Converting AC to DC

[Trains1937]

I am considering buying a Walthers accessory that runs on DC. Is there any way to connect wires to it from my ZW and change the outgoing ac to dc?

[phillyreading]

I think that you can buy a bridge rectifier and change it to a modified DC voltage. I did that with a Williams engine a couple of years ago. Maybe Bob Nelson knows more of what it may take besides just the bridge rectifier, not sure but I think that would be the only thing to add in.

[dbaker48]

If you know the current and voltage requirement, consider a walwort.  I save them from obsolete devices we accumulate.  They are very useful.

[David Barker]

Where's Bob?

[lionelsoni]

There are several ways to turn AC to DC:

The simplest is half-wave rectification.  You just put a diode in series with the ZW's A, B, C, or D terminal.  This will give you half of every AC cycle and is a pretty lumpy sort of DC.  The average DC voltage is about 45 percent of the RMS voltage that the transformer puts out.  The DC current flows through the transformer winding, which tends to saturate the magnetic circuit and heats the transformer more than the load would normally; so you wouldn't want to use this method if you needed a lot of current.

A more complicated way is a bridge rectifier.  This produces a less lumpy DC with an average about 90 percent of the RMS voltage and no transformer saturation.  However, the rectifier's output has no terminal in common with its input; so you can't use it for a control-rail accessory circuit (unless you dedicate a separate transformer to produce your DC).

You can smooth either of these waveforms out with a capacitor, and incidentally boost the voltage to 141 percent of the RMS voltage, but the capacitor may be quite large if you need a lot of current.  The bridge rectifier needs about half the capacitance of the half-wave rectifier.

What sort of accessory are you looking at?  Does it have motors, lamps, electonics, or what?  And what voltage does it need and how much current does it draw?

[Trains1937]

I am interested in the Walthers Operating Oil Pump. I presume it has a small dc motor in it. Not sure about the voltage or amperage but suspect the voltage and current are not very high.

[Firelock76]

Lionel was making an ac to dc converter several years ago, I got mine from Sidetrack Hobbies in Leonardtown MD, they do have a website.  Maybe they still have some.

Or, you could run the accessory with an inexpensive HO transformer, that's been done as well.

[lionelsoni]

It's probably a small permanent-magnet DC motor.  I would try putting a small bridge rectifier between the motor and your transformer--no filter capacitor.  Something like this will probably work:

http://www.radioshack.com/product/index.jsp?productId=12673807&filterName=Price&filterValue=under+%243.99

But you don't need a voltage rating any higher than 50 volts.

Connect + and - to the motor, connect the two ~ to U and whichever other terminal you want to use. 

[Trains1937]

Thank you. I'll purchase this from Radio Shack.