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Output Voltage vs. Firing Rate (fwd)
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From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent: Saturday, August 15, 1998 6:42 AM
To: Tesla List
Subject: Re: Output Voltage vs. Firing Rate (fwd)
JohnF, Anyonio, All -
I do not agree that the RMS metering for a Tesla coil is a problem. The
overall performance of a TC can be determined by properly measuring the RMS
input and the RMS output. The overall efficiency is:
Overall efficiency = RMS output/ RMS input
The TC measuring problem is in the method of measuring the output. A
single extra long spark is an instantaneous measurement of the TC output
not an RMS measurement. Antonio is correct in that the RMS current will
always appear to be high but this assumes instantaneous conditions. This
does not apply to RMS output conditions.
The TC RMS input conditions can be measured by using a standard volmeter,
a thermocouple ammeter, and a power factor meter as JohnF is doing. The TC
RMS output conditions can be measured by using a controlled spark length. A
controlled spark is a horizontal continuous spark between the toroid and a
ground point. This spark length can be corrected for standard air
conditions and the type of electrodes if desired.
The input units would be in watts and the output units would be in a
length of spark. The overall efficiency would be:
Overall efficiency = watts/ Ft of spark
There are other possibilities such as solid state electronic meters but
they are too expensive and difficult to use for the typical coiler.
John Couture
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At 11:45 PM 8/14/98 -0500, you wrote:
>
>----------
>From: FutureT-at-aol-dot-com [SMTP:FutureT-at-aol-dot-com]
>Sent: Friday, August 14, 1998 9:08 AM
>To: tesla-at-pupman-dot-com
>Subject: Re: Output Voltage vs. Firing Rate (fwd)
>
>Antonio, all,
>
>I hadn't realized about the rms problem. This wattmeter says it's
>accurate to 1/4 of 1 % up to 125 Hz. I wonder how severe the errors
>might be? Has anyone compared such wattmeters with true (electronic)
>reading wattmeters in TC circuits to get a ball park figure of possible
>errors?
>
>I posted a long post some time ago telling of my wattmeter vs.
>thermocouple tests and didn't get any responses, so i had thought the
>tests were valid.
>
>I wonder if we're talking 10%, 30%, or 200% error. Someone once
>suggested they thought the errors might be around 10% using a
>wattmeter. Does this seem reasonable?
>
>Also any clue as to how inaccurate the rms technique might be
>(ignoring power factor issues for now)?
>
>Thanks,
>
>John Freau
>--------------------------------------------
>
>In a message dated 98-08-14 01:31:18 EDT, you write:
>
><< ---------
> From: Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent: Friday, August 14, 1998 12:52 AM
> To: Tesla List
> Subject: Re: Output Voltage vs. Firing Rate (fwd)
>
> John Freau wrote:
>
> > At the 640 watts using 120BPS, I've carefully checked out the wattage
> > using a thermocouple type ammeter, checked the power factor, then
> > compared, etc. I found the wattmeter to be accurate within a few
> > percent.
>
> Some comments:
> A termocouple ammeter measures the RMS current, including harmonics. A
> fuse also "measures" the total RMS current. The problem is that, if the
> input voltage can be considered as a 60 Hz sinusoid, only the 60 Hz
> component of the input current contributes to the average input power.
> Power measurements using the RMS current will always appear too high
> (assuming that it is possible to measure the phase angle between voltage
> and the 60 Hz component of the current).
> A perfect moving-coil wattmeter -should- measure correctly the input
> power, even with distorted waveforms. The problem is that they may filter
> out high-frequency components. But if the voltage is a 60 Hz sinusoid,
> the filtering of the current harmonics is not important, as they do not
> contribute to the input average power.
>
> Antonio Carlos M. de Queiroz
> >>
>
>
>