Here's the deal, I'm doing a similar light setup like in this thread. The difference is that I have 4 bulbs in the front of my engine and 2 in the back. According to the results of this calculator, I need to use a 1K ohm resistor for the rear pair of bulbs and a 680 ohm resistor for the front four. When I hook up the resistors to the decoder outputs and then to the lights, they look good and all seems well. I use a multimeter to get a reading from both outputs past the resistor and I get 1.4 ~ 1.5 volts, so the resistors are working.
Now after I solder the resistors and the wires to how I want them, I hook up a bulb to either output, and the bulb seems a lot brighter than what it looked like before. I take off the bulb immediately so that I won't burn it out. When I get a reading from the multimeter, it shows 16 ~ 16.x volts past the resistors. The reading fluctuates but stays pretty much around 16 volts. So what happened to the resistors? Why are my resistors not working properly after I solder everything? I'm using a 25w soldering iron and I've also used a 15w iron with the same results. Am I damaging the resistors, if so how do I prevent that from happening? Any other ideas as to what it could be?
Some stats:
bulbs (1.5v 15mA microbulbs)
resistors (1K ohm 1/4w and 680 ohm 1/4w)
irons {25w (primary) 15w (just to test out if it was heat)}
decoder (bachmann decoder - nothing wrong with it)
TONY
"If we never take the time, how can we ever have the time." - Merovingian (Matrix Reloaded)
Tony:
Can you take the resistors out of the circuit and test them to see if the resistance is still the same as when you started?
Joe
jasperofzeal wrote:Here's the deal, I'm doing a similar light setup like in this thread. The difference is that I have 4 bulbs in the front of my engine and 2 in the back. According to the results of this calculator, I need to use a 1K ohm resistor for the rear pair of bulbs and a 680 ohm resistor for the front four. When I hook up the resistors to the decoder outputs and then to the lights, they look good and all seems well. I use a multimeter to get a reading from both outputs past the resistor and I get 1.4 ~ 1.5 volts, so the resistors are working.Now after I solder the resistors and the wires to how I want them, I hook up a bulb to either output, and the bulb seems a lot brighter than what it looked like before. I take off the bulb immediately so that I won't burn it out. When I get a reading from the multimeter, it shows 16 ~ 16.x volts past the resistors. The reading fluctuates but stays pretty much around 16 volts. So what happened to the resistors? Why are my resistors not working properly after I solder everything? I'm using a 25w soldering iron and I've also used a 15w iron with the same results. Am I damaging the resistors, if so how do I prevent that from happening? Any other ideas as to what it could be?Some stats:bulbs (1.5v 15mA microbulbs)resistors (1K ohm 1/4w and 680 ohm 1/4w)irons {25w (primary) 15w (just to test out if it was heat)}decoder (bachmann decoder - nothing wrong with it)
Wel that's a strange one. I'll assume you are positive that you are soldering the identical circuit that you tried first. Resistors are not horribly heat sensitive so I doubt you are damaging them witha 25W iron but just in case use a heat sink between the resistor and the solder joint. Aligator clips can be used as a soldering heat sink as well. It's basically a metal clamp that takes the heat away from the component.
JoeinPA wrote: Tony:Can you take the resistors out of the circuit and test them to see if the resistance is still the same as when you started? Joe
Joe,
I took a reading of just the resistors with my multimeter and the results were close to the resistors' value, 999 ohms for the 1K ohm, the other one was right on 680 ohm. So according to the tool, the resistors seem to be of correct value.
BlueHillsCPR wrote:...I'll assume you are positive that you are soldering the identical circuit that you tried first. Resistors are not horribly heat sensitive so I doubt you are damaging them witha 25W iron but just in case use a heat sink between the resistor and the solder joint. Aligator clips can be used as a soldering heat sink as well. It's basically a metal clamp that takes the heat away from the component.
...I'll assume you are positive that you are soldering the identical circuit that you tried first. Resistors are not horribly heat sensitive so I doubt you are damaging them witha 25W iron but just in case use a heat sink between the resistor and the solder joint. Aligator clips can be used as a soldering heat sink as well. It's basically a metal clamp that takes the heat away from the component.
Kevin,
I'm 100% positive that I'm soldering the identical circuit that I first tried. I am using some self-locking tweezers to hold the resistor while I solder the wire to it. I was only using it as an extra hand but it seems to work as a heat sink as well.
Here is a stupid thought: these resistors are years old, I'm talking more than 5 years old. Can they be "expired" and maybe not be good under electrical load? I know it sounds stupid but I did warn ya. I'm thinking no since I was getting working results on my test before I soldered. Thanks for the help so far, any other ideas?
If I read everything correctly, you have no problem at all.
The voltage drop across the resistors depends on the current bening drawn. So, when you have no lights, you have no current, and you see the full voltage.
When you only hook up one of the bulbs, all of the current is going through it, rather than being split between the 2, or 4, so get get a brighter bulb.
Hook everything back up the way you had it, before you apply power, and life should be good.
Jeff But it's a dry heat!
Jeff,
I didn't want to risk using the bulbs on the engine since if they were to burn out, it'd really make my day bad. Two of the bulbs are ditch lights and it would be a PITA to replace them. I did what you suggested, but I used an LED instead of the bulbs, well two 1.5v bulbs = one 3.0v LED (different mA though). So when current was running through the two bulb wire with one LED (rear), the meter read 4.3v going past the resistor. In the front wire (4 bulbs), I used 2 LEDs and got a reading of 7.2v past the resistor, I guess I should up the value of the front light resistor a bit. I know the mA was probably different in the LED than what the bulbs have, but I'm considering upping the wattage of the 1K resistor to 1/2w instead of the 1/4w, would that make a difference? Thanks for the help so far, everyone.
jasperofzeal wrote:Kevin,I'm 100% positive that I'm soldering the identical circuit that I first tried. I am using some self-locking tweezers to hold the resistor while I solder the wire to it. I was only using it as an extra hand but it seems to work as a heat sink as well.
When you say "hold the resistor" are you clamping the wire lead in the tweezers? If not you are not getting the benifit of the heat sink by holding the body of the resistor.
AHH! Of course...no load...
jasperofzeal wrote: Jeff,I didn't want to risk using the bulbs on the engine since if they were to burn out, it'd really make my day bad. Two of the bulbs are ditch lights and it would be a PITA to replace them. I did what you suggested, but I used an LED instead of the bulbs, well two 1.5v bulbs = one 3.0v LED (different mA though). So when current was running through the two bulb wire with one LED (rear), the meter read 4.3v going past the resistor. In the front wire (4 bulbs), I used 2 LEDs and got a reading of 7.2v past the resistor, I guess I should up the value of the front light resistor a bit. I know the mA was probably different in the LED than what the bulbs have, but I'm considering upping the wattage of the 1K resistor to 1/2w instead of the 1/4w, would that make a difference? Thanks for the help so far, everyone.
Changing the wattage of the resistors won't change a thing.
Try to jump between LEDs and lamps is going to be a bit of a challenge, since they don't act the same. So I'm not sure I'd put much stock in that test.
When it is "full on" a lamp looks pretty much like a fixed resistance. In the case of your bulbs, that's about 100 Ohms. The LEDs should look like a fixed voltage (I'm a bit surprised at your results there, the voltage across the LED isn't changed by the resistor.)
So, are the two and four bulb sets in parallel, or in series? If they are in parallel, then the resistance the two bulb circuit sees is around 50 Ohms. You've got about 16 volts to drop, you want 1.5 V of that for the lights, so you need about 450 (470 would be what you can find) Ohms in series with that. If they are in series, then the circuit sees 200 Ohms, but now you want 3 volts across the bulbs, so 1 kOhm (1000 Ohms) would work (a little less maybe, but this should work).
If the four bulbs are in parallel, then a 270 Ohm resistor should work, in series, I'd try 680 Ohms.
As a retired RadioShaft manager, the line about resistors being past their expiration date is hilarious. Look in the drawers of an older location and you'll find packs of parts so old they don't even have barcodes on them. Then again, today's Shackies wouldn't know a resistor if it ran up and bite them! Worst resistor joke ever: "Resistors are feudal!"-The Borg
Good luck people.
jasperofzeal wrote:When I hook up the resistors to the decoder outputs and then to the lights, they look good and all seems well. ... I solder the resistors and ... I hook up a bulb
This is just one reason why I am in the one bulb - one resistor school of thought.
Edit- after rereading the replys to this thread I guess Vail & Southwester already said the same thing. Just used different words.
TZ-
One bulb-one resistor is the best way to go, for sure! I'm in N-scale, so I sometimes don't even think of the obvious, when there is a little space around!
I finally got to mess with my "issue" some more. Here is where I stand now:
Vail and Southwestern RR wrote:...So, are the two and four bulb sets in parallel, or in series? If they are in parallel, then the resistance the two bulb circuit sees is around 50 Ohms. You've got about 16 volts to drop, you want 1.5 V of that for the lights, so you need about 450 (470 would be what you can find) Ohms in series with that. If they are in series, then the circuit sees 200 Ohms, but now you want 3 volts across the bulbs, so 1 kOhm (1000 Ohms) would work (a little less maybe, but this should work).If the four bulbs are in parallel, then a 270 Ohm resistor should work, in series, I'd try 680 Ohms.
...So, are the two and four bulb sets in parallel, or in series? If they are in parallel, then the resistance the two bulb circuit sees is around 50 Ohms. You've got about 16 volts to drop, you want 1.5 V of that for the lights, so you need about 450 (470 would be what you can find) Ohms in series with that. If they are in series, then the circuit sees 200 Ohms, but now you want 3 volts across the bulbs, so 1 kOhm (1000 Ohms) would work (a little less maybe, but this should work).
I have the bulbs set up in parallel and using the values you gave as a starting point, this is what I ended up with.
I started with the 4 bulb set up. Since I didn't have a 270 Ohm resistor, I used 2 resistors to get a 280 Ohm resistor (180 Ohm + 100 Ohm). With this set up the voltage output was 1.34 volts. All 4 bulbs were lit but they were kind of dim. I don't know how I did the math in my head, but I guesstimated that about 220 or so Ohms would get me close or slightly below 1.5 volts. I didn't have a 220 Ohm resistor on hand, so I combined two resistors and made a 218 Ohm resistor (150 Ohm + 68 Ohm). Now with this setup I got 1.66 volts going to the bulbs. With 218 Ohms, the bulbs burned the way they're supposed to, nice and bright, but the slightly higher voltage going to them concerns me. I'm thinking that I was right in assuming that 220 Ohms would put me at or slightly below 1.5 volts, so I'm going to see if I can find one at the store.
For the rear lights (two bulbs) I originally had a 1K Ohm resistor hooked up and these bulbs are also wired in parallel. I didn't try a 470 Ohm resistor because I thought that it was too low for two bulbs. I did burn out my 2 test bulbs (not the ones in the engine thankfully) because I had hooked up the wrong resistor. I wanted to use a 680 Ohm resistor (blue, gray, brown) but I mistakenly hooked up a 68 Ohm resisor (blue, grey, black) to the circuit and as soon as I turned on the lights, BAM gone in a flash....literally. It took me 2 more bulbs to figure out my mistake .
So when I finally got the correct resistor hooked up to new bulbs, they didn't light up, and the multimeter showed a less than 1 volt going through to the bulbs. 680 Ohms was too much, so I lowered it to 560 Ohms, and I got 1.35 volts, bulbs were on but still a bit too dim. I then lowered it to 538 Ohms (470 Ohm + 68 Ohm) and I got 1.48 volts. Success, bulbs are burning bright and safely under the recommended voltage.
My next task is to raise the value of the front headlight resistor from 218 Ohms to about 220 Ohms or so. What also concerns me is the heat that these resistors are putting out. Is there anything I can do about that? I guess I should have used see-through fans on my model to let the heat out. Seems like I'm done with my dilemma, thanks again for everyone's help.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
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There's no point in trying to go from 218 to 220 Ohms. The resistors you have are probably 5% tolerance resistors, so they are already +/- 10 Ohms, at least.
As far as the wattage rating, 1/2 W resistors have to dissipate the same heat as the 1/4 W ones, but they can handle it! A bit of quick thinking does suggest that 1/2 W restistors should probably be used, since your lights are in parallel. But the benefit is resistor life, not less heat, the heat still has to go somewhere.
I think I made a little flub in my calculations. but you've figured things out, so I am not going to redo it!
I don't take the credit for figuring out the resistor puzzle, I have you all to thank for that. I'm considering installing a make shift heatsink to help with the heat issue, or maybe I'll use surface mount resistors, not sure what route I'll take. It'll probably be easier for me to just install a see-through dynamic brake fan on my engine. The fun never ends......