[Prev][Next][Index][Thread]

Re: Math Doodling

Hi John,

Original Poster: FutureT-at-aol-dot-com
In a message dated 99-06-12 12:43:02 EDT, you write:
<<snip  >Afternote:
> I realize most of this has been posted, but I thought an example
> would clarify this subject. John Freau´s post on low vs. high
> input voltage empirically proved my thoughts. Thanks John!! and
> yes I really am pleased (;o)) + my low voltage coil is doing pretty
> good !!!

>Reinhard,
>Yes, your coil is doing very well.  I wasn't sure however how you
>are measuring the VA input.  Is this; wallplug VA measured with
>ammeter and voltmeter, or some other measurement?

I measure sort of "inbetween" ;o). I run the NST per variac (250v)
and measure the dead short current on the high voltage side (no
TC connected). Then I measure the primary current (once
uncompensated and once compensated), with an RMS meter,
the NST draws in this dead short configuartion. Using the rms
meter lets me ignore the fact that the wave shape isn´t exactly
sinusoidal anymore. Now, I connect my TC and let her rip.
During a run, I remeasure the primary (aka mains) current and
use my afore measured values (dead short) as a comparison.
As I do not use mains resocaps, the value is almost the same
as in a dead short (i.e.: I do not cheat the xformer´s stray
inductance). I don´t think the transformer losses change too
much from a dead short to coil operation. I do need to know
the losses, that are due to over current operation of my NSTs
(170mA from a 75mA NST), because the copper and core
losses go up as you overrate the xformer.

Output VA is Vhigh * Ahigh
Input VA is Vlow*Alow

Transformer losses are therefore: OutputVA-InputVA.

Example of what I mean:
HV voltage: 7500V
HV current: 170mA
Output VA = 1275VA

LV voltage: 250V
LV current: 6A
InputVA = 1500VA

Xformer losses: 1500VA-1275VA = 225VA.

Using this information during a coil run, I can calculate
the input power.

Example:
I measure 250V and 5A on the primary side. This means
the mains VA is 1250VA. Knowing that the losses in the
xformer (for the 250V primary and 170mA secondary
"setting" in this case) are 225VA, I can say 1250VAin -
225VAlosses = 1075VA. This is of course still a rough
(but I think somewhat closer) estimation of what actually
goes into the tank circuit. I do not account for losses in
the spark gap, etc. Some day I will give Terry´s fiber
optics probe a shot, so that I can directly measure
what goes into the primary tank circuit.


Coiler greets from germany,
Reinhard