I need a circuit to power 10-20 Miniatronics 1.5v 15mA light bulbs. These are 1.2mm and will be used for structure lighting in HO scale. Once I have a power supply, are they wired in series or parallel?
They are wired in parallel. Miniatronics has a nice 1.5 volt power supply.
If you are handy with electronics, you can make your own voltage regulator with a LM317 voltage regulator, two resistors and a capacitor. Just use the circuit in yellow. Use the AC output from a common model railroad power pack. Part of the transformer is what is in a power pack and would be about 14 to 16 volts AC.
http://www.awrr.com/1point5voltPS.html
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
That's what I was looking for. I figured I would build the circuit from parts and then supply it with an old TechII...sound resonable. Thanks alot for your help...my Army electronics background has faded over the years.
Axe,
For the most part, I agree with Rich. Wire your lights in parallel. That way you connect them to switches and control them individually - if you want. Where I differ from Rich is that I'd use an adjustable transformer (like a power pack) to power your lighting.
I chose an MRC 1370 power pack for my lighting and power it from the DC terminals. Why? Because I had one after switching to DCC and I believe the power is also regulated(?) (I could be wrong on the latter.) The big advantage of powering your lighting from the DC rather than the AC terminals is that you can "dial down" the power pack to run the bulbs at 50-60% capacity. It makes the lighting both easier on your eye and the bulbs will last a lot longer.
The 1.2mm are nice and more realistic for exterior lighting purposes than the 1.7 or 2.4mm incandescents. However, the downside is that they only have a 500-1000 hr. life span. Hence, the reason for wanting to run lighting at less than capacity.
I've also found that the tiny 1.2mm bulbs from Miniatronics are not consistent. Some of them diffuse the light well; while others concentrate the light in a narrow beam. With that being the case, I've had to individually test each 1.2mm bulb before using it for one of my exterior light poles. So far, ~40% have had the narrow beam issue. It is possible that it may have been just a bad batch of bulbs. I don't know for sure though.
Since then I've decided to go with 1.7mm bulbs for my exterior lighting. They are slightly oversized and not as prototypical as the 1.2mm but they are still believable. Rated at 5,000 hrs, they will also last 5X as long as the 1.2mm bulbs.
Axe, if you are doing any interior lighting, I would definitely go with larger bulbs. All the roofs on my structures are detachable when I need to make a lighting change. And I operate my interior lighting at below capacity for the same reasons given above.
I've also connected my interior lighting to switches so that I can turn a bulb or sets of bulbs on or off individually. This can help create all sorts of different lighting effects around my layout.
Axe, well I've probably have given you more than you asked for. If you're interested, go to my web site below and click on the "How to" Instructional Series link on the left hand side of the page. I have a tutorial on how to make your own exterior light poles for 10-20% of the cost of buying commercial ones.
I do need to update the tutorial to add a couple of improvements but it's all there. The separate diagram and step-by-step instructions can be copied and pasted into a Word.doc.
Hope that helps...
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Axe That's what I was looking for. I figured I would build the circuit from parts and then supply it with an old TechII...sound resonable. Thanks alot for your help...my Army electronics background has faded over the years.
Let me see if I can jog your Army Electronics background. Lamps connected in series will add their voltage rating , ie. 4 bulbs in series rated at 1.5 volts each would work at full brightness with a 6 volt power supply. Use the same power supply but connect 5 of them in series, you have the bulbs working at 1.2 volts each, a bit dimmer and will run cooler, plus probably last longer.
Buy or build the power supply first, then take an actual reading of the output voltage with a meter. Use this figure with the formula above to determine how to wire up your lighting.