I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

raypsi wrote:
Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu
I've sealed rewound filter chokes by dipping them in a bucket of
polyurethane varnish.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

A good trick for the lams is clear nail polish as you reassemble them.
Just a quick wipe, as it'll spread as you squeeze in the last few lams
under a "Quick-Grip" clamp.

Cheers!

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

I'll second that.

Varnish is the best thing. Warm the varnish and the
transformer first before you dunk it. That will reduce
the viscosity and improve penetration. A little thinner
in the pot may help too. Vacuum/pressure impregnation is
better than dipping... but dipping can work well on a buzz.

There is even special dipping resin to reduce noise that
leaves the part looking like it's been dipped in a candy
coating. It's a soft, rubbery, epoxy coating.

Oh, and the teflon isn't so great as a shim. You might try
nomex paper, G-10 PC board scraps, fish or kraft paper even
typing paper, calendered cardboard (like shoe box cardbord)
or wood. Teflon will withstand the heat but it tends to
cold flow which makes it dimensionally unstable. The amount
of mechanical force between the core halves can be surprising.
Though in your transformer teflon may be be OK. In a choke
it can be a source of bewilderment as the gap decreases. Yes,
I've had this happen.

Any material that will soften when it's hot, like perspex/plexiglas
isn't a good choice either. I found this in an inductor for a
10KW boost converter that an otherwise reliable supplier built
for me.

For varnish, I like Dolphs (Von-Roll.) Failing that I use
marine spar varnish. Some varnishes are corrosive to copper
and over time will cause windings of fine guage to open if
any copper is exposed.




ken scharf wrote in
:

I've sealed rewound filter chokes by dipping them in a bucket of
polyurethane varnish.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

"ken scharf" wrote in message
. ..
raypsi wrote:

n8zu
I've sealed rewound filter chokes by dipping them in a bucket of
polyurethane varnish.

This would work even better if you could pull a slight vacuum
on the bucket to get the air bubbles out. I believe that's how
the manufacturer's did it. There was a thread on this over on
AMFONE.NET a few month's back.

pete k1zjh

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Uh! Sorry Ray, it was near 2AM and I misread this. Of course
there's no gap in the core it's a linear AC transformer. No
DC in the windings and so no gap.

Usually I'd do everything I can to reduce any gap, inclduing
interleaving the laminations, to reduce the magnetizing current.

I just wasn't thinking, that happens sometimes.


raypsi wrote in news:ea79280c-6148-42a5-be23-
:

Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

As was suggested by Grumpy... missed it first time.

Pedro

"Tio Pedro" wrote in message
...

"ken scharf" wrote in message
. ..
raypsi wrote:

n8zu
I've sealed rewound filter chokes by dipping them in a bucket of
polyurethane varnish.

This would work even better if you could pull a slight vacuum
on the bucket to get the air bubbles out. I believe that's how
the manufacturer's did it. There was a thread on this over on
AMFONE.NET a few month's back.

pete k1zjh

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

If you have bolts thru the lams have you torqued them to the point of
twisting them off? If you haven't you might want to loosen then and add
some more varnish to the lams while they're loose and then torque them.
Another possibility: Many of the transformers in microwave ovens have a
bead of weld across all the laminations and I've seen this on rectifiers
used in Telco applications. Keeps them quiet and I and has some
negatives like letting line spikes thru but on a filament that is
meaningless. Lam eddy currents area dead issue as I've heard that the
old Bell Labs had accepted this practice.
I had a 30S-1 with minor buzz but when I added 100 volts to the screen
the hum was about to drive me nuts but torquing to lams solved the
problem, I twisted off a couple of bolts.

--
73
Hank WD5JFR
"raypsi" wrote in message
...
Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Hmmm!

Bolts through the laminations should have insulators
(usually fiber board washers) under the heads. Just
one end will do, there's no need for them under the
nuts. But shoulder washers are best so the bolts don't
short any laminations together deeper into the core.

If uninsulated the bolt can form a poorly coupled shorted
turn and that in itself can cause noise, heating of the
core and the hardware as well as spray flux around where
you wouldn't have expected any. How bad it is depends
on the locations of the holes in the core.

A bead of weld across the ends of the laminations won't add
to the eddy currents significantly. Steel isn't a great
conductor. The weld's cross section is small and it's very
poorly coupled to the primary.

Why would a weld across the laminations let line spikes
though?




"Henry Kolesnik" wrote in
:

If you have bolts thru the lams have you torqued them to the point of
twisting them off? If you haven't you might want to loosen then and add
some more varnish to the lams while they're loose and then torque them.
Another possibility: Many of the transformers in microwave ovens have a
bead of weld across all the laminations and I've seen this on rectifiers
used in Telco applications. Keeps them quiet and I and has some
negatives like letting line spikes thru but on a filament that is
meaningless. Lam eddy currents area dead issue as I've heard that the
old Bell Labs had accepted this practice.
I had a 30S-1 with minor buzz but when I added 100 volts to the screen
the hum was about to drive me nuts but torquing to lams solved the
problem, I twisted off a couple of bolts.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Grumpy
Years ago in 93 or so on a Telco fiber system by Alcatel we took severe
hits when the air conditioner came on and it was traced to the station
rectifier. The Gould rectifiers had a weld bead and when we replaced
them another make which I can't recall that didn't have weld beads the
problem went away. Its quite strange since the rectifiers floated big
batteries but a vco in system was sensitive to the spike. After doing
some research I found an explanation that I can't recall because I was
too busy with other problems and mine had gone away. Alcatel spent
several hundred thousand trying to find the problem and I stumbled on to
it by shear luck.

73
Hank WD5JFR
"Grumpy The Mule" wrote in message
...
Hmmm!

Bolts through the laminations should have insulators
(usually fiber board washers) under the heads. Just
one end will do, there's no need for them under the
nuts. But shoulder washers are best so the bolts don't
short any laminations together deeper into the core.

If uninsulated the bolt can form a poorly coupled shorted
turn and that in itself can cause noise, heating of the
core and the hardware as well as spray flux around where
you wouldn't have expected any. How bad it is depends
on the locations of the holes in the core.

A bead of weld across the ends of the laminations won't add
to the eddy currents significantly. Steel isn't a great
conductor. The weld's cross section is small and it's very
poorly coupled to the primary.

Why would a weld across the laminations let line spikes
though?




"Henry Kolesnik" wrote in
:

If you have bolts thru the lams have you torqued them to the point of
twisting them off? If you haven't you might want to loosen then and
add
some more varnish to the lams while they're loose and then torque
them.
Another possibility: Many of the transformers in microwave ovens
have a
bead of weld across all the laminations and I've seen this on
rectifiers
used in Telco applications. Keeps them quiet and I and has some
negatives like letting line spikes thru but on a filament that is
meaningless. Lam eddy currents area dead issue as I've heard that
the
old Bell Labs had accepted this practice.
I had a 30S-1 with minor buzz but when I added 100 volts to the
screen
the hum was about to drive me nuts but torquing to lams solved the
problem, I twisted off a couple of bolts.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Sat, 25 Oct 2008, raypsi wrote:

Date: Sat, 25 Oct 2008 10:25:23 -0700 (PDT)
From: raypsi
Newsgroups: rec.radio.amateur.homebrew
Subject: I built a 7.5VAC 21Amp transformer now it has lots of buzz

Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu


This might be a little "far-out" but, besides just buying more epoxy and
just doing it right, maybe you could find a can or metal box, put the
transformer into the box, and fill the box up with enough sand that you
have 1-2 inches all around the transformer, and that might muffle the
buzz. You'll need to worry about heat dissipation through that sand which
will act like an insulator, but if you are on the air only a couple of
hours per day, it should not get dangerously hot (however, many of the old
hermetically sealed transformers were burried in a waxy-tar that was
quite hard at room temperature).

Your other option is to figure out some clamping arrangement so that the
laminations are held close and tight.

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations apart
but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

Grumpy
Years ago in 93 or so on a Telco fiber system by Alcatel we took severe
hits when the air conditioner came on and it was traced to the station
rectifier. The Gould rectifiers had a weld bead and when we replaced
them another make which I can't recall that didn't have weld beads the
problem went away. Its quite strange since the rectifiers floated big
batteries but a vco in system was sensitive to the spike. After doing
some research I found an explanation that I can't recall because I was
too busy with other problems and mine had gone away. Alcatel spent
several hundred thousand trying to find the problem and I stumbled on to
it by shear luck.

73
Hank WD5JFR

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

It's not so far out of a suggestion. One of my Zenith console
radios has some remote control solenoid mounted inside a metal
box that's lined with rubber.

The sand is a pretty good thermal conductor (compared to air),
better than epoxy. In fact they fill the cheaper type of epoxy
potting material with coarse quartzite or powdered limestone
to improve its the thermal conductivity. It's the air trapped
between the grains of sand that provide some thermal insulation.
Mixing sand with epoxy or oil fills the interstaces which would
otherwise be filled with air.

Some one mentioned coating the laminations with nail polish as you
stack them up to glue them together. Either that or little varnish
would most likely have prevented any buzzing laminations.

Not taking the laminations off is a good suggestion too if it's
possible. For instance microwave oven transformers just chisel
off the secondary and wind a new one. Though for smaller
transformers that often isn't possible.




Stray Dog wrote in
.org:


This might be a little "far-out" but, besides just buying more epoxy
and just doing it right, maybe you could find a can or metal box, put
the transformer into the box, and fill the box up with enough sand
that you have 1-2 inches all around the transformer, and that might
muffle the buzz. You'll need to worry about heat dissipation through
that sand which will act like an insulator, but if you are on the air
only a couple of hours per day, it should not get dangerously hot
(however, many of the old hermetically sealed transformers were
burried in a waxy-tar that was quite hard at room temperature).

Your other option is to figure out some clamping arrangement so that
the laminations are held close and tight.

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations
apart but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Oct 27, 11:29*pm, Stray Dog wrote:
On Sat, 25 Oct 2008, raypsi wrote:
Date: Sat, 25 Oct 2008 10:25:23 -0700 (PDT)
From: raypsi
Newsgroups: rec.radio.amateur.homebrew
Subject: I built a 7.5VAC 21Amp transformer now it has lots of buzz

Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the *core window *with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

This might be a little "far-out" but, besides just buying more epoxy and
just doing it right, maybe you could find a can or metal box, put the
transformer into the box, and fill the box up with enough sand that you
have 1-2 inches all around the transformer, and that might muffle the
buzz. You'll need to worry about heat dissipation through that sand which
will act like an insulator, but if you are on the air only a couple of
hours per day, it should not get dangerously hot (however, many of the old
hermetically sealed transformers were burried in a waxy-tar that was
quite hard at room temperature).

Your other option is to figure out some clamping arrangement so that the
laminations are held close and tight.

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations apart
but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.- Hide quoted text -

- Show quoted text -

I have always dunked them in varnish but only got some success with
this by
drawing a vaccum then applying pressure. I used an old compressor
from
a refrigarator to do this. The tank was made from from pipe and
fittings. The best
results I got was winding the core on a block of wood cut the same
size as
the core wrapping the wood with cardboard then windng the coil then
pushed
then put the core together. I was 18 at the time and a very talented
man
named Olin Griggs helped me with this project and let me use his
shop.
Olin was a retired engineer that had worked for GE at their
Bloomington plant.
Since then the onl transformers I have wound that havent bussed to
much
was by modifying a ready built transformer. USually this meant one
that I
on which I could keep the primary winding intact. Lately I have gotten
interested
in SMPSs for doing this sort of thing. It is very easy to see why
industry has
has made the move to them.

Jimmie

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Hey Grump
A transformer is one of the simplest electrical machines and pretty well
understood in the classical design but when some of the parameters are
changed we don't have much experience or investigation and probably
wont. Hot swappable rectifier modules have made transformer based
rectifiers uneconomical kinda like carburetors and fuel injection. If
you have the time, check with some of the old time designers of
transformer rectifiers. Let me now what you find out. I had some notes
but those are long gone.
Hank
"Grumpy The Mule" wrote in message
...
Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

Grumpy
Years ago in 93 or so on a Telco fiber system by Alcatel we took
severe
hits when the air conditioner came on and it was traced to the
station
rectifier. The Gould rectifiers had a weld bead and when we replaced
them another make which I can't recall that didn't have weld beads
the
problem went away. Its quite strange since the rectifiers floated
big
batteries but a vco in system was sensitive to the spike. After
doing
some research I found an explanation that I can't recall because I
was
too busy with other problems and mine had gone away. Alcatel spent
several hundred thousand trying to find the problem and I stumbled on
to
it by shear luck.

73
Hank WD5JFR

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

I left out switch based hot swappable
"Henry Kolesnik" wrote in message
...
Hey Grump
A transformer is one of the simplest electrical machines and pretty
well understood in the classical design but when some of the
parameters are changed we don't have much experience or investigation
and probably wont. Hot swappable rectifier modules have made
transformer based rectifiers uneconomical kinda like carburetors and
fuel injection. If you have the time, check with some of the old time
designers of transformer rectifiers. Let me now what you find out. I
had some notes but those are long gone.
Hank
"Grumpy The Mule" wrote in message
...
Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

Grumpy
Years ago in 93 or so on a Telco fiber system by Alcatel we took
severe
hits when the air conditioner came on and it was traced to the
station
rectifier. The Gould rectifiers had a weld bead and when we
replaced
them another make which I can't recall that didn't have weld beads
the
problem went away. Its quite strange since the rectifiers floated
big
batteries but a vco in system was sensitive to the spike. After
doing
some research I found an explanation that I can't recall because I
was
too busy with other problems and mine had gone away. Alcatel spent
several hundred thousand trying to find the problem and I stumbled
on to
it by shear luck.

73
Hank WD5JFR

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Howdy Hank,

I've been designing switch mode magnetics for about
thirty years now. The more I learn the less I know.
It's true that the principles are well known but the
implementation is a morass of compromises. At the
power level many of my designs operate at, second
and third order effects can suddenly become serious
and unexpected design complications. Some people
enjoy puzzles. I guess that's why I like designing
this sort of stuff.

I've worked on a lot of weird stuff, big cap charging
supplies, pulse compressors, very high voltage or high
current, and tiny stuff with extremely low noise outputs.
But I don't have much experience with line frequency
magnetics beyond EMI filters. As you say there's
not much call for it now. But unfettered by
all the weak components the big iron can support
amazing overloads, so I think there's still a place
for it. At least for now. The cost of steel and
copper (and the transportation costs) for such heavy
beasts is certainly making them increasingly less
attractive.

Lately I've been working on equipment in the 10KW-60KW
output range switching at 75KHz range. The whole system
weighs much less than just the line frequency transformer
that would be required alone.

The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.


73


"Henry Kolesnik" wrote in
:

Hey Grump
A transformer is one of the simplest electrical machines and pretty well
understood in the classical design but when some of the parameters are
changed we don't have much experience or investigation and probably
wont. Hot swappable rectifier modules have made transformer based
rectifiers uneconomical kinda like carburetors and fuel injection. If
you have the time, check with some of the old time designers of
transformer rectifiers. Let me now what you find out. I had some notes
but those are long gone.
Hank

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

hey all:

A good trick for the lams is clear nail polish as you reassemble them.
Just a quick wipe, as it'll spread as you squeeze in the last few
lams
under a "Quick-Grip" clamp.

I could go to the nail shop get a peddicure and coat my lams at the
same time. A great idea if only I could handle the fumes.


Varnish is the best thing. Warm the varnish and the
transformer first before you dunk it. That will reduce
the viscosity and improve penetration. A little thinner
in the pot may help too.

I lucky I can stand the effects of epoxy but no way varnish. For nail
polish or varnish I gots to gits me a up or down draft venilator
exhastt system.

If you have bolts thru the lams have you torqued them to the point of
twisting them off? If you haven't you might want to loosen then and
add
some more varnish to the lams while they're loose and then torque
them

Thanks I retorqued them and that reduced the noise by 6db. Now I have
a less effecient buzzer

Bolts through the laminations should have insulators
(usually fiber board washers) under the heads. Just
one end will do, there's no need for them under the
nuts. But shoulder washers are best so the bolts don't
short any laminations together deeper into the core.

Good idea I seen many a transformer that had fiber spacers over the
whole length of the bolt plus fiber washers..


put the
transformer into the box, and fill the box up with enough sand that
you
have 1-2 inches all around the transformer, and that might muffle the
buzz. You'll need to worry about heat dissipation through that sand
which
will act like an insulator, but if you are on the air only a couple
of
hours per day,

I likes this one, but I gots alot of kittie litter that comes from
some place in Arkansas, it is mostly quartz and some other trace
minerals.

The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.

73 and thanks for all the good information.

n8zu

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.
==============
Followed this thread with great interest .
Reason : I have an Astron RS-50A , 13.8V -50 Amperes unit for 220V-AC
input which is buzzing heavily. Upon switch-on the group circuit breaker
in the house sometimes trips due to the high switch-on current surge .
This can be overcome by adding a soft start circuit which initially puts
a say 25 Ohms-50Watts resistor in series with the primary transformer
winding ,shorting this resistor after a second or so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .


TIA for any constructive advice/opinion

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Oct 29, 8:21*am, Highland Ham wrote:
The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.

==============
Followed this thread with great interest *.
Reason : I have an Astron RS-50A *, 13.8V -50 Amperes *unit *for 220V-AC
input which is buzzing heavily. Upon switch-on the group circuit breaker
in the house sometimes trips due to the high switch-on current surge .
This can be overcome by adding a soft start circuit which initially puts
a say 25 Ohms-50Watts resistor in series with the primary transformer
winding ,shorting this resistor after a second or so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .

TIA for any constructive advice/opinion

Frank * * GM0CSZ / KN6WH- Hide quoted text -

- Show quoted text -

Frank I emailed XXXXXXX's address to you. He designed the Astron Power
supply.


Jimmie

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

I suspect that you are right.

If I recall correctly, transformers designed for 60 Hz can suffer from
excessive quiescent current flow in the primary windings, if used on
50 Hz... the windings don't have enough inductance. Also, because the
frequency is lower, the transformer will be drawing more current
during the brief intervals (100 times per second) when the power
supply rectifiers are conducting and recharging the filter
capacitors... the abrupt changes in the current flow and the resulting
magnetic-field changes may be causing the windings or laminations to
move around and buzz.

Transformers designed for 50 Hz service generally work OK on 60 Hz...
it an "easier" job for them.

Transformers can also buzz if there's anything on the same mains
circuit which is generating harmonic currents (e.g. other linear power
supplies). Toroidal tranformers can be prone to buzz or hum if other
loads on the mains line are drawing current from the line in an
asymmetrical fashion and thus creating a DC offset on the mains... the
toroid goes into saturation.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Do you have GloBar resistors in the UK? These are high cold and go lo
with current. they used to be very popular in TVs over here.

--
Thanks & 73
Hank WD5JFR
"Highland Ham" wrote in message
...
The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.
==============
Followed this thread with great interest .
Reason : I have an Astron RS-50A , 13.8V -50 Amperes unit for
220V-AC input which is buzzing heavily. Upon switch-on the group
circuit breaker in the house sometimes trips due to the high switch-on
current surge . This can be overcome by adding a soft start circuit
which initially puts a say 25 Ohms-50Watts resistor in series with the
primary transformer winding ,shorting this resistor after a second or
so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .


TIA for any constructive advice/opinion

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Oct 29, 4:43*pm, "Henry Kolesnik"
wrote:
Do you have GloBar resistors in the UK? *These are high cold and go lo
with current. *they used to be very popular in TVs over here.

--
Thanks & 73
Hank WD5JFR"Highland Ham" wrote in message

...



The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.
==============
Followed this thread with great interest *.
Reason : I have an Astron RS-50A *, 13.8V -50 Amperes *unit *for
220V-AC input which is buzzing heavily. Upon switch-on the group
circuit breaker in the house sometimes trips due to the high switch-on
current surge . This can be overcome by adding a soft start circuit
which initially puts a say 25 Ohms-50Watts resistor in series with the
primary transformer winding ,shorting this resistor after a second or
so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .

TIA for any constructive advice/opinion

Frank * * GM0CSZ / KN6WH- Hide quoted text -

- Show quoted text -

I think some of the PC power supplies have a surge suppresor in them.
I you have some old power supplies around you coulld be in business.



Jimmie

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Grumpy The Mule wrote:
Uh! Sorry Ray, it was near 2AM and I misread this. Of course
there's no gap in the core it's a linear AC transformer. No
DC in the windings and so no gap.

Usually I'd do everything I can to reduce any gap, inclduing
interleaving the laminations, to reduce the magnetizing current.

I just wasn't thinking, that happens sometimes.


raypsi wrote in news:ea79280c-6148-42a5-be23-
:

Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

Actually "transformers" that carry DC (IE: filter chokes) have a gap
formed by putting ALL the "E"s in one direction and ALL the "I"'s in the
other.

For transformers that carry SOME dc (audio output transformers) group
the "E"'s and "I"s in bundles and assemble with a few groups of bundles
going in opposing directions.

For transformers that carry ONLY dc (power, filament) alternate each
lamination so no two in a row go the same way.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

ken scharf wrote:
Grumpy The Mule wrote:
Uh! Sorry Ray, it was near 2AM and I misread this. Of course
there's no gap in the core it's a linear AC transformer. No
DC in the windings and so no gap.

Usually I'd do everything I can to reduce any gap, inclduing
interleaving the laminations, to reduce the magnetizing current.

I just wasn't thinking, that happens sometimes.


raypsi wrote in news:ea79280c-6148-42a5-be23-
:

Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

Actually "transformers" that carry DC (IE: filter chokes) have a gap
formed by putting ALL the "E"s in one direction and ALL the "I"'s in the
other.

For transformers that carry SOME dc (audio output transformers) group
the "E"'s and "I"s in bundles and assemble with a few groups of bundles
going in opposing directions.

For transformers that carry ONLY dc (power, filament) alternate each
lamination so no two in a row go the same way.
I meant for transformers that carry ONLY AC! oops!

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Yep, It's all about core saturation. A large utility
transformer can be saturated by just a few amperes
of DC. Which is one reason improvements in load current
THD are important. Zero sequence currents and all
that jazz.


ken scharf wrote in
:

ken scharf wrote:
For transformers that carry ONLY dc (power, filament) alternate each
lamination so no two in a row go the same way.
I meant for transformers that carry ONLY AC! oops!

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Howdy,

I think I would measure the line current with no load on the
transformer. Then let it idle a while, maybe three hours, then
give it the finger test. If it's not warm and the magnetizing
current is small, I'd then run it with a heavy load and check
it again. If it's not stinky hot (the winding is below about
110C more or less) I'd say it's OK at 50Hz and the breaker
tripping is from the inrush current.

There's some inrush current charging the core. That's not a
defect though, it's just how things work. The first half
cycle peak might be five or more times the peak magnetizing
current. The inrush current charging the capacitors is more
prolonged. Depending on the curve of the circuit breaker one
or both might be to blame.

So if the soft-start circuit works for you just monitor the
temperature of the transformer. If it's reasonable don't
worry. Then look elsewhere for the cause of the buzzing.
The cabinet sheet metal you should be able to quiet with
the palm of you hand...

Ok, here's one crazy idea. The inrush current is mostly
on the first half cycle so it's magnetizing something, maybe
the cabinet who knows what, which is then a more efficient
transducer. If you soft start it either doesn't magnetizing
the part or perhaps degausses it.


73


Highland Ham wrote in news:KO-
:

==============
Followed this thread with great interest .
Reason : I have an Astron RS-50A , 13.8V -50 Amperes unit for 220V-AC
input which is buzzing heavily. Upon switch-on the group circuit breaker
in the house sometimes trips due to the high switch-on current surge .
This can be overcome by adding a soft start circuit which initially puts
a say 25 Ohms-50Watts resistor in series with the primary transformer
winding ,shorting this resistor after a second or so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .


TIA for any constructive advice/opinion

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Henry Kolesnik wrote:
Do you have GloBar resistors in the UK? These are high cold and go lo
with current. they used to be very popular in TVs over here.

=======================================
Haven't come across these ,at least not under this name. I understand
they are Power NTC resistors .
Wonder if these would heat-up quickly enough within the 'start-up
period' to prevent a current surge.

In the meantime I have tested my Astron RS-50A PSU.
When switched on at 230 V AC (50hz) it sometimes trips the circuit
breaker and is rather heavily buzzing ,but when the voltage is increased
to that value from zero with a variac the buzzing level is lower .
No-load current is 0.69 Ampere , Power is 28 watts as measured with a
multifunction energy monitor.
Having had the unit running no-load for 1 day the buzzing level is
acceptable with the transformer being luke warm.

I now intend to include a simple soft start unit ( 12V relay with 1-2
seconds switch-on delay which shorts a series 50 Ohms-50W resistor (from
junk box) in the primary transformer winding line.

Comments on quality of unit :
-Insulation between primary and secondary winding of transformer looks
rather 'iffy'

- Output connection posts are of the type normally specified for 30
Amperes max.
I shall replace these by more heavy duty posts.

Having done that I intend to test the unit on rated capacity with 4
(approx 1 Ohm) resistors made of iron fencing wire , put in a bucket
with water.

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

Howdy,

An NTC (or two) should work well in the transformer primary.
It's a common means for reducing inrush at the input of SMPS.
Works fine for linear supplies too. There are numerous
manufacturers of these world wide.
http://www.rti-corp.com/Electronics/surggard.htm

Typical numbers for magnetizing current are 1-5% of the
rated load at steady state. And as much as 10-20 times
the load current for inrush. I stated 5 times for inrush
earlier. It's more than that for commodity (cheaply made)
type transformers.

You probably have some load on the transformer, bias power
for the regulator, bleeder resistors and so forth. So I'm
guessing the idling current is more than the magnetizing
current alone. If the transformer is designed for ~1KVA
50A*13.6V times some factor for the regulator efficiency
say 0.7 at full load, that's about 970W, then 28W loss at
no load isn't unreasonably high assuming the core loss equals
the copper loss at full load.

The iffy insulation is a good argument for having the
output return of the power supply securely bonded to
earth ground.

Fence wire in water should make an excellent load. I've
never heard of anyone testing an RS-50 at full load.
You might want to sneak up on it. A working 25A supply
is better than a dead 50A supply!


73
Grumpy



Highland Ham wrote in
:

=======================================
Haven't come across these ,at least not under this name. I understand
they are Power NTC resistors .
Wonder if these would heat-up quickly enough within the 'start-up
period' to prevent a current surge.

In the meantime I have tested my Astron RS-50A PSU.
When switched on at 230 V AC (50hz) it sometimes trips the circuit
breaker and is rather heavily buzzing ,but when the voltage is increased
to that value from zero with a variac the buzzing level is lower .
No-load current is 0.69 Ampere , Power is 28 watts as measured with a
multifunction energy monitor.
Having had the unit running no-load for 1 day the buzzing level is
acceptable with the transformer being luke warm.

I now intend to include a simple soft start unit ( 12V relay with 1-2
seconds switch-on delay which shorts a series 50 Ohms-50W resistor (from
junk box) in the primary transformer winding line.

Comments on quality of unit :
-Insulation between primary and secondary winding of transformer looks
rather 'iffy'

- Output connection posts are of the type normally specified for 30
Amperes max.
I shall replace these by more heavy duty posts.

Having done that I intend to test the unit on rated capacity with 4
(approx 1 Ohm) resistors made of iron fencing wire , put in a bucket
with water.

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Tue, 28 Oct 2008 00:52:28 +0100 (CET), Grumpy The Mule
wrote:

Hmmm!

Bolts through the laminations should have insulators
(usually fiber board washers) under the heads. Just
one end will do, there's no need for them under the
nuts. But shoulder washers are best so the bolts don't
short any laminations together deeper into the core.

If uninsulated the bolt can form a poorly coupled shorted
turn and that in itself can cause noise, heating of the
core and the hardware as well as spray flux around where
you wouldn't have expected any. How bad it is depends
on the locations of the holes in the core.

A bead of weld across the ends of the laminations won't add
to the eddy currents significantly. Steel isn't a great
conductor. The weld's cross section is small and it's very
poorly coupled to the primary.

Why would a weld across the laminations let line spikes
though?


It's not just the laminations that make noise. The windings can
vibrate if they're not locked in place with transformer varnish or
epoxy. No amount of tightening the laminations will help if the
windings are free to vibrate. This is probably more likely in larger
higher power transformers (multiple kW) than in a filament or screen
supply transformer, but it can happen.

Also, depending on how much magnetic leakage your core has you can
couple to the steel walls of the cabinetry the transformer is housed
in if you don't maintain adequate spacing from the walls, in which
case the steel wall and the transformer can vibrate and make noise
even though no parts on the transformer are loose.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

That's a good point. The filthy leakge inductance will be
spraying its flux all about. But there are things we can
do a to contain it.

A belly band around the winding (but not though the core) helps.
End bells (covers) bolted down over the windows work too.

There may also be fringing flux spewing out of the unavoidable
gaps if it's a butt stack lamination core. Interleaving the
laminations will help.

I've done all of that on a design with the transformer mounted
directly beneath the neck of the CRT in a video terminal.
A requirment of the project manager because he feared
SMPS noise and demanded a linear power supply. Of course
everything had to be jammed into the smallest possible
enclosure and a mu metal shield was deemed too expensive :P





Jim Higgins wrote in
:

It's not just the laminations that make noise. The windings can
vibrate if they're not locked in place with transformer varnish or
epoxy. No amount of tightening the laminations will help if the
windings are free to vibrate. This is probably more likely in larger
higher power transformers (multiple kW) than in a filament or screen
supply transformer, but it can happen.

Also, depending on how much magnetic leakage your core has you can
couple to the steel walls of the cabinetry the transformer is housed
in if you don't maintain adequate spacing from the walls, in which
case the steel wall and the transformer can vibrate and make noise
even though no parts on the transformer are loose.

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Thu, 30 Oct 2008, Grumpy The Mule wrote:

Date: Thu, 30 Oct 2008 01:37:32 +0100 (CET)
From: Grumpy The Mule
Newsgroups: rec.radio.amateur.homebrew
Subject: I built a 7.5VAC 21Amp transformer now it has lots of buzz


Howdy,

I think I would measure the line current with no load on the
transformer. Then let it idle a while, maybe three hours, then
give it the finger test. If it's not warm and the magnetizing
current is small, I'd then run it with a heavy load and check
it again. If it's not stinky hot (the winding is below about
110C more or less) I'd say it's OK at 50Hz and the breaker
tripping is from the inrush current.

There's some inrush current charging the core.

Don't forget that the inrush current is also going into at least one and
maybe two high capacity electrolytic capacitors that, instantaneously
before initial charging are going to look like zero ohms. Peak current, at
say peak AC volatage when the on switch is turned on, is going to be
higher than you think.

The manufaturers are just too cheap to put any kind of Soft-start
circuitry in to limit this inrush.

That's not a
defect though, it's just how things work. The first half
cycle peak might be five or more times the peak magnetizing
current. The inrush current charging the capacitors is more
prolonged. Depending on the curve of the circuit breaker one
or both might be to blame.

So if the soft-start circuit works for you just monitor the
temperature of the transformer. If it's reasonable don't
worry. Then look elsewhere for the cause of the buzzing.
The cabinet sheet metal you should be able to quiet with
the palm of you hand...

Ok, here's one crazy idea. The inrush current is mostly
on the first half cycle so it's magnetizing something, maybe
the cabinet who knows what, which is then a more efficient
transducer. If you soft start it either doesn't magnetizing
the part or perhaps degausses it.


73


Highland Ham wrote in news:KO-
:

==============
Followed this thread with great interest .
Reason : I have an Astron RS-50A , 13.8V -50 Amperes unit for 220V-AC
input which is buzzing heavily. Upon switch-on the group circuit breaker
in the house sometimes trips due to the high switch-on current surge .
This can be overcome by adding a soft start circuit which initially puts
a say 25 Ohms-50Watts resistor in series with the primary transformer
winding ,shorting this resistor after a second or so.

However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .


TIA for any constructive advice/opinion

Frank GM0CSZ / KN6WH

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Oct 29, 1:21*pm, Highland Ham wrote:


However I fear that the main reason for the buzzing is that the
transformer (of US origin) was designed for 60 Hz ,whereas here in the
UK (like in all European countries ) the supply frequency is 50 Hz.
Can someone on this NG please confirm/reject my suspicion.

Another possible reason could be that the cabinet sheet metal which is
very close to the transformer is vibrating (transducer effect) .

TIA for any constructive advice/opinion

Frank * * GM0CSZ / KN6WH

I can confirm the 50/60Hz problem. Have been moving line powered
equipment (including microwave ovens, Astron P/S, and more - even real
Wahl hair clipper) between US/Canada and Europe for over 10 years and
found the increased level of buzz when running 60Hz eqpt on 50Hz in
practically all cases. My Astron P/S is just a 4A unit and the buzz is
bearable. Other stuff ranges from OK to loud like hell.

73,
Rich OK8RF/VE3FSF

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

On Oct 25, 12:25 pm, raypsi wrote:
Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

I finally got around to clamping the transformer down with grade 8,
1/4inch bolts and nuts That didn't help, luckily I found my 3 hour
epoxy, ran the transformer for 3 hours straight to heat it up, took
the bolts out and with a putty knife slapped on some microwave heated
epoxy on the lams. That took the buzz down to below the level of the
fan noise. In dead silence you can still hear it. Nowhere can you feel
the buzz.

73

n8zu

I built a 7.5VAC 21Amp transformer now it has lots of buzz
 

congrats on the fix..
now you have th epower and the time to contest..
Contesting is much like transformer winding..
Once you learn how to do one turn, you repeat and count until you reach
a goal...
In contesting you do one turn, then another till you reach the time
limit and count your turns.
hi hi
Hank
"raypsi" wrote in message
...
On Oct 25, 12:25 pm, raypsi wrote:
Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8
thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament
transformer.

So what is the cheapest I can gits away with sealing these
laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

I finally got around to clamping the transformer down with grade 8,
1/4inch bolts and nuts That didn't help, luckily I found my 3 hour
epoxy, ran the transformer for 3 hours straight to heat it up, took
the bolts out and with a putty knife slapped on some microwave heated
epoxy on the lams. That took the buzz down to below the level of the
fan noise. In dead silence you can still hear it. Nowhere can you feel
the buzz.

73

n8zu