[sigh]...One of those days

[grayfox1119]

Tom, another thing you could do is to use a zener diode and clamp the voltage at a safe level, no more blown bulbs.

[rrinker]

  Just multiply the current by the number of bulbs in parallel. 10 bulbs would be .045 W, or 45mW. Still ok for a 1/8 watt (.125 W) resistor. 100 would be .45W, so you'd need a 1/2 watt resistor. A 1/2 watt resistor pushing .45 watts is going to get a bit warm, but still be within limits. A 1/8 watt resistor with .045 watts flowing is going to be barely warm, if at all. So it depends on how many bulbs you intend to run.

                                           --Randy

[tstage]

Tom,

If you are wanting to drop 10% of the voltage across the resistor or .15V then the value becomes Resistor = Voltage / Current or .15 / .03 = 5 ohms .  If you are wiring to bulbs in parallel then Current becomes .03 x # of bulbs .  The only other thing to consider is how much power the resisitor must dissipate as heat.  Resistors have two major values in this type of application,  resistance and wattage.  Wattage is calculated by Power (wattage) = Voltage x Current or using the example above .15 x .03 = .0045 W or 4.5 milliwatts.   So using standard resistor values, a 4.7 ohm 1/8 Watt resistor would be fine for 1 bulb or up to

 

up to...???  Don't leave me hangin', Jeff!!!

Tom

[jbinkley60]

Tom,

If you are wanting to drop 10% of the voltage across the resistor or .15V then the value becomes Resistor = Voltage / Current or .15 / .03 = 5 ohms .  If you are wiring to bulbs in parallel then Current becomes .03 x # of bulbs .  The only other thing to consider is how much power the resisitor must dissipate as heat.  Resistors have two major values in this type of application,  resistance and wattage.  Wattage is calculated by Power (wattage) = Voltage x Current or using the example above .15 x .03 = .0045 W or 4.5 milliwatts.   So using standard resistor values, a 4.7 ohm 1/8 Watt resistor would be fine for 1 bulb or up to

 

[tstage]

 I'd consider putting a very low value resistor in the circuit so the bulbs don't see the full 1.5 volts.

My diode idea was to create a power source, sort of like how the stock lights are wired in a P2K loco. The power source goes through two diodes in series plus a resistor (in the loco, that's the motor, but there has to be something, otherwise it's nearly a dead short on the power supply and the diodes will burn up). You tap out power on either side of the diodes, and you have 1.2 volts, the drop across two diodes.

                                  --Randy

Randy,

How small of a resistor do you think I'd need to do that?  Are we talking 100ohm or <?

Randy, I do understand the disadvantage of relying on just one (1) resistor to drop power to my exterior bulbs.  To save effort and time of installing a resistor in each of the light poles, could I just add a resistor between the 1.5V transformer and where it wires into the first slide switch instead?  (All the other slide switches are either connected to or are daisy-chained from it.)  I know that if that one resistor goes then all the bulbs will be receiving the full 1.5V.  But, they're rated at 1.5V anyhow, so it's not going to harm them if that ever did happen.  Course, I could just solder the resistor at the very end of the wire, where it's connected to the slide switch, couldn't I?

Tom

[tstage]

Yeah, I can only run a couple of lights per outlet.   Thanks for catching my oversight, Dick.   I've amended my earlier posts.

Tom

[grayfox1119]

Tom: Wow, 1.5V "30A and 50A" bulbs!!! They can really handle that much current ?? LOL Just kidding big guy !!!!

BTW, the reason why you didn't see the usual bright flash before burn-out of the filament is most likely due to the fact that the filaments were already warm because you had had them lit already. When filaments are cold, their resistance is lower, and therefore they draw a higher current momentarely before they open.

[rrinker]

 I'd consider putting a very low value resistor in the circuit so the bulbs don't see the full 1.5 volts.

My diode idea was to create a power source, sort of like how the stock lights are wired in a P2K loco. The power source goes through two diodes in series plus a resistor (in the loco, that's the motor, but there has to be something, otherwise it's nearly a dead short on the power supply and the diodes will burn up). You tap out power on either side of the diodes, and you have 1.2 volts, the drop across two diodes.

                                  --Randy

[tstage]

Back in commission again.


(The repaired pole is the double light on the left.)  Not only did I keep the wires away from the tracks this time, I also unplugged my Power Cab from the layout.  Not taking ANY chances...

Tom

[jbinkley60]

Yes, I do see from your parts list that your bulbs are 1.2mm .  The ones I use are small also but are 2.4mm .

 

 

[tstage]

Thanks, Jeff.  I am using 12V 50mA(?) (5000 hr. life) for my interior lighting because I don't care about the size of the bulb.  However, the exterior lights I do want small for the realism so that's why I'm going with the 1.5V 30mA bulbs.  I may still rethink some things to see how I can make bulb changes are bit easier.  I'll definitely keep the 14V/16,000 hr. bulbs in mind for some variance in lighting.


Randy,

I'm using a Miniatronics 1.5V regulated "wall wart" to power the lights.  Each light fixture has its own slide switch so I can control them individually.  I had been powering them with an MRC 1370 at <10% before I bought the transformer.  This particular light pole was my prototype so the bulbs may have initially taken a beating.

Randy, you mentioned about wiring two diodes in series with a resistor to decrease the voltage and increase the life of the bulbs.  What about when you wire in parallel?  Can I still solder in a resistor to the voltage?  Thanks.

Tom

[jbinkley60]

I am using the Minitronics 14V 30ma bulbs for my building lighting.  They claim to have a 16,000 hr. life.  If you have bulbs burning out already, maybe look at longer life bulbs ?

 

 

[rrinker]

 So how are you powering them, anyway? If you wire two diodes in series plus a resistor and pull the light power from across the two diodes, you'll get 1.2 volt, which should make them last nearly forever. Unless you touch the lamp leads to track power   If you are just using a dropping resistor - bump it up so the lamps get something less than the full 1.5 volts, the increased lamp life is well worth it.

                                --Randy

[tstage]

Don't you just love learning those practical and valuable lessons that stick with you for a lifetime?  Well, I learned one last night.

Both of the 1.5V GOR bulbs in one of my scratch-built exterior light poles burned out so I sat down to replace them.  (One had been burned out for a while, while the other one hung on.  I just waited to both went before bothering to change them.)  It took me a little time to remove the old wiring and bulbs, clean out the glue from and repaint the light shades, prebend and feed the new lights through the light pole, and resolder both lights so that they were wired in parallel.

When I feed both sets of wires for the light pole through the 1/8" hole in the foam base to hook it up to the connector switch, I discovered that the light pole was a little too loose in the hole and was slipping down.  To fix the problem I wrapped a few turns of transparent tape around the base of the pole to stiffen it up.  Worked liked a charm!   Anyhow, as I was getting ready to position the light pole in the hole again, unfortunately the wires for both lights gently brushed across the mainline and...you guessed it - blink! - 14V of DC said bye-bye to two 1.5V bulbs.

The funny thing is, when the lights came on momentarily, it wasn't even a bright flash - just on and off - as if you had quickly flipped the switch to the power strip.  Hoping that it wasn't enough to fry the bulbs, I finished connecting up the light pole to the slide connectors.  Nothing.

After checking and rechecking both light wires on other connectors to make sure that there wasnt' a bad connection to this particular slide connector, I got out my new auto-ranging multimeter that I bought from Sears ($18, on sale!) and checked the resistance of the two wires..  The reading didn't seem high at first until I checked it against a good, known working light pole.  Yep, both lights were dead.  And that was my last two 1.5V bulbs.

Well, the downside is that I'll have to go out to Hobby Town and pick up a new 10-pak of 1.5V, 30mA bulbs.  The upside?

1. I'll now have enough light bulbs to make more light poles so that I can finally finish lighting my yard.
2. I found out that using Elmer's glue to hold the light bulbs up in the shade (instead of CA) makes removing the bulb and wiring much easier.
3. I shouldn't have to touch up the shade or light pole with any paint.
   
4. I got to try out my new multimeter.  (It's not a Fluke meter but it seems decent.)

So...it's not exactly how I wanted my evening to turn out.  But - at least it wasn't one of my locomotives crashing to the ground.  (Makes me shutter just thinking about that.)  Once I pick up the bulbs later today from Hobby Town, I should be able to have that light pole lighting up the area around my sanding tower again in about an hours time.


Tom