LED Turn Signals 101

LED Turn Signals Story
I recently installed LED turn signals on my custom hard tail, and here is the story and some things I found out, and in particular regarding that mysterious ‘load balancer’.

My custom hard tail rides (and looks) like a dream (at least in my dreams), but with a hard mount 1200 CC Sportster engine, can really shake my teeth out at high RPM. In addition to regularly blowing the incandescent bulbs in the turn signals, the electrical setup has been not as robust as it should have been. So I decided to convert to LED turn signals while doing some re-wiring and reinforcing. LEDs are not only highly shock resistant, but have just about an infinite lifetime, and can be made quite bright (and in choice of desired signal colors, lenses and housings).
Selecting and mounting the LED turn signals is no big deal one way or another, with many 3rd party ones to choose from and with many ways to install. But as forewarned, once you install them, they do not blink. I tried it and found this to be true. The recommendation is to use a ‘load balancer’. But being schooled by my friend in true Jockey Journal manners, I set about to find out why and how, and not just blindly install.
Here is how a typical turn signals and flasher circuit looks like:

Figure 1: Typical turn signals circuitry

If all you do first is replace the bulbs with LED lights, all is normal, except the lights don’t blink when you push the turn signal switch. It turns out that the root cause is very simple. Standard bulbs, at around 20-30 watts, and at 12-14 volts, draw a couple of amps. A note on values specified in the writeup: I purposely use rough numbers, or what in engineering is called ’dimensional analysis’, since exact microamps or milliohms do not matter for the basic problem at hand here. Back to topic: normal electromechanical flashers need an amp or two to flash on and off. But LEDs draw only a few milliamps, which is not enough to activate these flashers. Hence the edict to use ‘load balancers’. So what is a ‘load balancer’? Well, turns out it is nothing but a dummy load, or more simply called: ‘a resistor’. By installing a resistor in parallel with your light, when you push the turn signal switch the resistor acts as a dummy load, drawing the amps you need in order to make the flasher work.
So here is what I did and what the circuit looks like with the resistors installed:

Figure 2: LEDs with resistors circuitry
How to pick the resistor? Resistor is voltage divided by current (ohms = volts / amps). You figure you have 12-14 volts from the battery, and you need 1 amp – so a 10 ohm resistor does the trick (remember – just dimensional analysis here). How beefy a resistor? That is important. Power equals voltages times current (watts = amps x volts), so 12-14 volts times 1 amp yields a 10 watt resistor (dimensional analysis here again – our mantra). You can get away with a lower wattage resistor because current flows through the resistor – and hence heat generated - only during the light-on duty cycle. But anything much less and you will blow the resistor soon due to the excessive heat generated. In my case I used 10 ohm 10 watt resistor for each side, and all fits and works great. But at this point in your design dimensional analysis is to stop as you get to choosing specific parts; for your exact solution you will need to measure and try different values if you are not sure, and to account for different flashers, duty cycles, and resistor types. I actually held the resistor in my hand for example while signaling for 20-30 seconds, and found it to warm up slightly but not more, so all was cool. I also tested to see if I get even and consistent flashing, which I did, at about 50% duty cycle, about 1/2 a second on, about 1/2 a second off. Good enough to hit the road!
OK, so back to that ‘load balancer’ (which we now know is nothing but a fancy name for ‘a resistor’). You can use it, and you may even like the package, or it fits best on your motorcycle. Just be aware that it needs to be connected ‘after’ the switches (i.e. on the other side of the switches from the battery and flasher). This is shown in the figure below, and since most of these balancers are dual balancers (two separate resistors in one package) I show that. Sometimes they do not simply configure well with the bike’s existing wiring, but of course you will re-wire as you need to. As far as prices, two resistors cost $2-$3 bucks at Radio Shack, and a dual load balancer costs $20-$60 bucks at various online catalog stores. By the way, the load balancer I considered first appeared to be about a 10 Watt per side (in resistors power is proportional to resistor dimensions, so one can get a rough estimate by looking at them), and each resistor was about 7 ohms.

Figure 3: Wiring with load balancer


Finally, a word about flashers. An alternative solution to allow flashing at the low amperage of LEDs, is to use a solid state flasher designed for low currents. You need to pick a 12 Volt DC one. A Google search on ’12 volt DC solid state flashers’ will give you leads on that. These things are quite expensive and often bulky, as they are intended for traffic lights, police flashers, and the like. They also require three leads per flasher: one in, one out, and one to activate the flashing from a switch. I have no experience with these, but just wanted to ‘round off’ the story.
All feedback welcome!

This write up was originally posted by Leoj on the Jockey Journal

4 Responses to “LED Turn Signals 101”

  1. zigzagon says:

    Man! thats exactly what I have been thinking about the last few days… I have a set of LEDs that I wanna mount on the bike, but realized that I heard something or someone whispering about the resistors. Great move to publish this article!

  2. Soulfur says:

    I’m trying this out very very shortly - off to the store for taps…

  3. paul says:

    You can also use an electronic flasher. I think they are usually used with trailers to let the flashers blink together. Only bad thing about them is that they don’t have the “fast blink” feature to let you know that one bulb is out.

  4. casper says:

    hi there i had the same problem when i fitted leds,i didnt know about resistors so just fitted two dashboard bulbs in holders one each side i placed them in the batt box so cant be seen,prob sorted worked fine been 12 months no probs.
    cheers for the info will know in future.

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