Re: more noob questions - transformers


<caltus@xxxxxxxxx> wrote in message
news:1175127257.135044.188290@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Ok ... try not to laugh when i ask... tho i only have a few questions
on designing a home made transformer.. And of course i dont want to
burn my house down.. so lets start from there.

I would like to make my own hv transformer and thought i would start
by pulling a apart a regular 12 volt ac / dc 12 volt 1.5 amp
transformer and removing the rectification.

From what i see of ac to ac transformers on design is that mains
come into and go directly to the core however i would think there is
some kind of resistor before or hiden around the primary windings.
First questions is this dont make alot a sense to me as it is
esentially a short curcuit. However if it does actually work this
way then the windings are wrapped so that itself is a good resistor
to precent the short circuit. however that the main reason why I am
writing all this.
So my question is if there is a resistor what should it be. ( or how
can i calculate what it shoudl be) . Now i know there is a billion
formulas for making good transformers so that why i want to start
from a premade dc to and remove the rectification so i can run it
into another transformer to step it back up again. this shoudl
limit what i shoudl have to calculate for resistors if needed.

. this is again why i like to know why it works that way from the
mains as i will have to pass the secondary winding thru the primary
of the home wound step up transformer which again would be a short
circuit .. or at least what looks to be. i will put fuses ( and i
would expect resistors ) between the 2 transformers to prevent too
much current on my hv winding .
I plan on striping another laminated core . or at least the secondary
windings on a second core to wind my prefered step up

now if i use a 110 ->12vdc transformer and its a 1.5 amp . I will
choose my second core to be rated around 1 amp and my hv amperage
should end up in small ma rating for light usage without burn out.

I reviewed many diferent transformer designs and all they ever give
is is a direct input from the mains to the windings or there just
way to complicated as there beyond the scope of anythign basic.

im looking for such a basic design it just keeps the same frequency
so that why i thougth stripping the rectificatin should do from a dc
supply. I can figure out the insulation needed for the layers on my
core to prevent it from shorting out to the core or itself due to the
hv so lets not worry about that either.

If anyone could please let me know if this should really be more
complicated if it really is that simple.
Im looking simplest as possible design that will not blow up when I
plug it into the mains.

I appreciate any imput reguarding this. I have some HV experience with
whimhurst and those types of machines however not much when it comes
to current limiting. Im certianly not going to make something without
making sure i understand the safty parts of it first.

Thanks,

Caltus


There is no resistor in a transformer. There are 2 coils. The one that the
mains comes in contact with is called the primary. The secondary does not
make any contact at all with the primary, and therefore not the mains
either. They are 2 separate coils wrapped around a piece of metal (iron I
think). Since the mains voltage is AC, and therefore moving rapidly from one
direction to the other, it induces a current into the secondary. The voltage
you get out of the secondary depends on the ratio of the # of turns in the
primary to the # of turns in the secondary. So if you have 10x as many turns
in the primary than the secondary, there will be 12v (assuming 120v at the
primary) on the secondary. As far as choosing the type of wire or number of
wraps, that's a little out of my league, so I'll leave that to teh more
experienced in the group.

As always, be very careful when working with mains voltages......



.

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