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Mains transformer goodness

P

Paul E. Schoen

Jan 1, 1970
0
Robert Baer said:
Where did the trannie get the sex change?

A Massive Prong was removed, forming the hole in the donut.

Paul
 
N

N_Cook

Jan 1, 1970
0
Paul E. Schoen said:
The Wiki says otherwise. And I have had a lot of experience with high power
toroids and have seen the effects of high inrush current.
http://en.wikipedia.org/wiki/Inrush_current



I have personally observed this in our circuit breaker test sets. We take
care to apply voltage at about 70 degrees phase angle to obtain an initial
current peak equal to those that follow, and adjust the timing so that
there are equal numbers of positive and negative half-cycles. Inrush
current on successive pulses is minimal. But if there is an unequal number,
and a net DC component, there is always a much higher peak inrush current.
This is easily seen with short duration pulses of several cycles. In
breaker testing, of course, the breaker may trip at any time, sometimes
causing net DC, and the next operation usually exhibits high inrush.

Some other references:
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3206.pdf
http://powerelectronics.com/mag/power_magnetic_solutions_solving/
http://www.melcontransformers.info/images/transformer.pdf

Paul


Can a toroidal former become permanently magnetised and cause excessive
current draw. ? One, in front of me from an amp, drawing excess current ,
does not attract a small piece of iron. I don't know what the main
secondaries are supposed to provide, but can give 300 watts into 4 ohms.
I've wound off the primaries (yes external to the secondaries) to try and
understand what is going on with this transfornmer. Applying 70 volt ac ,
from a variac, across series secondaries is ok but increase to 75 volt and
the current draw goes up to 1/4 amp. Should be able to take twice that
voltage. Absolutely no visible problem , to the wiring or the coating of the
toroid and both secondaries measure DMM the same DC. Tomorrow will apply
something a bit over 70 volt with temperature sensitive labels fitted
around. I will even try a TV degaussing coil.
 
P

Phil Allison

Jan 1, 1970
0
"Paul E. Schoen"
"Phil Allison"

The Wiki says otherwise.


** The wiki is totally WRONG on this one.

The rather higher inrush surge of a toroidal mains tranny is explained by
the nature of the wound strip core itself - not on past history.


I have personally observed this in our circuit breaker test sets.


** Got nothing to do with the UTTER DRIVEL you just posted.

Normal users do NOT do the weird SHIT to transformers that you do - yet
still suffer from large inrush surges.

So YOU ARE 100% WRONG

- YET AGAIN.



...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"N_Kook"

Can a toroidal former become permanently magnetised and cause excessive
current draw ?


** No.

Normal use on an AC supply very quickly demagnetises the core - if it ever
becomes magnetised.



...... Phil
 
P

Paul E. Schoen

Jan 1, 1970
0
N_Cook said:
Can a toroidal former become permanently magnetised and cause excessive
current draw. ? One, in front of me from an amp, drawing excess current ,
does not attract a small piece of iron. I don't know what the main
secondaries are supposed to provide, but can give 300 watts into 4 ohms.
I've wound off the primaries (yes external to the secondaries) to try and
understand what is going on with this transfornmer. Applying 70 volt ac ,
from a variac, across series secondaries is ok but increase to 75 volt
and
the current draw goes up to 1/4 amp. Should be able to take twice that
voltage. Absolutely no visible problem , to the wiring or the coating of
the
toroid and both secondaries measure DMM the same DC. Tomorrow will apply
something a bit over 70 volt with temperature sensitive labels fitted
around. I will even try a TV degaussing coil.

Once you apply some AC voltage to the primary the remanent magnetism should
be neutralized, and you should be able to apply full rated voltage without
saturation. If the winding were made of the wrong material, such as perhaps
hardened steel, perhaps a powerful DC pulse could essentially make a
permanent magnet which would take a reverse pulse to neutralize. That seems
unlikely, but you might see the effect if you observe the current waveform
on a scope. I would think you would see peaking on one set of half-cycles
and not the other.

Most likely you have a shorted turn, and as the voltage rises, it starts to
break down. Again, if you observe current waveform on a scope, you might
see spikes near the peaks.

If you are talking about an audio transformer, 300 watts into 4 ohms is
about 35 volts. But it has to be able to work down to about 20 Hz, so it
would handle 100 volts at 60 Hz.

If this is a power transformer, it probably needs to generate a +/- DC
supply for direct drive into 4 ohms, which will require about 50 volts DC.
Two windings of 35 to 50 VRMS would be about right. So two in series might
be 70 VAC, which corresponds to your readings.

Paul
 
P

Phil Allison

Jan 1, 1970
0
"N_Kook"
I don't know what the main
secondaries are supposed to provide, but can give 300 watts into 4 ohms.


** So the amp's DC rails are about +/- 53 volts.

Means the tranny likely has two secondaries, each of 38 volts.

I've wound off the primaries (yes external to the secondaries) to try and
understand what is going on with this transformer. Applying 70 volt ac ,
from a variac, across series secondaries is ok but increase to 75 volt and
the current draw goes up to 1/4 amp.

** Spot on.

Should be able to take twice that voltage.

** Absolute, fucking BOLLOCKS !!

Wot moronic math is this anencephalic pommy turdbrain using ?

Tomorrow will apply
something a bit over 70 volt with temperature sensitive labels fitted
around. I will even try a TV degaussing coil.


** Fuckwit morons like YOU should be locked up for the safety of the
public.



..... Phil
 
B

bz

Jan 1, 1970
0
While it gives good background on PCBs it does not inform on the
regulatory situation. Moreover some of the background is missing,
like the presence of PCBs in varnishes and potting compounds used for
ballasts and transformers. Also regulation wise very nearly all uses
of PCBs are now banned.

The wiki DOES mention the use of PCB as plasticizes in insulation, and
gives a time-line for the production and use, thus gives us a good idea of
which products might contain PCBs.

As a chemist (BS 1970), I have some familiarity with PCBs and the hazards
and regulations associated with them. As a TEA Certified Electronic
Technician, I have experience servicing electronic equipment. I also have
practice in reading regulations. However I still found the Wiki much more
useful than the regulations.

The simple fact that REGULATION WISE, the use of PCBs are now banned, in
almost all cases, is easy enough to make without the reams of [almost]
unreadable regulations.

If there is a particular SECTION of the regulations that you found
particularly illuminating and informative, PLEASE point it out to us. My
quick skim of the regulations did NOT give me any useful information other
than PCBs are banned and must be disposed of carefully and under carefully
controlled and regulated conditions. What point were YOU trying to make by
citing that reference???






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Paul E. Schoen"


** Not true of any normal commercial toroidal sold for use with AC supply,

Depends on the working flux Phil. If one had been designed for very low
radiated field, it's entirely possible that effect would occur.

Graham
 
E

Eeyore

Jan 1, 1970
0
Paul E. Schoen said:
It would also be helpful to know how the toroid was mounted, and if the
failure occurred where pressure was applied. Toroids are usually mounted
either flat with washers and rubber gaskets with a single screw through the
hole, or vertically in an "Omega" bracket, with some rubber cushioning
material around the periphery. But in either case there may be additional
pressure on a "high spot" where two windings may be crossed, and softening
of the insulation from overheating may also contribute to a short.

Not to mention the possibility of overtorqueing on top of that. What goes on in
some places is unreal. I've even seen steel TO-3 flanges dimpled by the
mounting bolts pulling into the clearance hole !

Graham
 
E

Eeyore

Jan 1, 1970
0
N_Cook said:
Can a toroidal former become permanently magnetised and cause excessive
current draw. ?

Unbelievable.

Graham
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"N_Kook"


** So the amp's DC rails are about +/- 53 volts.

Means the tranny likely has two secondaries, each of 38 volts.


** Spot on.


** Absolute, fucking BOLLOCKS !!

Wot moronic math is this anencephalic pommy turdbrain using ?


** Fuckwit morons like YOU should be locked up for the safety of the
public.

He certainly shouldn't be repairing electronic equipment. I'm wondering if he
has the necessary qualifications.

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Eeyore"
Depends on the working flux Phil. If one had been designed for very low
radiated field, it's entirely possible that effect would occur.


** Utter bollocks.

The sharpness of the saturation knee is NOT a function of AC primary
voltage.



....... Phil
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeyore"

** Utter bollocks.

The sharpness of the saturation knee is NOT a function of AC primary
voltage.

It's a function of working flux density. A transformer designed for low radiated
field might be operating at a much lower working flux than a standard commercial
type, hence it would take much more magnetising force i.e. primary volts before
saturation. Simple physics.

Graham
 
E

Eeyore

Jan 1, 1970
0
JosephKK said:
No thanks, i already did that work twice for my cow-orkers. It was
not worth it, they did not learn a darn thing. Twice burned by others
whose job was to keep up with this stuff.

Tell me about it !

Graham
 
P

Paul E. Schoen

Jan 1, 1970
0
Eeyore said:
It's a function of working flux density. A transformer designed for low
radiated
field might be operating at a much lower working flux than a standard
commercial
type, hence it would take much more magnetising force i.e. primary volts
before
saturation. Simple physics.

Actually there are two considerations here that may prove Phil to be
correct in his assertion. The first is that the transformer I tested was a
custom wound unit which was essentially just a primary winding with the
secondary to be bus bars through the center hole, and it had been wound for
a particular output voltage on a specific size core, so it had more turns
than were optimal. Before management abandoned the project (and essentially
scrapped about 20 toroids), I removed about 20% of the primary turns and
increased the output voltage.

The second consideration is that I performed my measurements by using a
variable AC source and a transformer of perhaps 250 VA with a 480 VAC
secondary. So, as the voltage approached saturation, and current increased,
the waveform probably became distorted, which allowed a slightly higher RMS
value to be applied with less current than might have been drawn with a
better waveform.

But the values I posted were from my actual notes, and not from memory.

Paul
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore"
It's a function of working flux density.


** More bollocks.

The saturation knee curve shape is a property of the magnetic strip.

As usual - you have snipped and ignored the context.



..... Phil
 
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