Potentiometer for town lights

Something like this would be a lot cooler than a dropping resistor...

http://www.ebay.com/itm/AC-DC-...9:g:reAAAOSw44BYbprT

There are many such AC to DC power down convertors. A switching supply is best for coolest operation.

You would have to know how much current your lighting would draw. This module will supply 3 amps...probably around 12 or so incandescent bulbs. Connect your 14 VAC into the module and adjust the trimmer potientiometer for desired brightness. Start with the voltage turned down before you connect the lighting to adjust.

Well, it depends if any of the accessories need AC or all will work on DC.  If DC is OK, the module Chuck showed you is a good choice.  With 18 VAC in, it'll give you from 0-14 VDC out.

If you need AC, I'd look for a smaller PW transformer with a throttle control, that'll do from 6-18 VAC.

We used an HO transformer and created a 12 volt DC bus on the Eagle Scout museum project layout. That would provide power for all kinds of devices.(Look at the 11/14/16 and the 1/22/17 posts)

When we wanted lower voltages, we used these small adjustable out boards. Ours were the rectangular shape. These boards are small.

We had timers, audio players, rows of street lamps, action accessories and relays to control AC power just to name some of the toys we put to use.

My thinking was that I didn't want the heat of a conversion module or a conversion module at all just for simplicity. I didn't know who would come after me and have to repair or modify something on the display layout. Seeing a supply transformer for DC power, one would determine that everything connected to it was a DC powered device. The variable step down boards are something that is typically available.

AC accessories can be finicky. Gabe the Lamplighter liked 15v, most were ok at 14v, and some liked 12v. So, I never did "tune" those. They just ran on 14v. We didn't have any that had coil buzz. If we did, I would have converted them to DC.

We also tried to use LED lighting wherever we could. Streetlamps were converted, structures, signs. All ran off of the DC bus with dialed in voltage using the variable boards. It was easier to leave the MTH buildings on AC, but future work had them on the conversion to LED schedule. All of the AC powered bulbs summed up to quite a current draw and created heat that we didn't want for safety purposes.

I like that little module Carl, I created a sandwich board to allow powering it from track voltage with rectification, filtering, and a DCS choke.  I plop my board on top of the switching module and I have a track powered supply.  Note that they're not really good for 3 amps, a few hundred milliamps is more realistic without getting pretty hot.

eBay 161809202413 has them for 74 cents with free shipping.

Most of this seems a little over my head. As of right now there is just lighting that will be on the fixed voltage circuit. The track buffer and whistling freight shed will remain on the fixed 14v part of thing. 

I have some yard lights that will be going up as well, they will remain on the fixed 14v for brightness. 

Do what I said then. Get that 3 amp dc supply for the bulbs and connect your 14 vac output of the transformer to it.

cjack posted:

Do what I said then. Get that 3 amp dc supply for the bulbs and connect your 14 vac output of the transformer to it.

I was confused on how to adjust it? I thought it took a separate component I guess the screw on the end of the coil is for the adjustment. I will have to give them a try since they are cheap enough. One for the buildings and one for the street lights. 

No, there is a little rectangular blue plastic part with a tiny screw head showing on the top of it. That is a trimmer potentiometer and how you adjust the output voltage.

Here's a bigger pic of the adjustment screw.  Ted

TedW posted:

Here's a bigger pic of the adjustment screw.  Ted

 

They certainly make that easy to miss. And I'm sure any instructions would be chinglish at best

You'll like these converters. And, wish you had bought 3-4. Cause they're so cheap. TW

I'll figure things out with these 2 then maybe stockpile more. I think it would make sense to switch the ac input so when the lights are off the unit is cold and not making heat for no reason. I just ordered a 10 pack of micro switches to have on my block boards for lighting. I'm sure I'll go through those fast too. 

If you're willing to give the AC-to-DC converter a try, that's the way to go and you'll like the results.

But to answer your original question, it depends on how many bulbs and and much dimming (reduction in voltage) you want.  These might run $5 -10 for, say, a 10 ohm, 25 Watt variable resistor.   See photo below.

Another method which is the subject of many threads is using pairs of diodes or bridge rectifiers to reduce AC voltages in steps...about 3/4 Volt per pair of diodes.  Add more diode pair or more bridge rectifiers to cascade as much drop as you want.  A bridge rectifier which provides 2 "taps" or drops of either ~3/4V or 1-1/2V AC runs about 50 cents. 

What's nice about the bridge rectifier method is if you cascade several bridge rectifiers you can "tap" the string at various points so that different lights can use different taps at the same time.  The other two methods only offer a single output so if you want an additional output at a different voltage you need another variable resistor or another AC-to-DC converter module.

Here's a photo of what a cascade of 4 bridge rectifiers might look like which provides 8 "taps" that drop the voltage in ~3/4V increments.  So if starting from 14V AC, this provides drops/taps of about 13-1/4, 12-1/2, 11-3/4...8V AC which are simultaneously use-able.

stan2004 posted:

If you're willing to give the AC-to-DC converter a try, that's the way to go and you'll like the results.

But to answer your original question, it depends on how many bulbs and and much dimming (reduction in voltage) you want.  These might run $5 -10 for, say, a 10 ohm, 25 Watt variable resistor.   See photo below.

Another method which is the subject of many threads is using pairs of diodes or bridge rectifiers to reduce AC voltages in steps...about 3/4 Volt per pair of diodes.  Add more diode pair or more bridge rectifiers to cascade as much drop as you want.  A bridge rectifier which provides 2 "taps" or drops of either ~3/4V or 1-1/2V AC runs about 50 cents. 

 

What's nice about the bridge rectifier method is if you cascade several bridge rectifiers you can "tap" the string at various points so that different lights can use different taps at the same time.  The other two methods only offer a single output so if you want an additional output at a different voltage you need another variable resistor or another AC-to-DC converter module.

Here's a photo of what a cascade of 4 bridge rectifiers might look like which provides 8 "taps" that drop the voltage in ~3/4V increments.  So if starting from 14V AC, this provides drops/taps of about 13-1/4, 12-1/2, 11-3/4...8V AC which are simultaneously use-able.

 

That's a neat setup with the terminal strips and a quick solder free build. On this first round I'm going to run one converter for street lights, one converter for buildings then give the yard flood lights straight 14v off the buss.

I don't think that converter comes with instructions. If not familiar with that style of adjustment screw, be advised they are usually 20 turns or so. There is no indication that you've reached the end of rotation other than a faint click which you might not hear. The setting is absolute rather than ratiometric meaning full scale is the max voltage the unit is capable of. So if only feeding with 14V it is likely there will be no change in output for several turns on the upper end.  Linear (not log) taper - usually around 1V per turn.

Yup, as Stan sez, put a multi-meter on it and go to town. Here's a pretty crude video. Ted