Re: Ok.. where am I going wrong

• To: tesla-at-pupman-dot-com
• Subject: Re: Ok.. where am I going wrong
• From: RWB355-at-aol-dot-com (by way of Terry Fritz <terryf-at-verinet-dot-com>)
• Date: Sat, 14 Nov 1998 18:14:54 -0700
• Approved: terryf-at-verinet-dot-com

Hi Mike, all,

My 2 cents are posted below your mail

 I just finished wiring up my pig-training facility. This means the
 welder, 0.4 ohm resistor and 240V feed. I had thought to calibrate the
 switch settings on the welder to KVA numbers by taking voltage readings
 across the resistor. The infamous V=IR business. Only.. it didn't work.
 Or I don't think it did. At one point, I measured a drop of 17V. This works
 out to roughly 42 amps. This cannot be. I have 30A fast blow fuses in the
 line
 and I suspect that they would fry in short order at almost 50% overload.
 Therefor, there must be someting I am missing. I assume it is related to the
 fact that this is AC.
 Could someone help me out here? Tell me where I goofed.
 
 Michael Baumann
 Coiler, Homebrewer, Nerd. mycroft-at-access1-dot-net
 
I think you (will) have a problem "measuring" the current this way. First of
all I donīt think you have a pure sinusoidal waveform (It is being distorted
by the total inductive load) and more importantly donīt forget you have a
phase shift between the voltage and the current. The current lags behind the
voltage. So you canīt measure the effective current (the current doing the
"work"). A pure DC setup can be current measured this way (via a dropping
resistor), but in an inductive AC load setup, I dont think you can measure the
current in this manner. A 30A fast blow fuse will pop out long before that 50%
overload. Even a slow blow fuse wonīt take this type of overload for very
long.
 
 
Coiler greets from germany,
Reinhard

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