Electronics > Beginners
Identify giant transformer from 1978 tape reel
queennikki1972:
MarkF you have voltage for the 2 green wires on the secondary side but on the transformer they are on the primary side. They do not have any continuity to the other primary wires.
Jwillis:
The size requirement of the core is dependent on the total current draw on all secondaries .so if you take the example by cubdriver .you add the current of all secondaries which is 6.5 amps so hence the large core area.Of course that's very simplified because each secondary carries a different voltage
As stated before secondaries can appear on the primary side simply for convenience of winding the bobbin .
queennikki1972:
Im sorry I missed what you said about the green secondary wires on primary side in your earlier post.
MarkF:
--- Quote from: queennikki1972 on May 04, 2019, 10:49:51 pm ---MarkF you have voltage for the 2 green wires on the secondary side but on the transformer they are on the primary side. They do not have any continuity to the other primary wires.
--- End quote ---
The physical side the wires come out of the transformer is irrelevant to whether it is a primary or secondary winding.
Look at a toroidal transformer for instance. Most of the time all the wires come out at the same place.
--- Quote from: queennikki1972 on May 04, 2019, 10:38:16 pm ---Brown to gray 6.8 ohms
Black to gray 10.3 ohms
Black to violet 10.3 ohms
Brown to violet 5.7 ohms
Brown to black 3.7 ohms
--- End quote ---
BLK-BRN(3.7) + BRN-VLT(5.7) = 9.4 ? BLK-VLT = 10.3
According to your numbers, I think the transformer windings are like this.
It seems a little funny where the 120V tap is. Maybe that makes a wiring connection that is simpler.
Cubdriver:
Another thing to keep in mind about transformers is that they transform voltages and currents, but power (voltage multiplied by current) stays the same (less some relatively small losses; nothing is perfect).
As a simple example, if you have a step up transformer that has a 10:1 secondary to primary ratio, it will put out 10x the input voltage. Put 120 in, you'll get 1200 out. You'll also get 1/10 of the current that flows in the primary - if you pull 100mA (0.1A) from the secondary, there will be 1A flowing in the primary (ignoring losses). This would be considered to be a 120W transformer. Conversely, if the ratio is opposite with 1 turn on the secondary for every ten on the primary, the output voltage would be 1/10 that of the input (12V), but for that same 1A primary current, you would draw 10 amps. It would still be considered a 120W transformer, and would be about the same size as the previously mentioned step-up unit mentioned earlier.
Other than for transformers at the extremes (insanely high voltage or insanely low current, either of which might require specialized construction due to the need for insulation in the HV case, or very heavy wire in the LV, high current case), you'll find that transformers of a given power handling capacity are generally about the same physical size. Power capacity can be determined (if the secondary voltages and currents are listed) as someone mentioned above by multiplying each voltage by the associated current to get the power, then adding the power values to get the total. In short, just looking at a transformer usually won't tell you much about its input or output voltages, but will give you a feel for how much power it can pass.
I hope this makes sense rather than muddying the waters for you.
-Pat
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