Help with LED signals

[SuperNaked]

I'm trying to wire up some custom LED signals on an older (89) bike and am having trouble getting them to flash at all. At this point I plug them in and they come on solid. Has anyone else had any experience with LED signals that could give me some ideas?

Thanks, Jason

[Unregistered]

When I did all LED's on Martha's 600R we had to wire in resistors to put enough load in the systme to make the flash. Before they would just come on and stay on. I'll get the number off of the extra one I got left and PM it to you.

[notacuban]

Light Emitting Diodes - LED's

Now, in order for an LED to function properly, the current through the LED must be limited by a resitor. The resistor must be wired in series with the LED. In fact, the best performance is achieved by wiring all the LED's in your system (in this case, a turn signal) in series...that is, line them up in a row as opposed to side by side (parallel). How do we determine, what resistor(s) are needed for the system? Well I'm glad you asked. Let's take a look at Ohm's law, shall we.

Ohms law states that R = V/I R= resistance, V = voltage, I = current

Let's take a look at an example. Typical LED's are rated between 1.5V and 2.5V. Let's assume 2V. Let's say we have 4 LED's wired in series in a 12V system each rated at 2V.

V = VS - VL where VS = 12 and VL = sum of LED's = 2+2+2+2 = 8V

V = 12 - 8 = 4V

The max current of LED's is usually around 30mA, so let's just say that the required current in this case is 20mA to be safe.

I = 20mA = .020A

Let's put it all together now:

R = 4V / 0.02 = 200 Ohms

Now, the nearest value to 200 Ohms is 220 Ohms....so this is the resistor required for the system. Now make sure you wire the resistor in series with the LED's.

Now wasn't that fun kids!!!!



But what do Cuban's know about electronics??
:D :D :D

[srtpntman]

yeah, what Mark said....

[SuperNaked]

What if they are wired in parallel?

[CNI]

Mark, yous iz sew smarts! :D

[notacuban]

LED's V.2

The problem with running LED's in parallel is that due to the nature of LED's, the resistance through the LED is dynamic...that is...it changes as a function of current. This makes it very difficult to determin the exact amp draw of LED's. When running in parallel, the Voltage across each LED is the same, and the current is divided up between then. The current draw of 2 different LED's is most likely going to be different, resulting in some LED's being brighter than others.

Another drawback is that instead of 1 resistor for the system, you need 1 for each LED. But, if you don't care about any of this....here's how you figure your resistance.

Let's go back to Ohms Law...shall we.

R = V/I
R = resistance
V = voltage
I = Current

Assume: 12v system. 2v LED's. 20mA draw through LED's. LED's run in parallel.

So: R = V/I => R = (12-2) / 0.020 = 400Ohms. So you would get the next resistor size above 400Ohms and run it in series with EACH LED run in parallel. So if you have 4 LED's run in parallel, you need 4 resistors run in series with the LED's otherwise you'll let off the magic blue smoke :)

Another drawback is, that let's say you have 4 LED's as in the previous example, that's a 20mA draw for each LED in the system, so your total draw for the system would be:

4 x 20mA = 120mA as opposed to the LED's run in series where the draw is only 20mA for the whole system. When run in parallel, you're giving off alot more power in the form of heat from the resistors, therefore wasting more energy. Just food for thought.

Hope this helps!!!

[notacuban]

A little diagram...

[Pete 954]

When you buy LED's, you are supposed to buy the load equilizer also. The cost is $5 and it taps into the blinker wire without cutting or splicing, and has the correct size resistor already in it. Maybe you can go to your favorite parts store and get one.

[notacuban]

Good call Pete....sometimes it's a whole lot less pain in the a$$ to just buy the fix as opposed to fixing it yourself....

but not as fun :D :D :D

[Pete 954]

I hear ya, Mark. But you have to remember, what we call fun, others may find confusing.

You can be the teacher...I just want to take roll.....

Beuller?.............Beuller?