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RE: FW: Re: Tesla Coil Efficiency Test
Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
Bart, All -
The concept for the TC efficiency test is simple. It's the details that get
you. Wind a few turns of wire around the bottom of the TC secondary coil and
connect to an incandescent lamp and the lamp will light up when you energize
the TC. The trick is to find how well this lamp test represents your TC
output. The TC efficiency is the output watts divided by the input watts.
The input watts are found by an AC wattmeter connected to the input of the
NST or power transformer. If you don't have a wattmeter use an AC voltmeter
and ammeter. The power factor can be checked later. You will need a variac
to vary the AC input voltage and wattage. The variac is increased until the
input watts is enough to light the lamp to a resonable level. This would be
below the wattage to cause a spark output.
The output watts can be a problem. I have never heard of anyone who has
tried to find the TC output watts by using an incandescent lamp except for
my research. So we are trailblazing in new territory and will have to be
You will need to build a light tite box to hold a lamp and a small solar
cell with a 50 ua meter (Radio Shack) on the box. When the lamp is connected
to the pickup coil on the TC secondary coil the solar cell will activate the
meter when the TC is energized. The 0 to 50 ua scale is OK because only
relative light levels are needed. The type of incandescent lamp will be
determined by the size of TC to be tested. The characteristics of the lamp
are not important because only one value of light level is used per
I suggest you start with a small Tesla coil with a NST of about 200 watts.
For this size TC I used an auto lamp #1141 rated 12 volt DC, 18 watts. For
the pickup coil I wound 4 turns of #20 AWG hookup wire around the bottom of
the secondary coil and connected this to the lamp. The exact number of turns
will have to be found by experiment. The secondary coil and the lamp circuit
should be grounded.
For the TC efficiency test the input voltage to the TC is raised by the
variac until the lamp glows at about normal brilliance. This could be well
below the spark output point so the input wattage would be below the 200
watts. The input wattage is noted and the light meter ua noted. The lamp is
then disconnected from the pickup coil and connected to a DC ammeter and a
source of variable DC voltage. The DC voltage is raised until the light
meter is at the same ua as shown by the meter when connected to the TC. The
DC voltage and current for the lamp are noted. The output watts are then
found by multiplying this voltage by the current.
The TC efficiency is the output watts divided by the input watts. The input
is in AC watts and the output is in DC watts. Note that these are watt
seconds or electrical energy and breaks are not a factor. The current in the
secondary coil is in pulses but the lamp integrates this output. The
brightness of the lamp can also be used to tune the Tesla coil. However,
this may not be the best tune point for sparks because of the lamp load.
Keep in mind that this is all new ground and there is much more to be
considered. When you finish the test let me know and we can proceed further.
Let me know if you have any questions.
It would be a great help if other coilers would also make these tests so we
can combine our findings. This is not a private project and all comments
from other coilers are welcomed.
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, July 04, 2002 11:54 AM
Subject: Re: FW: Re: Tesla Coil Efficiency Test
Original poster: "Barton B. Anderson by way of Terry Fritz
Can you do me a favor and write up the test procedure for the lamp test in
detail and send here or
offlist (whichever you prefer). I'll make the measurements.