3-position reverse polarity switch for DC power lines to track?

(6) terminal.   Double pole, Double throw, cross over switch.  Can be momentary or fixed.   Used for reversing the spin direction of a turntable.  Pictured switch is momentary, center off.  Long shaft is variable speed resistor. 

Lionel had such a switch for their old HO line. If you wanted to take the effort, you can probably find one on Ebay. It is a 390c controller. No mounting holes required.

Mannyrock,

1) Welcome to the OGR Forum!

2) When starting a new topic, it's helpful to give a short intro on the background as to what you are trying to do.  I read your question and was wondering what you were trying to do (I had not seen your earlier posts from a few days ago).  It's impossible for everyone to read every thread that shows up on the board, so not all know the content of your previous discussions.  ( I was wondering why you were converting an AC transformer to DC to run AC trains (especially because you mention connecting the transformer to the track) before I saw Mike CT's reply and realized what you were doing)

3) For a turntable, yes, what has been described with a simple DPDT switch is the answer.  Depending on how you want to turn the power on or off, the "center off" type of DPDT switch Mike CT mentions is needed.  Otherwise if you buy one that is not "center off", you would have to remove the power via the transformer itself  to stop the turntable from rotating (and you say it has no adjustable control, just terminals , so you would have to unplug it - not the way to go).

Good luck with your project.

-Dave

Sorry I did not give enough background.

The train will be O gauge.  The transformer puts out AC only.  It only has two AC posts, and a lever for a throttle control. No other controls or buttons.

The rectifier kit says that it is for converting AC to DC power for O gauge trains.

The purpose of having the DC power running to the track is to run the DC train itself, not for an accessory or turn table.

I just want to be able to install a reverse polarity switch in the DC line before it attaches to the track, so that I can switch the polarity in the tracks, and run the DC train backwards if I want to.

I am hoping that this will work.  (If you think it won't, then please let me know.)

Thanks for all info.

Mannyrock

If you are absolutely sure you have a train that requires DC, your idea seems sound.  Do you know the make/model of the train itself?  (or have a picture of it?)  That can help determine if you really need DC or if AC will safely power your train.

As to the switch, take a look at the schematic here. (random example, the fact that the linked article is about motors for window shades doesn't matter, the circuit will work the same for a power supply to track polarity switching )

In that image, "power supply" is the output of your transformer after it's been through the rectifier to convert the AC to DC.  "Motor" is the connection to the track.

-Dave

No problem, 90% of 3pos on/off/on. AC to BR~~, BR-dc +/- to left and right center terminals (2-commons, isolated on dpdt), now make a jump from two opposing corners. Mirror the corner jump on the other 2 corners to have a two wire over/under X that doesn't touch. Tap wires to track off of either ends L/R corners.

Fuses protect components and wires that are smaller than the amps supplied really allow alone.

Thanks for the info guys.

I am setting up the system for both me, and my three five year old grandsons.

For me, I will route AC power to the tracks, and run nice post war, metal, AC engines.

But, when those kids come over, I will reroute DC power to the tracks, and let them play with and run cheap, DC can motor engines.   If they drop or destroy one, no big deal, only a $35 or so engine.   If the particular engine turns out to run OK on an AC track, then that will be great and I can switch the power to the AC.

All advice is welcome.  I am not a purest, and this will primarily be a hands-on teaching tool for my grandsons.  Get them hooked on running the many types and colors of the cheap DC engines,  then teach them about hand operated switches, and then teach them about electric switches.  At age 10 or 12, they can easily understand the concept of reversing polarity on a DC set of wires, and hopefully move on to AC trains.

I have seen far to many father's and grandfathers say that they are going to build a train layout "for the kids," and then co-opt it for themselves, with far too much detail and complexity.  The kids end up totally bored, watching Dad nail down cork or solder wires, and end up walking away.  ("Oh yea, the boys just love working on the trainset with me."   NOT!)

Mannyrock

Adriatic,

Thanks for that fantastic diagram.

My "starting out" transformer is a Lionel 4150, in excellent shape.  50 Watts, 7.5 amps, secondary voltage of 8-15 volts. (Paid $12 for it.)

Four questions:

1.  Is a 4.5 amp fuse considered "standard" for running DC trains?  Or, do I need to do more research about amps?

2.  What gauge of solid wire are you using in the picture?

3.  What do you guys mount your rectifier and polarity switches on?    I'm kinda nervous about mounting them on a plate of sheet metal, for fear of shock and shorts.  On the other hand, is it "considered safe" to mount them on a piece of plywood, or does this create a fire danger?

4.  Is this little transformer going to be able to run two DC engines, 027 size?  Or just one?

Thanks for any answers.

@Mannyrock posted:

My "starting out" transformer is a Lionel 4150, in excellent shape.  50 Watts, 7.5 amps, secondary voltage of 8-15 volts. (Paid $12 for it.)

 7.5 VA, not amps.

@Mannyrock posted:

4.  Is this little transformer going to be able to run two DC engines, 027 size?  Or just one?

 If they are truly Lionel starter set DC-only engines(practically all Lionel engines prior to 1996 run on AC or DC, except DC-only models), then you are good for 1-3 of these locos.

Thanks for all of the replies.

Chuck, I see a mint condition 390 control switch on line, for $25 plus shipping, but from the dark pictures, it is really hard to tell whether it has a middle "neutral" position, or whether it is just forward and backward.   If it doesn't, then it would still work, but the neutral position would bring the engine to a complete stop, which would be convenient for any reverse in direction.

Do you know whether it has a center "neutral" position?

Thanks,

Mannyrock

@Mannyrock posted:

...Chuck, I see a mint condition 390 control switch on line, for $25 plus shipping,..

These DPDT switches are MUCH cheaper and more robust.

Manny, Does not have a center off. It is a 2 position.

Why do you think you need a switch with a center off position?

Your postwar trains will run fine on DC except for the whistle.

Gotta have that whistle!   (That's 99% of the reason a 5 year old wants to run a train set.  :-)  )

OK!  You guys have convinced me.  I have gotten way too complicated, just by trying to go too cheap with my little AC transformer.

I'm gonna spring for either an LW or SW transformer to run the trains on AC, and use the little transformer (plus a bridge rectifier) just to run DC  accessories.

I managed to buy a Scout engine and tender, in VG condition, all working, for only $45.00, so that is why I am going to run AC in the tracks.  The LW and SW transformers have  whistle and reverse buttons, so that eliminates many of the problems in wiring a separate whistle.  (If it doesn't, I will power a free standing whistle with DC from the bridged transformer.)

I am starting a new post about the LW vs. SW choice.  If anyone has any pros or cons on these, I would greatly appreciate your replying to the new post.

None of the great info you provided so far on reverse polarity switches, whistle control boxes,  and bridges will go to waste, as I will run an separate inner loop, with yard runners, on DC.  (These won't be working a layout yard, but will just be cute little engines hauling a couple of cars around, between the main AC tracks.)

Thanks for all of your advice so far.

Mannyrock

Another option is Lionel's 4060 transformer. Has both AC and DC outputs to run trains and has it's own polarity  switch built in. Ebay has them listed, some at a very reasonable price.

If you know more today than you did a while back, nothing was a waste.

Another option is to put the DPDT switch in the locomotive using a standard Lionel E-unit and a rectifier.

Rob