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12V illum. switch on 24V system?

Woodsplinter

Woodsplinter

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Can anybody tell me how I can use 12V illuminated switches on my 24V deuce?
Using a resistor, etc?

Or can you point me to a vendor who sells 24V illuminated toggle switches?

I want to use them to turn on exterior LED floodlights, etc.

Thanks!
 
VPed

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If the switch has a ground terminal that is insulated from the switch itself, that is the ground for the light. you can put an appropriate sized resistor between that terminal and the ground point to drop voltage to the bulb in the switch. If the switch has no separate ground terminal, or the ground terminal it does have shows continuity to the switch housing, you cannot use this solution.
 
porkysplace

porkysplace

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Woodsplinter said:
Can anybody tell me how I can use 12V illuminated switches on my 24V deuce?
Using a resistor, etc?

Or can you point me to a vendor who sells 24V illuminated toggle switches?

I want to use them to turn on exterior LED floodlights, etc.

Thanks!
Click to expand...
A google search of " 24 volt illuminated toggle switch" brought up many results .
this being one of them ;
[h=3]24v Rocker Switch - Alibaba[/h]www.alibaba.com › ... › switch › rocker switch
 
Warthog

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Are the exterior lights 24v or 12v? Are you running the lights thru the switch or are you using the switch to control the a relay?
 
Woodsplinter

Woodsplinter

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Thanks everybody!

Vped- how do I determine the correct resistor size?

Porky- I have googled this many times and when you actually start researching the results you find that 12 volt switches are actually what is being returned. I think Alibaba requires dealing with Vendors in China and I can't use rocker switches because I don't want to cut square holes in the dash. Don't have room below the dash because of the a/c.

Warthog- the lights are 24V and I'm controlling them directly through the switch.
 
Woodsplinter

Woodsplinter

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Warthog- thanks for checking. I saw that once before. A little too pricey @ $23.46 and it comes with a 14V bulb- don't know what kind of bulb or if it could be changed.
 
VPed

VPed

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Woodsplinter said:
Thanks everybody!

Vped- how do I determine the correct resistor size
Click to expand...
Unfortunately, I do not know without knowing what the illumination in the switch consumes but if you find the wattage specified somewhere, you can use Ohm's Law calculators online to find the required resistance. If the illumination is an incandescent bulb, just read the bulbs resistance with an ohm-meter and get a similar resistance resistor. You would read the bulb's resistance by connecting the ohm-meter to the ground terminal and the switched terminal (not the power-in terminal).
 
Woodsplinter

Woodsplinter

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VPed said:
Unfortunately, I do not know without knowing what the illumination in the switch consumes but if you find the wattage specified somewhere, you can use Ohm's Law calculators online to find the required resistance. If the illumination is an incandescent bulb, just read the bulbs resistance with an ohm-meter and get a similar resistance resistor. You would read the bulb's resistance by connecting the ohm-meter to the ground terminal and the switched terminal (not the power-in terminal).
Click to expand...
OK, thanks- I'll check that out!
 
tim292stro

tim292stro

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Woodsplinter said:
...Vped- how do I determine the correct resistor size?...
Click to expand...
VPed said:
...If the illumination is an incandescent bulb, just read the bulbs resistance with an ohm-meter and get a similar resistance resistor...
Click to expand...
This won't work for incandescent. A filament light bulb is a Positive Temperature Coefficient Resistor, meaning it starts at nearly zero resistance when cool and then climbs in resistance as it gets warmer, until it reaches the designed equilibrium power for the voltage. If it's incandescent, you need the wattage of the bulb, then divide that by the voltage - that will give you the current of the light bulb at design rating. Then use Ohm's law to figure out what resistor you need in order to "consume" the extra voltage of the system over the design voltage of the incandescent bulb:

28.8 (alternator running)
-14V (light bulb)
=14.8V

14.8V / (lamp current) = RequiredResistance

Then take the resistor's voltage (14.8 here) tie the current to get the power the resistor needs to be rated for, example:

1watt 12v lamp = 83.333miliamps (0.083333Amps)
28.8 - 12 = 16.8V for the resistor to "consume"
16.8 / 0.083333 = 201.6Ohms

Look up a standard resistor value that is equal or just above that value (less resistance = less voltage consumption and will over-volt your bulb). I use 5% or 10% because they are cheaper and more common...

Closest one is 220 Ohm.

16.8 * 83.333miliamps = 1.4Watts

Again pick a resistor that is rated equal (bare minimum) or higher power (better) that this value. Resistors turn energy directly into heat, the power rating is what power the resistor can safely dissipate into the environment around it - you can imagine what happens if you undersize this (think electrical fire).

I your switch has an LED inside it, try taking one apart, they usually already have a current limiting resistor, and you can just put in a different one and keep it clean. Most small LEDs are good for 20miliamps, and any range from 15-20 will work fine - too little and it may have a color shift or not light, too much and you will have a color shift as it overheats and it'll burn out quickly.
 
Woodsplinter

Woodsplinter

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Tim292stro- I took a switch apart but no resistor inside. Once I have the correct resistor, how do I wire it in? The terminals on the switches are labeled "power", "acc", "ground".
 
Woodsplinter

Woodsplinter

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Well, to finish this thread, I never did find a 24V toggle switch. Lots of 12V or 24V rockers witches. :-(.
So, I happened to stop at Radio Shack for some other parts and discovered the clerk was a retired electrical engineer! :)
Wow, I couldn't believe it- so I asked him how to wire a resistor to a 12V switch to use it with 24 volts. I grabbed a switch just like one I had at home and wanted to use.

He looked at the specs on the switch, did some calculations, and determined a 1K ohm, 1W resistor should work.

I went home, wired up the switch connecting one end of the resistor to the ground terminal of the switch and the other end of the resistor to a metal ground on my dash panel. It worked! Using a voltmeter I measured just under 12 volts to the led in the switch- perfect!

I wish I had known about this a long time ago- well, live & learn.
 
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