View Full Version : Powering LEDs with AC?

10-09-2010, 03:18 PM
Will 12V AC damage LED lighting that is set up for 12V DC? I could put some additional diodes in the circuit to rectify the AC to DC but do I need to?

10-09-2010, 04:15 PM
don't know but it would be cool to know. Personally I don't think so since they use household xmas lights on the sailboats for the July 4th parade. They plug it into their batteries.

10-09-2010, 04:30 PM
almost all boats have ac-dc converters.

Uncle Ben
10-09-2010, 04:31 PM
LED's ARE Light Emitting Diodes! Being diodes, current can only flow one way through them thus they will create a DC circuit. If current is reversed they simply will not light and current cannot flow.

10-09-2010, 05:29 PM
so would they just flash at 60 Hz? i guess so huh?

Uncle Ben
10-09-2010, 05:50 PM
so would they just flash at 60 Hz? i guess so huh?

My guess would be the power supply is fluctuating. Not sure how you would clean that up other than a resistor and lower current LEDS. Someone "brighter" than I with micro electronics would know that answer.

10-09-2010, 08:59 PM
Well, it seems to work so far. I know LEDs are diodes but sometimes the simple solution isn't always the best so I thought I'd ask.

I'm not sure what frequency its running at but there doesn't seem to be a noticeable flicker. Although, I'm wondering if I put a bridge rectifier on it if it would be brighter.

10-09-2010, 09:55 PM
what is "it"?

10-09-2010, 09:57 PM
what is "it"?

X2!!!!!! (http://ilike.myspacecdn.com/play#Faith+No+More:Epic:116410:s299337.12757310.56513.0.2.279%2Cstd_41071a07309346ffb67ce818d1e5ea76)

10-10-2010, 08:52 AM
You are right that the LED is only going to conduct for at most 50% of the time. During the time it's conducting the LED on AC is going to be on average 71% as bright as the DC (the RMS of the AC voltage) and it's only going to be as bright or brighter for about 30% of the time. Although a lot of this depends on the LED's characteristics (they only turn on above a certain forward voltage, not simply above 0V). It's possible that the LED will only turn on for a very small part of the cycle and if so it will seem very dim compared to DC. Over time the LED on AC will provide about 15%-35% of the light as it might on DC.

Also remember that in the negative 1/2 cycle the LED is dropping all the voltage, so make sure you account for that. It's possible to exceed the reverse voltage rating of the junction. So you should put a reversed diode that bypasses the LED on the negative cycle. If you have the space you could use a second LED oriented the other way so that one or the other lights on each cycle. The combination of those two would be pretty close in brightness to a single LED on DC.

If this is just a wall wart, the frequency is 60Hz. You probably won't notice the flicker normally. But your eyes do tend to average the available light as the LED switches on and off. IOW, if you had a square wave with 50% duty cycle the LED would conduct exactly 50% of the time and would seem pretty much 50% as bright. This is the principle behind LED PWM dimmers.

10-10-2010, 04:44 PM
It is a KTM 450EXC - a birthday present to myself. I had no idea that the lighting on these things was AC until I went to modify the wiring harness. The front lighting is incandecent and the tail is LED. Everything is working pretty well but I've got a bit of a miss at idle. I think I'll learn about KTM carbs this week.

I took a ride up Sunshine Canyon to Switzerland trail for a shakedown run. Despite a bit of drizzle and some flurries, it was great. The burnt area near Sunshine was a bit spooky though.

10-11-2010, 12:17 PM
Sweet dude. That's a great bike!

10-11-2010, 01:39 PM
Cool, welcome to the orange world :)

ktmtalk.com will be your friend.

10-11-2010, 03:16 PM
Super sweet!!!!

That's awesome Bruce!!!

10-11-2010, 04:23 PM
Nice Bruce. Hit me up anytime you want to ride.

MMmmm that orange Kool-Aid sure is good.

I'm hooked on ADV rider Rocky's regional forum

'07 KTM 450XCW