Brake light for motorcycle. Which resistors to use?

[Hypersapien]

Hey all,

So my baja designs tail light has burnt out. Well something in the circuit burt out such that I now only have running lights and no brake light. I found some led clusters encased in acrylic (3 3x3 clusters already wired for a 12v car source) and I currently have it in there along with a weatherproof strip of leds but they are on separate circuits right now just so I can drive the bike.

What I want to do is just use the clusters as the tail/brake but to do this I expect I need to drop the current for the running lights using a resistor of some value (which?).

How can I measure the current light specs so that I have a running light which will be approximately 1/2 of the brightness of the brake light? Should I just experiment? I just want to run to radioshack and pick up something that will work. Can I get by with 1/2 watt resistors?

Also I'm pretty sure that all brake lights are wired this way but this is how it operates: Bike on- only the tail light wire is hot. Brake on- both wires are hot. I wont be getting a double dose of voltage when the brakes are on will I? I'm assuming not since they would be in parallel... Just checking. I should totally know this intuitively as I just completed a circuits course but for some reason I'm still wary of circuits that are not line drawings in a book.

Any help is fully appreciated!

 

[Diesel_Bomber]

Is this a street bike?

 

[Hypersapien]

Yup, it's all the factory wiring on a 2005 Suzuki DRZ400 supermoto bike. I've heard bad things regarding the durability of baja designs' leds now that I have looked...

So I just went ahead and bought an assortment of resistors just now... 10, 33 and 150 1/2 watt... I think I should be able to find the best one/combo...

 

[Mtrhd0024]

Alright... First off, this might be long, so bear with me! I'll try and answer all of your questions though...

Second, before I get going with my explanation, let me just say I love your choice in bikes! I'm currently in college, but my dad and I are self confessed motorcycle addicts... We have (at last count) between the two of us, 25 or 26 motorbikes to our names. My dad and I have two Suzuki DR200's, a 99 and an 01, and they're ok, but I am currently saving my monies to buy a DRz400sm, as I think it would be a perfect first streetbike for me. (I Have a Honda Hawk GT, and its awesome, but its a rather classic cult bike, so I'm afraid I'll drop it.)

My dad always poked fun at supermoto's, saying they were stupid, etc etc. Then one day, his VTR1000 Superhawk was in the midst of a brake job when his buddy invited him to go riding. Not being one to miss a ride, his buddy goes "Hey, why don't you ride my DRz instead!" :thumbsup: (He has an 08' DRz400sm)

Needless to say, my dad came back from that ride, with the biggest grin on his face ever. He told me that at first, before they got up into the twisties, he was kinda pissed at not being able to ride his Superhawk. But when he got up into the mountains, he said it was one of the most fun motorcycles he'd ever ridden, and he was actually dissapointed when his buddy made him get off and ride his Vstrom! :thumbsup: So there ya go, a DRz convert, from a guy who's been riding bikes for almost 50 years! :twothumbs

Before I get started, I'm sure you're hesitant to dump more $$ into a tail tidy, but have you considered a different one, like the edge tail light kit??
Scroll down here: http://www.wheelingcyclesupply.com/shop?action=category&cat_id=72

Its kinda expensive @ $60, but I think they look awesome on the DRz's! :thumbsup: http://www.thumpertalk.com/forum/thread/652665/drz400sm-edge-tail-tidy

NOW... On with the explanation...

I'm not sure I quite understand what you are saying about what you did with the tail light on your Baja designs tail... But I THINK what you did, is buy some 12v LED modules, and fit them inside your housing? And then, you wanted to know a resistor value that would cause the LED's to be "dimmer" and then once you hit the brake lights, the LED's would be supplied with the full amount of current they were designed for, and therefore be brighter?? If so, you might not exactly like what I have to say...

I'm pretty sure that the easiest way for you to go about recreating the increase in brightness that you get when you hit the brakes, is going to be to have two parallel "strings" or arrays of led's (so to speak). One of the "strings" or arrays will be on constantly whenever the bike is on (as per US law) and the second array comes on whenever you hit the brakes.

So it would end up looking something like this when the bike is off:

Two arrays of LED's:
(each "o" represents an unlit LED)

o o o o o o
o o o o o o

When the bike is turned on, it'll look like this:
(With the capital "O" representing an illuminated LED)

O O O O O O
o o o o o o

When you hit the brake, it'll look like this:

O O O O O O
O O O O O O​

The second array of LED's illuminating, increases the brightness of the tail light, in much the same way that a second fillament increases the brightness of a tail light bulb! :twothumbs

I designed an LED taillight module with a flashing brake-light for one of my motorcycles, and this is the way I went about duplicating the brake light effect.

The problem with doing it as you suggest (using a resistor to dim the LED's) is that LED's are very different from normal filament type bulbs.

With a normal halogen bulb, you supply less current, and the bulb dims gradually until you get to 0v and the bulb goes out. With LED's, you supply less current, and the LED goes out. Its not QUITE as cut and dry as that, but the operating voltage at which an LED runs at is much more sensitive than a light bulb, especially when you're talking about the little plastic LED's that you buy at Radioshack. They need to run on between 1.5 and 2.0 volts each.

The way those type of LED's are normally dimmed, is by flashing them on and off thousands of times per second. The more times you flash the LED, the brighter it appears to be. Pulse it at a slower rate, and it appears dimmer (until you pulse it so slowly that it just appears to flash )

The other problem with your suggested solution, is that you'll end up with a very dim tail light, until you hit the brakes, in which case THEN, the LED's will be running at their normal brightness. To me, having a second array of LED's come on is a better solution, because then you add brightness, instead of having a dim taillight, and just making it slightly brighter for the brake light. And as a fellow motorcycle rider, I know how important it is to be seen on the road! :thumbsup:

So... I'll end my very long post, by asking this question... Can you solder? Because if you can, I'll be glad to show you how you can make a pretty simple array of LED's using parts you can buy at Radioshack for a few dollars, that will do just like I mentioned above. Connect the first array to the tail light circuit, connect the second array to the brake light circuit, and voila, you're done! No calculating out resistor values or any of that, it'll all run straight off 12 volts... Its really pretty simple. :thumbsup:

 

[TorchBoy]

The second array of LED's illuminating, increases the brightness of the tail light, in much the same way that a second fillament increases the brightness of a tail light bulb! :twothumbs

I designed an LED taillight module with a flashing brake-light for one of my motorcycles, and this is the way I went about duplicating the brake light effect.

Remember that the difference in brightness between the twin filaments is more than just double - for example 5 W tail and 21 W stop filaments.

Is using homemade brake lights legal there?

 

[Mtrhd0024]

Remember that the difference in brightness between the twin filaments is more than just double - for example 5 W tail and 21 W stop filaments.

Is using homemade brake lights legal there?

Well technically I don't believe that the edge taillight, or the baja designs taillight are DOT approved in the first place... (Could be wrong on that) But you never get hassled for stuff like this on motorcycle inspections, and considering my LED tail light is brighter than the standard one, (using the standard Honda tail light lens) no one ever questions it, so I'm not really worried about it.

But in similar fashion to an OEM taillight bulb, the LED's I use for the brake light array are brighter than the ones that I use for the tail light which is on at all times. I use 10mm red LED's for the always on array, and 10mm high intensity white LED's for the brake light array. Couple that with the flashing brake light and you end up with a very noticeable tail light assembly! :thumbsup:

 

[TorchBoy]

I use 10mm red LED's for the always on array, and 10mm high intensity white LED's for the brake light array.

:thinking: There's very little red light in the output from white LEDs, and you're not allowed to show white light behind so they'd all be behind a bit of red plastic, which means...

 

[Mtrhd0024]

:thinking: There's very little red light in the output from white LEDs, and you're not allowed to show white light behind so they'd all be behind a bit of red plastic, which means...

That post just confused me...

Buttt... A motorcycle tail light lens is red. I use red and white LED's inside the red lense.

So either way, the light ends up looking red. :thumbsup: :laughing:

I just use the high intensity white LED's because they produce more light, and thus are better at getting your attention (and overpowering the normal red LED's) when you hit the brakes and they turn on with the red LED's.

Its much the same idea as the OEM bulb. The "always on" filament is not as bright as the "brake light" filament!

 

[TorchBoy]

Its much the same idea as the OEM bulb.

The same idea maybe, but in practice an incandescent bulb has plenty of red light in its output.

 

[Mtrhd0024]

The same idea maybe, but in practice an incandescent bulb has plenty of red light in its output.

I think I see what you're saying now... But even then, its not an issue because of the red tail light lens. Most of the aftermarket LED tail lights use high intensity white LED's behind red (or amber depending on the applcation - I.e. a turn signal) lenses, so its all good...

Plus, in some cases the tail light bulb is also used to illuminate the license plate via a clear window in the bottom of the tail light lens, so on some bikes you have to use white LED's! :huh:

 

[tay]

Most car manufacturers, AFAIK, use red-orange LEDs in the ~615nm range. I can't think of a single OEM application where white LEDs are used behind tinted lenses. They use red-orange LEDs behind clear lenses, or behind red lenses, but never white LEDs. I don't know where you got that information, but it isn't correct.

White LEDs are completely pointless to use behind colored lenses.

You're taking a blue LED with a narrow SPD, then hitting phosphor with it to give a nice wide white SPD, then filtering out the non-red light to finish up with a narrow red SPD? That makes absolutely no sense. Based off of looking at white LED spectrographs, filtering them behind red would be at least a 75% reduction in output. No qualified optical engineer would design something like that, when they could just use a red-orange LED (which is cheaper) and only have to deal with the standard 4% power reduction of hitting glass (not sure on the number for plastic, probably similar) at a normal incidence.

 

[Mtrhd0024]

Most car manufacturers, AFAIK, use red-orange LEDs in the ~615nm range. I can't think of a single OEM application where white LEDs are used behind tinted lenses. They use red-orange LEDs behind clear lenses, or behind red lenses, but never white LEDs. I don't know where you got that information, but it isn't correct.

White LEDs are completely pointless to use behind colored lenses.

You're taking a blue LED with a narrow SPD, then hitting phosphor with it to give a nice wide white SPD, then filtering out the non-red light to finish up with a narrow red SPD? That makes absolutely no sense. Based off of looking at white LED spectrographs, filtering them behind red would be at least a 75% reduction in output.

Except we're talking aftermarket motorcycle parts here, not an OEM Honda, Suzuki, whatever part... The DRz400sm comes standard with some big ugly azz tail light with an incan tail light bulb.

The edge tail light and the baja designs tail light are both aftermarket LED lights, designed to fit snug up under the rear fender of the motorcycle.

It goes from looking like this:

To looking like this:

From my personal experience messing with motorcycle accessories... They tend to use white LED's.

I'm not sure how this is even relevant to Hypersapien's question... He asked for help with a problem, I offered him a solution, the color of the LED's is completely irrelevant...

So far, nobody else has attempted to help him out, or offered a solution to fix his problem...

 

[TorchBoy]

Don't feel hard done by; he didn't need any help. He's on the right track with resistors (assuming it's legal where he is to fit a home made tail/stop light).

 

[tay]

The color does matter. Clearly, no qualified optical engineer was involved in the design of these modules. That begs a series of questions about what other mistakes were made in the design of these modules. The OP is modifying his non-functional tail light, so clearly a discussion about the correct type of LEDs for his application is necessary. Stick with red or red-orange, not white.

IMO, the OP should look into a PWM dimmer circuit board. This will allowthe LEDs to be run at any brightness level without requiring additional resistors. The nonlinear I-V relationship of LEDs means that controlling the voltage is not that great for controlling brightness. Half the voltage does not equal half the brightness. With PWM, you can set the brakes to be full brightness, and the tails to be anywhere from 0% to 100% of the intensity of the brakes (ideal value is probably in the range of 25%-40%)

 

[Mtrhd0024]

The color does matter. Clearly, no qualified optical engineer was involved in the design of these modules. That begs a series of questions about what other mistakes were made in the design of these modules. The OP is modifying his non-functional tail light, so clearly a discussion about the correct type of LEDs for his application is necessary. Stick with red or red-orange, not white.

I will leave this up to Hypersapien... If he feels like finding the perfect shade of LED then so be it, but at the end of the day, the same concepts apply no matter what LED choice he uses. He was looking for a simple way of piecing back together his tail light housing, not re-engineering it to OEM Suzuki specs...

IMO, the OP should look into a PWM dimmer circuit board. This will allowthe LEDs to be run at any brightness level without requiring additional resistors. The nonlinear I-V relationship of LEDs means that controlling the voltage is not that great for controlling brightness. Half the voltage does not equal half the brightness. With PWM, you can set the brakes to be full brightness, and the tails to be anywhere from 0% to 100% of the intensity of the brakes (ideal value is probably in the range of 25%-40%)

I already explained that (in simpler terms) in my initial explanation. But yes, you are correct about the relationship between voltage and LED's...

The problem with this solution, is that there isn't an entire engine compartment/interior/trunk to hide a mass of circuitry, just a little teeny LED tail light. Judging by Hypersapien's question of which resistor to use, I'm guessing that building an IC, or even a 555 timer controlled PWM dimmer circuit for his tail light, AND making it small enough to fit is a bit over his head... Not putting him down, I'm just trying to be realistic!

I simply offered up what would be the simplest means of solving his problem.

Anyway. I await Hypersapien's return!

 

[tay]

I already explained that (in simpler terms) in my initial explanation. But yes, you are correct about the relationship between voltage and LED's...

The problem with this solution, is that there isn't an entire engine compartment/interior/trunk to hide a mass of circuitry, just a little teeny LED tail light. Judging by Hypersapien's question of which resistor to use, I'm guessing that building an IC, or even a 555 timer controlled PWM dimmer circuit for his tail light, AND making it small enough to fit is a bit over his head... Not putting him down, I'm just trying to be realistic!

I simply offered up what would be the simplest means of solving his problem.

Anyway. I await Hypersapien's return!

Check out the Quickar PWM modules... I know a lot of the guys on HIDPlanet with LED tail light retrofits use the Quickar modules.

They're like ten bucks pre-assembled, and about an inch square. One is sufficient for the entire motorcycle. It can be configured to give brakes full voltage, and has a knob to adjust the tails brightness to a suitable level so that there is excellent contrast.

Your initial proposed solution would be functional, but I know most OEM tails have it set so that the entire assembly is dimmed for tails, rather than having part of the assembly on and part of the assembly off. I guess it is more conspicuous or something. But PWM doesn't have to be as complicated as most people expect, if you use inexpensive modules like the Quickar one.

I will leave this up to Hypersapien... If he feels like finding the perfect shade of LED then so be it, but at the end of the day, the same concepts apply no matter what LED choice he uses. He was looking for a simple way of piecing back together his tail light housing, not re-engineering it to OEM Suzuki specs...

It's not about choosing the perfect shade. It's about making something that is bright and effective, and reasonably priced. Due to how white LEDs work (they are a blue LED with phosphor to downconvert into longer wavelength colors), they are very inefficient behind a tinted lens. It will be far more difficult to make an adequately bright fixture if white LEDs are used instead of red or red orange.

 

[TorchBoy]

Does that PWM driver do any current limiting? If not, you'd need resistors or a driver of some sort for both tail light and stop light anyway.

 

[tay]

You'd still need the appropriate resistors or regulators for 12vdc operation. You would not need additional resistors that switched only for the tails and not for the brakes - the same resistors would handle both functions.

 

[tay]

I made a simple diagram that should hopefully explain why not to use white LEDs in a less complicated way.

The left side is what the SPD of the unfiltered source is. The red lens removes any wavelengths outside of red and some orange, so the right side is the SPD after filtration. White LEDs have low output in the red and orange part of the spectrum, so they are very dim when filtered compared to the correct red-orange LEDs.

 

[Mtrhd0024]

Check out the Quickar PWM modules... I know a lot of the guys on HIDPlanet with LED tail light retrofits use the Quickar modules.

They're like ten bucks pre-assembled, and about an inch square. One is sufficient for the entire motorcycle. It can be configured to give brakes full voltage, and has a knob to adjust the tails brightness to a suitable level so that there is excellent contrast.

Your initial proposed solution would be functional, but I know most OEM tails have it set so that the entire assembly is dimmed for tails, rather than having part of the assembly on and part of the assembly off. I guess it is more conspicuous or something. But PWM doesn't have to be as complicated as most people expect, if you use inexpensive modules like the Quickar one.



It's not about choosing the perfect shade. It's about making something that is bright and effective, and reasonably priced. Due to how white LEDs work (they are a blue LED with phosphor to downconvert into longer wavelength colors), they are very inefficient behind a tinted lens. It will be far more difficult to make an adequately bright fixture if white LEDs are used instead of red or red orange.

That looks plausible, and tbh I doubt I could buy all the parts in that module to even BUILD that for less than 10 bucks...

How do they normally wire up using that module? Just looking at the input/output wires on it, it only looks like you can dim one set of LED's at a time... Where is the input for the brake wires so that the module provides full voltage? Just curious, as I like the idea.

I do agree that this would be the better option, as long as we can keep things simple for him...

He's still going to need to build an LED array though. Those 12v automotive arrays are usually prewired with resistors and other such things, which might not allow the controller to work right.