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Re: old problem
Tesla List wrote:
> Original Poster: "Marc metlicka" <mystuffs-at-orwell-dot-net>
>
> hi all, yes it's the dumb guy again.
> i have a question that has been bothering me for some time.
> while i was building my system i needed to curent limit my pt. i tried
> to use my 20 amp veryac. it worked ok until i got to 70v output, at
> 330-1 this gave me 23100v. this seemed to be a threshold of sorts. if i
> went higher my powerstat would start to smoke. so my first question is
> how does evryone use a veryac to limit there current.
> my next idea was to use two dry type transformers, since i
> wanted my sys. to be able to plug into any 110 outlet for mobility, i
> thaught that i would input the 110v into the 240 primary side. steping
> it down to 55v, then conecting it to the 110v line side of the second
> trans. steping it back up to 110v. both transformers were the the same
> make model and 500va. but doing this resulted in a very large curent
> draw triping my 15amp breaker.
> can anyone tell me why this didn't work? am i missing
> something?
> thanks to all.and if anyone posted any info on "more new caps" would
> they please send me the info off list. my mail server had major problems
> over the weekend resulting in me not getting any messages and loosing
> them as well.
>
> thanks again. mem
Hi mem
im guessing that your trannie is a (pt) potential transformer...
therefore current limiting is needed :) you have about 3 options
1. resistive 2. inductive 3. combo of resistive inductive....
resistive works but in the process of reducing available current to the
trannie you get a voltage drop to the trannie
inductive works better very little voltage drop but not too easy to vary
in a linear manner and this type can induce "bucking" ( a current surging
between the trannie and inductor)
combo is nice you have the smooth current flow of the resistive element and
the current control of the inductor...
as far as using a variac to control current you will need a BIG variac to
handle the current ( its used like a huge rheostat ) and you can never
really use just a variac as a currnet controller by itself ... if you turn
the variac to the complete stop position you will allow full current to be
applied to the trannie ( aka direct hook up ... and there goes the fuse)
you probably already saw this start to happen as you turned the dial on the
variac... you reduced the number of turns to a minimum and the existing
turns between the brush and output began to sink way too much current ergo
the smoke .... a possible solution may be to use the variac with an
inductor wired in series with the output line to the trannie the inductor
will be used as a base limiter and the variac will offer a semi linear
current control ...
Scot D