help please with toroidal transformers selection

[Jonathan]

Jonathan this pcb is for 3x3A steppers which takes no more than 7A from my calculation, but real test by clamp meter revealed that was no more than 0.86A therefore even perforated prototype board worked fine (but should not)

You're probably mixing up the supply current with the motor phase current - the two are related, but the supply current will always be less.

For my 70VDC 7A motors I use the same layout but wider path on pcb.

You can avoid cutting the ground plane with one of the tracks by routing it another way ... not that it really matters for what you're doing.

Just checked current-carring capacity and 1mm2 will handle 11A.
For 16.5A i need exactly 1.5mm2 conductor, so 1mm pcb has 0.035mm of copper.
Path width=1.5/0.035=42.86mm - my entire PCB is 50mm wide, according to this calculation we both wrong

It's a thermal limit and a cable is somewhat different to a PCB - try this:

http://www.4pcb.com/trace-width-calculator.html

I like that drain resistor - how many ohms?

3.3kOhms. But that's not the right question. You size it based on the energy stored in the capacitors, time in which you want the capacitors to discharge, and acceptable power through the resistor.

Crudely, the capacitors are discharged in t=5*R*C and the resistor power dissipation is P=V^2/R. I used a 3W resistor, but to get good lifetime from the resistor and not set fire to things it's a good idea to use less than the rating, say 2W. R=V^2/P=80^2/2=3.2kOhm. t=5*3200*0.02 = about 5 minutes.

Where do you buy components if you don't mind me to ask - your price are better than mine:(

Generally Onecall (farnell,CPC) or Rapid Electronics. Also Mouser and Digikey have started doing free postage on smallish orders, so they're good bets.

Be extremely wary of components from eBay in China - rife with fakes, especially capacitors. I treated myself to an LCR meter so I can at least check the capacitors.