A unidirectional pulsing waveform has a DC component.
That analyzes to a sum of DC, fundamental frequency AC, and AC at
harmonic frequencies. The average as averaged over a whole cycle is the
It is fairly well known that a transformer driving a halfwave rectified
load can run into core saturation problems from the DC component in the
unidirectionally pulsing current waveform.
- Don Klipstein ( firstname.lastname@example.org)
On Apr 12, 8:49 pm, email@example.com (Don Klipstein) wrote:
Interesting theory. One helpful piece of info which it's quite
still don't have is what the currents are on both sides of the
For saturation to occur I would think the transformer would have to
to fully loaded. Which it could be, given the trends to lower cost,
On Wed, 13 Apr 2011 04:22:15 -0700 (PDT), " firstname.lastname@example.org"
As I posted in an earlier post (not sure what values I used, but I'll
run a scenario anyway), assuming a 2 ohm winding, a 2 volt DC
component will cause 1 AMP of current to flow in the winding. IF that
coil happens to be the primary of a 40va transformer, The full load
current on that transformer is about 350ma, so the probability that 1
amp of current in the primary, with no AC voltage applied, would have
more than saturated the core is pretty good.
Add the quiescent current of the primary, and you have a saturated
core. And that's just a 2 volt DC component on a 115 volt primary.
If the primary is 4 ohms instead of 2, you have half an amp with 2
volts, or 1 amp with 4 volts.
Doesn't take much to put 2 volts DC across a 115 volt line.
See http://sound.westhost.com/articles/xfmr-dc.htm for more
information from someone who may have a bit more credibility than you
guys may give me.
** A 40VA tranny designed for 120 volt 60 Hz operation has a primary
resistance of 16 ohms.
Getting a 2 volt DC offset on a 120 volt AC supply takes some doing.
** Like hell.
For a 2 volt DC offset to exist, the peak voltage in one polarity must be
6.3 volts higher than the other.
With a typical impedance at the outlet of 0.25ohms, this equates to 25 amps
peak load in one polarity and none in the other.
** I helped Rod write that article.
Toroidal trannys are very sensitive to DC offsets while regular E-core types
are hardly bothered by them - the difference is that while the former has
no air gaps in the core, the latter is full of them.
Not to be rude or anything, but a LOT of talk has gone on about your
problem and I have not seen any further posts from you on the matter. No
comments about any suggestions at all.
I'm not going to spend any more time on this thread until we hear back
from the original poster with more information otherwise we are simply
blowing smoke (sorry - couldn't resist).
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Just mentioned elsewhere that I have a new transformer on order and I can't
really do anything until that arrives. Rest assured I appreciate all the input
and I'm taking it all into consideration. Thanks.
What is fuse gonna do? Instead of blowing x-former,, blow fuses?
Then still it is not right. Let;s go back from begining. How old
is the system? When this blowing tranny started? From day 1 or some
time(month, years after the system is installed? If tranny is hot to
touch when in use, that is rad flag.
** The fuse will actually help you diagnose the problem.
If the fuse opens soon as AC power is applied - the tranny is being
If the fuse opens after some time because insulation in the primary side has
failed, replacement fuses will open immediately despite the secondary being
This isunthinkab;e crazy idea but is the x-former being put in backward?
Rgwew i a such thing as current limiting x-formers. One thig I'd try
then I'd put in proper Wattage low value resister to lower the primary
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