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/diy/ - Do-It-Yourself

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Anonymous 05/26/14(Mon)02:24 UTC+1 No.643367 Report

Hey /diy/, I posted a little while ago about a simple light switch circuit. After I got bored of turning it on and off I disassembled it for the materials, bought some more stuff and switches and this is what I have planned next.

The goal is to have a single pull switch to turn on the circuit and then a 3 way single pull switch to alternate between a 12v bulb and 3 christmas lights bulbs that I plucked out of a strand that I have.

The power is coming out of a 9v battery, I know that the 12v should be dim and the 3 xmas lights bright. I built the circuit in an app and got the following current measurements but I do know the resistance of the wire or really anything inside the circuit.

I can calculate the resistance of the bulb, the switches and the battery pretty easy I think but without the the resistance of the wire I'm not sure how accurate everything will be. I'm also trying to figure out how many volts will be running through the 3 xmas lights, though that isn't necessary, I'm just trying to estimate and see how accurate it all is.

Any information/insight is appreciated. I'm also looking for a program to build circuits in to see if they will actually work and to play around with, everything I've found seems to be pretty limited unless you buy a full version.
Anonymous 05/26/14(Mon)03:55 UTC+1 No.643397 Report

wires and switches have essentially zero resistance. your current measurements are useless. a 40W 12V bulb will have a resistance around of 3.3 ohms. so, using ohm's law 9V / 3.3 ohms = 2.7A.

your 9V battery will probably let you have 1A max, but it will die within minutes.

as for the x-mas lights, they'll probably have a resistance around 6 ohms each, so 9V / 18ohms = 0.5A, and power dissipation = 3V * 0.5A = 1.5W

as for circuit simulators, you can download Tina or anything you see on this list: http://en.wikipedia.org/wiki/List_of_free_electronics_circuit_simulators
Anonymous 05/26/14(Mon)05:00 UTC+1 No.643417 Report

>wires and switches have zero resistance
That solves the wire problem but the switches say 120v and 15A, wouldn't you be able to calculate a resistance higher than zero out of that or is that just what the switch can handle?

>but it will die within minutes.
I learned that from my last basic light switch circuit which is kind of disappointing as they aren't exactly cheap to keep using at that rate.
Some people here have suggested a transformer but it looks like quite a difficult project with a lot of theory behind it I don't fully understand.

So far though I've managed to wire up the 12v bulb to both switches. Connecting two more wires to the xmas lights and both lights back to the battery and it's done.

Definitetaly thought this would be a tougher project that this. I'll have to check the links in the sticky for something a little more complicated.
Anonymous 05/26/14(Mon)05:04 UTC+1 No.643421 Report

>is that just what the switch can handle?
>Some people here have suggested a transformer but it looks like quite a difficult project
or you could just buy one, they're not expensive.
Anonymous 05/26/14(Mon)05:33 UTC+1 No.643428 Report

What fun is there in buying one?
Anonymous 05/26/14(Mon)06:38 UTC+1 No.643441 Report

Anyway all done.
Although the center xmas light out, it does work. Wire slipped loose due to my lack of tools available to make clean tidy connections.
Anonymous 05/26/14(Mon)06:40 UTC+1 No.643443 Report

The 9V is already dying.
Anonymous 05/26/14(Mon)06:49 UTC+1 No.643446 Report

gnucap or spice
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