By mistake I connected the trustfire TR-3T6 4.8A driver to 3*XML wired in series. Battery configuration : 3x18650 in series.
This is a 4,8A driver and was designed to run 3 leds wired in paralel at a maximum of 1,6A for every led.
Luckily I quickly realized the mistake and powered off the flashlight after ~10 seconds or so.
The question is what happened with the voltage and the amperage? Did I compromise the leds or the driver itself ?
Thank you.
Three XM-Ls in series will need at least 9 volts to even get juice flowing. Hook it up the proper way and try it out. If it’s a real 3T6, the driver will be putting out that amperage at around 3.5-3.7v I imagine. And if it’s a real 3T6 then 4.8A divided among three XM-L’s isn’t going to be very bright. 0:) Let’s say current was still flowing, a XM-L can take five amps without blowing up.
Yes, it was the real trustfire 3T6 driver.
Interesting, first time I tested it with only 2*18650 in series and the leds barely turned on. This driver is known to function properly with 2 cells when connected to 3 parallel xml`s.
The question is what amperage and voltage it was forced to deliver when connected to 3 xml`s in series instead of parallel .
It's a buck driver, and input voltage (with 3 cells, though not when you tested with only two, which explains the very low output) was still higher than output voltage even with the LEDs in series. Not as much headroom though, with the cells completely or nearly flat it would drop out of regulation and start to dim, unlike what it would do with LEDs in parallel. Even if it freaked out and went direct drive, 3 LEDs in series run by 3 cells in series is still pretty safe, essentially no different than a single cell/single LED.
No problemo.
Just rework wiring and fire it up again. Which driver do you have? Picture? Serial number? There are some different 3T6 drivers out there…
Thanks for the answers guys !
Werner, I hope the leds are ok because it was much brighter than with leds wired in paralel.
Here are some pictures with the driver:
Looks like a standard “old” 3T6 driver…these are normally very reliable and easy to mod. Your sensing resistors look a bit dirty soldered(second picture), have you modified it?
I never used it with 3 series LEDs so I don’t know exactly what it does but I guess like the others that it will work like a charm if you install the wires in parallel. XMLs can handle 6A with no problem and if it was just a short time it is less problem.
Anyway you will find out if you try.
Most likely it was running less than the driver's rated output amps - if you assume each LED's Vf to be around 3.6v at 4.8A, that would mean the series string would need 10.8v and it's likely the voltage sag and losses through the springs and whatnot wouldn't let the input voltage stay that high. Then you also have to take into account any losses through the driver. So, effectively, the cells couldn't supply enough to let the driver hit its rated output, which means it was about the same as what it would do in direct drive, the only regulation coming from the cells themselves.
Werner, no, I did not mod the driver, it is exactly how it came out of a TR-J19 flashlight. It measured on high 1,6A, this is exactly as labeled, a total of 4,8A.
I will not rewire the leds because they are ready to receive a DRY driver soon. I will test it again beacause I want to install this driver in my scooter to power 2 C8 heads for my headlight.
comfychair, I have made a very quick tailcap test and the result was 2,8A(3cells), that is a total of 8,4A !
I do not know if in reality the tailcap reading is what the leds are receiving.
Convert to watts to get numbers that mean something. Multiplying tailcap amps by the number of cells is a shortcut that only works when the driver is truly in buck mode, which this one isn't. Direct drive (or with linear/CC drivers), amps is amps because the voltage in is the same as (well, close to) voltage out. Any difference between input & output voltage is eaten by the driver.
So, to sum it up, in my case the 2,8A tailcap reading(3cell series) means that every led was getting 3,7V at ~0,9A . Am I right ?
What`s interesting is that the light was still very bright.
If batteries and LEDs are all in series, than there is just one wire connecting all of them. Understand?
So if there is current flowing than all current flows through this on wire. Understand?
If so all parts see the same current, because everything what flows in at the beginning has to flow through everything. there can’t be on one spot more current or less.
Series connection everywhere same current.
Parallel connection everywhere same voltage.
—————-
To calculate that, use the power as comfy mentioned.
11V*2.8A=31W. Input power
20% losses 24W
So the LEDs are driven with about 8W each which is not to much, as these are kind of 10W LEDs.
But it will be bright.
LEDs were seeing 2.6-2.8A each but the regulation/runtime would be very poor, as opposed to the stock parallel arrangement that had the 4.8A divided amongst the three.
Brighter at the start with fresh batteries, yes, but as the batteries drain the voltage will fall and that means the current falls as well, continuously. Unlike the original series cells/parallel LEDs, where even with all cells fully drained (3v each, total 9v input) the driver only has to output ~3.3v for the LEDs to pass the full 1.6A ea/4.8A total (easy to get 3.3 volts out of 9v, impossible to get 10.2v out of 9v since it isn't a boost driver). In the original setup it would output the full rated amps all the way from start to finish.
Thanks for the clarification guys !