# fixture switches



## ship (Feb 5, 2008)

So I have this Mars ‘88 light I’m wiring up for the big boss. It is 12v DC using a 50w discontinued incandescent lamp. Bought the 100w transformer to compensate for the wiggle light motor amperage added to the 50w lamp and initially a McMaster Carr #7157K24 LED tipped toggle switch that changes colors between red and green. Gotta be cool if doing something for the big boss. What I didn’t read so well was the LED is 2.1MA at 2.1VDC. I than had the wacky idea of doing a mercury tilt switch #7689K52 and installing it on a spring. Spent hours in converting OD of the spring with wire size to ID of the .052" Dia switch. Concept was go boingie boingie to turn it on and reverse that in turning it off. Totally cool concept I was thinking. Finally after various test springs bought which were either too hard or soft, found one at home that’s part of a flaring tool which would work perfectly once cut to length. But in the end, I believe this switch is too exotic in concept so I’ll save the mercury switch for something else - who knows in going boingie boingie. I finally settled upon a switch from Allied Electronics that is a bit more simple but still cool but without being alien. This all given to house the transformer, I have also been thru a number of boxes that look cool and theoretically should fit the transformer, thermal breaker and switch but none at this point have been economical enough or the right size. Lots of R&D hours and materials so far on this project. In a few days I’ll know if the next box will be sufficient in size. In the mean time, my co-hert ME (the old timer) at work had a chance to see what I was up to. (We consult each other often and even if we have different styles always agree on safety and appriciate each others opinion even if only saying “gee you really polished up that turd well.”) He was not so hot on the boingie boingie in a design sense and I took his opinion to hart in changing styles by way of look and not working so well in concept with the old style ambulance light - though he admitted it was a curious concept for a switch if not really working as well as I say it could in being cool and that’s no doubt valid in observation. He than went into explaining how I could use the initial LED switch.

Anyway, onto the questions.

1) How does this mercury switch work and would mounted on a boingie boingie spring, it be safe and within the general principles of the NEC to use that way? 

2) Would it when mounted on a spring that while it might after bent below 11 degrees and not spring all the way to the 11 degee up for off work properly when mounted on the spring? Will the solid/liquid mercury manintain the contact while springing about while between eleven degree angles or would it only work momentarially within those bounds given the bubble does not stay at that angle and in fact gets moved rapidly and shaken up after turning on?

3) And more difficult in an electronics type of way, how could one wire the above LED tipped switch for a 120v service? I was explained two different ways, one that would work, and the second that would be better.

First was a resistor installed of ____ ohms resistance installed in-line with the LED lamp. 

4) And more recommended was a resistor of ____ (same or different resistance) installed in-line again and a second one installed of ____ ohms resistance installed in parallel with the lamp.

5) Why was the second option better? 

6) Beyond this, the SPDT on/on lighted switch has five poles/terminals below it Two are for the 6A switch and of a different size, three are solder lug with two of them marked for LED lamp, the other not marked. What is the other solder pole of the switch for or would it do given there is only two poles the center and left one marked with a bracket? Read the description of the LED switch to understand why three poles.

7) The above LED switch is specified to operate under DC voltage, how does it work given AC voltage applied in these circumstances and does it effect lamp life/output if signifigant?


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## BNBSound (Feb 10, 2008)

If you want it to go boingie boingie use a toggle style momentary on switch to trip a relay. I forget the exact name of the type you want, but they turn on with a trigger voltage and stay on till they see another trigger voltage. And there's no liquid metal sloshing around so it'll work upside down and sideways.

LED's aren't sensitive to voltage within reason. The important factor is the amperage, so the limiting resistor is crucial. You can easily run an LED on 120 VAC if you use a big enough resistor that's rated for enough power dissipation. (Did it myself in the shop a week ago) The formula to figure out the dropping resistor is:

(Vsupply - Vled)/Aled
So, 120v - 2v / .02A = 5900 ohms.
Anything in the realm of 6k should work, but it will need to be a big fat 2 watt type or you'll melt it.

The difference in where you put the resistor is this. With two resistors, you're creating a voltage divider network that will provide a dropped voltage to the LED. With one resistor, it's still a voltage divider network, the internal resistance of the LED is the second resistor, so the first (only) resistor has to be fairly large. Also, keep in mind that dual color LEDs are acutally two LEDs in a single case, so you'll need a resistor for each annode or one color will blow the first time you run it. I'm not sure of the configuration of your switch, but running it off AC may light both colors at once (or close to, one LED forward biased each half of the cycle) depending on how they're connected internally in the switch casing.


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## ship (Feb 10, 2008)

Hmm, very interesting. Similar to the explination on LED I got but differing thanks.


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## superdoo (Feb 11, 2008)

If you have space, you could build a simple voltage regulator. Go here: http://hades.mech.northwestern.edu/wiki/index.php/Image:Zener_voltage_regulator.gif

You can get zener diodes that are rated to handle the amperage you'll be using. But I would recommend using the above circuit along with a voltage divider.


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