LED Flasher (automotive or Motorcycle)

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Intro: LED Flasher (automotive or Motorcycle)

I replaced the incandescent turn-signal bulbs in my Kawasaki Concours motorcycle with LEDs because 1) they brighter 2) they last longer and 3) they require less current than incandescent bulbs. Because they require less current, the standard flasher unit (the little box that makes your turn signals blink) senses the low current and thinks there is a bad bulb and it therefore won't function properly. So the standard flasher unit needs to be replaced with one that is compatible with LEDs. You can buy these, but where is the fun in that? I designed a simple LED-compatible flasher circuit and retrofit it into the original flasher case.

Step 1: Locate and Remove the Flasher Unit

First locate and remove the flasher unit. This will be different for each vehicle. Consult your service manual for the location (or listen for the clicking noise when the flasher relay is operating).

Step 2: Remove the Old Circuit From the Flasher Unit

Some flasher units can be disassembled. If you can disassemble it, then by all means do so. In this case they had potted the timing circuit, so I used a hacksaw to cut open the flasher case.

Step 3: The Old Circuit

Here's the old circuit (encased in potting material).

Step 4: Re-use the Original Connector

We'll re-use the original connector and solder our new circuit to it.

Step 5: The Flasher Circuit Schematic

Here's the new flasher circuit schematic. It consists of a 555 timer circuit and a power transistor. The power transistor is probably way overkill, (it is rated at 10A) but it's what I had available. You can vary C1, R1 and R2 for to vary the flash rate and duty cycle. For the R and C values shown, then flash rate is about 1.4 Hz (which is about 85 flashes per minute). There is a ton of information about the 555 timer on the web, including programs that will calculate the R and C values for you.

Depending on the type of components that you choose, the R and C values can vary by 10% or more, so you may need to tweak some values. C2 should be a ceramic bypass cap, but it does not appear to be essential, my circuit worked fine either with or without C2. C1 should be a ceramic cap, but if you decide to use a tantalum or electrolytic cap for C1, then make sure that you install it in the correct polarity, or it could explode. If you have any doubts about your electronics capabilities, then you should not build this circuit.

Step 6: Parts List

Here's the parts list with DigiKey part numbers listed.

Step 7: The New Circuit Retrofitted

I point-to-point soldered the new circuit to the original connector. It's not pretty, but it works. An oscilloscope can be handy at this stage in case you need to debug the circuit. If everything is working correctly the D1 LED will flash at the desired rate.

Step 8: Button It Up

Once everything was tested and working properly, I used epoxy glue to enclose and seal the new circuit into the lower half of the original case. When the epoxy was cured, I re-installed the flasher in my Concours and it has been working well ever since.

Step 9: Voltage Filter Cap Fix for V12V Voltage Ripple Problem

An extra filter cap C3 was needed when this circuit was tried on a 1982 Yamaha XV750 Virago.
The problem was caused by excessive AC ripple voltage on the V12V voltage supply
when the motor was running at over 2000 RPM. The value of C3 is not super critical,
any value around 1000uF should be OK. C3 should be placed as close as possible to U1.

Thanks to Pofarm for testing and verifying this fix.

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40 Discussions

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admin

9 years ago

This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!

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scdadmin

Reply 9 years ago

I searched for my instructable, but could not find it. Is it published now? Thanks, Scott

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scdadmin

Reply 9 years ago

I've posted a picture of my Connie, which is where the new LED flasher is installed. It's working great :-) I've also updated a number of the steps with more detail.

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dew26m

2 years ago

What changes would have to be made to use a circuit such as this with standard bulbs and on a 6V motorcycle system with a two-prong blinker relay?

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JohnP460

2 years ago

Is this still working long term on your motorcycle? I'm designing a similar circuit, but I was going to use a voltage regulator, PTC resistor, and TVS diode to protect the 555 against voltage fluctations and static which can be pretty extreme, especially on an old motorcycle (I have an old BMW airhead). Is the 555 timer robust enough to handle that?

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scdJohnP460

Reply 2 years ago

My circuit is still working, but adding voltage-spike protection is an excellent idea. Once your circuit is working, if you send me your schematic, I will append it to this instructable. Thanks :)

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RxE

2 years ago

Sorry I should have uploaded details that I have available

Vulcan VN1600 Flasher relay.pngLED 5pin flasher.png
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RxE

2 years ago

This is very informative for those with a three pin relay :-)

However, I have a five pin relay on the Vulcan Mean Streak,

Purchased a replacement five pin for LED flashers but cannot workout the correct terminal match. If that's at all possible?

Anyone who "knows", I appreciate very much :-)

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MarsG1

2 years ago

Hey ! Thanks for the job, great tutorial and very helpfull. I have a few questions to ask you or the community though since I couldn't find my answer on the web.

I'm working on a old motorcycle which uses 1) a very old school relay with a big inductance (magnetic force if you see what I'm talking about) and 2) a 6v voltage. My questions are could I use the same kind of schematic for that bike since I can't modify the current relay and what would I need to change to operate it in 6v ? I can't put the finger on what makes a relay works on 12v or 6v.

Many thanks to whoever will be able to answer to one or both of my questions.

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scdMarsG1

Reply 2 years ago

I'm not sure I understand completely, but I assume the relay is not working and you want to remove the relay and replace it with this blinker circuit. If that is the case, then yes, this circuit can work at 6V, but depending on the amount of current your bulbs require, you may need a larger power transistor.

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MarsG1scd

Reply 2 years ago

Okay so you're saying this circuit would work on 6v/12v without adaptation ?

My current original relay is dead and I want to replace it, so in the same time I replaced the original bulbs by led bulbs. They consume something like 200mA each but I can adapt this load in case this doesn't work. Thanks I'll try then :)

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scdMarsG1

Reply 2 years ago

I think the flash rate is not very sensitive to the supply voltage, so the circuit should flash at about the same rate @6V as it does @12V. You can adjust the C1 cap to a larger/smaller value to change the flash slower/faster rate to your liking. What type of LEDs are you using?

a) If you are rolling your own, then a 6V LED supply is OK since a typical red LED only needs about 2V to turn on. Make sure you use the correct resistor in series with the LED to limit the current otherwise you will burn up the LED.

b) If you are planning to use pre-packaged automotive-bulb-replacement type LEDs that are designed for 12V systems, then they may not turn on @6V (or be too dim).

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MarsG1scd

Reply 2 years ago

I am using pre packaged led bulbs 6v (yes yes, it exists, Itested them). At first I adaptated the load with power resistor (one for each led bulb) but turns out my relay might be dead (it blinks one time when I turn it on on either side then goes back to no light and doesn't move again). So I'm looking for a solution which would work (whether I remove or not my adaptative loads). I'll try that and we'll see !

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MarsG1MarsG1

Reply 2 years ago

By I tested them I mean that they are brighter at 6-7V than the 12V-designed that I tested which need more voltage to make a decent light.

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MarsG1

2 years ago

Hey ! Thanks for the job, great tutorial and very helpfull. I have a few questions to ask you or the community though since I couldn't find my answer on the web.

I'm working on a old motorcycle which uses 1) a very old school relay with a big inductance (magnetic force if you see what I'm talking about) and 2) a 6v voltage. My questions are could I use the same kind of schematic for that bike since I can't modify the current relay and what would I need to change to operate it in 6v ? I can't put the finger on what makes a relay works on 12v or 6v.

Many thanks to whoever will be able to answer to one or both of my questions.

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Juan PabloI

2 years ago

Very nice and many thanks it really eorked great with a minimal changes in the resistances actually this never fail and worked so clean in comparison with 2 other I bought from e bay and they last only 2 months. I will attach a final pic.

12656285_10153357096817078_809939533_o.jpg
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munish4u911ex

3 years ago on Step 5

My bike flasher unit is having two terminals only. What do you suggest? I had made something like in the image attached with a 12V relay, but its flashing rate is noticeably dependent on battery voltage. It also stops flashing at, say, 10V, when rear brake light is activated on low battery voltage.

Flasher-simple.gif
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michaelleewebb

6 years ago on Step 5

hmm, seems your circuit pumps out 85 pulses of power per minute into ground when the bike is on and the turn signal is off. my bike doesn't have the power to spare. could i not place all the 12 volt power lines on the switch except for the 12 volts going into the transistor ?? also a big problem i have is that i turn on the blinker but i forget to turn it off. do you know how to add another 555 to the circuit that would turn off the blinker after 1 minute, even though the switch is still in the on position the blinker stops and won't start again until i turn off the switch and then turn it back on ???

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cdickinson2michaelleewebb

Reply 3 years ago on Step 5

What you need is a 555 in mono-stable configuration mode and then a 555 in a-stable configuration. Basically the mono-stable configuration provides a one shot trigger that powers the a-stable configuration. The a-stable configuration is used to create the actual flashes. The circuit described above is an a-stable configuration. The data sheet for the 555 chip should show you how.

Also, you could use a 556 chip. A 556 is basically two 555 chips in a single package. Another problem is that the mono-stable configuration is designed for a single pulse to trigger it. If your turn signal provides a continual power source, you may have to do some more research. Or you may need to reconfigure your turn signal switch to a momentary switch.

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cdickinson2

3 years ago on Step 5

C2 acts as a power filter. It absorbs any power spikes. If there is any fluctuation in your power generation, and there almost always is in any vehicle, you will want to have a C2 to filter the power.