Low voltage Dc lights

[ClintOHenry]

I got hold of some 3volt lights and want to use them but my light circuit is 12v. How can I make them work?

 

[Greg@mnrr]

Use a resistor on each lamp or wire four lamps in series to handle the 12 volts.

I run my lighting at 10 volts to prolong the life of the lamps.

 

[ClintOHenry]

what size resister is needed?

 

[Greg@mnrr]

I looked for my resistor sizing chart, but couldn't locate it. The size of the resistor will determine the brightness of the lamp. I would first try a 650 ohm 1/4 watt to see if the lamp is bright enough. Resistors are cheap so buy a selection.

If it were me, I'll buy some 14 volt lamps and operate them at 12 volts or less and forget about the hassle of installing resistors. I know of people who used lamps from Christmas tree light strings and their efforts exceeded the results.

Maybe one of the other readers has a resistor chart handy that they could post.

Thanks.

Greg

 

[CSX Robert]

what size resister is needed?

Depends on how much current the lamp draws. The equation is: (Vs - Vl) / I, where Vs=supply voltage, Vl = lamp voltage, and I = current draw of lamp.

For example, if the lamp draws 40 ma then (12 - 3) / .04 = 225 ohms. Since 220 ohms is not a standard resistor value, you would want the next size up, which is 240. This value is not set in stone, you can increase the resistance if the bulb is too bright or you want to extend the life of the bulb; however, make sure you do not go below the calculated value unless you want to shorten the bulbs life dramatically.

 

[montanan]

I'm like you Greg. I use an old MRC power pack and also turn the voltage down to about 8 or 9 volts. My lights (12 volts) have been in for about 15 years and so far not a single one has burned out. If you can get your hands on an old power pack, turn the DC voltage to the tracks down to 2 or three volts.

 

[trailrider]

I got hold of some 3volt lights and want to use them but my light circuit is 12v. How can I make them work?

Although it will make them rather dim, you could connect four or five of them in series (end-to-end). The only other problem besides dim light is that if one burns out, they all go out! That is how the old-time electric Christmas tree lights were wired.

Merry Christmas!