RE: FW: Re: Tesla Coil Efficiency Test

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Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Boris -

As I pointed out in my post both methods can be used depending on what you
are looking for. Normally an engineer would want to know the overall (black
box) efficiency. One reason is because overall efficiency would give the
true operating cost. However, operating cost is of no concern with Tesla
coils so the transfer efficiency can be of interest.

The few tests that have been made with Tesla coils has shown positively that
as the size gets larger the overall efficiency gets lower. I would be
interested if you know of proper tests that prove this is not correct.

I agree that voltages themselves are not losses. However, high voltages
create corona that are losses. High voltages also mean more losses in wire
insulation and capacitors, very important with Tesla coils. The TC primary
capacitor losses can be easily reduced by using very high voltage rating
(expensive) capacitors.

With well designed Tesla coils a larger size means higher voltages which in
turn mean higher losses. The unique characteristic about Tesla coils is that
the "losses per unit watt input" increase as the Tesla coil is made larger.
This means the overall efficiency will decrease as the TC is made larger.
The opposite happens with other electrical apparatus when correctly
designed.

The designer has some control over the overall efficiency during the TC
design stage. This is the reason I show the "watts per foot of spark" in the
JHCTES Ver 3.3 computer program. By selecting the proper inputs the designer
can find the minimum "watts/Ft of spark" for a certain size TC. This does,
however, require a good understanding of how a TC works so he does not end
up with an impractical design. The "watts/Ft of spark" varies from about 200
watts (high efficiency) for small coils to about 2000 watts (low efficiency)
for large coils.

John Couture

-----------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, June 26, 2002 6:50 PM
To: tesla-at-pupman-dot-com
Subject: RE: FW: Re: Tesla Coil Efficiency Test


Original poster: "boris petkovic by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<petkovic7-at-yahoo-dot-com>

Hi John,

 we
> are talking about two
> different types of TC efficiency. You are referring
> to a transfer efficiency
> based on  E = 0.5CV^2..
---
Now ,allow  me just to stick to a "transfer
efficiency" from now on.This one is more accepted (and
simplier per definition) in engineering world.
---
The efficiencies found by both methods will
> decrease as the TC
> becomes larger.
---
As concerns transfer efficiency theory,scaling up the
size of all the components (including primary gap and
firing voltage !) ,it goes in a favour of a bigger
coil.
In practice ,scalings are not indentical for every
parameter (especially not for Vp) and comparations
become pointless.
---
 This is contrary to most electrical
> apparatus where larger
> means greater efficiency. One reason is because
> larger with Tesla coils
> means larger voltages rather than larger currents.
> The higher voltages mean
> higher losses and they increase faster than the
> input wattage. This means
> there is a secondary voltage limit for every size of
> Tesla coil. Above this
> voltage the insulation breaks down and the coil is
> damaged.
---
Not again,if bigger coil is made lin. proportionaly
bigger to a smaller one in every its segment.As far as
it comes to a proper field control,600 kv/m of
secondary height can be achieved with todays materials
for a small and big coils without toomuch
diffculty.
Major of loss in TCs is associated with current (not
voltage) in primary components.
Nonlinearity of allowed voltage might be  expressed
only for megavolt+ coils I guess.

regards,
Boris