[JPL_SV]

I have a little challenge for you tech geeks who know everything about everything!;D

Okay here's the situation, I have to replace my OEM LED brake light with an aftermarket red LED tail light:

The SV (2nd gen) tail light is on when the key is on or the engine is running and when the brakes are applied they get brighter, if your farmiliar with the setup it has 3 wires; one for neg., one for running/park lights, and one for the brakes. The aftermarket LED tail light has two wires so it's either on or off.

I took apart the OEM tail light to see what makes it tick. I'm not real farmiliar with Capacitors, resistors, and diodes (but I know what they do). It looks like I need to run a diode and resistor in-line with the a "brake" power wire (3rd wire) so that the running/parking light wire puts out less power and when the brakes are applied full output resulting in brighter light output.

QUESTION: How can I set up this aftermarket LED tail light to work like the OEM LED tail light?

note: I'm not good with soldering and I don't want to mess up the circuit board.

Here's a picture of the inside of the aftermarket tail light:

Here is the OEM tail light internals:

Here's my setup I'm hoping to acheive.

Thanks for your time and I hope to figure this out!

 

[eternity7602]

first off, im sure there are some exceptions but most LEDS cannot run off 12V you will burn them up. thus, you would need a diode in both lines to prevent chatter/backflow, as well as a resistor in both lines. any general diode such as a 1n4001 should work. however, i cannot help you out with the resistances because it is dependent on your number of LEDs and if that assembly already has any resistors in there to protect them. i would just plug and play. find some resistors and play with the running light power until you find one that hits the brightness you want for your brake light. then, actually solder that into the brake line wire, this still leaves the running light wire to play with until you find the desired brightness for your running lights. then, simply solder it together and go homes!

does this make sense?

P.S. the reason i have you use the running light wire for all the testing is because with the key on it is constant so you dont have to keep hitting the brake.

P.S.S. you should be able to follow where the wires go into the stock lights and then follow the traces on the board.... make a note of the resistors you hit on each side and start with those values on the testing (the color bands = resistance and tolerance).

P.S.S.S. leave power to the resistors of your choosing for a fair amount of time.... if they seem to get very hot, move to a higher wattage

 

[eternity7602]

if you place a multimeter between a cathode and anode on one of the leds you can read the voltage running through it and adjust from there. most LEDs run at like 3.2V unless they are superbrights. others run around 6. just dont push the whole 12 through or you will probably damage them.

 

[TeeRiver]

-Can you post a link, or have documentation for you aftermarket light? Is it sold specifically for motorcycles, or is it just a generic tail light?

-Would you be happy enough to run just 6 of the LEDs as your tail light, and then light all 12 when the brakes come on? Not as slick as all 12 dim/bright, but maybe easier to implement.

-How much soldering are you willing to do? Are you associated with JPL and perhaps have an assembler buddy?

-Are you willing to cannibalize your OEM light? Maybe you could take the OEM board, and with a little massaging make it work with the aftermarket.

Cheers!

 

[PunkinDave]

LEDs run on current... if hte unit is a 12vdc light, all that should be required is a resistor in series with the taillight positive from the bike to drop the intensity.

 

[Maviryk]

You need to put a resistor and a transistor in there.

*EDIT* See my next post, this circuit won't work. I need more sleep.

Your PIAA LED is rated at 2watts, so in a 12VDC system it draws 166mA.

 

[JPL_SV]

Thanks everyone for your input. It really helped me get an idea on where to start. This is really helps me understand what I'm working with.;D

This LED tail light runs on a 12V system, I'm aware that LED's run on 3V or so, I figured they had a built in resistor to prevent any damage to the unit.

I'm not associtated with JPL (that is simply my initials and it's hard get a user name or custom plate with JPL)

The tail light is 12 LED rear fog lamp by PIAA (Deno3). When I figure out the best way to set it up I'll post up the results and pics.

 

[TeeRiver]

When the brake light is depressed, the transistor "switches" to the Base voltage source and your LEDs will receive the full 12 volts.

I dont' think you can get that much current through the base of a transistor.

 

[Maviryk]

They're LEDs... how much current you think they'll use?

 

[ZeroSpawn]

I dont' think you can get that much current through the base of a transistor.

Current is rated in amperes. It all depends on how much resistance you provide. I = V/R

 

[TeeRiver]

They're LEDs... how much current you think they'll use?

LEDs use much less current than incandescent, like what 15%?, but it's still more current than the base-emitter junction will pass.

Base current is related to collector current by the gain of the transistor, typically in the 100 to 200 range. At that ratio, the difference between running light and brake light would hardly be noticeable.

A more workable solution might be to install the current limit resistor you suggest in the ground lead from the light, and connect the transistor in parallel with it. When you hit the brake, the transistor will go into saturation and short out the resistor and provide full current. You would also need a current limit resistor in the base leg to keep from over driving the transistor.

Cheers!

 

[Maviryk]

Actually... I may have screwed up here... I got confused on how the circuit diagram would work.

Using an N2222 transistor:

Connect the brake light signal to the Base with a 47KΩ resistor, connect a 30Ω resistor between the Collector and Emitter. Connect the running light to the Collector, and the Emitter still connects to positive on the brake light.

When the Brake light isn't depressed, no juice flows through the N2222, and the running light powers the LED through the 30Ω resistor (6VDC gets through, spec sheet for the LED is 2W). When the Brake light is depressed, the N2222 connects the power between the Collector and Emitter, and the LED gets a full 12VDC from the running light.

 

[JPL_SV]

So exactly how would I hook up the tail light using all these components? (pretend I don't know all the tech terms or explain it like you would to a child)

Looks like I would need: A Transistor (N2222), and a Resistor (47,000 Ohm and 30 ohm).
Is the Collector and Emitter part of the LED assembly?

I was thinking that I could just run the Transistor and Resistors inline.
I'm also worried about sending too much current to the LED's and damaging the tail light.

 

[Maviryk]

I'm pretty sure like this:

The N2222 transistor can handle up to 600mA of current, if I read the datasheet correctly. Your LEDs will only draw 166mA at 12V. Base, Collector, and Emitter are part or the N2222 transistor.

 

[TeeRiver]

Connect the brake light signal to the Base with a 47KΩ resistor, connect a 30Ω resistor between the Collector and Emitter. Connect the running light to the Collector, and the Emitter still connects to positive on the brake light.

That's just about right. Just change the last bit. Connect the emitter to ground instead of the positive on the brake.

 

[TeeRiver]

Nice drawing. I sent my post before seeing it. That picture is worth... a lot. smiley

Yes, that's exactly what I would do, except I think you need to put the transistor in the ground leg, (*after* the the LED array) in order for it to work.

Cheers!

 

[JPL_SV]

Thanks Maviryk, TeeRiver, and everyone else! ;D The diagram is very useful.

 

[Maviryk]

That's just about right. Just change the last bit. Connect the emitter to ground instead of the positive on the brake.

Wait... if you do that... where does his PIAA LED go!???

 

[TeeRiver]

Uh oh, confusion due to posting time delay, LOL!

 

[Maviryk]

Lol yea I reread your sentence and it finally made sense.

JPL, basically, you can wire your LED taillight into 1 or 3 (before or after the transistor, respectively) and it will still work the same. TeeRiver may have a point in putting the LED before the Transistor so that it sinks the current instead of sourcing it.

Also, the 30 Ohm resistor was just a rough guess from me. It should give the LEDs ~6V, but that may be too dim or too bright, so you may have to play around with the resistance.