I posted this query on the model railroading forum. Several replies suggested that I post here instead.
I have a small loop of track in my O gauge layout that connects to a larger main line. I would like to be able to run smaller DC locomotives (Mickey's World Tour for example)on that loop, but with the ability to run larger AC units as part of the main line. (Not at the same time.) I plan on providing two power feeds to the small loop with disconnect switches at the transformers. I assume I will also need separate ground wires with disconnect switches. I have installed fiber pins in all 3 rails at the points the loop joins the main line. Do I need anything else to accomplish this?
I received a reply that perhaps using a full wave bridge rectifier would simplify wiring. Another reply cautioned against combing AC and DC at all.
To complicate things further, I would like to have turnouts in the smaller loop, If I operate the turnouts at a constant voltage, can that voltage be AC?
Do I understand correctly that you want to have two modes of operation: (1) both sections AC, and (2) main line AC and small loop DC?
Where are you planning to get your DC? What transformers or other supplies do you have?
Bob Nelson
bob may be better at this but Radio Shack use to sell a part that convered ac to dc and it was an inline item you could either put it between your transformer and the track or better yet small enough to open your mickeys world tour engine and connect it from where power comes in before it goes to your motor the only problem I believe is you can only go one direction.
Life's hard, even harder if your stupid John Wayne
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I'd totally isolate the DC loop from the main line with fiber pins in all three rails and then wire it using the AC and a DC transformer feeding the loop through a DPDT switch. This way you can select the power source as desired.
Most of the switches that I know of in either O gauge or H.O. use AC power for their switches. Constant voltage to the switches would be a very good idea.
Roger B. is correct in using a DPDT(double pole double throw)switch to isolate AC and DC power. Forget about using a bridge rectifier! It is not needed.
I have tried to use AC & DC voltages using a common ground but that didn't work for me, used that idea once for H.O. switch and track wiring, all I got was a direct short! Was using an H.O. power supply at the time.
Lee F.
you understand correct. The set xformer with the Mickey loco is DC with AC accessory output. Main line uses Lionel KW.
Any accessories should work fine on DC, in fact many old Lionel accessories are quieter on DC than AC. Classic Toy Trains had an article on that a long ways back, maybe 2001?? Can't recall right now, but I was looking at it not too long ago.
There is no need to insulate the outside rails. Connect the U terminal of the KW and one of the DC terminals of the Mickey supply to those outside rails. You can use a single-pole-double-throw-center-off switch to connect the small loop's center rail to either the other DC terminal or to one of the variable terminals (A, for example) of the KW. I suggest another SPDT-CO switch to connect the main line's center rail to either A or B of the KW. That way, you can run between the loops on AC from the A control, run the loops separately on AC with the small loop on A and the main line on B, or run the main line on AC from either A or B with the small loop on DC.
Do not run between the loops unless they are both powered by the same source. That would be the KW's A output in my suggestion above.
You could run your turnouts (on either or both tracks) from the D output of the KW; but that's a little high at 20 volts. If you are willing to use terminal C instead of U for the KW common, you would get a nearly ideal 14 volts from D; but then you would have to settle for no more than 14 volts on the track, which could be a problem. You may need to get another transformer or DC supply for the turnouts if you want to run them on constant voltage.
I strongly suspect that the AC output of the Mickey supply cannot share a common with the DC output, which rules out using it to power turnouts.
Thanks, guess I was partially on the right track. Typical operation would be AC on all loops. Mickey would run when the kids are here or neighbors bring grandkids.
I have additional transformers available (1033, R, 150W TAC2001, AF 8B) for switches, accessories, lighting and future loops of track. Can I run a common ground if the transformers are "in phase"?
Transformers do not need to be in phase to share a common return (outside rails). The only good reason for having them in phase is so that, if you accidentally run between blocks powered by different transformer outputs, the fault current will be less than if the transformers were not in phase. In the scheme I suggested, selecting between and AC and a DC source for the small loop and selecting between two AC sources for the main line, there is no way that the AC and DC sources can be in phase (because the concept of phase doesn't apply to DC). Yet no harm is done by connecting their commons.
The only circumstance in which you should run intentionally between blocks is when you have powered both of them from the same source. The two variable outputs of the KW absolutely do not qualify as the same source. The KW's service manual states, "Note that the circuit breaker does not protect binding post combinations A-B...". There is nothing special about the KW in this regard. The same is generally true for the multiple-output postwar transformers. The KW is the only one for which Lionel admitted the problem. It is a good precaution to add your own circuit breakers (or fuses, if you like) in series with the A and B outputs.
You can power turnouts and accessories associated with the track out of phase. This slightly reduces the voltage drop through the outside rails and is quite safe.
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