[ARC5] Fw: Smart People: 60Hz Transformers Faster

[Brian]

Hello Wayne,

Before embarking down this potentially lethal path, consider the 
relationship between your AC mains input Active, Neutral and Ground, and the 
positive and negative of your DC output. You may well find that you and your 
BC-652-A need special insulation; the DC negative and the mains Neutral and 
Ground are NOT at the same potential; the exception is a half-wave 
rectifier. Alternately, use an isolation transformer at the input to this 
death-dealing DC producer. Because the draw from the FWB will not be a 
sinewave, your isolation transformer will need to be bigger than your DC 
nameplated power delivery. Why not just get a properly-designed power 
supply? The life you save may be your own!

There is no deliberate frequency control in a free-running multi-vibrator 
power supply. This kind of design was all the rage in high-power car 
ignition systems that produced 400 Vdc across a 1 uF capacitor and used an 
SCR to zap that 400 V across the primary of the spark coil. However, good 
quality SS inverters and UPS devices use xtal control.

73 de Brian, VK2GCE.

On Tuesday, November 24, 2015 5:36 AM , Wayne said:

"As a designer of, among other things,  switchmode power  supplies, I will 
say that none of them that I have seen use  half-wave rectification. Diodes 
are cheaper than monster electrolytics."

I have given no thought to computer power supply design and have only 
examined discarded examples to see if there were any usable components.  But 
one junker I ran across not long ago was interesting in that it had a 
separate module in which they very clearly took the 125V 60 cycle wall 
current, ran it through a fuse and a full wave bridge, followed by some big 
caps and a toroid before sending it off to the rest of the power supply. 
The module was complete with the male power plug socket and tests showed the 
DC output just as you would expect it.  I figured that with some more caps 
added to the output that little module would be fine to provide the kind of 
DC power needed to run something like my BC-652-A.  I think I may even put 
it in a separate little box and plug it into my Variac when needed.

And David's questions also lead me to wonder again about something.  What 
controls the frequency of the power output of a solid state inverter or UPS? 
I built one of these once, from plans in an old QST.  It used two PNP power 
transistors, four power resistors, and a 24VCT secondary 115V primary 
transformer.  Worked the first time, too!

Wayne
WB5WSV