# need lamp help 36 volt LED or ????

Discussion in 'The Projects Forum' started by the13bats, Feb 25, 2013.

1. ### the13bats Thread Starter New Member

Feb 25, 2013
1
0
I can't seem to find a forum to get the help I need perhaps someone here can shine some light, ( No pun intended )
I do know basic wiring, I redo cars, cycles and work on different project, but that is where it ends.

What I am up against is an old Japanese pinball machine, it has a "matrix" in the center with 16 small incandescent lamps these lamps light up for different scores etc,
When I put a volt meter to the wires for the bulbs I get 35-36 volts direct current.
I can't find a bulb in 36V that will work, the old bulbs that do work are about the size of a small pinto bean with wire leads.
They look something like this http://www.amazon.com/2185-Mini-Indicator-Lamp-Terminal/dp/B005382HRS
But these are too low a voltage.

So I thought lets get modern and use LEDS but then when I was using resistor calculators on the net they say that 36v is too much that the resistor will get too hot.

If I run the 28v incandescent lamps as above it would be too bright and get too hot can it be wired with a resistor to run off 36v?
If so what is the easiest way to determine what resistor to use?
Also should I run a diode too?

I just need some options on how to get my lamps working again,
Many thanks!
Cheers,
P.

2. ### Babber New Member

Apr 19, 2011
9
0
A simple calculation to know what resistor you could use to run a 28V lamp from the 36V source would be to know how much current the bulb needs to operate. The above example is 0.04A and at 26V, the resistor in series would need to drop 8V. Power dissipated in the resistor would then be P=IV, 0.04A*8V = 0.32Watts. At 0.04A the resistor necessary would be V=IR -> R = V/I, 8V/0.04A = 200 ohms. I would try a 1Watt resistor to be sure the power rating is high enough, but a 1/2 Watt would certainly be okay. You'll need a resistor for each bulb.

Another option would be to find a DC-DC Converter to drop the 36V down to something on the order of a few volts for driving LED's.

Hope that helps.

Apr 28, 2012
3,682
491
4. ### #12 Expert

Nov 30, 2010
18,076
9,678
BS.

The resistors might get too hot for that calculator, but ve haff vays to deal mit deese tings.

A typical, small LED will max out at .02 amps and 3 or 4 volts.
36V-3V=33V
33V/.02Amps = 1650 ohms
Try a "standard" 1800 ohm resistor:
P= 33^2/1800
P= .605 watts
A one watt resistor will get pretty warm
A 2 watt resistor will handle this without breaking a sweat.

5. ### takao21203 AAC Fanatic!

Apr 28, 2012
3,682
491
You don't have to use them at 20mA, likely will be too bright.
Use resistors in parallel if they get too hot also is a solution.
Or screw them to the enclosure somehow with a piece of metal pushing them on the enclosure (if you have such things around).