What is Mains Isolation Transformer?
A mains isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety. Isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass.
How Close Can Place Two Transformers?
It is OK to place two transformers in a case? How close allowed to place them? Can they touch each other (of course, they will be electrically isolated)? Is their orientation with respect to one another important?
The importance of the placement varies depending on what each one is being used for (power, audio, relative signal strengths, etc) For example, a potential disaster is placing a low level audio input transformer next to a high level output mains transformer. A similar issue could be the power transformer next to an audio input (or possibly output) transformer.
Placing two transformers passing the same signal/level near each other is not much of an issue though.
Generally, to minimize coupling the cores should be placed at right angles to each other (flux lines at 90 degrees to each other), and as far away as is practical. You will see this done with input/output/power transformers in many audio amplifiers.
Different transformers have different flux leakage shapes, learning about this is useful. Toroidal are generally the best in this area. Shielding (e.g. Mu-metal) makes a difference also, though more expensive.
A good way to test for satisfactory placement is to apply a signal to one transformer (with a load on secondary) and measure any coupled signal in the other, whilst moving it around. You may need to use quite a high level "transmit" signal, and a simple amplifier at the "receiver" to make the signal easily measurable.
For power transformers, remember there are also heat and vibration considerations, so solid mounting/damping and ventilation needs to be looked at. It is better to avoid it.
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