Re: Mains Current Monitoring

here are a couple options for measuring power line AC current.

1.  You should re-consider a shunt.  You already have one connected.  If
you are using 117V (only one phase), you can use the Neutral conductor as
your shunt.  Since the Ground connection is only used for safety/shielding
reasons, there will be no voltage drop across this.  There will, however be
a voltage drop across the neutral wire.  The drop will be dependent on the
gauge of wire and the distance.  Just measure the voltage between the
Neutral and the Ground connection at the outlet.  If you know the distance
and the wire gauge, you can calculate the resistance value of this "free"
and already existing shunt.

2.  I have used an old transformer as a current transformer.  There are a
few transformers out there where the primary and secondary are wound next
to each other instead of on top of each other.  Remove the secondary.  With
piece of wire sized appropriately for the current to be measured, replace
the secondary with as many turns as will fit comfortably.  The original
primary will be your new secondary.  Through experimentation, you can place
a resistor across the new secondary that will give you a certain voltage
output for the desired current to be measured.  The value of the resistance
and wattage requires depends on the transformer you are using and the
voltage you would like to read for the measured current.

I have used the #2 where I work.  We did not want to spend alot of money to
measure the current and see the current waveform of some equipment that we
manufacture.  I created a transformer/resistor combination that gives an
output ot 1 Volt per Amp of current.  We measure this with a voltmeter and
also observe the current waveform on an oscilloscope.

I will provide the details of the ones that I made in the next week.

Skip Malley

>Original Poster: "Basura, Brian" <brian.basura-at-unistudios-dot-com> 
>I'm in the process of building a new power controller for my coils.  The
>question I have is on measuring input (mains) current which can be up to 50
>amps.  I'd prefer to do it without utilizing a shunt.  Can I build a current
>transformer by taking a toroid core, wrapping one turn of a primary leg
>around it, then winding 100 turns around it for a secondary, and hooking the
>secondary to a .5amp meter? 
>What other ways are available to measure this level of current (50 amps)?
>Should I reconsider using a shunt?
>Thanks in advance,
>Brian B.