[sdiy] Multiple Voltage Power Supply / design problem!

[harrybissell at copper.net]

 Paul wrote:
>>By the way, anyone looked at a scope trace of the mains lately? It
isn't a sine wave any more, more like the Matterhorn with the tip
chopped
off, thanks to all the switch mode supplies hanging off it. Oh, and I
wonder where those mains frequency spikes come from??


Amen from the choir. I work on welding busses... and with the new
inverter
welders (think 800KW switcher :^) we can totally flat top a sine wave.

All the FWB rectifiers take current at the peak of the sine wave.

One idiot company did a 'power line analysis' for a customer of ours.
They
reported the bus was OK because the voltage drop was only 50V max.
They did 
~not~ notice it was 50V and as flat as an airfield. We were losing
diode
modules left and right as they turned on-off MANY times each half
cycle
and died of reverse recovery losses.  SAME idiots said we had 300%
harmonic
distortion in neutral.  That was based on a Wye bus, with a nominal
ONE AMP
at rest, and a whole THREE AMPS when our equipment was running. All
the current was from capacitor noise snubbers... and the idiots did
not notice they had failed to ground ANY of the controls (which would
have given that
current a kinder, gentler path :^)

I'm probably making those mains spikes as well, but if they are
reaching 
Australia there is a big problem :^P

/rant

H^) harry