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#214236 10/31/14 09:09 PM
Joined: Oct 2014
Posts: 1
rtrg Offline OP
New Member
I am new here and I need basic info. I have a collection of small power transformers most with multi primary and secondary coils. These are NOT marked in anyway. Judging from the colors I srmise that the primary would be 100 through 240 volts and the secondary would be coils of 6,12,24,with center taps. The secondary has 2 or more coils of the same color with the tap in between. Of couse I am guessing. The primary has multi color leads with black, brown,white among them. From the various scematics I have black and brown, or white and brown are usually 110.

From all this is there anyway to determine the voltages of these coils? This also applies to my pile of solenoids, also unmarked. I know where most of them came from. The issue is that the voltages range anywhere from 12 to 110 DC. A 24 volt can be identical in size and shape to a 110. The plungers may or may not be the same diameter. My only conclusion is that the smaller the box and plunger the lower the voltage. But that varies.

Any simple rules/measureing of resistance that establishes the coils voltage is what I need. Is there a relationship between resistanc of the coil and its accompaning voltage? A chart? Counting turns, wire gauge, ect is impractical as well as not possible. The units that these transformers sols came from are not available. Thanks in advance.

rtrg #214237 10/31/14 10:09 PM
Joined: Jul 2004
Posts: 9,942
Likes: 34
It might be easier to google up every number on the transformer and hope for a hit that helps.

I have played with unmarked transformers before and if you can figure out the primary and guess a good voltage to start with you have a degree of success but I have also seen my share of magic smoke.

Greg Fretwell
rtrg #214239 11/01/14 12:47 AM
Joined: Jun 2004
Posts: 1,273
Transformers actually don't have an intrinsic voltage.

They transform a given (alternating) current from one voltage to another.

As long as the conductors can withstand the voltages a given design could transform 120 volts down to 12 volts or 240 volts down to 24 volts... and everything in between. The ONLY constant is the voltage ratio -- with turns on the turns ratio.

When one does not know much, then the impulse is to use lower voltage AC inputs -- with some effort at amperage control, too.

Then, it's easy to pull the transforming ratios off across the wire combinations.

Because transformer steels and common insulators are largely consistent -- one can weigh a given transformer to estimate its power capacity at a given ordinary and common voltage.

It's understood that all of these transformers are plain vanilla units designed for 600Volts or less -- not trick units designed for neon lighting. ( You'd know when you've got one of those -- they are well labeled. )

As a practical matter, unlabeled transformers are economically worthless. Small, dinky transformers are cheap as it is. I normally just send them to the recycler. I certainly can't install one on any job.

You might Google 'Edwards' as they manufacture lots of dinky transformers -- and are representative of the technology.

This forum is oriented towards field wiring by professional electricians and contractors. Hence, we don't 'look under the hood' all that often.

There have to be any number of hobbyist forums that have circuit diagrams and more on such units. They're your best bet.

rtrg #214240 11/01/14 01:42 AM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
From the Pri & Sec Leads descriptions, these Transformers kind of sound like Audio types (i.e.: Impedance Matching - 25V to 70V, etc...)

Other possibilities may be:
a.: Transformers were designed for use with a Vacuum Tube, or Discrete Component Push-Pull Audio Amplifier,

b.: Saturable Reactor Chokes - AKA "Magnetic Amplifiers" (how long has it been since these were mentioned!!!???),

c.: Block Transformers for small multiple output Power Supplies - such as <1990 Disk Drives (5.25" & 8" FDD), Terminal Concentrators / Controllers (like the older IBM 4700/4701 Controllers and the Bunko-Ramo Controllers).

I agree with Tesla; Finding the operating parameters for these Transformers may become more like an epic quest tired

Good luck with your search, and if you do find out the parameters (voltages per leads), please come back here and let us know the results.

--Scott (EE)

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
rtrg #214243 11/01/14 06:49 PM
Joined: Nov 2002
Posts: 794
Likes: 3
"Transformers actually don't have an intrinsic voltage."

Transformers do have an upper limit on voltage, depending on the line frequency as well. The limiting factor is the point when the core starts saturating. When that happens, the core acts like it's not there anymore, the inductance drops low, and current from the line soars. Not a good thing. Thus a transformer meant for 120V 60Hz will burn up if fed by 240V.

Back in olden days, there were a few areas served by 25Hz, and power transformers in consumer equipment had to be much bigger. You needed about 2.4 times the number of turns for the primary, given the same size core. Or a bigger core. But as the line frequency goes higher, that 25Hz transformer could operate at twice the voltage at 60Hz (assuming the internal insulation can take having all the secondaries running at twice their original voltages).

I have some radios from Australia (which is a 240V 50Hz country) whose power transformers are quite happy running off 240V 60Hz in the USA.

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