2 May
2005
2 May
'05
11:22 p.m.
Subject: CV Transformer - Capacitor on separate winding ?
From: Dave Dunfield <dave04a at dunfield.com>
Date: Mon, 02 May 2005 21:34:21 -0400
To: cctalk at classiccmp.org
Disconnecting this capacitor "cures" the excess current draw and
the chassis voltages come up fine (still running through variac at
reduced AC voltage with series light bulb as I expect this cap is
part of a "line voltage regulator".
The transformer is labled "C.V." (Constant Voltage?)
The cap needs to be there. An unloaded CVT runs hot and draws
more current due to the highly reactive load. A side effect
of storing power in a resonant circuit (floating coil and cap).
As the transformer is loaded the current remains the same but
more stored energy is transfered to the active load. I have
a Compupro Chassis, TEI and even a spare supply of that style.
I also have 120V/120V CVT for systems that do not have one
internally. They tend to run warm under normal cases. It
should with a modest load (auto headlamps are handy for this)
behave and also not blow primary side fuse(s).
By current switchmode tech they are scary but represent old
magamp thinking and are reliable devices.
Allison
3 May
3 May
3:11 p.m.
On Mon, 2 May 2005, Allison wrote:
Allison is correct; I'd like to amplify on it.
CV transformer power supplies are very inefficient; they draw tons
of current and make a lot of heat.
A CV transformer is basically a regular transformer with changes
to the core and usually an added winding that has a capacitor on
it. The extra winding and cap circuit is resonant at 60 (50) Hz as
Allison points out.
The core has a gap that makes it intentionally magnetically
inefficient; the core is magnetically saturated; when the line
voltage increases, more current flows, but no more magnetic field
is generated, the extra power going up in heat. This is a
"saturable core" transformer.
They're run saturated, with excess input current, so that when the
line voltage drops, the magnetic field does NOT drop -- because
input power caused saturation, magnetic field was at maximum,
dropping the line voltage to 100 (from 120, US) only lowers waste
heat, the magnetic field stays the same.
When the input goes below some point then yes, the output voltage
will start to drop.
THere's lots of variations, I don't know what your power supply
uses. Some put out "square" waves (clipped sines due to
saturation), or regulated sine.
Hard to imagine now, but this setup was once a lot cheaper than a
switcher.
Disconnecting
this capacitor "cures" the excess current draw and
the chassis voltages come up fine (still running through variac at
reduced AC voltage with series light bulb as I expect this cap is
part of a "line voltage regulator".
The transformer is labled "C.V." (Constant Voltage?)
The cap needs to be there. An unloaded CVT runs hot and draws
more current due to the highly reactive load. A side effect
of storing power in a resonant circuit (floating coil and cap).
As the transformer is loaded the current remains the same but
more stored energy is transfered to the active load. I have
a Compupro Chassis, TEI and even a spare supply of that style.
I also have 120V/120V CVT for systems that do not have one
internally. They tend to run warm under normal cases. It
should with a modest load (auto headlamps are handy for this)
behave and also not blow primary side fuse(s).
By current switchmode tech they are scary but represent old
magamp thinking and are reliable devices. 
4:26 p.m.
From: "Tom Jennings" <tomj at wps.com>
Sent: Tuesday, May 03, 2005 2:11 PM
<snip>
Allison is correct; I'd like to amplify on it.
CV transformer power supplies are very inefficient; they draw tons
of current and make a lot of heat.
A CV transformer is basically a regular transformer with changes
to the core and usually an added winding that has a capacitor on
it. The extra winding and cap circuit is resonant at 60 (50) Hz as
Allison points out.
The core has a gap that makes it intentionally magnetically
inefficient; the core is magnetically saturated; when the line
voltage increases, more current flows, but no more magnetic field
is generated, the extra power going up in heat. This is a
"saturable core" transformer.
They're run saturated, with excess input current, so that when the
line voltage drops, the magnetic field does NOT drop -- because
input power caused saturation, magnetic field was at maximum,
dropping the line voltage to 100 (from 120, US) only lowers waste
heat, the magnetic field stays the same.
When the input goes below some point then yes, the output voltage
will start to drop.
THere's lots of variations, I don't know what your power supply
uses. Some put out "square" waves (clipped sines due to
saturation), or regulated sine.
Hard to imagine now, but this setup was once a lot cheaper than a
switcher.
This system handles brown-outs, surges, huge spikes, etc.
It is especially handy in industrial areas that have heavy equpment
destroying line quality.
These systems can create an audible hum.
For any delicate equipment in industrial areas you will often find 120/120
or 240/240 ferro-resonate transformers added (especially for phone systems).
Randy
www.s100-manuals.com
3:13 p.m.
You pretty much have to put a load on the thing for it to work
right. The lightbulb test is just a go/no-go check, you can't rely
on it for fine interpretation, especially with non-linear devices
like the ferrorresonant or saturable reactor.
Stick some cards in it and measure the amount of smoke.
7092
days inactive
7092
days old
3 comments
3 participants
participants (3)
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ajp166＠bellatlantic.net -
cctalk＠randy482.com -
tomj＠wps.com