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I have been looking at two of the older (not sure how old, but they don't seem to be available new anymore) MRC solid state transformers that are available for cheap, the Tech II TrainPower 027 and Tech 4 600.  I noticed that these transformers have a pair of screws for the variable voltage and a pair for the fixed/accessory voltage, but no screws are marked "common".  Then I was reading this page about phasing transformers:

And it says: "Some transformers have power taps that do Not use the common. If you use a power tap that doesn't use the transformer common keep that wiring separate from all other wiring."

I'm wondering, are these transformers in this can't be phased category?  And do they produce a true sine wave output or something else?  Thanks!

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I don't think those are from the real sine wave product line(pure power/dual power).  I think they have a very strong output either ("va" and "a" are volt amp and amp, and are not the same value). I couldn't find much info on those two, but e.g. 20va at 14v (tech 7) is only about 1.5a. Good for accesories, or HO, but not for running bigger O trains.

(You may want to contact Model Rectifier Corp. to ask if nobody comes through for you.)

The outputs of two or more transformers can be put into proper phasing, regardless of how the terminals are labelled. The "warning" about no common connection on the ones you have may be referring to the fact that the two separate outputs per transformer do not share a common wire inside the transformer, making it difficult to use one supply for traction, while referencing the other output for signalling.

If you need to phase the variable outputs, just do it the way you would normally do it on two similar (or dissimilar) transformers.  

1. Connect one variable output terminal from each transformer together.

2. Set the outputs at the same voltage using a digital voltmeter to get them real close.

3. Use the voltmeter to measure the voltage difference between the other terminal on both transformers.

4. If the meter reading is very low, you have them in phase. If the reading is twice the initial setting of either, then they are not in phase.


Ok, 40-50va is a little better. As long as you know .

   Modern stuff should run on that, but I have half a dozen postwar that could trip a 3a breaker when running light. With a load, I bet half of those couldn't get rolling without the power dropping out. My 2046 and MPC GG-1 both peaked at 5.5-6a on startups and ran at 3.5-4.5a constant once moving well.

Arthur, how do you know which is the variable post on the MRCs if there isn't a common with the acc. terminals? I've never run across a situation to know how to approach that before. (If it were mine, I'd just look inside to know, lol)

(this varies on PW Lionel, but lists are easy to find and not being solid state, easy to visually it check fast.)

  I wasn't really looking for which was variable, but also don't recall mention of it in the three manuals for other mrc that I have read since my last post. The closest I recall was swapping wires around for whistle/bell reversal if they are wrong.

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