# why don't isolation transformers short out?

Discussion in 'General Electronics Discussion' started by Nikola Farnsworth, Apr 24, 2015.

1. ### Nikola Farnsworth

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Apr 24, 2015
If an isolation transformer is connected to the line with its load turned off why doesn't it short?
I know when the load is on it pulls in power.
I know with the load off some power would be used to generate a magnetic field and heat but still essentially a short.
I know I could put a resistor in series but I doubt thats what they do.
All I find online are overly simple drawings.
I'm embarrassed that I've been playing with electronics as long as I have and don't understand this.

I suppose it isn't just isolation transformers.

2. ### Scotophor

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Oct 8, 2014
The inductance of such a transformer, with its many windings and iron core, presents a large enough inductive reactance that very little current flows when the secondary is not connected to a load.

3. ### davennModerator

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Sep 5, 2009
aka impedance
This is for any power transformer

4. ### Harald KappModeratorModerator

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Nov 17, 2011
For an inductance teh relevant equation is: V = L * dI/dt.When you apply a sinusoidal input voltage, the input current will also be sinusoidal but phase-shifted by 90°. The amplitude of the current is limited by the value L of the inductance.
Due to the phase shift between currrent and voltage you have reactive power, but no real power: the power that is used to build up the magnetic field in the inductance is restored to the source when the magnetic field collapses.

5. ### Nikola Farnsworth

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Apr 24, 2015
T facilitate my understanding, suppose I wanted to make my own isolation transformer for hobby use. Could you give me some examples of what would "get the job done"? For example a single turn on a steel bolt isn't going to do it, but would 100 turns on a steel bolt work? I know steel is not the preferred core material but its easy to source. Is is so bad that I should forget about it and always find the better stuff? What if I make a point of disconnecting the transformer when not in use, could I then get buy with a lower quality transformer? What about current? As long as the wire is big enough are we good or does that change things alot? If I want to isolate a cell phone charger is that a world apart from a automotive battery charger or is it just a matter of sizing the wire?

6. ### Nikola Farnsworth

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Apr 24, 2015
Related question: Suppose instead of winding three layers of primary and three layers of secondary I alternate a layer of primary with a layer of secondary and so on. Is it much more efficient?

7. ### davennModerator

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Sep 5, 2009
no ... .for mains voltages 100's up to 1000 turns

soft iron and
with your obvious lack of knowledge, you shouldn't be doing any of this without direct supervision
you could easily electrocute yourself
find a technician who can mentor you

Harald Kapp likes this.