way - running either config, with my assumed 2400ma batteries, you'd get about 1.3hours of runtime @ high
Thats not to bad. It would be alot of light. Part of me wonders why this addiction is taking over me lol. The single bar and single head xml are pretty bright. I think I just need and excuse to buy a task led driver. With a daulnset up on the bar I might not even need to run it at the full 3a. Even at 2a per it would be plenty bright.

10. correction in my math - your runtime @ 3A would be about 1.6hr (1:3xmins)

If you back it down to 2A - you jump up to about 2.5hrs.

11. Keep in mind that you wont be running your light at full blast all the time, but only on descents. Riding uphill will force you to throttle down your light or your flex driver might if there's not enough heat sinking. So lets say that calculated run times will be almost double.

12. On my trails there isnt really a time that doesnt need full power. Plus when im exploring new places I dont want to be thinking about changin brightness. Theres a ton of rocks and possible crevises (sp?) and large rocky drops.

I plan on using some good heatsinks (I work in audio video and old amps have billet heatsinks)

So am I right in thinking with another pack in parallel shoud double run time ( in theory of course) or is 8 cells to much?

13. If you put packs in parallel there can be 8, 12, 24, ...... 1200 batteries as long as they don't exceed drivers maximum input.

14. Thanks. My wife isnt going to be pleased with me

15. Originally Posted by machine4321
Thanks. My wife isnt going to be pleased with me
been there - done that. Even got re-informed of it this week. :-)

Also - I will dim when I'm riding behind someone relatively close, especially if they don't have as much light as do, to avoid throwing heavy shadows directly in front of them. You just have to trust their lines at that point.

16. When you say pack in parallel, I'm assuming you mean to add a whole additional pack connected in parallel. It's fine to do that but you really need to charge each pack individually. You could also build a 4s2p pack where there are 4 sets of parallel connected cells all in series within the pack sharing a single protection PCB. Then you could charge and discharge that as a single pack.

17. As of right now, I have 2 chargers that charge 2 cells each. It takes for ever to charge the 8 i have now. About 9 hours for 4. I will definitly look into making it work as a single charge.

Thanks

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