I have bought several Walther’s lamp posts which utilize a 12 volt bulb. The directions say you can hook up either the DC power or the AC accessory power from a power pack to light them. However, when I look at the back of my MRC power packs, it says the AC output is 18.5 volts. That would imply too much power for my 12 volt lights. However, I think that because I’m going to hook up around 7 bulbs in parallel on the circuit, I should be okay, right? My understanding is that with 7 lights, they won’t each be getting the full 18.5 volts and therefore they shouldn’t burn out.
Wrong… if you hook up the 7 lights using parallel you will be sending the full 18 volts to each light. you could use a resister or you can hook them up in a series that would give you about 2.64 volts to each bulb.
The best I have found is to use an old PC power supply to control all the lights on your layout. I am currently using one on my HO layout powering around 100 or more lights with power to spare
Others will comment here as well, read all there comments and you be the judge as to what will be best for you. Hope this helps. Mike
I think you’re wrong on the figuring. each bulb takes 12V @ a certain amperage… as the electricity goes through the bulbs, you lose amperage, not voltage…
IE if they were 12 V bulbs and each took 1A to run at full power, you’d need a 12V power supply that can push out 7A to get teh bulbs at full brightness…
Parallel wiring does not reduce the voltage to each bulb.
I recommend trying wiring 2 lightposts in series, and seeing if the result is bright enough (approx 9.25 volts to each bulb). Or, try using a fresh 9 volt battery for power to check brightness. If the brightness is good enough, you have your solution. And running the bulbs at less than rated voltage will make them last much, much longer.
If you need more than 9 volts, than the best solution is a different power supply or 18 volt bulbs. 18 volt bulbs will likely run hotter (and brighter), so may not work.
A resistor in series with the bulbs (all wired in parallel) is possible, but you would have to know the current rating of the bulbs. Add all the bulb currents together and divide the sum into 6 volts to get the resistance of the resistor. Round up to the nearest available resistor size. Power rating of the resistor is at least (sum of currents)(squared) times (resistance of resistor).
I have always just used a old power pack TYCO, etc something cheap. Then I use the DC posts and just turn the thottle up till the lights just have a nice little glow to them. The bulbs last along time this way.
Thank you to all the guys who chimed in and ansered my question. It’s always nice to know that other modelers will take the time to help solve a problem.
I think I’m going to go ahead and use the DC terminals on my power pack and turn up the throttle till the lights are just light…not too bright and not too dim.
I went the route of the PC power supply and I think I’m the one who turned Mikesmowers on to the idea. I use clear christmas lights setup with two bulbs wired in series for each struture. Each bulb is rated for three volts, so 2 of them would take 6 volts. I have them running on a current of 5 volts. There are 37 structures and each structure has 2 bulbs wired in series. All the structures are hooked up to a parallel circuit. Many of these bulbs have been burning 24/7 for 10 years now.
I use a MRC Rail Command 1370 Power pack for running my 12V interior bulbs. The 1370 has DC terminals rated at 15VDC. So I keep it about 50-60% power (i.e. 7.5-9V) and achieve a nice soft glow for the insides of my buildings.
When I was doing stained glass work, I needed a soldering iron that I could adjust for temperature control. Being cheap, I bought a 120 volt light dimmer switch and powered my soldering iron through it. Worked like a charm. I don’t know if that would work for your 12 volt application. Dimmer switches work by increasing the resistance in the line. Dimmers made for 120 volts may not work with 12 volts. For the cost of the switch, though, it may be worth a try.
As you increase the load on a single powerpak past it’s Capacity, Yes, it’s voltage will drop, and it heats up. Even if you can calculate the current of 7 lamps I’m guessing you’ll overload your supply, even before running trains. Do you want to guess when that occurs - and at what voltage drop?
7 lamps in series drops your voltage to 2.64v each - barely enough to light, unless you go to 3 volt bulbs. 18v. in parallel will burn out your bulbs - quickly.
Best advice is to have a separate 12 Volt supply with enough amps. I’m blindly guessing 2.5a - 5a. Majority of MRC paks claim 1.4 or 1.5 amps. (17-18VA).
but I like to suggest using some fuse’s or some type of main power switch. so you can shut the layout down at night, if your like me, you may just forget and leave the lights on all night and we dont need a fire
Actually, they don’t work that way, or at least haven’t since solid state dimmers came on the market. (1970’s ???)
Dimmers work by adjusting the duty cycle of the AC sinusoid from the line. In effect, chopping out part of the waveform and giving a lower AVERAGE value.
They wouldn’t work on DC and probably not on low voltage AC. Something simple that you might try is a diode in series with the AC supply and the bulbs. It would cut out half of the waveform and lower the average voltage.
Still, using the DC supply is a FAR better option. Lightbulbs last far longer on DC than on AC and the ability to control brightness is a great extra.
In a series circuit everyone gets the same current and they all share the applied voltage. In a parallel circuit everyone gets the same applied voltage and the power supply must provide the sum of the individual currents.
I like that you can reduce the voltage. 12v max won’t harm your bulbs, but the “nice more realistic glow” effect mentioned earlier is great - just hook 'em up (in parallel) and step down the voltage until you get what you want.
Here’s another thought. For even more variety, you could add a small value resistor between an individual light and its switch for subtle differences in light intensity within the same structure or between structures.
Thanks for that reccomendation KC. I was thinking of going the “wall wart” route,but after seeing that power supple,I changed my mind.I like the ability to switch voltages and it has a clean enclosure also,and it’s priced about the same. One question,2 amps is more than enough for the 60 or so Tortises I’ll need,so I’m thinking of using the same supply for building lighting. Are there more than one output or does one choose the output voltage for evertything connected to it? Can I use 12v for Tortise and 9v for lighting similtaneously or do I need to choose one for both? Either way,I’m sold! Thanks again.
The output voltage you select is what you get, so it’s 9v or 12v but not both at the same time.
Shouldn’t be a problem using it for Tortii and lights if there’s enough amperage. That’s what I do: I use 14ga. wire and run a 12v bus around the layout from the power supply. Then I just tap into that as needed for whatever 12v items I use. I actually run two of these supplies and have two buses (each powering 1/2 the layout), but I use many turnouts, and each Tortoise machine has between 2-8 LEDs strung along for the ride, so one unit won’t handle the whole schmear.
STALL-MOTOR switch machines such as ‘Tortoise’ use very little current, since they are small motors (often 3 volts) that are geared down and use a resistor to work on 12 volts - I believe Tortoise’s is internal .
Incandescent Lighting, on the other hand needs amperage. So far you have ignored the amps needed to work (7)? street lamps. (I take it you don’t know). A $10 multi-meter will tell you. A $20 ammeter makes a permanent installation and gives a continous reading.
Decent regulated supplies can run up to $200-$300.depending on the amperage. A regulated 12 volt 2 amp supply for $20 is dirt cheap, I’d consider getting two.
Suplus Computer Switching supplies offer multiple voltage outputs within a specified total wattage as pictured here earlier, and is what I use, but requires wiring in an ON OFF switch and fuse - Only a few bucks and some work. Those that can, DO, and those that can’t BUY.
1.ON THE CHEAP: Run 18 v.AC with all 3 volt bulbs in series .
BETTER: 2 supplies.One for switch machines/One for Lights