Capacitors - Need Advice

Well, that's kinda' like the old question, "How long is a road?".

The selection is varied depending on exactly what kind of lighting and other projects you're doing.  I have a ton of values around, and I still find myself regularly ordering a handful from Digikey when I'm doing a project.

100uf,220uf,470 uf, 1000uf 35 volts (polarized electrolytic) will work with the majority of LED projects. (The standard 85 degree centigrade is OK also and not really a concern here).

1000uf usually removes all flicker in passenger cars. Sometimes size is an issue and only smaller ones will fit. For LEDs in buildings 220 uf will take out enough ripple. For DC relays using the insulated rail method 470 uf is usually enough to eliminate chatter but this can vary with relay type

For regulated power supplies for circuits using a 7805 or 7812 regulator (for example) 1000uf is usually good to drive some 555 circuits or switching transistors. Also advisable is to get some .05 or .1 uf NP 100volt ones to remove spikes on the regulated side. However a 100uf polarized one could also be used.

Regulated supplies for sensitive electronic circuits require bigger capacitors but for what we do the above is usually sufficient. No point in discussing that here.

WWW.allelectronics.com has a good selection of capacitors at reasonable prices as well as Mouser and others . Forget Radio Shack unless you just need something in a pinch.

Dale H

If you only want a few, Digikey has very low shipping, you can get first class mail for a couple of bucks on small orders.

If you want to save yourself a big headache you can get one of these converters

I just ordered one.  Someone had posted the recommendation here I cant remember who, but I am too busy to fuss around building a circuit, while the advise on the electrical forum is helpful I think the experts forget that some of us are complete greenhorns that need the explanations dumbed down about 100 levels from where the experts start.

That converter is pretty hopeless overkill to run a few LEDs!

TMack, you are correct in that some do seem to forget that not everybody can understand the answer provided but the reverse is also true; sometimes the person asking the question dosen't have the ability to understand the answer. "Any technology suficiently advanced will appear as magic to those unknowledgeable."

Al

But it's cheap & simple.  

I enjoy experimenting with a breadboard and jumpers, so I will stick with the bit pieces. Thanks all for the steerage. I've become LED crazy, and took apart a Lionel 195 Floodlight Tower for conversion. More to follow after I work out the details.

How many LEDs would that 1 amp converter run. Even though it would be great to build simple circuits (I'd learn something!!) I just don't have the time! Would it light up a few buildings? Many buildings? At 2.5 volts would resistors be needed? Thank-you in advance!!

Pete

Well, figuring most LED's have a max current of 20ma, you could run around 50 on that 1A converter.

Boy that's great, but does any other device like a current limiter or resistor needed?

 Thanks John!!

Pete

You would most certainly need a series resistor or other current limiting device for the LED's!

I use the CL-2 current regulator in some designs, it limits current to 20ma regardless of the input voltage.  It's perfect for LED's.

Thanks again, John! Years ago, I made LED signals in N scale. It easy-everything DC. Just used resistors & they were great! Can't remember the R values. maybe use them as tiny dwarf signals!!  

Pete

Well, if you assume you're running the LED's at maximum current, which is 20ma for many (most) common LED's, you can simply calculate the resistance needed.

Red or green LED's drop about 1.5 volts operating.

Blue and white LED's drop about 3 volts operating.

Take the difference between the LED operating voltage and the supply voltage, and multiply that by 50.  That's the value of resistor you need.

Typically, I rarely run LED's for locomotives at the maximum current, markers I end up using around 5-7ma, whatever looks right for brightness.  For headlights, I'm probably in the 10-15ma range.  To get 10ma instead of 20ma, just double the resistor value.

You've just graduated from Ohm's Law 101.

Hello gunrunnerjohn,

I like your rule of thumb, very helpful.

Cheers

Denny

A lot of this stuff is simpler than it first appears, how complicated can it be with an LED and a resistor.