LED Emergency Flasher

[n0ce]

I have built a LED Emergency Flasher unit for the top of my vehicle when doing snow removal. I am using yellow LED marker lights. It works pretty well, but it would be much better if I could step up the 13.8 VDC to an estimated 15 to 18 volts to get a brighter flash. (I could determine the desired voltage by using a variable DC voltage supply first.) I'm hoping the short duration flashes will not damage the LEDs. (It is only consuming less than an amp.)

The only way I can think of to do this, is to pulse DC through a step-up transformer, and rectify the output to feed to the LEDs. That may also be a good way to flash them. That will take some trial and error.

Is there a chip package that I can use for most of it, or perhaps a simple trick? (Adding a battery would be undesirable.) Perhaps someone can suggest a circuit to meet my needs.
Thanx, N0CE

 

[kchriste]

Do you have a schematic of the LED Emergency Flasher unit? You may just have to reduce the current limiting resistor's value. However, LEDs have an upper current limit which, if exceeded, would seriously reduce the life of the LEDs.

 

[n0ce]

Reply from N0CE

Good thinking, but these are marker lights sold for vehicles. The resistors are built in and there are several leds/resistors per light. I would like hit them with a little higher voltage. I would experiment on just one light at first, to see if it can be done without damage to the LEDs. Thanks

 

[kchriste]

Another problem with supplying the lights with a higher voltage is that the electronic flasher circuitry may fail at the higher voltage.

I have built a LED Emergency Flasher unit for the top of my vehicle when doing snow removal.

I was under the impression you'd built them yourself. Hence the advice to modify them too.

 

[n0ce]

I planned to only feed the higher voltage to the lights, only. My circuit is a basic 555 timer with the output going to the base of a transistor. The transistor switches 12V (13.8) to the lights. I am quite sure that it turns on fully.

I think what I need to do, now, is to feed the output of the transistor to the primary winding of a toroid, and use the secondary of the toroid to flash the LED lights. As the field collapses, a high voltage spike will be produced.

I will have to research to see what gauge wire, and how many turns to use for both the primary and secondary. I suppose the toroid type may matter as well. I could use some help with this.

 

[audioguru]

If your marker lights are too dim then maybe it is because they are not designed to be bright emergency lights. Emergency lights are high voltage zenon discharge strobe lights, not low voltage and low brightness LEDs.

If you increase the current to your LEDs then they will be bright .... only one time.

 

[kchriste]

As AudioGuru mentioned, a xenon tube would be better and would be just as easy since you are going to use a circuit/coil for voltage boost anyway.
What kind of LED lights are you using? I assume they have a built in current limiting resistor? Could you post a datasheet/link for these lights?

 

[n0ce]

Actually, emergency flashers are being made using LED's. You will see them on emergency vehicles. They are extremely bright, but spendy for my budget.

I'm trying to achieve a decent level of brightness using LED marker lights used for vehicles. At the present time, the unit I have built is brighter than some emergency flashers on the market, and much simpler.

I realize that there are several types of LEDs these days. The type I'm using is quite bright, and I'm trying to push the limit a bit. I have noticed just a couple volts makes a big difference. I'd like to supply 15V to them.

 

[Sceadwian]

N0ce, a couple volts to an LED is A LOT of current, if you read up a bit you'll also see that efficiency drops when you over current them, and their life expectancy drops faster than the brightness goes up. As a simple example a basic 20mm super bright LED will be 90% efficient between 5 and 10ma, then the efficiency drops to 80% as the current goes to 20ma, then it basically goes down linearly losing 1% per ma of higher current, and again brightness does not go up linearly with current, 5 times the current will only get you twice the brightness.

 

[n0ce]

That's interesting. Somehow, the commercial units are achieving great brightness. I thought it must be because they are suppying the LED's with a short pulse of higher voltage, thereby not damaging the LED's.

I am supplying 13.8 volts from a charging 12V system to the lights. The lights have dropping resistors built in. So a 2 volt increase in the supply will be a small increase in current to the LED's. I had hoped to use 15-16 Volts. That would be an 8-16 % increase to Vs. Also, the duty cycle was engineered for 100% and when pulsed, it would be a fraction of that.

 

[audioguru]

Your vision sees 30ms and longer as being a certain brightness. Shorter durations appear dimmer.

You can buy cheap Chinese no-name-brand LEDs that appear bright but are focussed into a narrow angle to appear bright.

Or you can buy name-brand high power, wide angle LEDs.

A huge difference.