31 Jul
2006
31 Jul
'06
11:31 p.m.
Hi Lee
Please try at least one of two experiments. Either actually measure
with an inductive load or do a simulation. For a transformer, zero
cross is the worst time to start. Don't confuse steady state action
with the first cycle. The response is not the same.
As you mention, turning off an inductive load is best when the
current is zero. With an inductive load, this is at 90 degees, or peak
voltage. This is also the best time to turn it on.
For a purely resistive load, this at zero voltage. A transformer is
somewhere
in between. A large core transformer that isn't heavily loaded is more
inductive than resistive. If it weren't, it would be useful.
Dwight
From: "Lee Davison" <lee at
geekdot.com>
Reply-To: "General Discussion: On-Topic and Off-Topic
Posts"<cctalk at classiccmp.org>
To: cctalk at classiccmp.org
Subject: imsai 8080 power switch
Date: Mon, 31 Jul 2006 19:47:32 +0200 (CEST)
One thing you should know about zero crossing.
You don't want to use
a zero cross relay on a highly inductuve load( the IMSAI might qualify
as highly inductive because of the large core used ). You want a peak
switching. Zero cross is the worst place to turn on an inductive load
and results in the highest current surge. This may even saturate the
core and cause a peak several times the normal running current.
That's just wrong.
A loaded transformer isn't an inductive load, it's mostly the same type
of load as what is loading the secondary.
Zero crossing is the best place to turn on nearly any load, it may not
be the best place to turn off some loads but for on it is usually best.
If you turn on an inductive load at the zero crossing zero current will
flow. There will be no surge.
Unless there is a serious fault, and even then it is unlikely, you won't
saturate the core of a transformer regardless of how you switch it on.
Lee.