I purchased a set of 3 “Old Fashioned Green and White Lamp Shade and Bulb” made by Miniatronics Corp, shown here. I’ve already installed a couple of them but need to know what the resistor is for, how and where is it used and for what reason. Anyone know?
The back of the package states:
" Use as indoor or outdoor building light.
HO scale 1.5V 40mA
1,000 hour average life.
O scale 120V 30mA
5,000 hour average life.
end quote
On the front of the package it is marked for HO Scale. On their website they say, “Resistors included to use up to 12 Volts 3 sets”
Those are not diodes. They are current limiting resistors for use with 12 volt power supplies. Power can be connected to either end. With lamps, polarity is not important.
Thanks for the reply, Rich. I just saw on their website that they’re resisitors, not diodes. If you’re using an old mrr transformer for power how do you wire these in, and when would you NOT use them? When it comes to electrical stuff I’m kinda challenged.
We use these at our mrr club by connecting twelve volts DC from an old power pack. Put one resistor in series with either wire.Connect both wires to the DC output of the power pack.
you can hook them up a couple of different ways. put the resistor in series with the bulb to drop the voltage so you can connect them to your power pack. or connect eight bulbs in series with each other and you won’t need the resistor. what is the meaning of the line o scale 120v 30 ma? don’t ever hook them to 120 volts. thats a 4100 ohm resister which will allow the bulb to be used on 12 volts.
Hope this does not seem too condescending but you did say you were electrically challenged…
Assume you are connecting 1 light to its power source. Take 1 wire from your power source and solder it to the resistor. Solder the other end of the resistor to a lead from the globe (The resistors and Lamps are not “polar” so it does not matter which way around) Solder the other globe lead to the other lead from your power source.
Your series circuit will then be power terminal - resistor end a - resistor - resistor end b - lamp lead a - lamp - lamp lead b and other power terminal.
Your other light globes will be parallel to this circuit but in series with their own resistors.
If you need clarification, feel free to email off list!
Do not put the bulbs in parallel. When one burns out, the load is reduced and the remaining lights get a little more voltage. Eventually, all the bulbs burn out. I know this from experience. In our club, 12 volts dc is run under the layout and we connect using resistors, the correct way.
A few people do this with a 12 volt regulated power supply so the voltage does not change when one bulb burnes out. Also, many Wall Warts are NOT regulated even the label says 12 volts DC.
Do it the right way the first time, especially when you do not know much about using electrical.
Thanks for the excellent explanations, guys. No, you can’t get too elementary for me when talking about wiring up anything 'lectrik. You shoulda been here when I wired a simple on/off switch to the service tracks around my turntable. Just couldn’t understand why everything shorted out in the train room and the coffee maker came on in the kitchen.
One day I might actually understand the difference between wiring something in series and parallel. I never have understood that simple concept, but after seeing the little drawing one of you posted (thanks!), I understand it better.
I had 2 sets of those to light my first subway station. I wired them up correctly, and then applied voltage until they “looked right.” I’m sure I was running them too bright, though, because they all burned out within a few months. But, I made the mistake of not using a meter and checking the voltages.
I replaced them with 16-volt bulbs which did NOT require the extra resistor. Besides greatly simplifying my wiring, this let me run them straight from the transformer. I found that running the 16 volt bulbs at 10 volts gave me the effect I wanted. And, at 10 volts these things should last until the cows come home. (Ha. No cows on my layout. They’ll last forever. Good thing then don’t say “until the moose come home,” though.)
This is the Scollay Square station, showing how I wired a couple of these to a pair of bare copper wires. Normally, you can’t see through from this angle, so the wires aren’t visible.
Here ya go Jacon. Series and parallel explained and shown. Basic electricity is not that difficult to understand, but it take some time and a little math to figure out. But once you do you’ll be like, wow, now I can do this and this and this!!!
This is true, but I think a little explanation is needed, so the reason isn’t misunderstood.
Hooking up loads in parallel does not divide voltage among them, but divides current. With an ideal voltage source, then, the voltage will always be constant, no matter how many bulbs burn out. However, if you parallel a bunch of bulbs and then hook them up to some real-world supply such as a wall-wart, you may get a significant voltage drop. Then, as bulbs burn out, increasing the load resistance, the voltage supplied will be observed to increase.
Connecting in series divides voltage, connecting in parallel divides current.
(Edit: I think I’m still confusing myself somehow…)
Edit again:
Okay, I did some calculations. Assuming the bulbs are 1.5v 30 mA, with 20 ohm resistance when operating, and the power supply is a 3v wall wart with 1A internal resistance (which seems high, unless it was pretty badly deteriorated), and 40 bulbs were paralleled, the voltage would drop to 1v, but after 39 had burned out, you’d have 2.5v across the one bulb left…it doesn’t seem like a super-likely situation, however.
Do you have more details on what you were using, Rich?
(I wonder if the bulbs weren’t just overloaded from the start, and burned out one by one, weakest first.)
In any purely parallel circuit–not series-parallel; that works just a little bit differently–no branch can ever draw any more amperage than is equated by the I=E/R formula of Ohm’s Law; as long as the voltage remains constant then the current through that branch of the circuit will remain constant. Vary the resistance, however, and the current is going to change. In a purely parallel circuit R = (R1xR2xR3)/(R1+R2+R3). Remove, for instance, R3. Your circuit now is: R = (R1xR2)/(R1+R2). Your effective resistance just went up! Under Mr Ohm’s law of I=E/R when R goes up I has to come down!
You do the math: 1 ohm x 1 ohm x 1 ohm =1 ohm; 1 ohm + 1 ohm + 1 ohm =3 ohms; 1 ohm/3 ohms = .33333 ohms, the effective resistance of that three branch circuit. Try it with two parallel circuits: 1 ohm x 1 ohm = 1 ohm; 1 ohm + 1 ohm = 2 ohms; 1 ohm/2 ohms = .5 ohms, the effective resistance of that two branch circuit. Now I’ll own up that I was pretty lazy in school but I do know one thing: .5 is greater than .33333. When a bulb or a resistor or whatever burns out in a parallel circuit the (effective) resistance of that circuit increases–we did go from .33333 to .5 ohms didn’t we?–and the resulting current in that circuit will decrease: Ohm’s law–I=E/R–says so!
You’re starting to sound like Mark Newton - only more so.[(-D][(-D][(-D]
Whenever somebody starts haranguing me about, “God’s Laws,” I always say, “Which one? P=IE, E=MV, S=A(T2)/2?” As far as I’m concerned, God’s laws all have mathematical definitions. All else is opinion.
BTW, if anyone wants a challenge, work out the track wiring for a fully-signaled analog DC MZL control system. Back in 1974, Ed Ravenscroft took four articles in MRR to explain the basics. Then I worked out my own complications modifications…
