Mounting toroidol transformers and other questions

[queennikki1972]

I'm sure this has been covered but I didn't find it or at least enough to understand. Here is a link to a previous discussion on another site, I just don't get it.

https://diy.stackexchange.com/questions/149993/how-to-mount-toroidal-transformer-in-metal-chassis

Is the image of the mounting procedure correct for a metal chassis or not?

And are these common in power supplies in the US aka 120vac primary options?

When would you use a toroidol vs a foot transformer?

[chris_leyson]

Image in the data sheet is correct. The 1st reply on stack exchange is also correct. The mounting bolt will make a shorted secondary turn only if both ends of the bolt are connected to chassis to complete the current path. If one end of the bolt is connected to chassis then there is no current path.
Edit: Toroidal transformers are used when you need low flux leakage compared to an E-I core. Audio amplifiers or sensitive instrumentation that covers audio frequencies might use toroidal cores to avoid additional magnetic screening that might be required for a traditional E-I core. The disadvantages of toroidal cores are the increased manufacturing cost and a higher inrush current. Most toroidal mains transformers have a pair of 120V primary windings so there is no reason why they wouldn't be used in 120V equipment.

[fourfathom]

The disadvantages of toroidal cores [...] higher inrush current.

Why is this?  Less leakage inductance and so tighter coupling to the load (wild guess)

[amyk]

Yes, a bolt through the middle is the normal way to mount these. Sometimes the bolt has a plastic cover to prevent shorting it to the chassis accidentally (I've had that happen before --- it's something you only do once! )

[mariush]

It's worth mentioning there's also R core transformers with their own pros and cons : http://jamestransformer.com/en/transformer/R_core_transformer.html

[fourfathom]

It's worth mentioning there's also R core transformers with their own pros and cons : http://jamestransformer.com/en/transformer/R_core_transformer.html

How is this R-core different than a toroid?  Just the squared-off core instead of the circular toroid?

Sorry to be asking so many (I assume) basic questions, I have virtually no practical experience with low-frequency power magnetics.

[mariush]

Well the obvious would be higher implicit safety, since the primary and secondary are separate spools of wire, separated by some distance.

I'm in bed typing on a tablet so i don't feel like typing a lot... here's a couple of forum threads that give some benefits:
https://www.stereo.net.au/forums/topic/55835-why-a-torroidal-instead-of-an-r-core-transformer-in-digital/
https://www.audiocircle.com/index.php?topic=76725.0