If you wire enough XM-L2’s together is it possible to run them off of 110v AC? If so how many? Or do you absolutely have to have a DC converter/driver?
Could an in-line bias resistor be used with AC and XM-L2’s?
I’ve got tons of older XM-L2’s that I won’t be using to upgrade lights with and was curious to see if I could use them with AC without having to spend a bunch of money on a specific driver for them. Any help on this would be greatly appreciated.
DC diodes typically don’t like AC, they effectively switch on/off in line with the frequency and this might kill them? I used a grow light (led) on 12V AC instead of DC and the array was dead in no time. current was controlled, they just didn’t like AC.
However, that wasn’t a XML so I would also like to hear more views on this.
No, LEDs only resist very little backwards voltage and will die instantly if you exceed it.
You need to use a driver that runs on AC or use an AC DC converter.
I was reading this on the digi key site and wondered if there was a way around this problem.
“A conventional form of direct AC-driven LED system uses two strings of LEDs, one powered by the negative side of the AC sine wave, the other by the positive. The strings of LEDs are able to deal with the high voltage because the combined voltage drop across all the devices is equal to the supply voltage. A bias resistor limits the input current and the strings are alternately energized and de-energized at the 50 or 60 Hz frequency of the AC mains power.
Another approach is a single string of LEDs in series with a bias resistor attached to the output of a full-wave diode bridge”
https://www.digikey.com/en/articles/techzone/2013/sep/multi-junction-leds-handle-direct-ac-supply
Thanks and that was what I was afraid of but I wondered if there was a way around this.
Use a 4 way recifier and a capacitor you get 160V DC 3.6V per LED so around 44LEDs
more for lower current
Thanks
Going the bridge rectifier + capacitor route? Given the steep voltage to current ratios leds exhibit flickering would be a problem unless an insanely big capacitor is used and an equally insane inductor too (probably, don't really know).
I have met with this before:
Related article: Running LEDs from an AC supply
Cheers 
Thanks for the link.
looks like I’ll have to get a driver if I’m going to do it.
I’ve seen cheap LED light strings do it with simple electronics (rectifier + capacitor). And yes, they do flicker, but it’s not that noticeable to the eye.
18sixfifty, may we know more setup details?
Generic led drivers are plentiful, cheap, reliable and readily available. Most common units are rated at 1W per series stage at ≈300mA (referenced to a relatively high Vf of ≈3.33V), with other driving currents common also. On top of this there should be no problem setting them in parallel for combined current output.
If, for example, you aim to drive 16 emitters at ≈1.2-1.4A that could be done:
I personally use one caseless generic 18-36W 300mA drivers in my kitchen lamp with great satisfaction. 
Cheers 
Originally posted on Fri, 03/09/2018 - 04:29. Edited for a grammar fix.
Thanks, I didn’t realize there were any cheap drivers for these. I’m planning on building a shop light is going under a shelf that is about 8 feet long the brighter the better, without over-driving the emitters.
Do you have 72 spare xml’s? 
Very easy experiment:
36 xml’s in series with another 36 antiparallel?
36 x 3V = 108V . 110V - 108V = 2V / 1.3A = 1.53 Ohm resistor to limit the current on each string.
It is the same as in the digi key article. One string will be powered by one half of the sinus and the other string by the other half of the sinus.
If you want to make sure the leds survive the reversed voltage you could put a diode (1n4007 for example) in each led string.
In that case the resistor needs te be a bit lower: 108V from the leds +1.1V from the diode = 109.1V. 110V - 109.1V = 0.9V / 1.3A = 0.7 Ohm.
I have way more than that if I include XML T6’s.
It should work, I have no idea how good and for how long. :smiling_imp:
These are similar to the driver I am using in my kitchen lamp, I bought it more than 2 years ago, paid $5.27 by the time:
The voltage output in these drivers ramps up quite high, I can remember someone said 150+V in a similar unit from FastTech long ago. Its lowest output should be just below 70V or maybe 60V. Attach an independent switch at each one's input to achieve variable driving current in 260-300mA steps. Aditionally, by setting a color emitter (red, green, blue, amber… etc XP-E2s for example) in series at each driver's output before going in parallel, such emitter will behave as a “working driver” pilot. 
Cheers ^:)
Very nice, thanks. That looks pretty good.
That’s what LED Christmas lights are. 2 inverse-parallel strings of LEDs, with distributed resistance (to keep any one resistor from getting fiendishly hot).
They also have a horrendous flicker, a strobing 120Hz that’s literally strobing, as in mostly off but with bright brief flashes of light at the peaks of the AC input.
Hmmm. Tons, huh? :laughing:
No your missing the chance to do an off grid shop light. rig to solar panel and small power wall. (use up some of those marginal 18650 cells)