Connect with us

Help with simple project

Discussion in 'General Electronics Discussion' started by beerdrinker, May 15, 2013.

Scroll to continue with content
  1. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Hello this is my first post in your forum and I appreciate your help to design/ create a simple project.
    The ideia is build two auxiliary braking light's to my motorcycle topcase.

    My idea is to have both leds lighted up at about 50% of their power as rear running light and at full power when the brakes are activated.

    Alternator info: 14 V/310 W at 5,000 r/min
    I will use: 2 X 10W LED chip
    LED Specifications: Voltage: 9V-12V; Forward Voltage: 10V; Power: 10w; Forward Current: 1000mA

    How do I switch from running to brake lights? Just occured me a relay. .Is ther any other whay? I Need a simple, reliable and compact scheme for this.

    I stop studing electronics at about 15 years ago, so my knowledge is almost gone.

    Thank you in advanced for your help!
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    652
    May 8, 2012
    Before we can provide accurate information we need to see the Data Sheet for the LED module.

    Chris
     
  3. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Dear sir,
    Thank you for your help.
    All the information I have about the LED is the one above. I miss the datasheet
    (LED Specifications: Voltage: 9V-12V; Forward Voltage: 10V; Power: 10w; Forward Current: 1000mA)
    [​IMG]
    The LED is this one.

    Thank you for your help
     
  4. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Some things that need to be investigated and considered:

    Do the running lights need their own on/off switch?
    Will you tap into a fused circuit for LED current? Is the fuse adequate for the additional current?
    How are the brake lights activated -- brake switch controls '+" power or '-' power?
    Will the LED modules be OK in parallel at half-power, or do they need individual current limiters?
    How will you drop the LED voltage from 14V source to the 9V-12V operating range? e.g., resistor or diode?

    These are just a few things I can think of that would affect switching from running to brake lights.
     
  5. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Hello, thank you for you answer!
    The running lights light up when the engine is running, no switches.
    the fuse of the rear lights circuit can hold the extra charge.
    the brakes are activated by "+" power.
    I will check if they work fine in parallel!!
    the voltage drop I don't know the better solution, as far as I remember from my electronic classes I pick the coal resistor because is the only one I'm familiarised with, I don't know if it is the best choise... I'm not familiarized with diodes... others than LED...

    Thank you for your help
     
  6. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    One other thing you might check is whether the LED modules run in series for the half-power operation from 14V. Is the brightness correct for running lights?
     
  7. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Many years ago in the UK cars were fitted with lights with two intensities. These caused accidents since the brake light was not noticed unless the change in brightness was seen.

    I suggest that you restrict your new lights to brake use only, separated from any tail lights.

    Do you have a 12V battery to provide short term extra power.
     
  8. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Hello, thank you for your help
    Most of the motorcycles work that way. I'm from Portugal and it's exactly like in the UK.
    I thought in the possibility of adding just brake light, and that's the easy part. But since I ride all year round, day night, fog rain... and the stock rear running light it's 5w (21w/5w bulb) it's almost invisible in the rain at night... and if the bulb blows up...
    I thought in incandescent lamps like w5w. four of them, two running lights and two brake lights, but I think they will heat to much and, also, use to much power from the bike, by the way it's a Yamaha FZ6.

    Thank you for your patience!
     
  9. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    The easy way to get two intensities from an LED is to use two diodes and two resistors. The resistors will be of very different sizes. The larger resistor will cause the LED to be dim. A diode on each input is used to isolate the inputs from one another. Both circuits are tied together to drive the LED. With running lights on, the LED will be dim, hit the brake and they will increase in intensity.

    Another way to do it would be using a PWM signal, most commonly created by the use of a Micro Controller anymore. A simple program to watch for inputs and vary the PWM signal will do the same thing.
     
  10. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    You don't need any diodes. You simply need two resistors. The high setting will put the two resistors in parallel.

    Bob
     
  11. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    No...

    They are isolated circuits, or should be.

    If there were no diodes, then if only the brake was the input, it would then back feed and try to also power the (other) parking lights.

    If only the parking lights were on, it would back feed to the brake circuit, and possibly turn on a 3rd brake light, if equipped.

    I guess I'm going to have to draw a schematic to explain why the diodes are needed.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Whether you can avoid the diodes or not depends on the details of the circuit and components. For example if the other lights in the circuit are incandescent, they won't be affected noticeably by 12V through two LED current limiting resistors in series. But their presence will affect the values required for the resistors to give the desired LED currents. Diodes are not essential in many cases but using them will keep everything tidy and independent.
     
  13. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Thank you for your help.
    My idea is basically this one:
    [​IMG]
    If they can be connected in parallel, one circuit (running lights) in parallel, and another circuit to the breaking lights. My biggest doubt is how do I switch the circuits, I am only familiarized with relays, and they are bulky and consume some power.
    The power consumption and heat are my main problems because I don't have much room to dissipate the heat and don't have much power available because the motorcycles don't provide it, like the cars, that's why I think power LED's are the best option.

    Once again, thank you for your help... and sorry about the schematic, I think it's the first I try to do in... 15 years!
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    652
    May 8, 2012
    While others are focusing on the particulars of running vs, brake lights I'm still stuck on the specs of this LED. It can't be a single LED (9V-12V) unless it employs a constant current circuit or limiting resistors, which I don't see in this photo. I know of no bare LED with Vf=10V. Is this an LED stack?

    Chris.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Yeah, they are "chip on board" construction. There are multiple dies, connected in series/parallel (I'd suggest this one has 3 strings of 3 LEDs).

    There are no resistors. Current sharing is achieved by having very closely matched devices all in excellent thermal contact with each other.

    I've used a number of these with a cheap constant current source to replace "tea lights" in outdoor lamps. The whole module ends up about the size of the tea light they replace, and at low power you don't even need a heatsink. (As an aside, I also use cheap chinese constant current LED drivers that I replace the current sense resistor on to allow them to operate at a much lower current -- as a side effect, everything operates well within spec)

    The unfortunate thing is that their combined Vf makes it somewhat tricky to power them from a 12 volt source (especially one that varies significantly around 12V). For once it makes me wish they had more parallel and less series in them. 6V to 8V would be great.

    Whilst probably overkill, there are a number of regulator modules you can get which have a boost then a buck stage, frequently with current limiting. One of these could be used to get a reliable (say) 100mA to the module. Another could deliver 300mA (both via diodes of course). Alternatively, some method of changing the current setting on the current source could be implemented.

    As another aside, Duke37 points out an important issue. But perhaps more important is that simply doubling the brightness isn't going to make a hugely noticeable change. You probably want to have 1/4 and full power (at least). You might also consider a circuit which flashes the brake lights a couple of times on initial application, since it is the change in brightness that people will have to notice, not a new light source.
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    652
    May 8, 2012
    Steve, thanks for clearing that up for me. Honestly, I saw nothing in the image of that LED that would have clued me in. ;)

    Chris
     
  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Steve, that's an excellent explanation.

    I'm concerned by the quoted specifications:
    "Voltage 9~12V" and "Forward voltage 10V" do not compute.
    I was going to suggest two linear current sources with very low voltage drops, one for each LED, both controlled together to give low or high brightness. But that spec is too vague and contradictory to be sure that it would work.

    Yes, that's what I was thinking.

    I agree that it sounds like overkill.
    He wants 1A at the maximum brightness setting, I think. That would be 10W dissipation, so I guess that would cause a problem with heating unless there was some good heatsinking, right?

    Excellent suggestion, although it might be illegal.
     
  18. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Thank you all for your help and interest,
    I see this is more complicated that I ever tought!
    Flashing the brake light is very visible but also very illegal.

    I buy these LED's from China, Ebay, so I guess the contraditory information it's explained...

    The use of LED's I thought it was best since the motorcycles produce very few energy, compared with cars, and also the incadescent bulbs release much more heat. And I need something small, sturdy, visible and energy eficiente.

    If you have any other idea for this please, I appreciate!

    Thank you all for the help!

    P.S. Givi, the topcase brand, produce brake lights to this topcase, but the contact problems are well known and the price of it it's outrageous.

    [​IMG]
     
    Last edited: May 17, 2013
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Since this is going on a motercycle, I'd prefer to make something simple and rugged that's likely to survive lots of vibration.

    It may be simpler to get some high power red LEDs and wire them up in strings that will operate from a lower voltage and simply use resistors to set the current.

    Something like this would be a good starting point.

    They're already on "stars". These need heatsinking, so you would screw them carefully onto a metal (preferably aluminium) plate.

    They're rated for 700mA, but I'd probably not operate them above 300mA (and you may not even need that much). A string of three of these will drop about 7.5V, so nominally, a resistor of 120 ohms (1W) in series with them would operate them at 50mA -- which may be sufficient for a taillight.

    An 18 ohm (5W) resistor would operate a string of three at 300mA, and that would be good as a brake light.

    Add 2 diodes and you can operate the same string as both a taillight and a brake light.

    I would recommend that you play with the resistor values until you get a suitable brightness for both tail and brake light. For experimenting, you could get away with 1/2W resistors for the taillight resistor, and 1W for the brake light resistor. They may be cheaper and although they'll operate pretty hot, they will be OK for testing on a bench.

    You probably need to mount these inside an existing waterproof enclosure. If you have room, there is no reason why you couldn't have 2 or more strings of three LEDs.

    The ones I've seen go on-off-on (and stay on) as the brake is applied. They don't flash continuously. But yeah, probably illegal.

    And also sometimes overgenerous specs. Try to run the LEDs at half power or less. It will help. It's actually not so important in this case because the brake light is not on for long periods.

    What are the ratings for bulbs used as tail and brake lights on your bike?

    You'll find that 1W of red LED is the same as maybe 8W to 10W of incandescent. If you use a red LED, it's even better because almost all the power is in the colour you want (could be a factor of 2 improvement)

    With 1 string of LEDs, I have suggested 0.375W and 2.25W which might be comparable to 6W/40W. But this is just rule of thumb. You need to do the comparison yourself.

    This suggests that these figures are in the ballpark.

    The brightness will vary as the battery voltage rises and falls. This is another reason to de-rate the LEDs. I did my calculations for 12V (perhaps I should have used 13.8?). If the voltage rises to 14.5, the LEDs will be a lot brighter, but will not be operating over their specified maximum ratings.

    I hope the above helps.
     
  20. beerdrinker

    beerdrinker

    8
    0
    May 15, 2013
    Pardon my absence.
    First of all, many, many thanks for all the help!

    That's exactly what I need!

    Do you think is better the LED's already applied on the "star" or just the LED like here?

    If they blink just one or two times, I think I can live with that illegality!

    It's a single lamp with two filements, 12V 21W/5W; 5W for running Light and 21W Breaking.

    It sure do, many many thank's, and once again I'm sorry for my late reply!
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-