Flasher for LED's

Thanks Chuck, but automotive flashers are not adjustable, and will flash 10 LED's at a rate that is way too fast. Tried several a while ago while i was working (45 years) in the auto parts business.

jackson

Try Dallee. Call them up and discuss with the owner. He is pretty good with ideas along this line.

Chris

LVHR

How slow?

Take a look at this on on the bay HERE This should do what you need cost is $8.00 free shipping. Check the video for functions it can do.

How are you getting ten LED's to draw 3/4 of an amp???  The rating for most common LED's is 20ma max, that would give you 200ma for all ten in parallel.  In addition, if you more than a few volts available, you can wire them in series for far more efficient running. 

With a 12V DC source, I'd wire groups of five of the LED's in series, that will give you a current draw of 40ma total for all ten LED's.  With that configuration, you can flash them on much lower current, not to mention not dissipating lots of heat in whatever is regulating the power to the LED's.

John, Am not sure of the current draw as i'm using a cheap Harbor Freight meter, one lead to the + side of the source of DC other lead to + side of LED's. Sign itself is quite complex and to rewire the LED's in series would mean destroying the sign and starting the project over from scratch. Power to LED's is not regulated (altho i can regulate it) but just from a Lionel RW through a full wave bridge rectifier.

jackson

You're running the LED's WAAAAAAY over their ratings, and they will likely burn out very quickly.  You're putting 70-80ma into each of them if they're all in parallel, that four times their maximum current rating!

I'd invest in some sort of regulator to limit the current!  One of the cheap eBay DC-DC power supplies would do the trick.  Personally, I'd see if I could rewire it without starting over, but that's just me.

Next time you do such a project, think about the wiring before you put it all together.

John, Do you mean something like a LM2596? I have almost 40 of them, as i've been using them to convert passenger cars to LED's for over a year now.

Thanks again.

jackson

LEDs in parallel...I take it they are all connected on both ends? and cannot be separated easily, eh?

Because I want to put a resistor in series with each one, either end of the LED, doesn't matter, to even out the current. Then 12 vdc thru 470 ohms in series with each one would limit the current in each one to about the 20 ma current.

For the flashing, you could use a 555 timer set up as an astable. I think a 555 can do 200 ma if it has to and operates up to 15 vdc

http://www.ti.com/lit/ds/symlink/lm555.pdf

forum Sponsor Model train software has flashing LED's.

http://www.modeltrainsoftware.com/bl-213-f.html

I have powered as much as 4 led's with thier circuits and thier circuits are very small.

Chuck,

The LEDs are in very small "H" column that has the "+ " wire on one side and the "-" wire on the other, and each LED has one of its legs soldered to the appropriate wire. Hence parallel, so if one fails the others remain lighted. Would be impossible to separate them without destroying the sign. They are being powered by 12v DC without any resistors in the circuit. Resistance could be added on the main (+) feed - what value?

Am clueless as how to wire a 555 would be wired into this circuit without a drawing or schematic.

I looked at Evans products before starting this project - they wanted me to use their LEDs and when i contacted them, was informed their product would not achieve the results i'm hoping to achieve.

jackson

You could use something like this...

http://www.ebay.com/itm/1PCS-N...;hash=item27ebaede0d

...with a 47 ohm resistor in series with the output.

Here's another one...

http://www.amazon.com/NightFir...keywords=lm555+timer

but it's a kit...I think the first one above is simpler to use.

I don't think you're going to want to try to run 200ma through the 555, it'll get pretty toasty.  You need a hefty circuit to drive all these parallel LED's.

FWIW, I don't spend any time worrying about LED's failing.  If they're operated within their design parameters, they'll be running long after you're pushing up daises!

Chuck, that 47 ohm resistor you recommend will be dissipating 2 watts at 200ma, so you'd really want at least a 5W resistor there.

I think I'd use the 555 timer with a big honkin' switch transistor or perhaps a small signal relay.

Am about to go and wire the LEDs from the out put of a LM2596 regulator, and then measure their current draw. Then some other stuff to do in the train room; be back a little after 9.

jackson

http://www.youtube.com/watch?v=gJmTzIFKvys

For parallel LED's, you need only about 1.5 volts for red LED's.  Just putting the power supply there won't help if you don't set the voltage properly!

OK just returned from the train room. Have it lit to the desired brightness from the output of a LM2596 (11 volts DC) regulator then through a 100 ohm resistor. Current draw is .09 amps. Now to find a flasher.

jackson

eBay module cjack mentions above ought to do the trick.  Power it from the LM2596 set to 11VDC and insert your 100 ohm resistor between the module's output and your LED fixture.  Seller appears to be in the US.

Stan (stan2004) & Chuck (cjack) thanks for the suggestion regarding the

•  NE555 pulse module LM358, and John (GRJ) thanks for steering me in the right direction.

I ordered one and it arrived today, installed it in a few minutes, and it's doing exactly what i wanted. One question though; can i change the value of the resistor to make the LEDs just a little brighter? They are fine as is, but a little brighter would be nice. It came from a company called Direct Voltage in KS; they have some interesting stuff on their website.

jackson

Since you apparently have a meter that measures current, slow down the flash rate to the point where you can get a stable current reading when the LEDs are ON.  So the meter should read the ON current, then 0, then the ON current, then 0, etc.

Apparently with the 100 ohm resistor, you are getting less than 0.09 Amps of ON current (which produced the desired brightness from the previous experiment). According to the eBay listing, the drive capacity of the module is 0.5 Amps.  So you can lower the 100 ohms which bumps up the ON current.  If all you have are 100 ohm resistors, try two in parallel (making 50 ohms).  This may increase the ON current to above 0.09 Amps when the LEDs are ON, but that's OK since it's the average current that you're interested in.   For example, if the ON current turns out to be 0.15 Amps with 50 ohms, and the LEDs are ON half the time, the average current is 0.075 Amps and you're good to go.  Re-adjust the flash rate and you're off to the races.

GRJ: are your LED "passenger car boards" ready for shipping? I've been away.

Wally

I'm hoping Henning's can get them up on the website next week, I do have them in hand.