25 Jun
2013
25 Jun
'13
10:34 p.m.
On Tue, 25 Jun 2013, Chuck Guzis wrote:
On 06/25/2013 05:49 PM, Jim Brain wrote:
Also known as class II low voltage or limited energy wiring. These
circuits are limited to a maximum of 100VA, but 20VA and 50VA are very
common. Typically the transformers to power these circuits can be had in a
standard transformer case with 'ears' to mount inside of control cabinets,
with a threaded conduit nipple on the primary (mains) side for mounting
into a 1/2" knockout in an equipment cabinet or junction box, permanently
attached or fit through a 4" square junction box cover, or DIN-rail
mountable (somewhat more expensive compared to the others).
My main concern was pumping that much AC into the
64, but it's
potentially not a significant issue.
I wonder if there is a 230V variant for the non US/CA/JP crowd.
Well, there are things called "control transformers" that are almost
universally 24VAC output with a wide variety of primary configurations.
Since they're a commodity product (used on heating and HVAC systems),
they're rated for continuous use and priced quite reasonably. But usually, they're not the "wall wart"
sort of thing. To get that,
you probably need to go to transformers used with security systems
(usually 18 or 9VAC and not quite as beefy as the control transformers).
Class II transformers are definitely not wall warts. I think Jim is more
leaning towards a brick-style supply, more like what the C64 originally
used (but probably smaller since larger magnetic transformer bricks are no
longer the norm).
Another thing that comes to mind regarding some of the regulations are the
energy efficiency regulations. Going forward, keeping these power supplies
legal to sell/export/import worldwide is pretty much going to rule out a
magnetic transformer based design. Magnetic transformers tend to be more
expensive than switch mode power supplies now anyway, due to all the bulk
copper and iron in the transformer.
With the US regulations, "The Energy Independence and Security Act of
2007" did specifically exempt power supplies that are designed to supply
more than one voltage, but the US DOE already wants tighter regulations
and even higher efficiency standards for external power supplies.
http://www.eebeat.com/?p=5808
http://en.wikipedia.org/wiki/Energy_Independence_and_Security_Act_of_2007#T…
http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/…
http://www.afdc.energy.gov/laws/eisa
http://www.gpo.gov/fdsys/pkg/BILLS-110hr6enr/pdf/BILLS-110hr6enr.pdf