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Someone posted on Diyaudio about this, but I'm seeing the same thing - with a typical full wave rectifier circuit I'm seeing higher RMS current in the transformer than I think I should be.
With a 150mA load, I see 220mA RMS current in D1, and 312mA in T1.

Hi Joel, could you post the .psu file here as an attachment? (hope that's possible, the forum is quite a new venture and still finding my way around it)

Also if you could let me know which version you are using; Mac/Windows, also the build number from Help|About.

Regards,
Duncan

Okay, I added the psu file here. I tried it with the latest build (75) and saw the same behavior.
I'm running on Windows.

Thanks for the attachment, I had a look and can now explain the different numbers.

The current in the transformer is through the winding and for both directions. Let's say the RMS value is X and the average will be zero or near-zero.

The current in the rectifier is for one half cycle, the RMS value will actually be X/SQRT(2). This seems counter intuitive because you think it would be half, but that's not the case - it's really 70.7%.

I even had to convince myself, and made up an Excel spreadsheet to step through some example numbers to check it out (attached).

Part of the problem here is that a full suite of min/max/diff/avg/rms is provided for all points and while some of the numbers are useful (i.e. max and average for a rectifier), some of the results like RMS current in a rectifier are of limited or dubious value in the real world. Whereas in a capacitor, it's a very useful value to have.

Hope that explains the background and why the numbers are not what you would intuitively expect - I'll put a "health warning" in the documentation about this.

Regards,
Duncan

I understand what you're saying.
I wonder though how one could utilize this software to assist in determining ac current requirements for a power transformer?
Or are you saying that this higher rms current output is indicative of how a power transformer should be rated for a rectifier like this?

I just noticed that Sowter, and Hammond both indicate that Idc = Iac with a full-wave capacitor input configuration.

The only way I can think to do that is to work out the average transformer current, however this will always equate to zero over a period of time as each half-cycle will cancel the other.

One example of the way the transformer average current could be worked out is to do a reporting delay of 1 second to let everything stabilise then do a simulation for just half of a mains cycle to prevent cancellations. If you do this, the average transformer current is 150mA which ties exactly with the links you posted showing IAC = IDC.

However, the RMS current in the transformer (which is what makes it hot) is around double this, the reason being that the rectifiers are only conducting for part of the half cycle.

I'm guessing that this difference is "baked in" to the transformer margins as they know the intended use of say a 350-0-350 transformer will be a capacitor input supply of some type where RMS > Average. A choke input will give RMS and average numbers closer together due to the longer conduction angle.

Regards,
Duncan

There is also a nice description about that at the ValveWizard's page:?