Re: Current Limiting

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Gregory Hunter <ghunter31014-at-yahoo-dot-com> 

Hello Matthew,

--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: Matthew Smith <matt-at-kbc-dot-net.au>
 >
 > Hi All
 >
 > We can limit the current from the incoming mains
 > with:
 > * Resistance (high wattage light bulb; fan heater)
 > * Inductive reactance (welder, MOT with secondary
 > shorted)
 >
 > My question:
 > * Which is the best method OR

Ohmic ballasts are simple--foolproof, but they are
grossly inefficient and also cause a significant
voltage drop in the high voltage transformer.

 > * What are the advantages of each method.

Inductive ballasts are a bit more complicated to
design, but they are far more efficient. Many coilers
start out with ohmic ballast (electric stove elements,
water heater elements, etc.) but most quickly migrate
to inductive ballast.

 >
 > My only concern with using an inductor is that we
 > already have an inductor
 > in the form of the transformer so I guess we'd be
 > throwing the power factor
 > even more askew by adding another.

Not an issue. Short out the high voltage side of a
distribution transformer and the primary will draw
almost infinite current--for about half an eyeblink.
Then the breaker will trip. For highly efficient power
transformers, you can't count on them to self-limit at
all.

Of course, you can avoid the ballast issue altogether
by using shunted transformers such as NSTs.

 >
 > Cheers
 >
 > M
 >
 > --
 > Matthew Smith
 > Kadina Business Consultancy
 > South Australia
 > http://www.kbc-dot-net.au
 >
 >

Regards,


=====
Gregory R. Hunter

http://hot-streamer-dot-com/greg