Re: [CAD_CAM_EDM_DRO] Re: panel meters

To: CAD_CAM_EDM_DRO@yahoogroups.com
From: "caudlet" <info@...>
Date sent: Fri, 12 Mar 2004 00:37:32 -0000
Subject: [CAD_CAM_EDM_DRO] Re: panel meters
Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com

These welders are old Lincoln AC and AC/DC welders.
I don't try to measure the DC output but have had the
CT in the circuit on DC and it didn't seem to hurt anything.
Just not the right reading.

Bob
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--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bob McKnight"
<bobmcknight@c...> wrote:

> To: CAD_CAM_EDM_DRO@yahoogroups.com
> From: "caudlet" <info@t...>
> Date sent: Wed, 10 Mar 2004 23:11:46 -0000
> Subject: [CAD_CAM_EDM_DRO] Re: panel meters
> Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
>
>
> Panel Meters and Current Transformers
>
> The setup I have consists of
>
> a Panel Meter which says it has a basic meter movement of 5 VAC (5
> volts alternating current)
>
> a Current Transformer which is 20:1 to be used with a 5VAC meter

If they specify the output voltage then the CT was a built-in load
resistor calibrated to give that voltage out. The raw CT transformers
like sold by Jameco have to have an external resistor but they are
rated up to 200A primary current. They are sold as 20:1 ratio CT
transformers but if you just pass a wire through the middle you will
get 1/2 of the current you expect in the secondary. We know this from
emperical data from a design we just finished on the THC project for
MACH2 where we used said transformer to sense the AC primary
current
of the plasma unit to trigger an "arc Good" signal. Not all plasmas
have an arc good that can be accessed easily. > > I run my welding
wire thru the center of the current transformer > and when I am
welding, someone reads the meter and I multiply > the reading times
20.

I don't know how you do that if your welder is pulsed DC so the
current waveform would be one sided. Transformers don't like
unbalanced waveforms since the magnetic flux in the core tends to
have
no demagnitization path other than load. If it is one of the new PWM
inverter types I would think it would be even worse. Are you getting
accurate readings ? >




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