suprchf Several people have responded to this with suggestions of a 5 volt voltage regulator and/or an electrolytic capacitor in the circuit. Can someone provide me with specs for these items, and where to put them in the circuit, as I would like to obtain and try them. Many thanks for the help thus far. Tom Cockle McKinleyville CA
Several people have responded to this with suggestions of a 5 volt voltage regulator and/or an electrolytic capacitor in the circuit. Can someone provide me with specs for these items, and where to put them in the circuit, as I would like to obtain and try them. Many thanks for the help thus far.
Tom Cockle
McKinleyville CA
Below is a useful link. The stuff might be available from Rat Shack. Use to be at one time. They use more capacitance but I have used 470 ufd and sometimes 1,000 ufd. Depends on what I have in the junk box as I have stripped old electronic circuits. More capacitance and the LED will stay lit, longer.
The circuit I have used is the one that shows the bridge, cap, one resistor and one LED. I like to put a resistor across the cap for a minimum load.
http://www.trainelectronics.com/LED_Articles_2007/LED_102/index.htm
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Yeah the OP has a flashing LED< which is usually something similar to an LM3909 LED flasher integrated in the LED die, they usually need a few more volts.Which is why it worked fine when he tested with a 9V battery - 9V - 1.2V drop in the bridge = 7.8V to the LED flasher. Assuming a halfway decent loco, it should move nicely on 6V DC or less, which is only 4.8V to the flasher.
Now that I mentioned the 3909, that might be a better option. It's a larger circuit since the 3909 is an 8 pin IC, but there is an advantage - the 3909 actually works down to 1.5 volts and below, yet can still supply the LED with at least 2V that it need. So assume fronting it with the rectifier so the flasher works in forward and reverse, it should start flashing with a track voltage of 2.7V, at which point the loco will either be moving very slowly or not at all - a few diodes in series with the motor (if it already has constant headlights, it may already have this - Proto 2000 locos do) and the track voltage will be high enough to activate the flasher before the motor even starts turning.
That's the problem with all this already integrated stuff. You never know what you get. Sure it's smaller than a discrete LM3909 plus the required support components, but you are also stuck with whatever operating voltage it's designed for, no way to change it.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Most LED;s are 2 to 3 volts at 20 ma. I and many others use the bridge and cap with 1 k resistor. Some might use a 1000 ufd cap. I have used 470 and 1000 ufd successfully. Check you decoder main filter caps. The values are written right on the cap. At the average DCC freq, it does not take as much capacitance as a lines powered DC supply.
Same basic components used by a decoder to provide a DC operating voltage. The decoder includes a voltage regulator for the five volt logic voltage to power the IC's.
Keep in mind this won;t make it work any better, really. If the LED needs 5V, then a 5V regulator is correct, but a 5V regulator can;t put out 5V unless the input is slightly higher. Plus you'll still be dropping 1.2V in the bridge. So once again you will need 7-9V on the rails before the LED gets enough power to start flashing. Adding the cap may help if the DCC supply is very "pulse-y" as the peak DC voltage achieved from a rectifier and filter is a tad higher than the nominal input voltage - you get peak instead of RMS voltage, in the case of sine wave AC this is actually significant, with pulse power DC it's highly dependent on the nature and aplitude of the pulses - like my example where a similar sort of thing worked great on one brand of power supplt but not on another. And if the DC supply is already filtered DC - none of this will make a bit of difference.
The bridge rectifier has symbols on tt for connection as does the cap.
Bridge rectifier, 470 ufd cap, 1 k resistor. I have done this. Look at the link below. I would put a resistor across the cap for a minimum load.
.http://cs.trains.com/mrr/f/744/t/189055.aspx
You can see he jumped into this without understanding how LED's work. Some burn out the LED by attaching to the track without a resistor and wonder why the LED does not light when they use the proper components.