HEEEELLLLPPPP no matter what I do I blow 1.5 volt bulbs

[Lester Perry]

I use the resistors recommended by the decoder company and blow the bulbs. Then I try what worked in another locomotive and blow the bulb. I have more with no lights than with lights and I am running out of bulbs. I am not buying any more bulbs until I find out what I am doing wrong. With DC I used a bridge rectifier to reduce the voltage. can this be done with DCC ?

[Gary S]

Any more info you can give? What kind and wiring diagrams on the decoders? How you hooked them up? Wire colors from the decoder? What kind of bulbs exactly? What size resistors?

[tomustang]

What model are you using it on?

I know LEDS don't last long if it encounters too many shorts

[ezdays]

There's only one reason a bulb will blow like that, it's overvoltage. What is your source voltage set at, what is the current rating of the bulb and what is the value of the resistor you're using? Also, are you sure you have the right resistor value? Can you read the color code?

[Lester Perry]

The voltage is 13.? the resistor is 330 ohm 1/2 watt and the bulb is 1.5 volt grain of wheat not sure of manufacturer, I think it is minilights. Now I have another question. If I wire everything up and not connect the bulb shouldn't I be able to check the voltage going to the light? When I check with Multitester it shows 0 DC & 0 AC. One of the locomotives is a Mantua with metal light. I think I am going to use 12 volt bulb here.

[woodone]

This posting is in the DCC section- So I guess hhat you are trying to light a bulb via decoder. Is this correct?
We need a little more information, to solve your problem.
What scale are we working on- who's decoder- model of locomotive- who made it? All the good stuff. And you might want to check to see how many amps the light bulb draws. This will be in mil- amps more than likley. Waiting of the facts, and I am sure we can save some lights.

[Lester Perry]

Decoder This time Lenz but has been MRC, Digitraxx, Soundtraxx.
Scale is HO
light not sure who
Model of loco steam, diesel, Proto, Heritage, Athearn, Bachmann, the latest attempt Mantua.

I solved the problem with the Mantua. Just use 12 volt lamp it is a metal model.

[Gary S]

Are you certain the resistors are sized as you think? Check them with a VOM. Could be a factory mistake? What is the color code on them?

[ezdays]

Les,

Without having the current rating of the lamp, I would start out with a much higher value resistor. I'm guessing, but I'd say that a grain of wheat lamp would be in around the 50 milliamp range. If you have a resistor that's around 1K to 1.5K ohm, you might not get the brightness you want, but you won't blow the bulb either. I'd then drop the value a bit more, but a 330 ohm resistor in a 13.8 (12 volt nominal) circuit sounds a bit low.

If you are using a decoder, I'd listen to what Woodone has to say since he has the most experience with decoders than anyone else that I know.

[woodone]

Thanks Don. I think I can help Lester- but the link that I need to post I need help with. DCC I am OK,- coumpters not so good.
Lester Perry- here is a link that will help you with several ways to use 1.5 volt bulbs.
<!-- m --><a class="postlink" href="http://litchfieldstation.com/DCC-University/Lighting1.5volt.htm">http://litchfieldstation.com/DCC-Univer ... .5volt.htm</a><!-- m -->
OK, Don I need your help here looks like I did not get the link to post right- Can you clean it up?
Thanks in advance.

[woodone]

Thanks Don. I think I can help Lester- but the link that I need to post I need help with. DCC I am OK,- coumpters not so good.
Lester Perry- here is a link that will help you with several ways to use 1.5 volt bulbs.
<!-- m --><a class="postlink" href="http://litchfieldstation.com/DCC-University/Lighting1.5volt.htm">http://litchfieldstation.com/DCC-Univer ... .5volt.htm</a><!-- m -->
OK, Don I need your help here looks like I did not get the link to post right- Can you clean it up?
Thanks in advance.

Well after posting, the link looks to be OK.
It was not high lighted when I previewed it.
Thanks anyway Don.

[ezdays]

Gee, and I didn't even have to do anything. Once in a while a link will not appear to be highlighted, then it will, so it wasn't computer skills or lake thereof.

[Squidbait]

Lester,

I have found that not all 1.5v bulbs are created equal... some need a larger resistor than others. If you've got an electronics store in the neighborhood, go get a few small packs of 1/4W resistors (1/2 W is overkill, and they're bigger) starting with 1K, and working down through 820, 640 to about 330 or so. Here I can get a pack of 10 for $1, so for less than $10 you'll get an assortment that will do you for 1.5V bulbs and LEDs.

When I'm starting off with a new bulb, I put the 1K in line with it and apply full voltage from a DC power pack (very briefly - just touch the lead to the contact on the power supply). If the bulb lights very brightly (white) then you need a larger resistor. If the colour is a warm white, then you've probably got a good resistor value. If the bulb barely lights, or is an orangey-yellow, the resistor is too large, so swap in one the next size down. Repeat this until you get to a light level that's both bright enough for your tastes but not so bright it's going to burn out in 5 minutes.

The alternative (one I prefer, if I can get away with it) is to use a 16V bulb. That way there's no resistor required, and you don't need to worry about lifespan, either. Unless I'm trying to fit the bulb into a diesel headlight casting (1.2-1.5 mm), these will fit in most steam loco headlights, and work very well inside the shell where you have a plastic lens extending out into the headlight casting.

[woodone]

Yes, 1.5 volt llight bulbs come in differant amp ratings. Most that we see on model RR locomotives will be in the 15 ma. range. You will find some in the 30 to 60 range but they not as common. Athearn locos I have worked on have 1.5 Volt bulbs and they fit them into the plastic shell of the loco. If you put a 14 to 16 volt bulb in on of these you will more than likely melt the shell where the light bulb fits. We are talking about running with DCC. A 16 volt bulb will generate a LOTS of heat.
When you are running on DC, most of the time you will not be running FULL power so they will be dim. The bulb not getting full voltage as like 14 to 16 volts because we don't run our locos full tilt. There for, you can get away with a 14 or 16 volt bulb. The bulb does not genereate as much heat when it is only receiving about 8 to 10 volts. When you use DCC and turn on a head light or what ever light it will receive 12 or more volts. The voltage will depend on which sclae trains your are working with, or system.
The link that I showed on a earler post shows how to use resistors- diodes and a resistor and a IC. to control voltage to the bulb.
When I do a locomotive conversion to DCC on some locomotives, I will spend more time on getting the lights hooked up than I do on the initall DCC install.
Trying to find room- run wires - and such takes up time AND room. With a sound install you don't have a lots of room to work with on some locomotives.
There for I use LED's most of the time. 1 LED and one resistor and I have one light up and running.
And I use just a 1/8 watt resistor for this. It is not much larger that a wire, so it does not take up a lot of room. The LED uses so little amps, the resistor justs gets warm.