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"Humming from unplugged transformer"

I have two blocks separated by insulated pins. Each block is powered by a transformer. I have looked for any common wire and have found none. The transformers are about 15 inches apart and sit on a particle board shelf. Any ideas?

All I can say is that is a level of dangerous and to be avoided. This humming on an unplugged transformer potentially has 120V AC live on the end of that plug that has bare contacts you could accidentally touch or short to something metal.

I highly suggest using an Ohm meter to find out what you missed for insulated connections regarding the track and wiring and also a good idea to phase the 2 transformers.

Similar discussion regarding 2 transformers.

Last edited by Vernon Barry

I have to be honest, this is why devices like the ZW, ZW-L, Z4000, and I'm sure other multi-channel single core transformers are much more ideal. By design, the multiple channels are in phase from a single power source.

Edit, in American flyer, ideally use a dual channel transformer like a 30B or some other typical 2 channel transformer.

You don't have the risk of back feeding another transformer that might be unplugged, you don't have to concern phasing multiple transformers, you just have single device that is much safer and easier in this aspect IMO.

Not trying to sell you on a different transformer, I realize you have what you have, but also be aware the situation you appear to be describing has a potentially lethal problem as you have described it.

Last edited by Vernon Barry

Sorry, I should have noticed this was S scale, and maybe these are American Flyer transformers, that said, nothing really changes because of brand or this being 2 rail S gauge track. Phasing is still important whenever using more than one power source, as is one rail being common, and the importance not back feeding an unplugged transformer.

Might be good if you can diagram your track plan, highlight your insulating pins, and show the models of the transformers and how they are wired to the track.

Last edited by Vernon Barry

There is definitely backfeeding through the secondary connections. YakimaMarxist, I am assuming your two blocks are  each powered from single handle transformers such as a 4B, 8B, 15B, 19B etc. Your post was not specific but it sounded like the transformer humming occurred even if the other train was not running. If so that means  both the Base Posts and the 15V Posts have a common connection point in the wiring.  The second common connection is not in the 7V-15V track connections. Do not connect the Base Posts of the two transformers together, it simplifies the wiring and reduces the number of fiber pins needed to isolate the blocks if the Base Post wiring for each transformer is separate. If there are turnouts make sure all the slide switches are set to 2 -Train operation. If the transformer only hums when the second transformer is operating a train let us know.

Many Gilbert accessories have the 15V connection always hot with the control button in the Base Post return. This makes it easier to inadvertently connect the two 15V posts together, especially with accessories that power isolated blocks such as the 755A .

Location of the 690 track power clips is also important to preclude tying the transformers together. It is possible to backfeed around the 2-Train feature of the turnouts if the 690's are on the frog side of the turnouts. Additional fiber pins may be needed.

As mentioned, there's crossover somewhere.  Phase your transformers (unplug them, disconnect them from tracks, connect a wire between their Base posts, connect a wire to one's variable power post, leave the other end free, put both to about 1/2 power, plug them in assuming no on/off switches, then take the free end of the variable power wire and gently touch it to the variable power post of the other transformer -- do you see a big spark?  If so flip the orientation of that transformer's plug in the wall and try again -- a lot less spark?  Good then put a red or white mark on the top surface of both plugs and be sure to keep them oriented that way.  If you don't see a big spark then they might already be phased.  Flip one plug and try again to confirm by comparison.)  I suggest then you make the outer rail your base rail and make it shared or in common between the two transformers (i.e. with no insulator pins) and your inner rail your variable power rail with purpose built plastic insulation pins (AF track) or plastic rail joiners (SHS or MTH STrax) where you want one or the other transformer to provide power, not toothpicks or the like b/c they don't have a vertical element or fin to prevent rail creep from creating even the slightest crossover connection.  Also inspect all your separation points.  Sometimes the smallest build up of gunk, stray solder specs, wire bits, etc. can form there and create a solid or partial (leak) connection between rails (similar to carbon build up between armature commutators if allowed to go to far).  My layout once had three 30B's and four TPC's for multi-loop and segment power with conventional as well as TMCC/Legacy control.  All of their Base posts were connected to the same outer rail bus bar.  Insulators were only on the inner rails without ever an issues or crossover.  But the 30B's were always phased and only positive (by design) insulators were utilized.  

It helps then also to have fast acting short circuit protection on each loop or block inner rails, especially if running modern engines with electronics in them.  7A Fast blow fuses work and are inexpensive.  PSX units cost more but are way more convenient and also provide spike protection.  The key is to use fast-acting (which the breaker in a transformers is not).  You decide.   Have fun.

Last edited by Sgaugian

I finally traced the humming to an improper fiber pin. After I made the fix the humming stopped. Tested the unplugged cord at the plug, no voltage. Tested other power connections from that transformer ( it powers a block separated with the fiber pins) with no voltage. Plugged it in and tested the other transformer the same way-no voltage. Plugged both in and the individual transformer and track connections tested 16 volts each.

Appreciate all the feedback I received.

I'm glad you were able to work that out.  Track pins can play a surprisingly significant role in AF train operations.  Metal pins, for example, can effect the power distribution efficiency of your layout by robbing power between sections of AF track.  They oxidize and build up with gunk causing them to create resistance between track segments (like mini resistors in series).  If you get a reduced power stretch of tracks somewhere on your AF track layout before you drop another power lead into the middle of it, remove that section plus one extra section on both ends.  Then pull apart each piece of track, wipe every pin with 91% isopropyl alcohol, then run a Dremel 220 grit paddle wheel (at about 5K rpm) on all four surfaces of every pin, and wipe them clean with 91% isopropyl alcohol.  Reassemble and install that section of track.  You'll be surprised how that section springs back to life with more power than before.  I test for power distribution and isolate trouble-sections with a RRampMeter that has a 1.5A automotive lamp attached on one end (see instructions included with the meter).  A voltmeter alone (measuring open or no-load potential differences) won't indicate as well the location or significance of power loss that you could be experiencing while running engines (particularly conventionally controlled units) on your tracks.

Last edited by Sgaugian

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