Re: Coil Efficiency (was more mini coils)
From: John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: Friday, June 20, 1997 1:21 AM
To: Tesla List
Subject: Re: FW: Coil Efficiency (was more mini coils)
At 12:58 PM 6/19/97 +0000, you wrote:
>From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>Sent: Wednesday, June 18, 1997 5:46 PM
>Subject: Coil Efficiency (was more mini coils)
>Hi Greg, all,
>> > As we (that have actually gotten our hands dirty and
>> > built coils that is, and I'm not saying you haven't) know well, the
>> > ratio between input power and output spark length is far from linear.
>> > Streamers issuing from a topload terminal seem to crave increasing
>> > power at an exponential rate to their length.
>> All too true :^< Perhaps a more direct measure of coil effectiveness
>> would be to normalize the W/ft ratio to operating power level.
>> None the less, Malcolm's 'little wonder coil' does provide an
>> interesting data point, in a sparsely populated area of tesla coil
>> parameter space. Way to go, Malcolm!
>Thank you. Perhaps it's time I brought in what figures I have compiled
>on length vs actual coil power.I have about 16 at the mo. Some of the
>figures had to be estimated because of the gap systems used so may
>be totally out of touch (esp. those achieving multiple fires per 1/2
>cycle for static gaps). Seeing those beside claimed wall-plug figures
>might be a real wake-up call for some. Will do in the next day or so.
There are several tests shown in the TC Construction Guide. One of these
tests shows how I found the efficiency of a small coil like the one you are
using. The challenge was not only to find the efficiency but to also see how
the graphs, computer printout, etc. shown in the book agreed with the tests.
I had never done this before and I do not believe this has been done by any
coiler unless he has a computer program like the JHCTES program.
The test is done while the coil is in operation at low input voltage. The
power transformer is a 7500 volt, 30 ma neon. The input watts to the neon
varies as the square of the input voltage. The secondary output current is
in surges and must be integrated. The best way to measure the wattage under
these conditions is to use an auto lamp (18 watts for this test) and light
meter. The efficiency is equal to watts out divided by watts in.
The test scheme is to vary the input voltage with a variac until the auto
lamp in the secondary circuit is at normal brightness according to the light
meter. This means that the secondary output is 18 watts. With everything set
up properly the overall efficiency was found to be 56 percent. This compared
favorably with the computer printout at 51.4 percent or within 8.2 percent.
This test can also be done with larger coils using larger lamps or
current shunts. It will be found that the efficiencies are much lower with
the larger coils. Because small coils are so efficient, magnifiers may
provide no additional gain. However, because the efficiencies of large coils
are so low, magnifiers may show a gain. I have not seen a true comparison to
prove this conclusion.