I need to make a cct to change over between 2 mains supplies (they are
in phase). The hard part is it needs to change over within around 5 ms
which makes changeover relay out of the question. The current switched
will be about 5A @ 240v (metal hallide lights). Ive tried a changeover
relay but the nature of the lights is they will drop out for about 5
mins with an interuption of about 15ms or greater.
What type of ballasts are you using- electronic or regular
transformer? If you are using electronic ones and you are reasonably
handy, then it would be a simple matter to modify them to bridge the
required relay cutover time. The input mains are rectified and
filtered to produce a DC voltage which is then switched at a high
frequency (~20KHz) through a toroid transformer to drive the lamp. The
switcher is electronically current limited to control the power fed to
the lamp.
All one would have to do is increase the input filtering capacitor(s)
to bridge the time required for a DPDT 240 volt AC relay to switch
between the off-peak and regular feeds. The 240 volt AC coil would be
permantently connected to the
off-peak mains. The relay tongues go to the load (ballasts in this
case). The normally open contacts go to the off-peak mains feed and
the normally closed contacts go to the regular feed mains.
Many years ago, I did a similar modification to several PC power
supplies at work once to compensate for a rather slow to kick in UPS
we once owned (really ugly unit). It was eventually replaced with a
true on-line unit.
Cheers from Canada
Bob Morgoch