# Re: MOT core

```Original poster: "Richard W." <potluckutk-at-comcast-dot-net>

Hi Ken,
Actually you'll need more copper to handle the additional VA.

Rick W
Salt Lake City

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 03, 2004 5:45 AM
Subject: Re: MOT core

> Original poster: "Crow Leader" <tesla-at-lists.symmetric-dot-net>
>
> I think I'm interpreting something wrong here.
>
> Say I have two transformers, each has a core cross sectional area of
1"sq.,
> and each is rated 39VA.  Together than can handle 78VA.
>
> Now if I strip the windings off, and put the cores next to each other
giving
> me a cross section of 2" sq. (pretending and generic EI core set) and put
> the wire back on, (I connected the wires from each transformer to make for
> the extra winding circumference) do I now have a transformer capable of
> 156VA, AND have leftover copper from the rewind? This sounds too good to
be
> true. What's the difference between the single and parallel tranformer
> situations?
>
> KEN
>
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Monday, February 02, 2004 8:58 AM
> Subject: Re: MOT core
>
>
>  > Original poster: "Richard W." <potluckutk-at-comcast-dot-net>
>  >
>  > Actually decreasing the core cross-section by half will drop the power
>  > capability almost by a factor of 4.
>  >
>  > Let's say we have a core who's center leg measures 1" x 2" for 2 square
>  > inches.
>  >
>  > CS = 2 sq.in. (Cross Section)
>  >
>  > VA = (CS/0.16)^2
>  > VA = (2/0.16)^2
>  > VA = 12.5^2
>  > VA = 156
>  >
>  > Cutting the core in half = 1 sq.in.
>  >
>  > VA = (CS/0.16)^2
>  > VA = (1/0.16)^2
>  > VA = 6.25^2
>  > VA = 39
>  >
>  > Rick W
>  > Salt Lake City
>  >
>  > ----- Original Message -----
>  > From: Tesla list <tesla-at-pupman-dot-com>
>  > To: <tesla-at-pupman-dot-com>
>  > Sent: Sunday, February 01, 2004 7:34 PM
>  > Subject: Re: MOT core
>  >
>  >
>  >  > Original poster: "Hydrogen18" <hydrogen18-at-hydrogen18-dot-com>
>  >  >
>  >  > The only thing I know to say here is stack the cores. Alternatively
you
>  >  > could use very small wire for the secondary to achieve the HV
output.
>  >  > Stacking the cores(inserting 1 E into each end of the "bobbins")
will
>  > halve
>  >  > ----- Original Message -----
>  >  > From: "Tesla list" <tesla-at-pupman-dot-com>
>  >  > To: <tesla-at-pupman-dot-com>
>  >  > Sent: Sunday, February 01, 2004 6:49 PM
>  >  > Subject: MOT core
>  >  >
>  >  >
>  >  >  > Original poster: "Dan" <pbursa-at-cfl.rr-dot-com>
>  >  >  >
>  >  >  > Hello !
>  >  >  > I am curious if someone here has experience with rewinding
microwave
>  >  >  > transformer.
>  >  >  > I cut of the I part of the core, removed old windings and split
the
> E
>  > core
>  >  >  > in half so now I have two identical E cores .
>  >  >  > Together they make 5.5 inches long, 4.15 wide and 1.35 thick core
> with
>  >  >  > about 1.72 square inches area...
>  >  >  > This looks like I'll need over 400 turns on primary... this would
>  > require
>  >  >  > 40000 turns for 12KV secondary and there is not enough space for
> this,
>  > I'm
>  >  >  > afraid.
>  >  >  > My question is - if I use less primary windings (say 150 - 200),
how
> it
>  >  >  > affect performance, core saturation, ...
>  >  >  > I noticed that original MOTs primary was also less than proper
> amount
>  > of
>  >  > turns.
>  >  >  > Also, since MOT core is welded together, how the weld affect the
> core
>  >  >  > losses and eddy currents? isn't the very purpose of using
laminated
>  > core
>  >  > to
>  >  >  > minimize these loses ?
>  >  >  > How about potting finished transformer in oil ?
>  >  >  > Thank you in advance