DC-DC converters

[wine&dine]

Considering parameters like whether this is a one-off or a design for production, and how much you value your time, you may well be tempted to go back to your original idea of using DC/DC converters.

For example, my local RS sells the RECOM RI-1212 at EUR 9,69 (QTY 11+). These will do 12V/12V, 2W and are rated at 1kV isolation, 10 GOhm || (30-85pF). You'll have a hard time beating these 50pF with a multi-secondary 50 Hz trafo, or the 10 EUR with a bunch of homemade flybacks (if you figure development time, assuming small quantities - 10+k pieces is another story altogether).

[wine&dine]

one more idea ... combine powerbecker's suggestion of using cheap common-mode chokes as transformers with DL2YEO's wondrous ways of using halogen lighting "transformers" (really small SMPS) - http://www.qrp4u.de/docs/de/tube_smps/index.htm

In short, open a 60W "electronic halogen trafo", add a primary cap to get continous output, then feed the 12V 18 kHz (or what you get) to a bunch of 1:1 chokes, rectify and filter.

Using separate little trafos lends itself nicely to modular construction.

Alternatively, you might manage to put 24 * (a couple of turns) directly onto the toroid normally found in one of these. The toroid is usually plastic-potted for primary insulation (DL2YEO has pics).

[powerbecker]

Cheap small power supply ???

here (also a nice service!):

http://www.pollin.de/shop/shop.php

click left side:

"Stromversorgung"

than:
"Netzgeräte"
than
"Steckernetzgeräte" or
"Festspannungs-Netzgeräte"

Regards
Heinz!

[Bakmeel]

Or similar to wine&dine said:

Buy yourself a bunch of cheapo 230V to 24V adaptors, rip em out of their casings and put them in your application...

Cheers
Bakmeel