AC to DC converter

[Burdar]

I've got an idea for some lighted garage art. I want to take an old grill/headlight bezels and tail lights and mount them on the wall. The headlights will have LED halos and I'll use LED 1157 bulbs in the grill's turn signal housings. For the tail lights I can just use a generic trailer LED light behind the stock lenses.

I see some inexpensive converters online. One converter I'm looking at is listed as 60w and has an output of 12V @ 5A. Would this be enough to run these lights?

Secondly, what if I wanted the headlight bulbs to light up?(very dimly) I assume just wiring the low beam side of the bulb with the rest of the LEDs, would cause the bulb to fully light. Could I use an old ballast resistor to cut the power to the bulbs?(55w H4s) I've got a couple old four prong ballasts. I could run the wires through both sides of the ballast...in series. Would that work?

Would the 60w converter still work?

[Cuda Cody]

LED use such a small amount of power that almost anything can power them.  Dimming them is not as easy as lowering power unless they are designed to be dimmed.  I haven't done what you are trying to do, but I've installed a lot of LED's in signs and they are pretty easy to work with.  I'm sure you can make it work with not much power.

[Roadman]

   I was just thinking a cheap battery charger would work.   

[Brads70]

    Just learning, I have the back half of a 68 Charger I was going to use for some sort of garage art...?

[Burdar]

I don't want to dim the LEDs. What I'd want to dim is the headlight bulb. The headlights I have are those H4 conversion lamps. They came with 55w bulbs. Don't daytime running lights just cut some power to the headlight bulb so they are dimmer?

I just read that amps is watts divided by volts. So 55w divided by 12v = 4.6amps per light. That converter wouldn't support both headlights shining at full brightness. If I could cut that in half though, it should work.

How much would a four prong ballast cut the voltage? I could connect the output from one side to the input of the other side. I be going through both sides that way. I only need the bulbs to come on a little bit.

The ballasts would run hot. Maybe an aftermarket ballast specifically designed for something like this would run cooler?

[dodj]

How much would a four prong ballast cut the voltage?

Depends on the resistance of the lamp. If the lamp and ballast resistor are the same resistance, the voltage would be cut by 50%. The 12vdc will be 'dropped' across the load(s). How much voltage is dropped across each load depends on how big (or small) it is in relation to the other.
If your lamp is .6 ohm and you use the 1.2 ohm side of the four prong ballast, then 8 volts will 'drop' across the resistor and your lamp will see 4 volts.

[Burdar]

I'm dumb. That means nothing to me. I was thinking about using BOTH sides of the ballast. I thought it was just 12v in = a given amount out.

Run 12v through one side = a certain amount. Then run that through the other side = another amount. I guess not?

[EDL94]

A ballast resistor is a load that is how it drops voltage and why it creates heat. Putting one in line with the light may increase the amperage / wattage used. I think a ballast resistor is only about 1 ohm and will only drop drop the voltage from 12v to 10v. If your retrofit lights have replaceable light bulbs you might consider fabbing a socket and putting an led 1156 equivalent bulb this would dramatically lower the overall power usage and if they are still to bright you can put in resistance to dim them.

[HP_Cuda]

Darren

Here is an idea for ya. Grab and old computer power supply and put some 12V rails, 5V rails and even 3.3V if you want then you are set!

https://www.youtube.com/watch?v=3WfZzpW3_uU

[dodj]

That means nothing to me.

Think of it as a ratio. 12V being 100%.
Add the resistance of the bulb and the ballast together. That will be the total resistance for the cct.
The system voltage of 12v will be 'used up' by the lamp and ballast.
How much each component 'uses up' will be determined by their percentage of the resistance.
If your total resistance of the cct is say 15 ohms, and your light has a resistance of 10 ohms and your ballast resistor is 5 ohms
then the math would be 10/15 = 0.66
Take that .66 multiply it by system voltage and you have the voltage that light will have applied to it.
.66 X 12 = 7.92 volts.

[Burdar]

A ballast resistor is a load that is how it drops voltage and why it creates heat. Putting one in line with the light may increase the amperage / wattage used.

I see what your saying now.

55w bulb divided by 12v = 4.6amps per bulb.  IF I use a ballast to cut the voltage down to 6v...That's 55w bulb divided by 6v = 9.2amps per bulb.

If your retrofit lights have replaceable light bulbs you might consider fabbing a socket and putting an led 1156 equivalent bulb this would dramatically lower the overall power usage

This sounds like the easiest option I think.  First, I'll probably just hook up the LED halo lights and see if that's enough by itself.  If I want more light, I can just shove an 1156 in the housing.

This will probably be a winter project.  Thanks for the info everyone!

[ViperMan]

Hey we're speaking my language now... 

First of all, Burdar, you need to know what voltage the LED's require.  Most LED's run on 3-4 volts, but most "store bought" LED lighting accessories - for cars at least - are MADE for 12 volts, and have resistors built-in to reduce the voltage from 12 to whatever the LED's require.

If you have raw, unwired LED's and you put 12 volts to them, they'll burn out IMMEDIATELY.  (Been there, done that...)

If they're pre-wired for 12 Volts, then ANY AC-DC converter that puts out 12 volts will power them, regardless of amperage output (I say that - you need at least 1-2 amps or 12/24 watts.)  The amperage output of a converter like that is the maximum amperage that the converter can "feed" without burning out/overheating/catching fire.  So if it's rated for 55 watts (4.583 amps) then it'll power anything that draws UP TO 4.583 amps without issue (though at that upper range, it'll get pretty warm.)  If the "consumer" draws less than the maximum amperage, that's totally fine.

Now, for the headlamps - that's a tad trickier, as headlamps draw some significant amperage.  Tip: check the fuse of a headlight circuit - they're usually 10 amps if I recall - and that'll be too much for that converter, UNLESS you use a resistor to drop the voltage before it hits the headlamps.  You could actually buy an aftermarket headlight dimmer and just wire it between the converter and the headlamps.  Just make sure you set it to a dim setting before you turn them on.  Then, make sure to frequently monitor the temp on the converter for the first hour or two to make sure it's not getting too hot.

One other tip, don't wire the headlamps AND the LED's in the same series circuit - make sure you run a parallel circuit - with separate wires running from the converter output to each consumer (the LED's and the headlamps) and then you can join the ground-side circuits before running back to the ground of the converter.  Otherwise the LED's and headlamps will attempt to share the amperage and the LED's probably won't survive that.

Oh - and a battery charger probably won't work - those don't often supply a constant supply of voltage, and they also usually output very low amperage.  They tend to "pulse" current which works better for the batteries.  I tried that once for my little Viper jockey box and I got squat.

EDIT - okay I went back and read all the previous comments - looks like you've already got most of what I mentioned figured out.  The only thing I wanted to mention is that LED's don't "dim" very well - you can drop the voltage to them a little, but once it drops too low they'll just go out (not burn out, just go out).

Lastly, check out Oznium.com - they have a TON of automotive lighting LED applications, and I think you'll be able to find a low amperage LED light that'll replicate the glow of an older car headlight (I believe it's called Warm White).  They also have converters and all kinds of stuff.  They're just a tad pricier than say eBay or Amazon, but they have way better selection and are very, very reliable.  I've been buying from them for years.

[Bullitt-]

Have any old PC's sitting around?


http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/


https://makezine.com/projects/computer-power-supply-to-bench-power-supply-adapter/

[Burdar]

First of all, Burdar, you need to know what voltage the LED's require.  Most LED's run on 3-4 volts, but most "store bought" LED lighting accessories - for cars at least - are MADE for 12 volts, and have resistors built-in to reduce the voltage from 12 to whatever the LED's require.

Yes, I'll just run automotive LEDs that are already set up for 12v.  I've just been looking on Ebay and they have some cheap LEDs that should be fine for what I want to do.  They even have some "flash back" 1157 turn signal lights that might be cool.  I can switch the power input so they either light up amber or white.

Have any old PC's sitting around?

Thanks for those links.  That looks interesting.  We might have gotten rid of our old PC.  I'll have to look.