Date: Mon, 22 Oct 2012 17:12:31 -0400
From: "Gary Smith" <Gary@ka1j.com>
To: Amps@contesting.com
Subject: Re: [Amps] Great Transformer Discussion!
>From a standpoint of reduced hum I like the idea of the interweaved
terminal laminations (his E & I interweave description) as opposed to
a pair of C cores with approximating tips. If his method will also
give a higher CCS rating as Dhal used, and fit with the same
dimensions, it would be worth looking deeper into.
There aren't that many transformer makers I know of any more.
Gary
KA1J
## A pair of C cores will blow away EI any day. His plate xfmrs are not EI
per his website. He has cut the ends of a c core differently so they inteweave.
Notice the big gaps with the spacers, when looking down on his plate xfmrs.
The drawback to that approach is there is way less room on the core for the
windings. On the old hypersil pole pigs, in oil, they used cut cores, but not
interleaved.
But they did use ‘dogbone’ spacers to create gaps in the windings...to allow
oil to
flow between the windings.
He mentioned about the use of a 105 deg C temp rise....and presumably over
ambient.
Now that’s bloody hot. Most xfmr makers spec temp rise over a 40 deg C ambient
when used in CCS mode. 105+40 = 145 C = 293 deg F !
Dahl specs his plate xfmrs.. ( in CCS mode, 100% duty cycle) at 55 deg C temp
rise
over a 40 deg C ambient + a further 10 C rise for spot heating deep inside the
cores.
55+40+10 = 105 C = 221 F Big diff between 221 F and 293F.
Dahl does not go cheap on the temp rating of the insulation between windings.
It’s
good for well over 175C = 347 F.
Its actually cheaper to make a xfmr with higher temp insulation and smaller ga
wire
vs lower temp insulation + bigger ga wire. Some dry typ xfmr makers... like
for
vault xfmrs used for 12.5 kv 3 phase down to 208/120 variety, will run them
blazing hot,
and I mean hot, no different than cracking your oven door open. The better
ones
will use a 50 deg C temp rise over a 40 C ambient. But some are as high as
175 C
over a 40 C ambient. Then you have everything between those 2 x extremes.
You have to be real careful when spec’ing any xfmr. I asked hammond for a
quote
on a custom built 7V @ 80A CCS xfmr....and since I did not spec a temp rise
over ambient,
they used a 60 C temp rise over ambient... which is blazing hot for a fil xfmr.
With the really big stuff, you also have another unique problem..and that’s
your 240 vac
line will sag by 8-10 vac. Your B+ regulation ends up not being what you
would like, simply
cuz of the huge V drop from xfmr on the street, via the Aluminum drop wires to
your home..
which are typ 2 x gauges smaller than the CU wire they splice into at your pot
head on
your home. Hence you want pri taps at 225-230-235 even though your line V
is 240 vac
with no load on it. I got mine tapped at 198-208-218-230-240-250 His
tapping scheme
is actually better, with 7 taps..and all 6 volts apart.
240-234-228-222-216-210-204
What would be even better would be 240-235-230-225-220-215-210
My dahl fil xfmr also came with 6 pri taps, same taps as my plate xfmr. By
juggling the various
pri taps on the plate xfmr with loads of sec taps, you end up with endless
combo’s. If you
folks ever buy a plate xfmr for a hb amp...get loads of pri and esp sec taps.
Then at least u
end up with a plate xfmr that will run anything and everything. Drove me nuts
using surplus xfmr
that were in perfect shape, but only had one sec V to use.... which was usually
either too high...
or too low.
later......... Jim VE7RF
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