# LEDs for high impact environment

Discussion in 'Electronic Basics' started by SR, May 12, 2004.

1. ### SRGuest

Hi,

Looking to use LEDs as decorating lights inside clear acrylic music drums.
Will these stand up to the beating? . I was thinking of mounting them in
clear plastic tube about 1/4to 1/2 inch diameter , looped to fit inside the
drum, and connected in parallel (?) say 20 . What sort of power supply will
I need? could I use dry cells?

TIA,

SSR

2. ### John PopelishGuest

The LEDs are quite vibration resistance, since they are solid (chips
potted in epoxy). The only thing you might have problems with are the
connecting wires breaking off from flexing, and fine stranded wire
should make that pretty unlikely. I would connect them in series and
drive them with a single current. The exact voltage you need depends
on what color LEDs you use. Red ones drop about 1.7 volts, orange,
yellow and yellow-green ones about 2 volts and green blue or white
ones drop 3 to 3.5 volts each. The cheap way to control the current
is to have a DC supply that is 20 to 30% higher than the drop of the
LEDs and waste the extra voltage with a series resistor. For
instance, if you connected 20 3 volt, 20 milliamp green LEDs in series
(60 volts total) you might use a 75 volt DC supply with a 750 ohm 1/2
watt resistor in series. Or you could divide them into two strings of
10, (30 volts needed to light the LEDs) and use a 40 volt supply with
a 510 ohm 1/2 watt resistor in series with each string.

If you connect them in parallel, you need to add a small resistor in
series with each one to help them share current better. Otherwise the
one that takes the least voltage to light will hog all the current and
burn out. If you were using green LEDs you might use a 5 volt supply
and add a 100 ohm 1/4 watt resistor in series with each LED. This
passes about .02 amps to each LED but 20 in parallel would require a
supply capable of delivering 20 * .02 = .4 amperes. But small DC
receptacle mounted supplies (wall warts) in this range are available
for 5 to 10 dollars.

3. ### SRGuest

All the info I needed in one reply - Well thank you Sir, very much
appreciated.

Gotta love the internet for enabling the BEST of humanity to cut through!

SSR