power switch thingy...

This isn't especially audio related, but hopefully it'll stimulate some interesting discourse...

a buddy of mine has a piece of equipment in his computer rack, which has two power cords plus a bunch of outlets, and a big switch. One power cord goes to the wall, one goes to a UPS, there's a lamp for each one to indicate power available, and the big switch lets you decide which power source is feeding the bank of outlets on the front.

I haven't been able to convince him to let me take it apart

what all would be involved in something like this? I imagine it could be done with just a make-before-break switch, but would there be issues with two separate power sources connecting to each other briefly? break-before-make would run the risk of dropping power briefly, wouldnt it?

> would there be issues with two separate power sources connecting to each other briefly?

Yeah. Infinite current, instant breaker-blow.

> break-before-make would run the risk of dropping power briefly, wouldnt it?

Safer than tying two power lines together. Keep the switch-over under 1mS, most gear won't know.

does 'most gear' include computer equipment?

First thing that happens inside a computer switch-mode PSU: raw AC is rectified and smoothed to a rough DC which is than switch-chopped to a small, cheap, low-loss transformer.

A hiccup to any computer PSU (unless one that is within a couple of weeks of death) should pass unoticed. After all, the rectifiers are turned off most of the time anyhow, since the charge on the smoothing cap (the BIGgest cap inside the PSU, normally near the incoming power connector, by a large rectifier) is higher than the incoming power apart from at the peaks. If you were to interrupt the supply for a brief instant at the peaks, all that would happen is that the switcher timing might hiccup briefly, but I'll lay long odds that you can pull the juice for up to 10mS and still see absolutely nothing 99% of the time!

Keith

[quote author="tmbg"]does 'most gear' include computer equipment?[/quote]
Yes. If you want power with no interruptions you'll need an online UPS (AC to DC. DC or battery to AC).

Best regards,

Mikkel C. Simonsen

Look up the switchover speed specs on UPSes (or whatever the plural of UPS might be!!).

The first one I see says "2 to 4 milliseconds". I'm sure that some cheap ones are slower than this.

HTH!