LED Self Flashing LEDs, Stange Things!

[Industrial Toys]

I know this isn't an electronics site, but there are some smart people on here.

So, I buy a Cole Hersey Type of Rocker switch off E-Bay from China, advertised with LED illumination.

No drawings, no support, so I go experimenting with it, trying various dropping resistors to use on my 50 volt gator. Nothing makes sense! I open it, to find an incandescent bulb. So I get my money back and keep the switch.

So, I order a bunch of White LEDs to put in the switch. Since the switch controls a strobe, I figure, why not use a self flashing 2HZ LED. It might make determining if it's on in daylight easier.

Order 50 clear flashing LEDs off Ebay from China.

They arrive. They don't flash!

Get my money back, well half of it, and keep the non flashing LEDs.

Order 100 self flashing Clear LEDS from E-Bay from China. $3.50 cdn! Free shipping.

They arrive. They flash nicely at 12 volts with a 2K dropping resistor.

AT 50 Volts with a 20K dropping resistor, they flash for a few minutes, then fail, either flickering or just go steady.

The LEDs are rated at 3.2-3.8 volts, 20 ma.

Note: At 20 K with 50 volts this circuit could deliver no more than 2.5 ma.

I have run regular LEDs up to hundreds of volts with no problems using only a sufficient dropping resistor.

So, I am curious what's going on here? I'm guessing that when the LED goes off, there is high resistance in the circuit and the 50 volts appears at the (on/off flasher) junction.

I wonder if putting a 3 point something volt zener diode across the LED with the dropping resistor would clamp the voltage and prevent destruction of the junction.

Thanks for any thoughts.

 

[MossRoad]

You lost me at the 50 volt gator....

 

[Mendonsy]

That sounds right to me, but I have never worked with any of the flashing LEDs so that's just a guess. The question becomes how to calculate the resister to get 20ma through the LED with a zener in parallel. I think that is going to take some experimenting. Maybe you could use a higher voltage zener since they didn't blow at 12 volts??

 

[Industrial Toys]

Hi:

The E-Gator is 48 volts, so around 50 something fully charged.

I was thinking the same thing. It might be a question of what I have for Zeners.

I have a few extra LED to blow up!

Maybe I should assemble one at 12 volts just to try my theory in sun light.

 

[MossRoad]

Ah. E-gator. Makes more sense. Thanks.

 

[Industrial Toys]

I am happy to report that with the inclusion of a 4.7 volt 1 watt zener diode the flashing LED seems to survive at 50 volts. Brightness excellent in the rocker switch and the LED fits perfectly in place of the grain-of-wheat style bulb.

Zener voltage just chosen arbitrarily. Others I had were all higher voltage.

 

[mbohuntr]

Your solution sounds right. Remember, the Vf(led) must be subtracted from the Vs to calculate the current and the dropping resistor.

just went to Jameco, self flashing LEDs had a limit of 15V.

LED Resistor Calculator

 

[Mendonsy]

It sure seems like limiting the open circuit voltage to 4.7 should solve the problem with the flasher circuit. Time will tell.

 

[Industrial Toys]

I assembled it and got the zener polarity backward so had to redo it. But today, installed it and am quite pleased. It's nice to see the visual indication flashing and not wonder if it's on.

I ordered another switch, this time to use on the JD with 12 volts. Funny. The E-Bay Chinese vendor apologized profusely for advertising his switch as LED and it was not, but they are still up advertised as LED. For a couple of bucks and free shipping, I ordered another and will put in my flashing LED.

 

[CNC Dan]

Self flashing LEDs sometimes don't use a resister. And you have to limit the input voltage below their max rating, not just limit the current with a resister. You should be able to get a spec. sheet.