# Power output of a transformer with many secondary coils, each coil of turn exactly equal to that of primary?

I am not a full fledged electrical engineer, and I couldn't find it on google, may be because I couldn't think of better combination of keywords. My question is, if we have a simple transformer with a primary coil of 500 turns and on the secondary side of transformer, we have 10 different independent coils of 500 turns each of exactly same thickness of wire to that of primary coil; and if we input 100 volts, 20 ampere AC into primary coil, will it produce 100 volts, 20 ampere AC into each secondary coil individually, or the voltage among each individual secondary coil will be (100 x 10)/10 and will the current be (20/10)/10 = 0.2 amps?

Another quick question is, will the length of transformer core affect the total magnetic flux, if the transformer core is very long and there's huge distance between single primary and single secondary coil of same turns and thickness, will the induced voltage in secondary be lesser because less flux will reach secondary coil and some flux will be absorbed in the core during travel of long distance?

• Iron is a conductor for flux, like copper is a conductor for current. What goes in must come out. – StainlessSteelRat Aug 28 '20 at 18:27

## 5 Answers

If all coils have the same number of turns, they will all (theoretically) have the same voltage - 100VAC in on any coil, and all others will output 100 VAC.

The total current from all secondary coils will theoretically equal the current in the primary coil. (There will be some losses in the transformer, so the input current will be slighty greater than the total output current.)

The currents in the individual secondaries will depend on the loads connected to each secondary winding. One secondary could deliver 10 amps, another 5 amps, five delivering 1 amp each, and the remaining 3 secondaries not delivering any current.

From the electromagnetism theory, the voltage will be the same on all 10 secondary windings. However, the current will be split among them. Otherwise you'd have a power gain in a passive device, which violates the physic law of energy conservation.

The flux is never "absorbed", it can just deviate from the core, ie. to the air. But yes, you'll have a lower induced voltage on the secondary, as the flux deviates to the air and less reaches the secondary.

The voltage on the secondaries will be the same as the voltage on the primary, since the turns ratio is 1:1. But you can't say anything specific about the current. Each secondary will have a current flowing that depends on the load connected to it, and to a first approximation, the primary current will be the sum of the secondary currents.

• Will the primary current be the sum of all secondary currents even if all the secondary coils are completely independent of each other and connected to different independent loads? – Yogie Aug 28 '20 at 2:08
• Yes, each load is independent of the others. – Dave Tweed Aug 28 '20 at 3:33

Imagine that when winding your ten secondaries you took the approach of twisting ten lots of insulated wire and creating a single secondary where the ten wires were soldered up at the ends. That is equivalent to winding your secondary with one single thicker wire. Power out has to equal power in and hence, if your "multi-strand" secondary has the same number of turns as the primary, then the output current from this multi-strand winding has to be equal to the input current in the primary.

In each of the ten wire strands, the current would be one-tenth of the primary current.

I’m neglecting magnetization current in this simplified picture. Magnetization current flows in the primary come what may.

That's just a transformer used to isolate heavy loads. The isolation is done by the core. If I sell a UPS to supply a heavy industrial motor or anything like that, we advise that they use a double conversion online UPS with an isolation transformer between the output of the inverter and the actual output of the UPS. It's stops AC feedback causing trouble for the output of the machine. It does step the voltage up a bit.. From 200VAC (output of inverter) to the actual output of the machine which here in SA is 230VAC 50Hz. Maybe that will give you a bit more clarity. Three phase isolation transformers will that, to split the phasing (so it can be used as a single phase supply) to go to various areas of an electrical environment, all the while still having a common neutral. So all three phases just need to use one earth and one neutral. Instead of an earth and neutral for each phase.

• My very first downvote ever. This answer does absolutely nothing to answer the original question. This actually appears to be an answer to a completely unrelated question. Was this posted in the wrong place by mistake? Maybe meant for DYI.SE? – Hitek Aug 29 '20 at 9:12
• @Hitek: I second your downvote - this "answer" has nothing to do with the question. – Peter Bennett Aug 29 '20 at 15:45