LED lights on AC power

[RaWarrior]

Here's a question for anyone in the know about LED technology.

I know that LED lights will work off a AC circuit...when the rectifier on my minibike died, I got a generic AC regulator and the LED tail light worked OK, though at slow engine RPMs it noticeably flickered. Since LEDs are a diode, they only "use" half the AC pulse when it's on the "positive" wave, or at least that's what I figured to explain the flicking that became noticeable at idle.

Question is....is it "safe" to run LEDs designed for 12v DC on 12v AC for any length of time? I only had that taillight on AC for maybe a minute. It

Reason being my Odyssey is missing it's headlight, and only has a 60w regulated AC output (measures about 15v AC no load). I'd like to use dual lights in the front and found a pair of LED driving lights at advance auto for $20 I'd like to use(everything else is dual 55w, too much load), while the pair of LED lamps said only took 5w for both. I'm not too concerned if they're not ultra bright since I'm not going to use it at night real often but I'd like to have some sort of lighting.

So is there any detriment to trying to "force" current constantly the wrong way across a diode? Will it eventually ruin it?

 

[98Redlne]

You should be ok as long as the voltage on the negative half cycle does not exceed the reverse breakdown voltage of the LEDs. What that breakdown voltage is really depends on the specific LED but I believe that it should be sufficiently high to preclude your -12V voltage from killing it.

The other thing that you could do, relatively cheaply, is to add a rectifier to the line that drives the headlights. This would give you +12V on both the positive and negative AC half cycles. It would also double the light output of the units as the lights would be on for 2x more time. This would still give some flicker at the lower RPMs, however it would be 2X as fast as what you currently see.

Most electronic stores should have full wave bridge rectifiers. I took a look and Radio Shack has a 25A, 50V rectifier for about $3.50 (model: 276-1185).

 

[RaWarrior]

Thanks, think that's what I'll do. I assume the rectifier bolts to ground and accepts the "raw" 12V hot line, and outputs a DC line? Should be simple....

 

[Fastatv]

Ra, the flickering is probably also caused by lack of steady 12 vdc.......no battery.......like your Blaster.

 

[satariel666]

One of posible solutions.

 

[RaWarrior]

Ra, the flickering is probably also caused by lack of steady 12 vdc.......no battery.......like your Blaster.

While I'm sure the headlight on the Blaster did technically "flicker", it was never noticeable. It just got real dim at idle but didn't seem to pulse.

I picked up the bridge rectifier from radio shack ($3.43 after tax), an the $23 set of LED driving lights.

Now I just have to get the stupid motor running right. It ran great for about 2 minutes, just long enough for me to go ripping up the road about a mile and then shit the bed, forcing me to push it back home. Now it's being a real PITA to start.

 

[Fastatv]

While I'm sure the headlight on the Blaster did technically "flicker", it was never noticeable. It just got real dim at idle but didn't seem to pulse.

I picked up the bridge rectifier from radio shack ($3.43 after tax), an the $23 set of LED driving lights.

Now I just have to get the stupid motor running right. It ran great for about 2 minutes, just long enough for me to go ripping up the road about a mile and then shit the bed, forcing me to push it back home. Now it's being a real PITA to start.

$3.43....so inexpensive unk:. Do you have a fuel filter installed? Is the tank metal or plastic? Anyway, let us know what the "ailment" was....I'm curious.

 

[RaWarrior]

Turned out to be a combo of carb issues. First, the float was set way too high, so the bowl would get almost empty before it started to allow flow again. That was simple. Second....this carb had the little "cup" around the main jet that I suspect was getting airlocked. Tossed the cup and suddenly it's much easier to start.
Third, this carb had a #150 main jet, which seemed about right for a 250cc 2 stroke, my 200cc blaster with a similar carb ran great on a 145. But with the odyssey motor, it was running really, really fat. Swapped in a #120, which was the jet size in the original carb. Running much better now and goes WOT no problem without bogging out and dying.

I brought it to work, and using some various tools and a bit of math, created a TDC mark on the case, and timing marks for 16,20,and 25* bTDC. Shot the timing and found it to idle at around 16* before, and from just off idle to WOT, at around 20* before. I'd heard the flywheel key tends to shear on these motors and screws up the timing, but that seems pretty much on-par for a 2-stroke like this. But the carb was definitely the problem in this case.

 

[johnpclynch]

LED lights on 12V AC? Make your own rectifier with 4 diodes