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transformer constantly steps down in LTSPICE

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Zak28

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Regardless of inductance of either winding the transformer always steps down, there is hardly a load on the secendary also and the primary voltage source has no series resistance. How are transformers properly utilized in LTSPICE?

Screenshot_20180716_213816.png
 

Hi,

I didn't check the series resistances.

But with a L1/L2 ratio of 30/300, I expect a coupling factor of sqrt(300/30)...which is about 3.16.

Klaus
 
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    Zak28

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Hi,

I didn't check the series resistances.

But with a L1/L2 ratio of 30/300, I expect a coupling factor of sqrt(300/30)...which is about 3.16.

Klaus

Resistances are 1 ohm per coil and it does not matter what values the coils are, even extremely far in inductance still yeilds lower voltage on secondary.
 

Resistances are 1 ohm per coil and it does not matter what values the coils are, even extremely far in inductance still yeilds lower voltage on secondary.

It matters well. Problem is that you apparently never calculated the 20 Hz reactance of your transformer magnetizing inductance settings, otherwise you won't use ridiculous small µH values. Try again with 30 and 300H.
 
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    Zak28

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Agree with FVM. You have to consider impedance as well as voltage. The impedance of the coils at 20 Hz is far higher than the 1K you are trying to drive.

Bob
 
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    Zak28

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It matters well. Problem is that you apparently never calculated the 20 Hz reactance of your transformer magnetizing inductance settings, otherwise you won't use ridiculous small µH values. Try again with 30 and 300H.

Yes, an ideal transformer has infinitely high inductance and therefore draws zero current on its own (all current is due to the secondary load).

I'm willing to put some blame on basic transformer resources which do a poor job of articulating this fact and explaining magnetizing inductance in general.


Ltspice is actually great at teaching this because it models transformers as they are: two coupled inductors and forces you to grapple with the inductance values from the start. I recall having this same confusion.
 
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    Zak28

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