I wonder if instead of using a bridge, just put a big ol' capacitor on the LED side of the string. That could smooth out the peaks and not add any energy.
If not, plugging the string into a lamp dimmer would cut down the energy, if the LEDs are getting too bright (and hot).
-- --Marc
Yesterday I tried experimentally running one of the Forever Bright strings off a bridge rectifier, no capactitor. It seemed only slightly brighter. That's puzzling because although instantaneous brightness would stay the same having twice as many flashes per unit time ought to seem something like twice as bright.
Also, I noted an alleged 10V drop across the bridge (121V in, 111V out) but I think this may be a figment of my DMM's imagination, perhaps unable to give an accurate RMS reading of the pulsating full wave rectified DC. I guess I should dig out my analog VOM. And maybe visually compare a couple of C9's incandescent bulbs (considerably more current draw than an LED string) on either side of the rectifier.
The brightness is mainly due to a greater on-percentage. It probably depends on your sensitivity and ambient light. One easy test to see if the rectifier is working properly is to wave a bulb sideways in front of you. You should be able to see it turning on and off.
-- If there is a no_junk in my address, please REMOVE it before replying! All junk mail senders will be prosecuted to the fullest extent of the law!! http://home.att.net/~andyross
Yes, with the full wave rectifier you will see very short off period (when waving the lamp). With half wave, you see the 50% on and 50% off. I did notice a strange thing in the strings which I bought (LED Lights). The one color 70 LED string (2 series strings of
35) has the limit resistors in sockets 2,3,33,34 for the 1st half and 37,38,68,69 for the second string of 35. You can actually feel the heat on these sockets. I have them on a full wave rectifier. The multicolor sting of 35 apparently has distributed resistors in every socket as there seems to be no socket getting warm. Also, on their web site they mention that some color LEDs (white and blue) are run at higher currents than red. So, my guess is that there are resistors in each socket.
Yeah I waved two bulbs back and forth, one on a string running on AC and the other on the rectifier and it was easy to see that there were twice as many flashes on the rectifier.
Monitors have very little and TV phosphors same or not much more. Phosphor output is a fraction of peak within half a millisecond, although sometimes they have a dim afterglow that fades more slowly than that.
Try blocking all of a monitor or TV screen (CRT type of course) except for a narrow horizontal strip. Then roll your eyes up and down.
- Don Klipstein ( snipped-for-privacy@misty.com)
The capacitor will charge up to close to the peak voltage, and the LEDs will be steadily getting about 160 volts DC. That would make the average current through the LEDs even more than with a bridge rectifier and no capacitor.
- Don Klipstein ( snipped-for-privacy@misty.com)
The loss of 2 volts from the bridge rectifier may be part of the explanation. But I think a bigger part is that human vision is nonlinear, and doubling light output of a lamp does not make it look doubled.
Look at the lumens on packages of various wattages of lightbulbs. A "standard" or "soft white" 100 watt one produces close to twice the output of a 60 watt one, and that is almost twice as bright as a 40 watt one. A
100 watt lightbulb produces about 3.5-3.75 times as much light as a 40 watt one. Does it look that much brighter?- Don Klipstein ( snipped-for-privacy@misty.com)
In my experience, halfwave in an LED string has duty cycle a lot less than 50%, since much of the time the instantaneous line voltage is too low to make any current flow through the LED string at all. With fullwave, expect the duty cycle to be not that high despite being doubled (or a bit less than doubled due to voltage drop of the bridge rectifier).
- Don Klipstein ( snipped-for-privacy@misty.com)
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.