In the Feb 2002 issue of MR there was an article on building a lamp resistance tester, does anyone have a copy they can scan and send it to me??
Thanks in advance,
Gloria Wells
Homosassa, Fl
It would be illegal to scan and send it to someone. Get a multimeter and measure the lamp resistance.
You can buy a copy of the magazine from MR. I just did that recently and it is very easy to do online.
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.
Maybe I am missing something... was there something about this lamp resistance tester that allowed you to do something a simple multimeter can't do? I missed that issue, so this is a legit question. (aka, no sarcasm intended)
Dave Loman
My site: The Rusty Spike
"It's a penny for your thoughts, but you have to put your 2 cents in.... hey, someone's making a penny!"
you can use it to find the resistance that will give you the brightness you want with either bulbs or LEDs. You have a power in thru a variable resistor and adjust the resistance to the desired brightness. I have done this but I was told they had a chart on the box around the resistor knob to make chooseing a resister a little faster. That was all, just trying to have something less cluttered to speed up the process. Didn't mean to upset the people here!
sorry for the post, believe me
You can make your own tester. Just remember bulbs are voltage devices. There is a reference to current for bulbs but that is for recommended brightness.
LEDs are current devices., somewheres between 10 to 20 ma with 20 ma being maximum. Don't worry about voltage when powering a LED. Just monitor current.
I have linked to a site concerning lamps and LEDs You can get a rotary switch and various resistors and a small plastic box.
I saw a DIY tester on the 'Net but cannot remember where. Start out with the highest resistance and work your way down. You will need a multimeter to read voltage and current.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
It wasn't a bad question! you can't directly measure the resistance of a lamp, it varies depending on the current through it. If you know the rated voltage and wattage you can get a reasonable stab of the normal operating resistance by just dividing the wattage by the voltage. Otherwise, you can but a small resistance in series with the bulb, and measure the voltage across both. Then you can figure the current through the resistor (and hence the lamp) as the voltage divided by the resistance. And then the resistance of the lamp as the voltage across the lamp divided by the current.
Jeff But it's a dry heat!
Glo4U you can use it to find the resistance that will give you the brightness you want with either bulbs or LEDs. You have a power in thru a variable resistor and adjust the resistance to the desired brightness. I have done this but I was told they had a chart on the box around the resistor knob to make chooseing a resister a little faster. That was all, just trying to have something less cluttered to speed up the process. Didn't mean to upset the people here! sorry for the post, believe me
I looked at the article, and it does not use a variable resistor. What it actually does use is 12 individual resistors of known value and a single pole/twelve position rotary switch (plus other "stuff" like a decoder, terminal strip, experimenter's circuit board, and a box to contain everything). One end of all the resistors is tied together, the other ends terminate at individual positions on the rotary switch. Each position of the rotary switch is marked on the outside of the box with the value of the associated resistor.
Don't be sorry about the post...if you don't ask a question you won't get an answer. If articles in the magazine are like the prototype drawings they have, then I believe that the "you can make a copy for yourself but can't distribute it to others" rule applies. That's why the illegal to send you a copy comment was made. That being said, I see no reason why some nice person could not make a hand sketch of the circuit and send it to you and let you figure out how to assemble it (I'm computer illiterate and don't have a scanner). Your other option, aside from buying the magazine, would be to check the public library. If you live in a large city, some libraries keep copies of various magazines. If there are train shows in your area, some of the vendors sell used magazines. And if there is a model railroad club nearby, some of them collect the magazines. Maybe you could borrow one.
Most LED installations use between 680 ohms to 2000 ohms. One resistor, one LED is the way to go.
Sometimes the intensity of LEDs in the same batch can vary a little in case you really want to match intensities of different LEDs.
Some people use a miniature 1000 ohm potentiometer and adjust for the desired intensity. Mouser Electronics is one company that carries a large variety of miniature potentiometers.
I have a loco with a 680 ohm resistor which allows 14.8 ma.
My other locos have a 1000 ohm resistor which allows 9.8 ma.
My Spectrum 4-6-0 has 2570 ohms with a diode and only allows 3.8 ma current. Quite a dim headlight.
Radio Shack does not have anymore twelve position switches that I am aware of.
Get a bunch of double clip leads which you will need.
Light bulbs will be a little different story. They vary in intensity with a slight change in current. That might be important in some installations such as MARS lights or strobes. Some people do this quite well with LEDs. Experimenting.
Every golden white LED I have used was exactly the same, or sloe enough that without expensive equipment you couldn;t tell there was a difference - and they all us 1K resistors for about 9ma. PLENTY bright, most any variety of 'white' LED is insanely bright. I mean, you can do the calculatiosn every time, but I've given up since 1K just 'works' and I buy them in quanity from Mouser for cheap.
Bulbs - not nearly so easy to figure out. The multiple resistors on a rotary switch, commonly called a 'substitution box' is the easiest way, just always rememebr ot strat with the highest value resistor and work down, othewise you'll just pop the bulbs. You also should use higher rated resistors, dropping 12 volts for a 1.5 volt bulb can exceed half a watt depending on the bulb current. 1/4 watt resistors are definitely out for such a device. Half watt and 1 watt are what should be used.
For DCC, unless you are doing a special effect like Mars light with a decoder that doesn;t have good LED support, I'd use an LED every time. Unless you screw up badly, the LED will last forever. If you screw up the wiring and forget the resistor, the LED will last about 1 millisecond.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.