Re: Ammeter Question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Robert Jones" <alwynj48-at-earthlink-dot-net> 

Hi, Peter,

That may be a quick way of making a current transformer. The usual way a
current transformer is configured is by loading it with an ammeter for
minimum output voltage hence minimum magnetization current so that the turns
ratio accurately reflects the current ratio. Did you design it to work or
just get lucky.  The only limitation I could come up with in your
configuration was the voltage across the existing winding must be say less
than half its normal operating voltage to avoid saturation.  Because of the
way a current transformer works the capacitor is probably not needed as it
will read average magnitude regardless not peak as the presence of the
capacitor would suggest.  How linear it would from your calibration point I
don't know but it will give comparative measurements in your circuit..

Bob

 >
 > To make an ammeter, I used the smallest mains transformer I could buy or
 > scrounge. eg old 9 v power pack. Remove the low voltage secondary windings
 > and discard.  Wrap 1 1/2 to 2 turns of heavy wire in place of the
secondary.
 > When current passes through the heavy winding a voltage gets induced in
the
 > other winding such as 10 - 50 VAC. depending on the transformer.  This is
 > rectified by a bridge rectifier and smoothed with a small eg 1uF
capacitor.
 > This can be dropped with resistors to a suitable voltage for whatever
spare
 > voltmeter you have or scale you are using. Calibrate it with a device of
 > known wattage eg fan heater and there you have it. Stepping up the voltage
 > in this way removes most of the non-linearity created by the fixed voltage
 > drop with the bridge rectifier. I've used this technique to keep mains
power
 > away from the meters in my control board.
 >
http://members.iinet-dot-net.au/~pterren/tesla_coil_latest.htm#The%20variac%20co
ntrol%20box
 > Cheers
 > Peter (Tesla Downunder)