Which one goes on the long end of an LED?
And while we’re on the subject of mysteries, what is a crossover vehicle and why is everyone making one all of a sudden?
In a DC circut red wire is generally positive
Don’t forget to hook up a 1000 ohm resistor to either leg of the LED before it’s connected to 12 volts. As long as the resistor’s connected to the LED, you can test it either way; hook it up one way and if it lights up, it’s right, if it doesn’t, flip the wires.
Modelmaker-Don’t you mean 100 ohm? (brown,black,brown,gold 10x10)
No he meant 1k Ohm, brown,black, orange. EDIT red (sometimes the fingers go faster than the brain!)
You need to drop in a bit over 10 Volts, at a current of no more than 20 mA (both depend on the LED). 1k Ohm will limit the current to around 10 mA. (ish) 680 Ohms might work well, also. The ‘best’ value depends on the LED, but 1k is a good generic place to start.
Red goes to the long end, which is positive.
A crossover vehicle is a one that combines car-like handling and fuel economy, with truck and suv-like utility. Most have 4WD or AWD as an option, an important consideration in the northern climates. Imagine a station wagon on steroids. Some of the more popular domestic models are the Ford Escape, Mercury Mariner, Chrysler Pacifica, Saturn Vue and Buick Rendezvous.
Why are we building so many? The price of gas is the main reason. They are lighter with a smaller frontal area. They will continue to become more popular as people migrate away from full size trucks and suvs. A recent internal study has shown this will be the fastest growing new vehicle segment.
We just got a new one and it is very nice.
I have been enjoying the PR from Train City.
Jim
That’s interesting. I was playing around with some 3 volt led’s yesterday and anything over about 500 ohms was WAY too dim. I found 150-180ohm worked well with my MRC which actually reads out 13.89 volts. I had to go a little over 1000 ohms when I tried them on the Acc terminal which reads 18.3 v AC. Hmmm…Wonder what’s up with that?
Granted, it was a Radio Shack led grab bag.
I just rented a 2007 Chevy Equinox and found it to be a uncomfortable and poorly designed vehicle. I will say that it had a nice bit of “get up and go”. I can’t speak for fuel economy since it only had 6 miles on it when I rented it, and it wasn’t quite up to it’s full potential yet.
Wow!! Talk about getting off topic (as I make my contribution to it all).
The Red wire… no wait!
My bad!
-George
OK, here is the abbreviated lesson on LEDs and resistors…
The point of the resistor is to limit the current through the LED. The LED has two ratings that are inportant for our purposes. There is the forward voltage, and the max current. The forward voltage is what the voltage drop across the LED is going to be. You don’t control that. The purpose of the resistor is to drop the remainder of the supply voltage, and by selection of its value to limit the current to something under the max rating of the LED.
So, let’s say you have a 3V LED, with a max current rating of 30 mA (a number picked out of the air, don’t even know if there is such a thing). For a 12V supply, you need to drop 9 Volts over the resistor. Let’s start by limiting the current to 20 mA. So Ohm’s law is V=IR (don’t ask why current is I, it just is!) So 12=0.03R, R=12/.03= 400 Ohms. If that doesn’t make the LED bright enough you can adjust R down, so long as you keep the current under the max.
So, there isn’t a one-size-fits-all number, it depends on the LED and the supply voltage.
Jeff-Thanks. Yea, I get that. What happened is I have a grab bag full of unknown LED’s that I was playing with. The couple that I was using would barely light over 500 ohms. I opened a known pack of 3.3v, hooked up a 1000 ohm and they lit up fine. Got the proper voltage drop on my meter too. (guess that’s why the grab bag was so cheap.)
Hate the color of those clear golden colored ones. Yuck!
Chip-Sorry. Didn’t mean to jump on your post.
Just for the record, a 1000 ohm resistor would be color-coded brown(1), black(0), Red(two more 0’s). (I hope I didn’t miss a correction above.) The resistor must carry the voltage difference between the LED voltage and the supply voltage. The voltage it will carry is the current in Amps multiplied by the resistance in Ohms.
Jim
To keep this discussion in the area of trains. Crossover SUV’s are similar to the ill-fated END Aerotrain of the fifties when GM attempted to make passenger cars out of bus bodies. They lacked the suspension technology to provide a smoothe ride. The original and current large SUV’s are based on truck bodies. There typical “spotting feature” is the rigid, solid axle in the rear. Modern SUV’s are called crossovers because they are built on automotive chassies and have automotive type independent rear suspensions. The 'spotting feature" on these vehicles is the differential that is attached to the body and does not follow the motion of the wheels. The wheels are able to move “independently” of each other and relative to the differential. of Solid axle vehiclehandling is poor because
So what your saying is the Aerotrain with the independent suspension has both a better ride and better traction?
Not an expert on LED’s, but crossover’s that’s a different story! [:P]
Not an expert on LED’s, but crossover’s that’s a different story! [:P]
Sorry about the double post. I have no idea what happened there…
-beegle55
Yeah, as I was walking the dog late last night I was thinking I might have done that. But I realized the point wasn’t the colors, but to point out the reason for the resistor, and why there isn’t any one value. The resistor drops the voltage that does not drop across the LED (a number we know, based on the LED). The value of the resistor determines what current must flow through it to drop that voltage, and hence determines the current through the LED, which we want to keep below the max allowed.
That is a distinct possibility. The buses produced back then did not have smoothe rides. Traction is a non-issue since railroad wheels have flanges, but the suspension dynamics have to match that of solid-axled vehicles.&n
I thought I was being clever when I used the word Aerotrain–I really wanted to know it the crossovers were smoother and had better traction.