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Re: Dr R's 16KV 300ma transformer



Original poster: "Sean Taylor" <sstaylor-at-uiuc.edu> 

Eric,

It doesn't take power to magnetize a core - it does take power to saturate 
a core, which MOTs do at 120V.  A "magnetizing" current is one that is 90 
degrees out of phase with the voltage and thus doesn't do any net work.
It has a power factor of zero, and the power is zero.  If you have 1600 
WATTS being consumed, then it's going somewhere - whether to heat or light, 
etc.

>I thought the voltage drop relative to current draw was intrinsic to a
>transformer. My mains voltage drops when current draw increases.

I'm a little confused as to what you mean.  Yes, any time you draw current 
from a transformer, the voltage is going to drop due to losses.  The core 
itself as well as the windings contribute to this.  The mains voltage drop 
can be attributed to all the wiring in your house: both to the breaker box 
and from the breaker to the outlet.

Sean Taylor
Urbana, IL

On Mon, 02 Aug 2004 18:11:01 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
>The 1600 watts isnt going to heat, it is magnetizing the core.
>
>I thought the voltage drop relative to current draw was intrinsic to a
>transformer. My mains voltage drops when current draw increases.
>
>---Eric
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Monday, August 02, 2004 8:07 AM
>Subject: Re: Dr R's 16KV 300ma transformer
>
>
>  > Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz>
>  >
>  > On 1 Aug 2004, at 19:15, Tesla list wrote:
>  >
>  >  > Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
>  >  >
>  >  > I guess shunted transformers can be done right(although the only other
>  >  > kind I can think of are welders, which dont really matter much as long
>  >  > as they burn well). But with my 4 pack I have a HUGE magnetizing
>  >  > current(1600 watts!). I guess part can attributed to bad power factor
>  >  > and the fact that the cores are running at 70000+ lines of flux per sq
>  >  > inch. But why dont all transformers have shunts? I know the winding
>  >  > over winding method prevents the use of them, but I'm sure shunts
>  >  > could save more than one small transformer which was accidentally
>  >  > shorted/wired wrong/etc.
>  >
>  > Time for a bit of basic transformer theory perhaps. The reason most
>  > transformers don't have shunts is because it would degrade their
>  > regulation. NSTs and other current limited transformers are designed
>  > to have poor regulation so that they don't deliver an unlimited load
>  > current with a short circuit parked across the output. You can
>  > imagine the mayhem that would be caused by shunted distribution
>  > transformers - as soon as someone turned on a heater, the lights
>  > would dim. The winding-over-winding method ensures that the coupling
>  > between the primary and secondary is as high as possible given
>  > insulation requirements.
>  >
>  >       Shunts *do not* prevent core saturation. Using enough pole area
>  > so that the flux density is kept within the ratings of the core
>  > material does. Any transformer which has an excessively high
>  > magnetizing current flowing in its primary either doesn't have enough
>  > pole area for the core material used or has too high a voltage
>  > applied to it.
>  >
>  > Malcolm
>  >
>  >
>  >
>