The lights on my layout are very dim

Discussion in 'FAQs' started by Insey, Apr 1, 2005.

1. InseyMember

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They are much dimmer than what they should be..does this mean there's a short someone along the line? Or maybe a bad light bulb somewhere? My volt meter is reading 13 volts out from the power pack, yet it is rated for 20. Without the load, it's pushing 19.9. All my lights combined are only using 1/100 an amp of current. All my lights are wired in parallel to a main bus. What could be the problem?

Also, what does it mean if a light bulb lights up much brighter than others of the same type? Does that mean it shorted?
2. ezdaysOut AZ way

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Let's answer one question at a time. Firstly, if your rated for 20 volts no load, it's conceivable that your only going to get 13 volts with a load, but that is dependent on the load. I cannot believe you are only using one milliamp with all you lamps. One lamp along can draw 100 mA. I don't know how many lamps you have in parallel, and I don't know the current or wattage rating on your power pack, but I can conclude that you are probably overloading the power pack.

What voltage is your bulbs rated at? If you have one bulb much brigher than the others, I would say it is rated to run at maybe 12 volts while the other might be rated for 18 or even 24.

I don't think you have any shorts, you have more load than your power pack can supply. Try disconnecting all but one bulb and start there. Measure the voltage and current and then compare that with the power pack rating. Watts equal voltage times the current for a quick calculation.

Let us know how you're doing.
3. InseyMember

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I have my layout wiring divided in half right now and when I have only one of the halves running, my powerpack is pushing 19 volts. The problem, I believe, lies with the other half. Something in there is draining all my voltage. Is it possible for a lightbulb to drain voltage like that?

I'm not sure what my bulbs are rated at. I probably bought them about 5 years ago from a hobby shop. I have two different types on my layout - wheat bulbs and house bulbs. They are all exactly the same in regards to each other. Yet one of the wheat bulbs (I use them as street lights) is glowing brighter than the other. Even when disconnected, my layout is still dim.

Btw, I meant to say 1 amp instead of 1/100th. I miscalculated my volt meter's decimal place.
4. ezdaysOut AZ way

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What happens when you connect the second half with the first half disconnected? If it's still running aroun 19 volts, then you are overloading the supply. If it is significatly less, then I think you have a bulb that is rated lower than the voltage you are trying to run it at. It will indeed run brigher. Look at your power pack, it should give you an output rating somewhere, in terms of amps, or watts. Some just say "overall watts" and don't specify either the accessory output or the rail output.

Again, how many bulbs are you trying to run? Mini-bulb voltages are rated at as low as 1.5 volts, up to 24 volts, but the most common usage is 12 volts. If you are running them at 18 volts and they are still dim, I'm still convinced that you are overloading the amount of current you power pack can put out.

Keep isolating the different bulbs, and I'll bet you can run some of them, but not all of them at any time.
5. InseyMember

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Ok, when I just connected the second half, it was dim. My power pack is rated for 20 volts AC output and 7 amps AC.

I have 27 bulbs total on my layout. It never was dim like this. When I first built it, everything worked fine with no shorts and the lights were all very bright. I am thinking I will just redo the entire wiring on it, which would include replacing all the lights and rerunning the main bus. It would only cost me \$40 to do it.
6. ezdaysOut AZ way

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Well, seven amps AC at 20 volts is a rather large transformer and would be difficult to load down. Your power pack could be the problem, but one other thing, can you disconnect the lamp that is burning brighter that the others? Just a thought, but if it was pulling so much power that the rest of the lamps would go dim, you would know it, it would get extremely hot. You could have a high-resistance short, like something laying across the wires, if you do, you should be able to feel around for some heat. If it was working at one time and isn't now, then something changed and I guess you'll have to poke around until you find it, but right now, from what you're saying, I'm suspecting the power pack, and that one bulb that is running bright.

Keep at it. If you do buy new stuff, be sure that the voltage rating on them match the voltage output of your power pack, and also check the current draw. Some bulbs run brighter than others and use more current. You also might consider the use of LEDs.
7. InseyMember

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Ok I just disconnected the other half again and now neither half will light up. This is driving me nuts. I just went ahead and ordered all new bulbs and wiring. Came out to \$37. This is what I got:

Model Power Economy Lighting Set 16V (6)
Life-Like Grain Of Wheat Bulb 14V (2)
Model Power Peel/Stick Light 12-16V (20)

Is it bad to have those two 14V wheat bulbs running at 17V?
8. ezdaysOut AZ way

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Yes it is. They will burn brighter, run hotter and burn out a whole lot quicker. It is much better to run a 14 volt bulb at 12 volts, then their lifespan increases appreciably. Putting a resistor in series with them will drop the voltage enough that it doesn't become a problem, but you need to know their rated current draw to calculate the resistor values. You might consider running them at using a 12 volt transformer that usually puts out around 16 volts at no load.

I've done a lot of troubleshooting over the phone with customers, and I gotta say, without being there, it is difficult to actually tell what's going on, that's why I'm asking these different things. I'll keep working with you as much as you want, just don't get frustrated, that makes things a lot harder.
9. InseyMember

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Ok well I just re-ran the two wires for the main bus. Now I just have to wait for my shipment of lights to get here.

Do you think putting on resistors would be better than running them in a series? RadioShack sells quarter-watt resistors with an assortment of different ohm ratings. It's been forever since I've studied Ohm's law, but do you know off-hand what ohm rating I would need to go from 17 to 14?
10. InseyMember

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11. ezdaysOut AZ way

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I would need to know the bulbs current rating. Do you have a link to that lighbulb offhand? If not, I'll see if I can find it.
12. InseyMember

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13. ezdaysOut AZ way

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No, the 1/4 watt refers to the amount of power the resistor can handle before it burns up. I can find no information on the amount of current your grain of wheat lamps take, but I'm assuming that it is very low possibly in the 20 to 50 milliamps. Your series resistor will probably be around 100 ohms, and 1/4 watt should do fine. Try it and measure the voltage across the lamp, and it it's too low, then decrease the resistor value, if it's still too high, than increase it. It's going to depend on how much current the lamp takes, but maybe there's someone here that has used these and can tell you right off. There's nothing wrong with trial and error. Try a value and see it it works. The higer the resistor value, the lower the voltage across the lamp and the dimmer it will light, but the longer it will last.
14. InseyMember

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Ok thanks for the tips on the resistors. But it looks like I have even bigger problems now. I just redid all the wiring for my layout (took me 3 hours). I mocked up all the new wiring (I didn't solder) and I hooked it up to the powerpack. I got everything to light up, but it only stayed lit for about 15 seconds and then the "OVERLOAD" light came on and the entire thing shut off. What in the world is the problem?
15. ezdaysOut AZ way

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At one point I mentioned that I thought you may have power pack problems which was why I was trying to get you to reduce the number of lamps in the circuit. I really don't think you have a seven amp power pack. It could be .7, or 700 milliamps, in which case you don't have enough power to light all the lamps fully. "Overload" means just that, you have exceeded the capacity of the power pack output significantly. Let it cool down, some have a button reset, some thermal. Start off with just a few lamps and add them on one or two at a time. At one point you will reach the maximum you can put in the circuit. The solution: get a second power supply just to run the lights.

Good luck,
16. InseyMember

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Hmm...where can I get a power supply that just runs the lights? I haven't seen those around anywhere.

By the way, I just disconnected about 8 lights and now the power pack seems to be running without problems.
17. ezdaysOut AZ way

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Yeah, I think that comfirms it. I think you only have about 1/10 the power you thought you did. Radio shack has 12 volt transformers it you feel compfortable wiring them up. I think you can get them up to about 4 amps. You can also get something like a MRC power pack that gives you AC out for your accessories, 12 volt DC and variable rail power, all in one nice package. Or you can buy a few really cheap power packs and use the accessory outputs from them, but they only have a few watts of power so unless you have a few laying around the house, I wouldn't go out and buy any. You can even go a buy a fixed DC supply from Radio Shack, or even use an old power supply from a scrap computer. Lots of ways to get the power you need. Computer power supplies give you 5 VDC and 12VCD usually at around 5 amps.
18. InseyMember

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20. kf4jqdActive Member

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Fire Hazard!!

I want to mention one thing. You could have a potental fire hazard! I had the same problem. I disconnected the load (lights) and checked it with my meter. The voltage was at 14.5vdc. Which was correct output. Then I reconnected the load. The lights came on dim and the meter read around 12.5vdc. This wasn't good.

There had to be a short somewhere. I found it in a Brawa plug in street light. The wire inside the pole had no insulation and was shorting at the pole! I unpluged the lamp. The light went up to their normal brightness. The meter now read about 13.9vdc.

Hope this helps,
Andy

PS
The lamp pole was warm to the touch!