richg1998My NCE Power Cab has a 3mm red LED and 1k resistor tied to the output to indivate DCC, a form of AC and does not blink.
Well all the LED's need a resistor for its self. I have used LED's on DCC using just the rail power with a resistor to the LED On one leg. I can't see any flicker of the LED. USED on loco's all the time with DCC for H/L.
I guess my point would be, since I have worked with LED's since 1972, I would never try that. Always used DC. What I was taught.
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.
OvermodWhat he means is this: imagine there are two LEDs in parallel, hooked up so they are opposite in polarity. They share a common resistor.
That's not the part I had trouble with.
The part I had trouble with is that Greg said since with AC, the current switches the LED on only when it is flowing in the right direction, it is only on half the time, so it only needs half the resistance.
It seems to me, the LED is either on or off even if it's only for 1/60th of a second. It would still need full resistance.
He's probably right. I just can see how.
Chip
Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.
wvg_cayou can also use a diode, either single or in two, to convert AC to DC, it's easier on the LED I think ...
Diodes in a bridge rectifier have the effect of reversing the polarity of every half-wave of the AC, so it turns into DC with ripple at 120Hz. You can smooth this with a proper LC circuit (where the cap evens the voltage and the inductor evens the current) to get rid of any visible on-off flickering, but you may still notice 120hz brightening or dimming -- most people don't find that objectionable.
One fun thing you can do is see the effect of persistence of vision with an LED running on AC (or better yet an LED digital clock with matrix drive) -- light it up in the dark and then quickly wave it or move your head...
SpaceMouseGranted you are talking to someone who gets the heebee-geebees when you start talking Ohm's Law, but this doesn't make sense to me. The current is either going the right way or it isn't. It seems the resistance would still be the same.
Now feed it 60-cycle AC. First one diode lights, then 1/120 of a second later it goes off and the other lights up, and they go on alternating 60 times a second each. But the only electricity going through the resistor is that which is going through whichever diode is on at the moment.
I guess that is why everyone seems to use 12vdc for accessories. Much easier to deal with.
My NCE Power Cab has a 3mm red LED and 1k resistor tied to the output to indivate DCC, a form of AC and does not blink.
Make sure you have fuses with that much power from a computer power supply. I know what those are capable of.
There are online companies that are much cheaper than Amazon for parts.
wvg_ca you can also use a diode, either single or in two, to convert AC to DC, it's easier on the LED I think ... plus a dropping resistor in line ... from 12 volt to the two to three that your LED will use .. a diode or resistor is only a few cents
you can also use a diode, either single or in two, to convert AC to DC, it's easier on the LED I think ... plus a dropping resistor in line ... from 12 volt to the two to three that your LED will use ..
a diode or resistor is only a few cents
I already have a bus with 30 LEDs pre-wired in parallel.
MisterBeasley You could use a single bridge rectifier for a single LED bus with multiple LEDs. The LEDs will now pulse at 120 Hz, since you are giving them full wave rectification, not half.
You could use a single bridge rectifier for a single LED bus with multiple LEDs. The LEDs will now pulse at 120 Hz, since you are giving them full wave rectification, not half.
Okay, I guess I'm getting an education. If I understand Professor Google correctly, a single bridge rectifier effectively converts AC to DC.
If I had one, that would be great, but for the cost of 5 with free shipping, or one if I pay shipping, I can get two 12V DC power supplies from Amazon.
It takes an iron man to play with a toy iron horse.
On the other hand, and it might be slightly overkill, I have an 800W computer power supply that delivers 12V DC.
Gregyou would use half the resistor value for the same intensity if only driven half the time. if you have multiple LEDs to drive, connect two to the same resistor but with one with opposite polarity
Granted you are talking to someone who gets the heebee-geebees when you start talking Ohm's Law, but this doesn't make sense to me.
The current is either going the right way or it isn't. It seems the resistance would still be the same.
On the otherhand, using the same resistor for two LEDs and cross wiring them does make sense, because one will be getting juice while the other isn't.
the intensity of LEDs is often controlled using a PWM signal, turning it on an off quickly. you would use half the resistor value for the same intensity if only driven half the time. if you have multiple LEDs to drive, connect two to the same resistor but with one with opposite polarity
you should be able to use the same AC source for LEDS wired above and incandescent bulbs with the appropriate voltage rating
greg - Philadelphia & Reading / Reading
1) Okay, I get that it will blink on and off 60 times a second. But can you tell? Will it send an autistic person into seizures?
2) Can you run LEDs and grain of rice bulbs in parallel off the same circuit. (Without the resistors.) Here's the LED part.