Parameters for a dc power suppluy for Lionel train accessories

[San Jose]

I would like to use a dc power supply for my Lionel accessories, at least those that don't depend on ac. 

If I use 14 to 15 volts ac on my accessories, what dc voltage/current would be suitable for units like the 445 switch tower, 252 & 262 crossing gates etc. that make a buzzing noise.

Thanks,

Nino Yannoni

 

[lionelsoni]

For accessories that involve only resistive elements, like incandescent lamps (signals, for example) or heaters, the answer is simple:  Use a DC voltage equal to the RMS AC voltage that you would have used.

However, I suspect that you are really concerned only with the ones that buzz, which usually involve electromagnet coils.  In these accessories, the current is limited not only by the coil resistance but also by its inductive reactance.  The root-sum-square of these two quantities is the impedance; and the current drawn is the voltage divided by the impedance, not just the resistance.  For the same operating force and for the same temperature rise, you need to lower the DC voltage to keep the DC current (I = E/R) about the same as it was for the AC case (I = E/Z).  The problem of course is that we don't know what the impedance Z is.

Often, what operators do to select an AC accessory voltage is simply to adjust the voltage to the lowest value that produces reliable operation.  The same method is just as good for selecting a DC voltage.  If you plan to get your DC by rectifying the AC put out by a transformer, you can use this method easily.

I would advise against going to the trouble of using a filtered DC supply for this purpose.  You probably will get satisfactory quiet operation with nothing more complicated than a bridge rectifier and a transformer.  That's a lot cheaper than a filtered and regulated adjustable DC power supply.

[JTrains]

San Jose

If I use 14 to 15 volts ac on my accessories, what dc voltage/current would be suitable for units like the 445 switch tower, 252 & 262 crossing gates etc. that make a buzzing noise.

Are you asking what V/A would be necessary for a particular accessory -or- how many output V/A the transformer/power pack you would purchase needs to be capable of?  If the latter, to Bob's post the DC transformer should be capable of roughly the same voltage range as your AC transformer; as for the amperage, you might want to hook up an ammeter and see what your maximum AC draw is to ensure you don't get an underpowered DC power pack.  A single "buzzing" accessory can easily draw 1 amp - and if it's possible in your layout that two (or more) of these accessories are operating simultaneously you could need a DC power pack that's a bit beefy.

[pullman jct]

I have installed a small bridge rectifier in my 445 switch tower to eliminate the buzz. There is a lot of ripple but it works fine and doesn't buzz. If you use a regulated DC supply, be careful to use the minimum voltage for good operation. Solenoids in Lionel accessories can easily overheat when overpowered with pure DC.