Friday Electronics - LED turn signals

[leoj]

NOTE: This is my neighbor's handiwork. He's only in the past year found out about JJ (he's a lurker hence my posting this for him), stripped down rigid frame scooters and all the fun. Now he's unstoppable and wanted to share this with anyone out there interested.

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 3^rd 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!

[sentinelT]

Great post, good general tech...

[squatch]

Great post. I love LEDs. Even though I know how to do all of the calculations for ohms, volts, and amps, I don't think I could have explained it as well as you did. Great job.

I love being able to melt people's faces with my 40 LED brake light. It really gets their attention. If I ever get hit from behind and the person says they didn't see me, I can prove to the office (if I'm still alive) that they were talking on their cell phone or drunk.

[Goatbastard]

I have a couple of questions. Why do you need to place the resistors or dual load balancers after the switch? And instead of wiring the resistors in line with each turn signal could you wire it as the dual load balancer is wired? Or is it as such in case you need 4ways? Not the greatest with the electronics.

Chris

[Gazza]

Originally Posted by Goatbastard

I have a couple of questions. Why do you need to place the resistors or dual load balancers after the switch? And instead of wiring the resistors in line with each turn signal could you wire it as the dual load balancer is wired? Or is it as such in case you need 4ways? Not the greatest with the electronics.

If the resistors were before the switch, then the blinker would blink all of the time. The lights wouldn't be flashing, but you'd hear the blinker ticking all the time, and if you didn't have a mains switch it would run all night but be done by the morning.

The resistors in the resistor drawing are wired where the load balancer is. One load balancer resistor wire to each side of the circuit and the common to ground.

Four ways don't really matter, it just means you turn both the left and the right button on at the same time. The only thing you'll notice different with both side blinking is that the blink rate will be slightly faster.

Gazza

[Billdozer2]

Leoj, tell that dude to start posting! I could care less about turn signals, but if he can explain things like that so well, then I'm sure there is more to learn from him. Thanks.

[Gazza]

Here's a little upgrade to the circuit. This has more parts... 1 extra flasher and 2
extra relays... but... it will give you extra brake lights. When you are just braking
the brake light and both turn signals will come on solid. If you are braking and
have a turn signal on that turn signal will flash and the brake light and other turn
signal will come on solid. If you have a turn signal on and no brakes just that
turn signal will flash. This won't let you eliminate the brake/tail light altogether
because it doesn't provide a rear running light, but if you can follow the circuit
you should be able to see how using rear dual filament bulbs (leds) would let you
eliminate the middle tail light, just like HD does with the Nightsters.


As in the point of the first post, the resistors are only necessary if you are
running LED bulbs. If you are running incandescants you can leave them out.

How the circuit works:

When the turn signal switch is off the relay passes the brake light signal (NC
on relay) to the rear bulbs. So they only light when the brake is on.

When a turn signal switch is on, the relay coil energizes and switches the bulb
drive (NO on relay) to the flasher circuit (just as in the original post). Since
current will be passing through the flassher and the resistor (or bulbs), the
flasher will flash that pair of LEDs (bulbs).

Gazza

[Larry T]

Well thought out tech post about making standard flashers work with LED lights. I'm looking forward to more of your tech posts.

But the aftermarket is starting to catch up. You can buy flashers to work with LED bulbs now. Grote 44891 is one of them. I think they retail for less than $20.00.

[20M3S]

Originally Posted by Larry T

Well thought out tech post about making standard flashers work with LED lights. I'm looking forward to more of your tech posts.

But the aftermarket is starting to catch up. You can buy flashers to work with LED bulbs now. Grote 44891 is one of them. I think they retail for less than $20.00.

Yup.

Plug-n-Play LED Flasher units are easily available for under $20, for about $45 you can get them with multiple flashing flashing patterns.

[Brundlefly]

Great post. . .thanks for the info.

[HappyBoy]

Hi everyone - I am the original writer of the post - having now been duly committed as a JJ subscriber by my friend LeoJ. Thanks for the nice replies and also for the answers to the questions and for the additional design ideas posted.

[HappyBoy]

As I indicated at the end of my post, and as indicated by the fine replies, solid state flashers are now becoming available, and at reasonable prices. I just did install one on my custom rigid mentioned, and removed the resistors ("load balancers") shown in my diagrams. The one I used is "standard DOT flasher" from Custom Dynamics (found through online search). The flasher costs $20, is the size and weight of a regular electromechanical flasher, and the best part is, it flashes at recommended DOT intervals independent of the load. Good luck and happy riding.

[HappyBoy]

As I indicated at the end of my post, and as indicated by the fine replies, solid state flashers are now becoming available, and at reasonable prices. I just did install one on my custom rigid mentioned, and removed the resistors ("load balancers") shown in my diagrams. The one I used is "standard DOT flasher" from Custom Dynamics (found through online search). The flasher costs $20, is the size and weight of a regular electromechanical flasher, and the best part is, it flashes at recommended DOT intervals independent of the load. Good luck and happy riding.

[hotsos]

thanks, great info

[ca180]

Originally Posted by hotsos

thanks, great info

+1, excellent info!