# Plotting current across wires and transformers

After reading almost the entire Help section, I’m first trying some supplied examples, as the “Transformer saturation”: very nice to have this new transformer symbol, but is there any way to quickly plot the current across one winding? I understand it is a graphic, not logic double symbol, so the mouse pointer over it very likely cannot understand what winding I’m pointing to…but at least I should be able to plot the current into a wire entering the transformer symbol. Is this possible without adding 0 V generators or any other fake componet?

I didn’t find any “help” section pointing out how to cross probing Voltages, Currents or other quantities, like the recently added Dissipated power. Is this my fault, or this Help does really not exist?

Francesco

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Hi,
I use .plot directive
For example,

.plot V(OUT) V(GATE, SOURCE)
.plot V(FB)
.plot I(L1)

You will have three plot panel in this case.
Much faster then using probe.

– regards,
Victor

Hi Victor,
In the specific case of the new transformer symbol, what should I type in for plotting the current across a selected winding? I’m still referring to the Transformer Saturation built-in example.
Say you want to plot the current of the leftside winding: .plot I(what?)

IMHO it is quite faster clicking onto a schematic diagram element than typing in a plot directive…don’t you think so? And probes are already implemented into QSPICE, why are they not documented in the Help?

Regards!
Francesco

Hello
Sorry, I was mistaken.
I can`t find direct way for measurement winding current…
For demo circuit you can use .plot I(R1) (already placed on schematic)
Or add .plot I(R2) for secondary…

In real life transformer winding always connected with “something” and you can measure indirect because currents the same.
Drain of Mosfet , for example. And you can probe current as .plot Id(M1)
M1 - ref. des. for appropriate MOSFET

For any circuits you can simply add small resistor in series with winding.
and use .plot V(N1,N2)*1000
N1 and N2 - resistor nodes, 1000 for 1 mOhm resistor

P.S.
I like .plot because no need click on schematic, add plot panels manually, move waves between panels and so on. Especially if I need test 8-10 signals.
Also .plot directive is nailed forever on schematic and always called during modelling.

– Regards,
Victor

Hi Victor,
Thanks for clarifying.
Ok, you can use a fake component like the usual 0 V generator and check the current across it.
Let notice that very often you have the winding connected to many components at the same time, for instance a bridge rectifier or a full bridge drive. In that case you need to add a fake component or to manually build an expression for the cumulative current.

Anyhow, the current probing works for native symbols like R, D, C, Q, M and similar…would be nice to have for transformers and other “new” symbols as well, that’s all.
Also having the current across a wire might help.

Thanks
Francesco

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Hi Francesco,
It will be very cool if Mike add possibility to place current probe on nets (wires).
Similar as current probes work in real life.

– Regards,
Victor

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