Foo - 12V DC Wiring Diagram

Need a little assistance guys. My battery for a home brew bike light setup should be arriving tomorrow and am in need of a check on my wiring setup for these lights. I've purchased a single ON/OFF/ON toggle switch to control my dual 20W lights. Thing is I want the setup to be ONE LIGHT/OFF/BOTH LIGHTS. Its been a while since I've done my electro-physics class with batteries and such so I need a check on this wiring diagram.

Some how I think this is wrong...




thanks in advance, brain has been fried lately.

The more I look at this... the more I think I'm screwed with this switch... what say ya'll smart Foo'ers

Can't help without knowing more about that switch. If the middle position is "off" and the others are like on1 and on2, then it might work.

It has 3 leads, but is it a simple on/off?

You also need to make sure the switch is spec'd to take the power source you'll be providing (e.g. Don't get a 1V switch if you'll be putting 3V from batteries into it).

You have the positive side hooked up twice. You need to cut on of the positive connections probably the one right above the switch.

Aaron:)

Assuming that is a single pole double throw switch, you are going to have either no lights or both lights. You can add either a switch to the wire connecting the positive leads on both lights and switch that for both or just one, or put a diode instead. The diode will allow the current to only flow in one direction.

I marked where I'm talking about with a red box.

Diode! That sounds like exactly what I need. Thanks! :beer:

Your circut has the light wired in series, shouldn't they get wired in paralell as per...

Yes, wire in parallel! Also, as was mentioned, in your current schematic, if you will either have both on or both off. If you want simple, you can always just add another switch.

Diode! That sounds like exactly what I need. Thanks! :beer:

A zener diode will work best for this application.

Your circut has the light wired in series, shouldn't they get wired in paralell as per...

A paralell circuit would work also, but this diagram is both lights or none. Placing a diode betwen the two lights will enable one or both lights to work.

Both a paralell and a series circuit will work. Both have their positive and negative attributes.:)

cuda2k's original circuit here does have the lights in parallel.

Every schematic on this page is parallel.

A paralell circuit would work also, but this diagram is both lights or none. Placing a diode betwen the two lights will enable one or both lights to work.

Both a paralell and a series circuit will work. Both have their positive and negative attributes.:)
Doh! <slaps forehead>

Every schematic on this page is parallel.

Bingo. We have a winner!

QUOTE=edp773]Both a paralell and a series circuit will work. Both have their positive and negative attributes.:)[/QUOTE]

If the light bulbs are LEDs then a series circuit would not work. This is because Light Emitting Diodes will only light up wired in one direction.

Bingo. We have a winner!

QUOTE=edp773]Both a paralell and a series circuit will work. Both have their positive and negative attributes.:)

If the light bulbs are LEDs then a series circuit would not work. This is because Light Emitting Diodes will only light up wired in one direction.[/QUOTE]

sorry, try again. LEDs can be wired in series, but one will be very bright and the other dim. Same with a regular bulb. Think voltage drop.

Both lights are Halogen MR16 bulbs.

If the light bulbs are LEDs then a series circuit would not work. This is because Light Emitting Diodes will only light up wired in one direction.

sorry, try again. LEDs can be wired in series, but one will be very bright and the other dim. Same with a regular bulb. Think voltage drop.[/QUOTE]

LEDs are diodes that glow. What happens when you wire a diode in backwards. There will not be enough current flow for the circuit to work, unless it is a properly working zener diode which allows no current flow in one direction.

In series, each progressive bulb will only be slightly dimmer than the bulb before it. Think of the old Christmas tree lights wired in series.

In paralell the bulbs are the same brightness as long as there are good connections between them.

Both lights are Halogen MR16 bulbs.


Wire the lights like chadasm,s wiring diagram. You will not need to worry about which direction you install the diode.

Stacey's diagram will work also, if you place the diode between the two positve sides of the bulbs.

Thanks all, just got to figure out what size diode I need. Battery is a 13.2V, 5Amp. Bulbs are both 20W.

sorry, try again. LEDs can be wired in series, but one will be very bright and the other dim. Same with a regular bulb. Think voltage drop.Nope, if both LEDs or bulbs are the same impedance/wattage, they will both be equally dim in series:

Total current through circuit is:
I = V/(R1 + R2)

Voltage-drop through 1st bulb/LED is
V1 = I*R1

Voltage-drop through 2nd bulb/LED is
V2 = I*R2

Since R1 = R2, then V1 = V2 = 0.5V or V = V1+V2

Basically the voltage-drop is 1/2 the total through each bulb/LED. Try it out yourself.


Some how I think this is wrong...Yeah, it won't work because both your lights will be on in either positions of that switch. You don't need to get so complicated with diodes and stuff, just use a DPDT switch (http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/DualLightSwitch.jpg) (with centre OFF position)...

http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/DualLightSwitch.jpg

Danno is right. If the LEDs or bulbs are the same, the voltage drop will be the same. And and DPDT switch will work if wired up correctly.

Try it out yourself.

I did DC wiring for 24 years. I believe that is enough.

I think I have showed you this before Cuda

http://www.lasertagparts.com/lightbrain/2002_twin.htm

http://www.lasertagparts.com/lightbrain/art/twin_schematic.gif

Think of the old Christmas tree lights wired in series.

If one goes out do they all go out

Jsharr - over kill perhaps.

Jsharr - over kill perhaps.
too much is never quite enough

sorry, try again. LEDs can be wired in series, but one will be very bright and the other dim. Same with a regular bulb. Think voltage drop.

LEDs are diodes that glow. What happens when you wire a diode in backwards. There will not be enough current flow for the circuit to work, unless it is a properly working zener diode which allows no current flow in one direction.

In series, each progressive bulb will only be slightly dimmer than the bulb before it. Think of the old Christmas tree lights wired in series.

In paralell the bulbs are the same brightness as long as there are good connections between them.[/QUOTE]

I was just saying that you can indeed wire the LEDs in series, but one will be bright and the other dim.

Why would one be dim?

Because they think one bulb is greedy, and they don't have a solid grasp of elementary electrical theory. (Not intended as a dig.)

I often forget how mysterious invisable energy flow can be for a lot of people. I've always had an inherent undertanding of all things physics related and I have a degree in electrical construction.

BTW, just because a diode is in a series circuit does not mean that it has to be installed backwards.

Parallel? Series? The great delta 3-phase series-parallel-resistive-capacitive-inductive alternating current with full wave rectified direct current sections?
What is your prefered circuit? Personally I just like synchronizing 3-phase alternators.

Nope, if both LEDs or bulbs are the same impedance/wattage, they will both be equally dim in series:

Total current through circuit is:
I = V/(R1 + R2)

Voltage-drop through 1st bulb/LED is
V1 = I*R1

Voltage-drop through 2nd bulb/LED is
V2 = I*R2

Since R1 = R2, then V1 = V2 = 0.5V or V = V1+V2

Basically the voltage-drop is 1/2 the total through each bulb/LED. Try it out yourself.

Yeah, it won't work because both your lights will be on in either positions of that switch. You don't need to get so complicated with diodes and stuff, just use a DPDT switch (http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/DualLightSwitch.jpg) (with centre OFF position)...

http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/DualLightSwitch.jpg


I think you neglected the threshold voltage of the led's, like any diode they have a threshold voltage you must account for

Because they think one bulb is greedy, and they don't have a solid grasp of elementary electrical theory. (Not intended as a dig.)

I often forget how mysterious invisable energy flow can be for a lot of people. I've always had an inherent undertanding of all things physics related and I have a degree in electrical construction.

BTW, just because a diode is in a series circuit does not mean that it has to be installed backwards.

Parallel? Series? The great delta 3-phase series-parallel-resistive-capacitive-inductive alternating current with full wave rectified direct current sections?
What is your prefered circuit? Personally I just like synchronizing 3-phase alternators.


Well, I think a heavy and expensive synchronized 3-phase alternator on a bike is a little overkill. I don't think I'd take the time to design a transmission line when speaker wire would suffice. :D

I think you neglected the threshold voltage of the led's, like any diode they have a threshold voltage you must account for


This thread is getting a bit too complex for the original purpose.

cuda2k, Danno's DPDT switch circuit will work just fine (assuming you get one that is rated to handle your voltage) and should be fairly cheap.

Well, I think a heavy and expensive synchronized 3-phase alternator on a bike is a little overkill. I don't think I'd take the time to design a transmission line when speaker wire would suffice. :D
You would need at least two alternators to synchronize. What is the sound of one hand clapping?

But that triggered a hugely grand idea. Which I just typed out, here in this very spot, and almost posted but decided to keep it to myself as it's good enough to patent. Hugely grand.:D

You would need at least two alternators to synchronize. What is the sound of one hand clapping?

But that triggered a hugely grand idea. Which I just typed out, here in this very spot, and almost posted but decided to keep it to myself as it's good enough to patent. Hugely grand.:D


Ok, so he connects the alternator to the socket on the wall inside his bedroom, synchronizes it with the power plant in Timbuktu, connects his bike lights to the alternator using some very small, but brilliantly designed microwave antennae... He wasn't asking for people to show off their electrical knowledge, he was just asking for a little help.

Now if you really came up with a hugely grand idea, don't be greedy and keep it to yourself making millions of dollars, share it, but do so on another thread. :p

I think you neglected the threshold voltage of the led's, like any diode they have a threshold voltage you must account forYes, Vf is typically 1.7-3.5v for LEDs, as long as you have that minimum voltage, LEDs are a simple resistive load on a DC circuit. Operating amperage is around 17-25ma so you'd want to have the proper ballast resistor to limit current. In the OP's case with 12v power, you can run one LED to 4 or 6 LEDs in series provided you limit current to correct ranges. The LEDs will end up at the same brightness at 20ma regardless if you've connected in series or parallel.

And the mistaken assumption is that the very first one gets the most power. What they're forgetting is that the ground side is no longer pure ground due the successive resistive loads in a series circuit. It's like a waterfall, instead of falling from 12ft down to 0ft, the water(electrons) are falling in steps from 12ft down to 6ft, then from 6ft down to 0ft like volts. Each 6v drop across the bulb/LED burns off a certain amount of power P=VI and both bulbs/LED ends up getting the same power if they're identical bulbs/LEDs.

Another way to think about this is to substitute the 2nd bulb/LED with a resistor of the same impedance. Obviously with the resistor in place, the bulb will be dimmer. However, does it matter if the resistor came before or after the bulb? Nope, not one bit, try it out yourselves... :)


In case the OP can't figure out my wiring-diagram, here's how you'd wire up the switch, simple really:

http://i42.photobucket.com/albums/e346/DannoXYZ/Cycling/DualLightSwitch-1.jpg

Do to the thresh hold voltage, does one need a special ohm-meter for testing the resistance of diodes? Or would it be best just to hook up a circuit with the diodes and a known resistor, just measure all the voltage drops(including overall drop) and calculate the ohms from that?

All my meters are big jobbers with 400amp 1000V capacities for hooking up power supplies, rather than fine resolution for testing small parts.




Ok, so he connects the alternator to the socket on the wall inside his bedroom, synchronizes it with the power plant in Timbuktu, connects his bike lights to the alternator using some very small, but brilliantly designed microwave antennae... He wasn't asking for people to show off their electrical knowledge, he was just asking for a little help.

Now if you really came up with a hugely grand idea, don't be greedy and keep it to yourself making millions of dollars, share it, but do so on another thread. :p

We weren't showing off, we were sorting out the correct help from the incorrect help. Then fine tuning on the specifics with some asides thrown in for good conversation.

That microwave antennae idea sounds like one of Tesla's main pursuits.

I will in fact share my hugely grand idea... for a fee after it's complete, and make millions of dollars.:)

Some engineer you are... trying to make money off an idea, psht. :D

Some engineer you are... trying to make money off an idea, psht. :D
I didn't say I was an engineer.