Flickering LED's

Run the leds on dc voltage 

A full wave bridge rectifier and a filtering capacitor should work towards eliminating the flicker when powered via an AC source.

bmoran4 posted:

A full wave bridge rectifier and a filtering capacitor should work towards eliminating the flicker when powered via an AC source.

I'm not an "Electronics Kinda' Guy".  Could you please show me what these items you speak of look like and where I may find them?  Will using these diminish the brightness of the LED's?  Thank you for your reply.

Chief Bob (Retired) 

cjack posted:

Run the leds on dc voltage 

The reason I am using AC power is because it was handy.  Thank you for your reply.

Chief Bob (Retired) 

The suggestions for a full-wave rectifier and filter cap are the hot ticket, that will eliminate the flicker.  I'd recommend at least a 1,000uf 35V capacitor for your application.  With DC from a bridge, you'll also get more voltage, so the resistor will have to be sized appropriately.  Compute the values as if you're getting around 20 VDC from the supply.  I'd probably start with a 33 ohm 2W resistor if both strings of those LED's will be in parallel, that will be totaling 240ma.

For a guy who claims not to be an "electronics type", you knew enough to use an LED serial/parellel calculator from the internet. That's not bad.

Unless you are comfortable with soldering and prototype circuit boards, I would suggest that you buy an AC to DC wall wart that outputs 12 vdc. Then use the calculator again to figure the resistor values.

When you run LEDs on AC, they only light during half the AC cycle, so you get flicker.  Also you will shorten the life of the LEDs unless the 2 parallel strings are connected with opposite polarity.

Here is a filtered rectifier circuit:

Connect AC to the two bridge rectifier leads marked ~, and you get DC voltage from the + and -.

Make sure you match the polarity of the capacitor to the bridge rectifier (+ to +, - to -) or you will have an exploding capacitor.  The capacitor "fills in" the gaps between the peaks so you won't get any flicker.

Pay attention to GRJ's advice about the filtered rectifier circuit increasing the DC output voltage and requiring a bigger resistor.  He's smarter than most of us with half his brain tied behind his back.  

I was about to question your entry of 120ma in the LED calculator, as most LEDs only draw 20ma.   You must be using the "high power" LEDs that do draw 120ma.   That's going to be one bright tower!!  Pictures, please!

Bob

John markets an led driver circuit that has some adjustability...

http://hennings-trains.shoplig...regulator-2-pcs.html

I don't recall the current capability but John will. It's quite capable for lighting a passenger car from too bright down to sleeper car.

Chuck, it's not suitable for high current applications.  It's a constant current design and ranges from 5ma to 45ma current output.  My board is pretty much for small lighting projects, especially rolling stock and passenger cars.  I just used one in my Tie-Jector work car, the single bulb the factory used was pretty lame.  Now it has work lights for the deck, one at the rear, and a lighted cab.

PUFFRBELLY posted:

bmoran4 posted:

A full wave bridge rectifier and a filtering capacitor should work towards eliminating the flicker when powered via an AC source.

I'm not an "Electronics Kinda' Guy".  Could you please show me what these items you speak of look like and where I may find them?  Will using these diminish the brightness of the LED's? 

The bridge rectifier is a 4-legged device, the capacitor is a 2-legged device.  The above are representative listings from eBay showing you'll have leftover parts to share.  If you go this approach, one of us will give you exact hookup instructions.  The brightness is controlled by the size/value of the resistor.  It appears you entered 16V to the LED-calculator program; these programs assume smooth DC voltage in calculating the resistor value.  If you actually supplied 16V AC, you actually getting less brightness than you think; the math is a somewhat tedious but do not be concerned about brightness.  Using the approach suggested, you will eliminate the flicker AND have at least as much brightness available based on choice of resistor value.

Separately, you have the 1033 available so it's "free" but if you don't want to mess with bridge rectifiers and capacitors, I like Leo's suggestion about finding a DC wall-wart that puts out a fixed DC voltage.  Then all you need to mess with is the resistor value.  This would be a good approach if, say, you need to fit all the components on the tower itself.  Or if you plan to do more LED lighting of buildings, station platforms, streetlights, etc. that would of course also require DC voltage.

In either case, I see you are messing with resistors that have power ratings of 1 Watt or more.  Apparently you have some 22 ohm, 1 Watt resistors in hand for your initial try.  I see that on eBay you buy a pack of 20 1-Watt resistors for about 5 cents each. In other words, you don't have a variety of 1-Watt (or 2-Watt) resistors lying around!  The point is if all you have are a bunch of 22 ohms resistors, and you want to experiment with brightness, you can "make" a 11 ohm or 44 ohm resistor using two 22 ohm resistors.  And by combining 3 or 4 of them, you can "make" any resistor value relevant to your floodlight application.  Then, once you find a suitable brightness, you can choose to buy a single resistor of the chosen value...or just neatly bundle up what you have! 

Consolidated Leo posted:

...

Unless you are comfortable with soldering and prototype circuit boards, I would suggest that you buy an AC to DC wall wart that outputs 12 vdc. Then use the calculator again to figure the resistor values.

Note that Chief Bob's LEDs are configured as 2 banks of 4-LEDs-in-series that nominally requires 4 x 3.4V = 13.6V DC per bank.  So a 12V DC wall-wart, while obviously a widely available voltage, would be insufficient. 

Of course he could change his LED configuration to run off of lower DC voltage... for example 4 banks of 2-LEDs-in-series that nominally requires 2 x 3.4V = 6.8V.  Or just use a DC wall wart with a 14V, 15V, 16V, etc. output voltage.  Should be less than $5 for a suitable DC wall wart.

First, thanks to all of those who took the time to reply to my request for help.   It is extremely heartwarming to see the outpouring from so many members willing to help a fellow member.   That is exactly what makes this a tremendous hobby with an equally tremendous forum such as we have here!

Further, I would like to specifically thank Stan2004 for his detailed explanation and examples of components needed to eliminate the flickering that I am experiencing.

All that being said, I'm pretty sure I'm going to go the "Buck Converter" route.  I have one that is AC input with a variable DC output which I can adjust for the 16 volts needed to run the LED's.  Perhaps I'll experiment on a similar project in the future but for now I'll take the easy way out.   Again, A HUGE THANKS to everyone that responded!

Chief Bob (Retired)  

PUFFRBELLY posted:

...

All that being said, I'm pretty sure I'm going to go the "Buck Converter" route.  I have one that is AC input with a variable DC output which I can adjust for the 16 volts needed to run the LED's.

That works too.  You might find when you set the Buck Converter to 16V DC with the 22 ohm resistors, your floodlight will be a tad brighter than when powered by 16V AC as per your initial diagram.  Perhaps obvious, but since the Buck Converter voltage can be adjusted, you can lower the brightness by lowering the voltage (rather than messing with different resistor values).   I'd guess the LEDs with 22 ohm resistor will turn on dimly at about 10V DC and smoothly ramp up in brightness as you increase the Buck Converter output voltage to 16V DC. 

No flicker arrangement of LEDs.

Bobby Ogage posted:

No flicker arrangement of LEDs.

I'm at a loss to see why that would do anything about 60hz flicker.  Each pair of LED's lights on alternate half-cycles of the AC, so they're still flickering.  Perhaps the combination of the two flickering at different times tends to blend them, but they're still flickering.  The only way to truly prevent the visible flicker is to either run then at a higher frequency or on DC.