12v DC Conversion / LED brake light Q's


So I need some advice/a look over by someone who is more familiar with electrical stuff or has done this before.

I am looking do to a electrical overhaul/switchover for my moped. I'm planning on making a halogen headlight as well as a LED brake/running light, both running off 12v DC. I am currently planning on using two of these LED strips, one in red for my brake light, one in white for my running light. Although the running light will be running at all times, I would like my brake light also to be illuminated, but not at full intensity unless the brake is engaged.

A little background: The moped is a Tomos A3, kitted and all that jazz. It will be running fast, at high RPMS. It has a korado CDI system on it, which outputs 12v AC current.

My current plan is to run my 12vAC into a rectifier, and then through a capacitor to change it over to 12vDC, with a smoothed output (capacitor).

Then to create the brake light effect, I plan on running in parallel two wires(paths) to the red LED strip. One will be running through a resistor, which will power the LED when the brake is not engaged. The other will run through the brake light, and meet up with the other path after the resistor. My thought process here is that while the brake switch is not engaged, the current going to the LED strip will be limited by the resistor, dimming the lights, while when it is it will bypass it and go full-blast to the LED, making them brighter-den-a-mutha-fugga.

I've got a few parts of this plan I'm not too sure about, and would love some input.

1. The rectifier + coil combo. Since my coil is grounded and has only one wire coming out of it, I will have to "float" the ground, right? From what I've gathered, this just means removing the end of the coil grounded to the core of the coil, and running it to the rectifier..., right?!

2. The actual rectifier. Any suggestions on one? as in a actual link and review? The ones on Treats look alright, but I've read suggestions that a simple 10$ scooter 4-prong rectifier/regulator combo will work just fine. I'm figuring this is what the ones on treats are.. just at a "moped convenience" mark up if ya' will.

3. Rectifier + Capacitor. So this capacitor will be used to act as a "supper-mini" battery that effectively smooths out the output right? How will I know what sort/level of capacitor to purchase? Anyone with previous experience here?

4. The brake light configuration. Does my plan make logical sense to an electrically knowledgeable person? If so, how might I go about deciding the resistor level to use?

5. Power usage. Will all of this be able to be powered by my components? I've figured that since both the LEDs im using for brake/running lights and the halogen headlight are less power hungry then their stock counterparts, this will not be a issue. But I'd like some input here, as it'd be a real pain downunder if I get this all wired just to have dim lights.

I know this is a hell'uv a read, and my electrical terms are probably all over the damn place, but I'd appreciate any and all help! Any other relevant suggestions/comments are welcome as well.

thanks! (edited)

Re: 12v DC Conversion / LED brake light Q's

Justin Sonnett /

Man im glad you asked this. I am planning on doing almost the exact same thing to my a3. I have a projector housing from a car that takes a h3 bulb and was wondering how much power that sucka is gonna draw

Re: 12v DC Conversion / LED brake light Q's

Martin did this setup on his Moby (diodes dont really give a heck if it is ac or dc)


Re: 12v DC Conversion / LED brake light Q's

Yeah I used this idea, just changed it a little so both banks of LEDs face rearward with one bank acting as tail light and the other working as the brake light. No problems so far, cheap and easy to do.

Rebel Moby Wrote:


> Martin did this setup on his Moby (diodes dont

> really give a heck if it is ac or dc)

> http://mabecanemobylette.freeforums.org/viewtopic.

> php?f=31&t=1771

Re: 12v DC Conversion / LED brake light Q's

So you think I'd be fine skipping the rectifier, and just running the 12vAC to the LEDs as well as the headlight? I guess there is no harm in trying that, and if it doesnt work I can always throw the rectifier in later. The only thing I'm worried about is the fact this moped will be throwing serious RPMs (its got a 70cc kit, 21 mm mikuni, and is tuned for the stars) and I don't want to be dealing with bulbs blowing, or headlights melting down the road. The whole run-DC-components-with-AC thing just doesn't seem like it will be conducive to all the parts lasting.

Re: 12v DC Conversion / LED brake light Q's

if you pass on the rectifier, the leds will only be on half the time. Diodes are 1 way valves for electricity, led's are diodes. Get a $5 50+ volt, 10+ amp bridge rectifier from radioshack. for a capacitor, 35-volt, 4,700uF should be enough, about $5 at radioshack. remember polarity, or the capacitor can/will explode.

I just used a pair of 4 amp diodes in series to rectify half the cycle and not have to deal with floating the ground, but yes, you will have to remove the wire from the coil that goes to the frame and hook it to the rectifier. If this coil also powers your ignition, you will run into lots of problems. Also, I don't see why you can't hook one side of the rectifier to the frame (or ground wire) and the other side to the coil output, since ground changes polarity with output. just don't wire the light's ground wires to the frame, wire them straight to the rectifier's ground. I'm planning to try this in the future.

your brake light setup sounds good, just use a 1+ watt resistor between 5 and 50 ohms, trail and error isn't hard because they're like $1 for 5.

as for the high revs, more load is your friend. Or use one of those 4 pin rectifier/regulator combos. I'm not sure how to hook them up, but I would think it would be the same as a radioshack rectifier.

Re: 12v DC Conversion / LED brake light Q's

Tara Titsoff /

I've been told that even though they're only on half the wave, it doesn't matter because they're off such a short time you can't see it. Only at low idle can you bearly tell it flickers a little.

Even a normal house light bulb goes on and off 60 times a second. Can you see that?

Re: 12v DC Conversion / LED brake light Q's

Bad Cadillac™ /

I use LEDs from here, the same place I get my pinball 6v and 12v LEDs from. I use prepackaged bulbs in the stock assembly and sockets. That's it, no conversion caps, extra diodes, or rectifiers needed.

I get some plusating at idle but with the red lense on, you can't really see it. All are very bright and the LED tailight is much lower wattage, it made my headlight brighter which was badly needed.

Why not get prepackeged LEDs, buy some sockets and make your own set up?

http://www.cointaker.com/ (edited)

Re: 12v DC Conversion / LED brake light Q's

Bad Cadillac™ /

Tara Titsoff Wrote:

> Even a normal house light bulb goes on and off 60

> times a second. Can you see that?

Nope, can't see this with an incandescent light bulb.

Some LEDs ghost, or flicker if in a circuit, getting small amounts of power from the circuit. This can be seen using LEDs in pinball machiens where there are many circuits flashing at all different times. You can't see this with old incandescent bulbs used in pinball machines. Thus there are no ghosting, no flicker LEDs out there that can fix most of this. Some rare cases these bulbs cannot though.

Re: 12v DC Conversion / LED brake light Q's

I run all my lights off 12 volt dewalt batteries. plug and play

Re: 12v DC Conversion / LED brake light Q's

Its a good idea to think things out, never a good idea to over think things.

Run automotive LED bulbs (which are rated for somewhere around 16v) or build ones that someone else already designed and wotks (like Martin's design) unless you find either of those present a problem in use.

Re: 12v DC Conversion / LED brake light Q's

I dont think I'm over thinking this, Rebel moby. I just want it done right. I'd rather these lights not flicker at all. But thanks anyway.

And let me clear up, I am not looking to simply switch out the bulb in the stock tail light. I am not using the stock tail light. This is going on a build. I want it to look custom.

Martin's design is nice, but I want a strip of LEDs, not just 6 or so. Actually, what I truly want is two strips of LEDS (one white, one red), as you would have got from my first post. And doing this martins way would cost a good deal more from the looks of it, not to mention the LEDs would not be pre-housed in a nice waterproof epoxy.

Alex, I think I'm gonna go with what you suggested. Thanks alot!

I'll post photos here when once I get all the parts sourced and am ready to build. (edited)

Re: 12v DC Conversion / LED brake light Q's

Bad Cadillac™ /

Just keep in mind, even the brighest LEDs need a reflector or magnifier to really be seen at a distance.

I've got enough experience with LEDs in my pinball machines, arcade machines, house, car interior and car brkae/tails and so on to know. I've even built third brake lights for cars. I've experimented with many types to get the effect I want. CREE are the brightest and have a magnifier, those strips are not CREE but high power, there is a difference.

Re: 12v DC Conversion / LED brake light Q's

Do this. Works great. I'm running LED's and a halogen up front. Magical Pancake said he used this diagram for his turbo charged puch and it worked great for him too.

Just buy big caps and be done with it - as long as they aren't too small it really doesn't matter. I'm probably going to get rid of one of them becuase 3300's are HUGE. My lights don't flicker.

You could also do it with a 12v regulator and rectifier separately - you don't have to use the trailtech.

The whole resistor thing for your brake light is fine I guess... I think you're over complicating things trying to do that, but to each their own.



Re: 12v DC Conversion / LED brake light Q's

house bulbs use a hot filament. during the 120th of a second they're off, the filament keeps lighting because of the stored heat. Led's don't use heat, and unless you have a good capacitor, you can still see the flicker or a dimming effect up to about 2,500-3,000 rpms. Even if you don't see the flicker, it will significantly dim the led's, by up to 50% near idle, compared to using a capacitor and/or full wave rectifier. Half wave is fine, but use a diode and large capacitor to smooth the current out, as this will also reduce any high voltage spikes from the alternator that would otherwise damage the leds.

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