Transformer

That looks like a Hammond transformer number, but I don't see the 280 series listed on their site.

You might ask them...might be an older series, etc.

https://www.hammfg.com/electro...transformers/classic

and go to page about #41 for some hints on wire markings and windings...

https://www.hammfg.com/files/literature/5c.pdf

You can take either of the red secondary leads and the center tap to create 14 VAC.  You'll have to figure out what the primary leads are, I'd use a ohmmeter to determine what you have.  I'm guessing they may be voltage adjustment taps, but it would be easy to determine with a meter.  The green filament outputs will probably be a low voltage like 5V.

Hammond has a few transformer outlines with the same lead colors. As you say with an ohmmeter it should be pretty obvious what the primary scheme is.

I looked at Hammond, but I couldn't find any tech data on something like what he describes.  Do you have a link?  If so, that might be a shortcut to at least getting the primary connected so you can then measure to determine what else is you need to know.

Ok. This is page 41 of their catalog. The transformer is not the exact one in question but the leads are colored the same for the windings that he has on his. The primary should be easy to diagnose now. Looks like he needs to connect 120vac to the black and white and insulate the other two primary leads.

I believe for that one you posted, you have to parallel the two primary windings to run it on 120V.

He has two blacks, which is odd...

Yes...with an ohmmeter, he should be able to figure out what the two blacks are.

Thanks for all the help !!  Based on the schematic posted by cjack it looks like the primary is white and the last black with the middle taps.  I'll put an ohm meter on it to check.  The green is probably 6.3 vac for filaments.  The reds have me wondering.  The only paper work I have is the sales slip which says 28 vac @ 12 amp.  I'm now wondering is that is 50 vac  center tapped ?  I'll have to fire it up and measure.  I'll post my results.

I suspect it's 28V-CT.  The specification is normally the highest voltage as 50V-CT would be twice the power and a much more expensive transformer.

The results are in.  There are 3 winding's:  blacks & white, greens and reds.  Resistance between the white starting with the closest black in ohms is:  0.7, 2.7, 2.8 and 3.9.  I connected the white and last black to 115 vac with the following results:

11.5 vac between the greens

37 vac between the reds with 18.5 using the center tap.  Not exactly 28 or 14 vac anywhere ?

Maybe  115 vac should be between the white and black with red stripe for 28 VAC on red ?

Connect the primary 120V to whichever leads give you the highest resistance reading between them and see what you get.

Note that you are checking the voltage unloaded, the transformer specifications are for a loaded output.  Try putting a decent load on the 28V output and see what you get.

gunrunnerjohn,  tried your experiment:  37 vac no load, 36.7 with 1 amp load using the highest resistance primary.

Well, I did say they rate them at load, so one wonders what voltage it would be with a 10A load.

Try moving down to the next highest resistance, that should be a few less windings and maybe will change the voltage downward.  The taps are probably for voltage adjustment.  See what the 2.8 ohm winding gives you.

I tried the 2.8 ohm but the output went up to around 60 vac.  I also tried the black to black input, the output went up to around 40 vac.  That kinda makes sense.  The transformer is designed for constant spec output.  Lower applied voltage at the appropriate tap should yield the spec output.  If you applied the same 120 vac to the lower voltage tap, the output should go up which it did.

Apparently transformers are stamped with EIA codes identifying the manufacturer and date codes.  Guessing the 8317920 marking is this.  EIA code 831 is the Better Coil and Transformer Company.  Date code 7920 would be the 20th week of 1979.  Better Coil was purchased by Traid Magnetics in the 1970's.

Yep, my thinking was backwards, fewer windings would step up the voltage.  The only thing I can think is you have to be drawing rated current to get to the 28 volts.

It sounds like a good 18 vac transformer...for the most part.

I was wondering though what was the pre-testing evidence was that it's a 28vac transformer?

You better stay clear of that high voltage secondary winding used for a "plate supply".

You might just receive one heck of a tingle !

KRK

I purchased this transformer 15 years ago mail order from a hobby shop. Guessing it was surplus they sold.   The sales receipt is in the box with the transformer.  The receipt says it's a 28 VAC @ 12 amp transformer which makes sense since I needed 14 vac for accessories.  I presume the original advertisement stated it was 28 vac center tapped.  I never used the transformer since I didn't want to address the lead identification issue at the time.  In stead I built another 14 vac supply, the capacity of which I'm about to exceed.   Since I'm retired now, using existing assets is higher on my priority list.  So either the hobby shop was mistaken in specification or it's a mystery to be solved.  

It seems this is a universal power transformer with a tapped primary to support an array of input voltages.  There are 5 primary leads color coded as stated previously.  The color code is similar to industry standards.   Usually, the taps are for something like 100, 110, 115 & 120 vac.  I would expect the primary resistances to follow.  However, the resistances on this transformer are: 0.7, 2.7, 2.8 and 3.9 ohms.   Why the big gap between 0.7 and 2.7.  Also between 2.8 and 3.9.  I'm not wondering if there isn't another combination of leads that will provide 28 vac ?

Thanks Ken,

That's what is odd about this transformer.  There are only two secondary windings, neither of which are high voltage used for B+  ?  One secondary is green wires (2) which is 11.5 vac, filament I presume.  The other secondary wires (3) are 37 vac center tapped.

After further testing I'm guessing this transformer is designed to support 115, 120, 220 or 240 primary.  Doesn't appear it would ever product 14 vac.   It would make a nice 18 vac supply.  Could have used it when I was powering the Woodland Scenics buildings.

Triad magnetics offers a historical catalog reference. You may be able to find your transformer there.

When you look at some of the models you get a drawing of the connections for primary voltage in and secondary out configurations.

I was looking in the '70's tab under TR79-80 based on the information that you posted from the numbers on the transformer. Had to do some other stuff before finding a match. It may take you some time, but it's a start.

Thanks Moonman for your efforts !!!

I've come to the conclusion that the highest turns ratio I'm going to get out of this transformers is 3.24.  120 vac / 3.24 = 37 vac which is what I'm getting.  I'd need 4.28 turns ratio to get 28 vac.   I can get less turns  with the taps but not more.  Looks like I'll have to purchase a new transformer.  I'm looking at the Hammond 185G28, probably two, feeding  a 10 amp 4PDT relay. Each transformer leg should provide 14 vac @ 6.25 amps.  I doubt I will ever exceed that although bulbs @ 100 ma each suck up the power.  I've changed a lot of them to LEDs.  May current 14 vac supply consists of two 6 amp legs and two 4 amp legs.  The two 6 amp legs operate NJ switch machines.  One of the 4 amp legs operates accessories.  The other 4 amp leg is unused.  The used 4 amp leg is overloaded with an output of 13.6 vac.  I have a MTH accessory that needs 14-16 vac to work.  There's a warning not to use since the unit stalls.  It's sucking the 13.6 vac even lower.   I have a lot more accessories to add so it time for a change, hence the need for additional 14 vac source.

I was using four CW80s for my accessories and lights set to about 14 vac. But some accessories require a little change from week to week, notably the two guys going in circles in the tower. I tried to use the throttle variable side of the CW80 for that, but then some lights connected to the throttle side of the CW80 showed the oscillation of the throttle setting and I was forced to use the accessory side of the CW80 which is harder to change but was a more stable output voltage.

THEN A LIGHT WENT ON...I sold the CW80s, got out my restored post war ZW which perfectly fits the job. Four outputs with handles for adjusting the voltage on the fly. No programming, etc., just goes to what it was set to last time I adjusted it. And plenty of amps...

I'm with Chuck, one or two PW transformers seem made for this requirement.

Yes, that is a solution.  I have a KW just sitting which would do the job but I have no place to put it.  I also have grand kids who love the trains.  The Hammond transformers I can package in a single vented/fused enclosure out of the way under the table and control the output via relays.

I use 2 ZW's to power the track via 3 TIU's but i don't want to load them with accessories.  I also have several Z-500's which I use to power the TIU's and provide the 18-20 vac for the Woodland Scenic buidings. I use a 12 VDC supply primarily for LEDs.  There's rectified DC coming off the 14 vac supply to power the DC motor in the Bowser turntable. A small 4.5 VDC supply provides for the Miller Engineering displays.

No reason you can't hide the KW or a ZW in an enclosure.

I could hide the KW I have.  I also have a CW80 hanging around that I use at Xmas time.  Also the 1033 that came with my first train set, a 2055 Hudson. I considered placing the KW under the table but it's more of a space/access issue.   The most logical space is already occupied by the all the DCS stuff.  I still have to make room for the 3 wifi units on order.   Most other places I would be blocking access to something.   The 14 vac transformer enclosure I can mount directly under the table out of the way.  I do appreciate you thinking of me.  Thanks to all, you have been very helpful !!