RE: Re: How to work out what type of power generator?

["Keith Doxey" <ukha@xxxxxxx>]

> -----Original Message-----
> From: John Benfield [mailto:yahoo@xxxxxxx]
>
>
> However, my understanding (limited) is that they basically
> take the top and  bottom of the voltage out of the sine wave.
> If the voltage drops, the amount of power that can be taken
> is reduced.

Early Switch Mode PSU's did cause problems to mains power supplies because
of what you describe above but not by design. If the smoothing capacitor
had
only dropped to 200V then no current would flow into it from the mains
until
the sinewave had reached about 202V. This led to surges of power being
snatched from the mains as it approched it peak value and the combined
effect of many such power supplies would introduce horrendous noise onto
mains supplies. That is why new Switch Mode PSU's have power factor
correction.

Modern SMPU's also have much improved control circuitry and many require no
user adjustment to work on voltages from 90-250V AC. Early SMPU's had a
much
more limited input range (typically +/-10% so 216-264 for a 240V supply)
and
at one site where I had problems with the phone system I watched the mains
voltage drop to around 210V quite frequently which as long as only one call
was in progress the system worked but it would crash as soon as another
phone was lifted. Installed a Constant Voltage Transformer to feed the
system and it was fine after that. The later power units were vastly
superior and I have seen fully loaded systems working fine on mains
voltages
well below what it should have been.

Keith

www.diyha.co.uk
www.kat5.tv