What would you do?

I'm trying to find a voltage source to function as illumination, but have more current than the dimmer switch/illumination wire at the radio.

Why you ask? I have replaced all of my cluster, radio, and climate control lighting with led's and I need a higher voltage source. I don't think the illumination wire will have enough oomph to push that many led's

 

Relay...

the relay is powered by the illumination... and then the switched is +12v from the battery


----------edit---------

basing it on how i understood your question...

"I'm trying to find a voltage source to function as illumination, but have more current than the dimmer switch/illumination wire at the radio."

i thought you just wanted a better power line..... that was switched....


Modified by bpr0422 at 11:03 PM 11/14/2007

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bpr0422 &raquo;</TD></TR><TR><TD CLASS="quote">Relay...

the relay is powered by the illumination... and then the switched is +12v from the battery</TD></TR></TABLE>

Either I wasn't clear enough or you didn't understand me.

The output needs to be variable voltage, not the input. I need to be able to have a dimmer for the led's.

I would like to find a simple solution without having to use a pwm, but can't think of one.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">Either I wasn't clear enough or you didn't understand me.</TD></TR></TABLE>
Because what you said doesn't make a lot of sense.

LEDs don't typically require more voltage then light bulbs.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">I'm trying to find a voltage source to function as illumination</TD></TR></TABLE>
Since when does voltage illuminate?

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">but have more current than the dimmer switch/illumination wire at the radio. </TD></TR></TABLE>
Again what the hell does this mean?

What I think you are trying to ask but I cant completely tell for sure is you want a variable voltage source that offers more current capabilities then the dimmer switch?

Light bulbs typically require more current then LEDs so not having enough current is not your problem. That is unless you installed significantly more LEDs then you had light bulbs. What kind of LEDs did you buy?

Put a resistor in series with each LED to control the current through each LED. You can calculate the voltage at 14V so that you can still use the dimmer switch.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">
Because what you said doesn't make a lot of sense.
</TD></TR></TABLE>

Touche. After rereading what I wrote it doesn't make much sense at all.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">
What I think you are trying to ask but I cant completely tell for sure is you want a variable voltage source that offers more current capabilities then the dimmer switch?
</TD></TR></TABLE>

Correct. I'm running roughly 60 red led's that I ebayed. I'm running them in series in strings of 5 with a 100ohm resistor, and strings of 3 with a 330ohm resistor. If you want exact specs I can find the auction and list them if you'd like.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">
I'm running them in series in strings of 5 with a 100ohm resistor, and strings of 3 with a 330ohm resistor. If you want exact specs I can find the auction and list them if you'd like.</TD></TR></TABLE>

Why would you run them in series this is a bad idea!!!!!! If one fails they will all fail.

A better idea is to run each in parallel. I could help you with this but I would need the specs for these LEDs.

Why do you think you need a pwm? You dont need anything more then the 12V the battery supplies.

 

I believe the stock dimmer switch should work just fine for what you are trying to do.

Oh and be sure to post pics when done, I'm interested to see how good she looks

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

Why would you run them in series this is a bad idea!!!!!! If one fails they will all fail.

A better idea is to run each in parallel. I could help you with this but I would need the specs for these LEDs.
</TD></TR></TABLE>

Well, they're not all in series, as in not the whole run of 26 is one big chain so to speak. For my cluster for example, I have four "runs" of 5 led's and two "runs" of 3. Each run is ran in parellel.

The only reason I brought up a pwm is because I know they are often used in led tail light retro's to vary brightness.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by White Smoke &raquo;</TD></TR><TR><TD CLASS="quote">I believe the stock dimmer switch should work just fine for what you are trying to do.

Oh and be sure to post pics when done, I'm interested to see how good she looks </TD></TR></TABLE>

Well, it's already done, and has been for a while. It's been a side project I've been doing at work, so when I'm home I try to concentrate on getting the car going.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">Well, they're not all in series, as in not the whole run of 26 is one big chain so to speak. For my cluster for example, I have four "runs" of 5 led's and two "runs" of 3. Each run is ran in parellel.

The only reason I brought up a pwm is because I know they are often used in led tail light retro's to vary brightness.
</TD></TR></TABLE>

Putting them all in parrallel would be a better idea. You could use surface mount resistors if you're worried about space. PWM is used because LEDs dont dim really well by varying voltage and manufactureing diferences will cause some to be brighter then others. They flow a specific amount of current. You can dim them a little but not over a wide range. PWM controls the on off time of the LED thus allowing far more range and control when it comes to dimming. Probably more complicated then you want to do though.

A really simple way to do this is with a basic 555 timer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">
Probably more complicated then you want to do though.
</TD></TR></TABLE>

Well, for this project yes. I'm actually planning on doing a tail light retro once the car is going, using some superflux led's, a voltage regulator (LM317 iirc) and a pwm to control running lights/brake. I'd also have another set of led's for the turn signal function.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

A really simple way to do this is with a basic 555 timer.</TD></TR></TABLE>

Care to explain? A 555 timer changes the rate of on/off, or something else? Googling right now

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">
Care to explain? A 555 timer changes the rate of on/off, or something else? Googling right now</TD></TR></TABLE>

Go to digikey.com and download the datasheet for a 555 timer.

It varies the duty cycle thus the term pulse width modulation.

You want a high enough frequency so not to visibly see the flickering but not to fast that the LEDs are unable to turn on and off fast enough. I would guess a couple hundred hertz is fast enough. House lights turn on and off at 60hz.

You then vary the duty cycle to control the dimming. Its a really simple circuit. Should be easy enough for you to experiment and use.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

You then vary the duty cycle to control the dimming. Its a really simple circuit. Should be easy enough for you to experiment and use.</TD></TR></TABLE>

Is a single one of these sufficient or do I need multiple 555's?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 8520 &raquo;</TD></TR><TR><TD CLASS="quote">
Is a single one of these sufficient or do I need multiple 555's?</TD></TR></TABLE>

You need a single one but you need a transistor to carry the load. Meaning the 555 drives the transistor the transistor drives the LEDs. The 555 timer does not have enough switching current to drive the LEDs by itself.

555 is a really old timer I only suggested it because you can probably find tons of projects on the net built with it.

Something newer would be http://www.onsemi.com/pub/Collateral/MC1455-D.PDF

Either will work.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

You need a single one but you need a transistor to carry the load. Meaning the 555 drives the transistor the transistor drives the LEDs. The 555 timer does not have enough switching current to drive the LEDs by itself.

</TD></TR></TABLE>

if you use a transistor make your you find one with the correct specs to bias it into active region, and also that the power disipation of the transistor will be enough to power all those LEDs

another idea you may want to look into is wiring a 555 timer in conjunction with a few SCRs or other type of thyristors, having the gate of the SCR wired to the output of the timer, and 12V to your anode, LEDs wired to the cathode. Most diodes are able to handle a decent amount of current without the use of a heat sync unlike a transistor.

Whats the total calculated power dissipation of all the LEDs you have??

 

You could also use a power opamp, such as opa541 or opa 549 from TI. Set the gain to get the desired output voltage (gain = LED output voltage / 555 timer output voltage).

 

Since your just turning a switch off and on I wouldn't worry about bias. Just turn the transistor on and off no reason to worrk about being in the linear reigon or anything. I would just go with an Nmos trasistor. Put a 100 ohm resistor between the output of the 555 and the gate of the mosfet.

No reason to make this more complicated then it needs to be.