[Amps] power supply transformer

[Tom W8JI]

> Paul, you have to have a line transformer for isolation - 
> it is life and death - no discussion possible...

Not that he should do it (for other reasons), but there is a 
great deal of equipment we use every day that runs power 
supplies that are not isolated from the power line.
The problem is getting the home builder to understand what 
to do to make it safe.

Switch mode power supplies run directly across the power 
line, as do many TV sets and computer supplies. They do the 
isolation later, after the power line is rectified, 
filtered, and chopped back into higher frequency AC.

In contrast to that there are many devices built by Hams 
that use transformers and are not safe. Some even appeared 
in the ARRL Handbook over the years. Just look closely and 
you will find many Ham projects that connect one side of a 
filament transformer primary or blower to the chassis.

It depends more how you do things than anything else. If the 
neutral of the mains connects to the chassis it is not safe. 
This is especially true when the chassis is a common point 
for 120V systems like blowers, relays, or filament 
transformers.

73 Tom