Are these through bolts supposed to be insulated?
73/gw
In a message dated 5/3/2008 7:20:02 P.M. Central Daylight Time,
n3db@radix.net writes:
Hello all,
I am seeking input on a potential problem with my "almost new" B+
transformer. It is a 240V input, output 4 taps from 2800-3000V rated 2 amp
full load.
Transformer was tested in situ today, first stand-alone. Has a slight hum
but not significant, and as mounted no detectable vibration on the
laminations. AC output tested fine on all taps. Second test was with full
wave bridge
feeding a 12 x 800MF (series) homebrew cap bank attached- expected DC Voltage
measured fine on the cap bank. 3rd test was with 100k ohm 250w R across the
cap bank from B+ to B-, ~100 volt drop.
Now the "problem": The transformer is a typical E I Core (roughly 9"x7"x7")
with primary taps on one side fed to binding strip & secondary on the other
side to an EU style strip opposite the mains. Core is held together with 4
pieces of allthread, nuts on each side, around 1/4" in diameter. Transformer
is not potted. With mains fed to the transformer & even with cap bank
removed from the secondary side, the 4 allthread "bolts" get hot. Not a
"little
hot" but "blister your finger hot" with just a minute or 2 of mains voltage
applied. I understand this was new when I bought it- that said, I can smell
some
heating varnish, apparently from the bolts. The laminations themselves stay
completely cool, but granted it is so massive (84lbs) that it would take a
good long while for it to heat up. I am not sure but the allthread appears to
be standard steel. I have never run into this strange effect before- this
can't be normal, can it? I am guessing this is hysteresis, magnet
ostriction and heavy eddy currents in the bolts- does this sound plausible?
What is going on here?
Because they are getting so hot after just a short time under power I am
concerned about using the transformer in the amp (GS35b 50 MHz in mid-build).
It has been suggested that I pull one of the allthreads and check for hotspots
on it, which I plan to try. If they are steel would it pay to replace them
with non-magnetic stainless bolts & get rid of the allthread completely?
Also, in its current configuration I cannot tell whether the bolts are
actually
a proper fit for the holes in the E I plates- it appears that it may be
slightly undersized, and of course they are threaded the whole way, ans
therefore
may not be effectively transferring heat to the laminations.
Any input would be most appreciated.
73 Dave N3DB
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
**************Wondering what's for Dinner Tonight? Get new twists on family
favorites at AOL Food.
(http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001)
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|