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'[EE] 115V 50Hz and hot transformer'
2006\11\29@170514 by Brent Brown

picon face
I have a mains powered PIC based design that is intended for operation in the US
but I want to test my prototypes here first. Local supply here in New Zealand is
230V 50Hz.

I've tried a 230/115V transformer (measured 120V) but my PCB mount transformer
on my board gets too hot for my liking (85 deg C, or 185 deg F, no load). FYI it is
too hot to touch for more than a second or two!

I was expecting it to be warmer on 50Hz than 60Hz but not this warm. The
transformers I'm using are Hammond 183G24, intended for universal operation,
10VA, dual primary 115/230V, 50/60Hz, sec 2 x 12V. They have insulation rated to
155 deg C, but should I expect it to run this hot? Surely my measured 120V is not to
high? I've tried 5 transformers and they alll run about the same temp.

http://www.hammondmfg.com/183.htm

I've checked and double checked that my two primary windings are wired in parallel
for 115V operation with the correct polarity, the output is also OK and my no load
test above even had the secondaries completely disconneted. I will wire one up for
230V operation now and check to see how hot it runs on 50Hz.

Trying to figure out a way of getting a 60Hz supply to test the transformer before I
complain to the transformer manufacturer. I thought about 12V or 24V to mains
inverters, but everything available here seems to be fixed 50Hz. Would also need to
be a sine wave for a proper test, and with 100VA or more I could test my complete
product.

Ideas? Thanks.
--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz


2006\11\29@172300 by peter green

flavicon
face

> Trying to figure out a way of getting a 60Hz supply to test the
> transformer before I
> complain to the transformer manufacturer. I thought about 12V or
> 24V to mains
> inverters, but everything available here seems to be fixed 50Hz.
> Would also need to
> be a sine wave for a proper test, and with 100VA or more I could
> test my complete
> product.
buy one from the USA?


2006\11\29@174158 by Daniel Dourneau

flavicon
face
50 Hz or 60 Hz operation should not really make any difference.

What I cannot understand is why your transformer gets so hot in the
first place. Is it under rated? What is your load current? What type
of rectifier are you using (bridge, single diode)? What value is the
capacitor.

One thing is sure, if you cannot touch it, its too hot and forget
about any type of certification of your product (if you intend to
apply for that)

At 23:04 29/11/2006, you wrote:
{Quote hidden}

>

2006\11\29@174714 by Steve Baldwin

flavicon
face
> Trying to figure out a way of getting a 60Hz supply to test the
> transformer before I complain to the transformer manufacturer. I
> thought about 12V or 24V to mains inverters, but everything available
> here seems to be fixed 50Hz. Would also need to be a sine wave for a
> proper test, and with 100VA or more I could test my complete product.
>
> Ideas?

I haven't tried it, but how about a sig-gen into a sub-woofer amp driving into
the low voltage side of a transformer.

Steve.



==========================================
Steve Baldwin                          Electronic Product Design
TLA Microsystems Ltd             Microcontroller Specialists
PO Box 15-680, New Lynn                http://www.tla.co.nz
Auckland, New Zealand                     ph  +64 9 820-2221
email: stevespamKILLspamtla.co.nz                      fax +64 9 820-1929
=========================================


2006\11\29@180422 by Brent Brown

picon face
Daniel Dourneau wrote:
> 50 Hz or 60 Hz operation should not really make any difference.
>
> What I cannot understand is why your transformer gets so hot in the
> first place. Is it under rated? What is your load current? What type
> of rectifier are you using (bridge, single diode)? What value is the
> capacitor.
>
> One thing is sure, if you cannot touch it, its too hot and forget
> about any type of certification of your product (if you intend to
> apply for that)

Each winding of a transformer is an inductor, so 50Hz/60Hz does make a difference
to the current that flows. Current will be higher at 50Hz because inductive reactance
is lower (Ohms).

I tested it no load (open secondary). No diodes,caps or anything.

I agree: it's too hot. Perhaps the combination of 50Hz and 120V (slightly above the
nominal 115V) pushes it to the edge of magnetic saturation and hence a dramatic
increase in temperature. In that case I'm dissapointed. But I will test a bit further yet.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  .....brent.brownKILLspamspam.....clear.net.nz


2006\11\29@180638 by Brent Brown

picon face
peter green wrote:
> > Trying to figure out a way of getting a 60Hz supply to test the
> > transformer before I complain to the transformer manufacturer. I
> > thought about 12V or 24V to mains inverters, but everything
> > available here seems to be fixed 50Hz. Would also need to be a sine
> > wave for a proper test, and with 100VA or more I could test my
> > complete product.
> buy one from the USA?

Maybe. Any reccomendations where to buy on-line? Must be a good sinewave, if it
does 50Hz and 60Hz then so much the better.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  EraseMEbrent.brownspam_OUTspamTakeThisOuTclear.net.nz


2006\11\29@180926 by Brent Brown

picon face
Steve Baldwin wrote:
> > Trying to figure out a way of getting a 60Hz supply to test the
> > transformer before I complain to the transformer manufacturer. I
> > thought about 12V or 24V to mains inverters, but everything
> > available here seems to be fixed 50Hz. Would also need to be a sine
> > wave for a proper test, and with 100VA or more I could test my
> > complete product.
> >
> > Ideas?
>
> I haven't tried it, but how about a sig-gen into a sub-woofer amp
> driving into the low voltage side of a transformer.

I had thought about an audio amp, but would need high voltage rails. Hadn't
considered the step up transformer - but that could do it! I've got a good sig-gen but
no sub-woofer amps lying around (he says looking at his PC speaker sub with a
glint in this eye...)

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brownspamspam_OUTclear.net.nz


2006\11\29@181110 by Jinx

face picon face

> I haven't tried it, but how about a sig-gen into a sub-woofer amp
> driving into the low voltage side of a transformer

That's an old technique for speed control of synchronous motors
(eg turntables). Should work if the amp can handle the secondary's
impedance

2006\11\29@183419 by olin piclist

face picon face
Brent Brown wrote:
> I've checked and double checked that my two primary windings are
> wired in parallel

Oops.

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2006\11\29@185004 by Bob Blick

face picon face


> I've checked and double checked that my two primary windings are wired in
> parallel
> for 115V operation with the correct polarity, the output is also OK and my
> no load
> test above even had the secondaries completely disconneted. I will wire
> one up for
> 230V operation now and check to see how hot it runs on 50Hz.


Have you tried just one primary? Does it still get hot? Then connect one
lead of the other primary and measure the voltage of the final connection
of the primary to absolutely double-check the phase.

Cheers,

Bob



2006\11\29@185749 by Brent Brown

picon face
Olin Lathrop wrote:
> Brent Brown wrote:
> > I've checked and double checked that my two primary windings are
> > wired in parallel
>
> Oops.

No, (checking again), that's right... 2 x 115V windings in parallel, operating on 115V.
This is for use in the US. Checked phasing of the windings too.

In series would be for 230V operation. Incidentally I use a completely different
transformer (single 230V primary) when I build this for 230V operation as they are
very much cheaper.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  @spam@brent.brownKILLspamspamclear.net.nz


2006\11\29@191435 by Richard Prosser

picon face
If your 2 primary windings have an even slightly different number of
turns then they will load the transformer like a shorted turn does.
I'm not sure how important it is that the leakage inductances etc
match but that may come into the equation also. If they're not bifilar
wound it could be the problem.
RP

On 30/11/06, Bob Blick <KILLspambblickKILLspamspamsonic.net> wrote:
{Quote hidden}

> -

2006\11\29@192719 by peter green

flavicon
face

> In series would be for 230V operation. Incidentally I use a
> completely different
> transformer (single 230V primary) when I build this for 230V
> operation as they are
> very much cheaper.
does the transformer manufacturer provide a data sheet and if so does it state that the windings are suitable for paralell operation (you could also do 120V by using just one primary)?

have you tried replacing the transformer with another identical one in case the first one is faulty?


2006\11\29@193859 by Spehro Pefhany

picon face
At 06:57 PM 11/29/2006, you wrote:
>Olin Lathrop wrote:
> > Brent Brown wrote:
> > > I've checked and double checked that my two primary windings are
> > > wired in parallel
> >
> > Oops.
>
>No, (checking again), that's right... 2 x 115V windings in parallel,
>operating on 115V.
>This is for use in the US. Checked phasing of the windings too.
>
>In series would be for 230V operation. Incidentally I use a
>completely different
>transformer (single 230V primary) when I build this for 230V
>operation as they are
>very much cheaper.

What happens if you just power up one primary?

Are you sure there's not a short on one (or both) of the secondaries, or that
they are not connected in parallel with the wrong phase (a series short)?

Have you powered the transformer up, just sitting on the bench, not soldered
into a board?

Could you have destroyed the transformer or could the transformer otherwise
be defective (overheating can lead to a shorted turn)?

This is a very simple device, and you should NOT be getting the heating you
are observing unless something is VERY wrong.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2006\11\29@194902 by Herbert Graf

flavicon
face
On Wed, 2006-11-29 at 23:47 +0100, Daniel Dourneau wrote:
> 50 Hz or 60 Hz operation should not really make any difference.

With magnetics like a transformer it DOES make a difference. For some
equipment it can make so much of a difference that the magic smoke
appears. The op's situation however shouldn't be one of those cases.
TTYL

2006\11\29@195029 by Herbert Graf

flavicon
face
On Thu, 2006-11-30 at 12:04 +1300, Brent Brown wrote:
> I tested it no load (open secondary). No diodes,caps or anything.
>
> I agree: it's too hot. Perhaps the combination of 50Hz and 120V (slightly above the
> nominal 115V) pushes it to the edge of magnetic saturation and hence a dramatic
> increase in temperature. In that case I'm dissapointed. But I will test a bit further yet.

I don't understand why you're having the problem, but being in a country
with 120V, I can say that there is NO way 120V should be "too high",
every outlet I've tested at home and at work has been AT LEAST 120V,
some as high as 123V, so if your transformer is rated for 120V/50Hz
operation there is NO way the 120V is the issue.

TTYL

2006\11\29@201310 by David VanHorn

picon face
>
> I agree: it's too hot. Perhaps the combination of 50Hz and 120V (slightly
> above the
> nominal 115V) pushes it to the edge of magnetic saturation and hence a
> dramatic
> increase in temperature. In that case I'm dissapointed. But I will test a
> bit further yet.


"inexpensive" transformers tend to skimp on the iron, both in cheap iron
with higher losses (more heat) and not so much iron (closer to
saturation)..  You may be working with one that's barely in spec at 60Hz.

2006\11\29@204316 by Brent Brown

picon face
I have now tested one of these transformers in the alternate configuration of 230V
50Hz (2 x 115V primary windings in series).

It seems to be getting just as hot... approx 60 deg C (140 deg F), no load, after a
couple of hours or so on the bench. Previous measurement of 80 deg C was with
the transformer in a sealed plastic box (finnished product). Tends to discount the
theory of miss-matched windings in parallel. Also not a single transformer problem -
tried 5 or 6 so far.

If the phasing was out (and could only be 180 deg out) then I'd expect near zero
output voltage and that's clearly not the case. ASFAICT the windings are intended
to be used in parallel...

http://www.hammondmfg.com/5CHook.htm

Will try a single primary winding on 115V for comparison.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  spamBeGonebrent.brownspamBeGonespamclear.net.nz


2006\11\29@205441 by peter green

flavicon
face


{Quote hidden}

what brand is the transfomer?

is the transformer meant to be heatsunk?


2006\11\29@205932 by Brent Brown

picon face
peter green wrote:

> what brand is the transfomer?
>
> is the transformer meant to be heatsunk?

Hammond 183G24. No.

I'm writing them an email now.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brownEraseMEspam.....clear.net.nz


2006\11\30@030758 by Ruben Jönsson

flavicon
face
Hi,

Transformers do get hot. The difference between unloaded and loaded is also
less with lower VA. What may seem to be too hot at the touch is not allways too
hot. You can measure the temperature rise in the windings with the resistance
method. Do this with an unloaded and a shorted transformer if it is short
circuit proof otherwise use the current your limiting device (the fuse or the
PTC resistor) will allow in contiuous operation.

Trise=Rhot/Rcold*(234.5+Tambstart) - (234.5+Tambend).

Tambstart is the ambient temperature at the start of the test and Tambend is
the ambient temperature at the end of the test measured where the generated
heat in the transformer doesn't affect it. Let the transformer run for at least
4 hours.

You have to measure the resistance very quickly after it is switched off since
the temperature drop can be rather fast the first degrees. For the secondary
winding you may also have to adjust the resistance with the probe and lead
resistance.

The temperature rise should be added to your maximum rated ambient temperature
and the temperature rise you get inside the enclosure. Then check this
temperature against the datasheet for the transformer. Check the maximum
winding temperature, the temperature for the insultaing materials, the potting
materials etc.

50Hz will generally produce more heat than 60Hz for mains transformers.

/Ruben

{Quote hidden}

> -

2006\11\30@044017 by Alan B. Pearce

face picon face
>> 50 Hz or 60 Hz operation should not really make any difference.
>
>With magnetics like a transformer it DOES make a difference. For some
>equipment it can make so much of a difference that the magic smoke
>appears. The op's situation however shouldn't be one of those cases.

I agree. My father used to have to deal with projectors bought in the USA,
that had cooling fans which were not 50/60Hz. These were generally shaded
pole motors. A typical cure was to remove the winding and fill the bobbin
with as many turns of wire 1 or possibly 2 gauges thinner. This gave enough
extra inductance for 50Hz operation.

As for Brent's problem - are you running a full bridge rectifier? If so the
peak current of the rectifier waveform may be the problem. Put a half ohm or
1 ohm resistor in series with the transformer to limit the peak current.

2006\11\30@071533 by olin piclist

face picon face
Brent Brown wrote:
> No, (checking again), that's right... 2 x 115V windings in parallel,
> operating on 115V. This is for use in the US. Checked phasing of the
> windings too.

Your original post said you had 230V power available in New Zealand and were
trying to make 110V for testing a device intended for the US.  That would
mean the primary windings would have to be in *series*.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2006\11\30@083021 by Peter P.

picon face

> Ideas? Thanks.

The 20% difference in frequency from 60 to 50Hz can mean 20% more core flux for
50Hz. Tightly designed small transformers cannot cope with this esp. if the
voltage is in the high range and ventilation is poor. Paralleling primaries
usually causes no problems on small transformers because the primary resistance
is relatively high, but it should be specified for this.

Afaik for small transformers with 2 primaries in series for 220V, and one
winding body (EI shape, not O shape) only one should be used for 110V operation
(the one that shows higher R on the ohmmeter - this will be the one that is
'outside' in the winding pack and gets better cooling in air - this is
counterintuitive).

Core saturation can be 'measured' with a small speaker in series (!) with the
primary. The sound it produces becomes 'harsh' and much louder than normal when
there is saturation in the core. Notice that I put '' around 'measured'. The
impedance of a small speaker is of no consequence when used like this. Usually a
small bass speaker of 5-15W is used. This will cope well with the inrush.

The manufacturer always knows best. Unless he is not the OEM and just quotes the
datasheet he has ...

Peter


2006\11\30@162849 by Daniel Dourneau

flavicon
face
There is usually "plenty of room" in the calculation tolerances and
for most designs 50 Hz or 60 Hz does not make any difference. Same
for 110 Volts or 120 Volts. Most transformers are calculated for
mains +/- 15 %, there again, plenty of room. You have to try very
hard to drive the cores to saturation. Are you sure of the way you
have connected the windings connected to the mains. Try with one
winding only, you will have half the power available but you can
check for overheating, try with the other and if it runs cool try
connecting both.
then you might be able to see where the problem is coming from :-)

At 00:04 30/11/2006, you wrote:
{Quote hidden}

>

2006\11\30@203730 by Brent Brown

picon face
I've been in contact with the transformer manufacturer and so far they sound very
helpful.

They say I'm using it correctly, ie. it's appropriate to wire the two primaries in
parallel. They discussed core losses and copper losses, and did a quick calculation
on temperature rise that agrees with the temperatures I am observing. They point
out that this temperature is well within the specifications (insulation rating of 155
deg C) BUT they say they would like to see it lower than this (so would I !!!). Further
to this they will take a transformer from their warehouse and do some testing at
50Hz to confirm, and look at what changes if any can be made to improve
performance under these conditions.

Thanks for all the responses, I'll report back when I know some more!

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  RemoveMEbrent.brownspam_OUTspamKILLspamclear.net.nz


2006\11\30@234409 by Robert Ammerman

picon face
> I've tried a 230/115V transformer (measured 120V) but my PCB mount
> transformer
> on my board gets too hot for my liking (85 deg C, or 185 deg F, no load).
> FYI it is
> too hot to touch for more than a second or two!
>
> Trying to figure out a way of getting a 60Hz supply to test the
> transformer before I
> complain to the transformer manufacturer. I thought about 12V or 24V to
> mains
> inverters, but everything available here seems to be fixed 50Hz. Would
> also need to
> be a sine wave for a proper test, and with 100VA or more I could test my
> complete
> product.

Use signal generator to high power audio amp to old tube amplifier output
transformer wired backwards = high volt, high power sine wave.

You can also probably find an appropriate "power supply" transformer that
will work as well as the tube amp transformer.

I had to do this once to test a phase difference transducer used in power
plants to determine when it is safe to close a breaker (ie: you better be in
phase on both sides of the breaker). I built a little PIC app that generated
a 60Hz sinewave output. The actual frequency was slightly adjustable so I
could actually simulate a generator speeding up and slowing down in response
to control pulses from the system attempting to get the gen in phase with
the line before closing the breaker.

If you like, I can send you the source for the app. It is just a little bit
of assembler for a PIC 16F876, IIRC.

Bob Ammerman
RAm Systems


'[EE] 115V 50Hz and hot transformer'
2006\12\01@164346 by Gerhard Fiedler
picon face
Peter P. wrote:

> Afaik for small transformers with 2 primaries in series for 220V, and one
> winding body (EI shape, not O shape) only one should be used for 110V
> operation (the one that shows higher R on the ohmmeter - this will be
> the one that is 'outside' in the winding pack and gets better cooling in
> air - this is counterintuitive).

Isn't sometimes the winding that is to be used for 115V done with a thicker
wire (as it has to be able to handle twice the current that the other
primary winding gets)? Then it would be the one that shows lower R, right?

Gerhard

2006\12\01@172403 by Peter P.

picon face
Gerhard Fiedler <lists <at> connectionbrazil.com> writes:

> Peter P. wrote:
>
> > Afaik for small transformers with 2 primaries in series for 220V, and one
> > winding body (EI shape, not O shape) only one should be used for 110V
> > operation (the one that shows higher R on the ohmmeter - this will be
> > the one that is 'outside' in the winding pack and gets better cooling in
> > air - this is counterintuitive).
>
> Isn't sometimes the winding that is to be used for 115V done with a thicker
> wire (as it has to be able to handle twice the current that the other
> primary winding gets)? Then it would be the one that shows lower R, right?

Yes but ime it is marked as such in this case (and usually you can see the
thicker wire soldered on the posts). I have bad experience with some 'universal'
equipment which used the same transformer for US and EU, and it was very tightly
dimensioned. The transformers were a special size and did not get good
ventilation and used to burn out with boring regularity when used on 220V (with
the voltage switch in the correct position obviously).

Peter P.


2006\12\02@092830 by Gerhard Fiedler

picon face
Peter P. wrote:

>>> Afaik for small transformers with 2 primaries in series for 220V, and
>>> one winding body (EI shape, not O shape) only one should be used for
>>> 110V operation (the one that shows higher R on the ohmmeter - this
>>> will be the one that is 'outside' in the winding pack and gets better
>>> cooling in air - this is counterintuitive).
>>
>> Isn't sometimes the winding that is to be used for 115V done with a
>> thicker wire (as it has to be able to handle twice the current that the
>> other primary winding gets)? Then it would be the one that shows lower
>> R, right?
>
> Yes but ime it is marked as such in this case (and usually you can see
> the thicker wire soldered on the posts).

Right. But when it is not marked specially and is the same size wire (you
only have two apparently equal 115V primary windings), why wouldn't you use
both in parallel on 115V?

Gerhard

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