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I'm actually replacing my front signal lights with my own custom LED signal lights. I won't go into too much detail but I'm just making a couple of circuit boards to power them. I've added in a 12V 5Watt Zener Diode and a LM7805C Voltage regulator (just to be on the safe side). I've put all the LEDs in a paralelle configuration for this with each LED having it's own 470 Ohm 1/4W resistor. I just hope the load is enough to get around the load sensitive Signal Relay. I don't want to have high speed ticking lights. I don't know how easy it is to get a non-load sensitive relay or if it's just cheaper to add in some more load. We'll see...

I Dont think it's a good idea to use a 12v zener because its intended to kill of the spikes....

Normally the generator could put out up to 14-15 volts in worst case,so if the zener is 12v the 3volts its trying to ground has all the currentpower of the generator behind it(unless you have a seriesresistor infront of the zener) youre most likely gonna fry it

And are you sure about the 470 Ohm resistor?? in bestcase your only gonna put like 7-8mA through the LED's

The 12V Zener is before the regulator. I thought it wouldn't really hurt to have it there but I can always remove it if I need to. The 470 Ohm resister should be enough to feed at least 19mA to a 3V LED.

R = (12V - 3V)/0.020
R = 450ohms (430 or 470 Ohms as a close match)

Let me know you're thoughts...

<small>[ June 28, 2004, 12:45 PM: Message edited by: WyldSide ]</small>

Yeah but you said it yourself that youre going to use a LM7805 regulator (78xx meaning the circuitfamily and the numbers in the xx the regulated voltage)LM7805 = 5v regulator...

Resistorvalue should be: (5-3)/0.020 = 100 Ohm excactely

And maybe you missunderstood me,dont remove the zener,just alter the value to about 16v so its only eating the lowcurrent "High-voltage" spikes and not the "High-current" voltage from the battery/generator from 12v up to where the generator stops at 14-15volts (But remember to put a fuse infront of the zener! if the wattage youve chosen for it is to small it could short out thereby burning your wires)

Can you follow me with the zener?

James, you need to use a solid state flasher unit for 12v. Just like truckers use. You most likely find it at a place like NAPA. Just do not get a three prong, just a two. That is what I remember from previous discussions on the issue.

Ahh Crap, I should have grabbed a 7812. I remember thinking that before. I should quit trying to plan this stuff out early in the morning. Either that or get stronger coffee. Should I just remove the Regulator or would you suggest I still use it. Now that I look at it, it's not all that necessary. Correct me if I'm wrong but another thing to keep in mind is that the Voltage is lower during normal marker light operation and then jumps to +12V during signaling. The rest of the circuit can handle up to 15V if it's not for an extended period of time. I'll try and dig up a larger zener diode though. Perhaps a 1N4745A. Your right, grounding all that extra voltage would not be a good thing. Thanks Taras, I'll try and check what NAPA has to offer. Looks like I opened a much larger can of worms than I had originally thought.

<small>[ June 29, 2004, 02:19 PM: Message edited by: WyldSide ]</small>

He he it wont work good with a 7812 either,you have to keep in mind those regulators need atleast 2-3volts over their specified output to funktion,or their output wont be stable at all

I dont know what you're talking about with "normal marker light/Signaling" maybe thats your bumpermarkers?? we dont use them over here...

Ummm i think a 1W zener i WAY too little what about something like a 1N5353B instead but with a higher breakdown voltage,you can search around for that yourself

I thought that the extra voltage from the alternator would be sufficient to keep the reglator at 12V.

Oh well! That's it! Good bye regulator! I'll just use the new zener diodes and take it from there. I'm running out of time to get all this done. Thanks from all of your advice. I learned a lot about putting LEDs in cars.

<small>[ June 30, 2004, 08:05 AM: Message edited by: WyldSide ]</small>

Youre welcome

If you have somekind of problem with your electronic projects you could give me a PM and ill try to help, I repair it at work and have designed many circuits in my sparetime over the years

Good luck with your markers/blinkers..

Many Thanks! I've done a lot of design work to but it is mostly at the microprocessor and low voltage area. That's probably why I was lost. That and the lack of strong coffee...