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!

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

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

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.

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!

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!

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

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

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

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.