christmas lights - sealing connections

[Marc]

Make sure the LEDs don't overheat from getting twice as much average
current! But if nothing goes wrong, they will not only not flicker but
they will also be brighter.

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).

 

[Steve Kraus]

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.

 

[Andrew Rossmann]

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

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.

 

[Art Todesco]

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

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.

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.

 

[Steve Kraus]

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.

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.

 

[Don Klipstein]

I'm going to say one word, and you decide if you still like your theory.

Persistence.

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 ([email protected])

 

[Don Klipstein]

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.

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.

If not, plugging the string into a lamp dimmer would cut down the energy, if
the LEDs are getting too bright (and hot).

- Don Klipstein ([email protected])

 

[Don Klipstein]

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 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 ([email protected])

 

[Don Klipstein]

Andrew Rossmann wrote:
Yes, with the full wave rectifier you will see very short off period (when
waving thelamp). With half wave, you see the 50% on and 50% off.

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 ([email protected])