Typical bandwidth of 60hz wallwart transformers

[Jim Flanagan]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application? What about using some small
audio transformers? I need the output to be around 160 Vrms
and am not sure if a miniature audio transformer has sufficient
dielectric properties to handle this. Obviously, I am trying
to do this on the 'cheap'. Any suggestions?

thanks for any input
Jim
WB5KYE

 

[Bob Eld]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application? What about using some small
audio transformers? I need the output to be around 160 Vrms
and am not sure if a miniature audio transformer has sufficient
dielectric properties to handle this. Obviously, I am trying
to do this on the 'cheap'. Any suggestions?

thanks for any input
Jim
WB5KYE

Any 60Hz transformer should work well at 400Hz. The reverse is not true,
however. This assumes a sine wave without a spray of higher harmonics from
switching circuitry.

 

[SuperM]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application?

At a one watt draw? I hardly think you need to worry about your
losses in such a circumstance.

 

[SuperM]

What about using some small
audio transformers? I need the output to be around 160 Vrms
and am not sure if a miniature audio transformer has sufficient
dielectric properties to handle this. Obviously, I am trying
to do this on the 'cheap'. Any suggestions?

Hand wound pot core transformers of about a 25 to 37 mm diameter
should be much more efficient at your operating frequency, but at your
power level, I hardly think worrying about a custom xfmr is needed.

 

[John Popelish]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application? What about using some small
audio transformers? I need the output to be around 160 Vrms
and am not sure if a miniature audio transformer has sufficient
dielectric properties to handle this. Obviously, I am trying
to do this on the 'cheap'. Any suggestions?

thanks for any input
Jim
WB5KYE

Small 60 Hz transformers work pretty well to at least a
kilohertz, at no more power than their original rating.

 

[Barry Lennox]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application? What about using some small
audio transformers? I need the output to be around 160 Vrms
and am not sure if a miniature audio transformer has sufficient
dielectric properties to handle this. Obviously, I am trying
to do this on the 'cheap'. Any suggestions?

No problem, I have used el-cheapo transformers (designed for 50 Hz)
several times at 400 Hz (for aircraft test sets) and variable from
about 100Hz to 3-4 Khz. They work fine, even though I'm sure the
efficiency drops off. At the other end of the scale, they also work
OK down to 16 Hz, again I'm sure the efficiency drops off
dramatically, but for the power I required (and your 1 Watt) it did
not matter.

Barry

 

[Tony Williams]

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application?

Avoid lamination transformers because they can
have a poor output impedance due to their higher
leakage inductance.

Toroidal mains transformers will work ok.

The flux density will be about 1/7th of what it
was designed for, so you can run what was a 115V
primary as a 160V secondary with no trouble.

 

[Tam/WB2TT]

No problem, I have used el-cheapo transformers (designed for 50 Hz)
several times at 400 Hz (for aircraft test sets) and variable from
about 100Hz to 3-4 Khz. They work fine, even though I'm sure the
efficiency drops off. At the other end of the scale, they also work
OK down to 16 Hz, again I'm sure the efficiency drops off
dramatically, but for the power I required (and your 1 Watt) it did
not matter.

Barry

I don't see any problem. I once measured the frequency response of a
standard laminated core 12 V filament transformer, and the minimum loss was
actually somewhere between 300 and 400 Hz. Also used the 12v center tapped
secondary of a Radio Shack transformer as a 16 to 4 Ohm autotransformer for
audio. It was quite usable, but sounded a bit mellow.

Tam

 

[MooseFET]

Avoid lamination transformers because they can
have a poor output impedance due to their higher
leakage inductance.

Toroidal mains transformers will work ok.

The flux density will be about 1/7th of what it
was designed for, so you can run what was a 115V
primary as a 160V secondary with no trouble.

I assume the OP is making a sine wave with a linear drive to the
transformer. The transformer may be enclosed within a feedback loop.
This would make the output impedance low at the frequencies below the
gain cross over point.

If this is the case, the laminated transformer would not be a big
issue. The gain cross over point could be at several KHz. He is only
drawing 1W from the supply so the load impedance will be quite high.
This would allow Xl to also be fairly high before it started to push
down the practical limit on the gain cross over.

The OP may want to consider placing a modest capacitor across the
secondary windings. This would make the high frequency impedance
lower at the cost of making the circuit resonate with the leakage
inductance. with a good control loop design, this would be a low Q
resonance.

 

[MooseFET]

I don't see any problem. I once measured the frequency response of a
standard laminated core 12 V filament transformer, and the minimum loss was
actually somewhere between 300 and 400 Hz. Also used the 12v center tapped
secondary of a Radio Shack transformer as a 16 to 4 Ohm autotransformer for
audio. It was quite usable, but sounded a bit mellow.

I think it is good enough for voice and perhaps an AM radio but not
really HiFi.

IIRC, the cutoff frequency on the transformer I used was about 4KHz.
It was a 110-220 transformer but I was using the two primaries to make
a 1:1 isolation transformer.

 

[Phil Allison]

"MooseFET"

I think it is good enough for voice and perhaps an AM radio but not
really HiFi.

** Nonsense - a centre tapped or multi-tapped secondary winding ( when
used as an auto-transformer) has wide bandwidth, more than the audio band
for sure.

The bandwidth of a transformer has little to do with the core and everything
to do with the arrangement of the windings - ie side by side on a divided
bobbin is the poorest.



........ Phil

 

[John Popelish]

** Nonsense - a centre tapped or multi-tapped secondary winding ( when
used as an auto-transformer) has wide bandwidth, more than the audio band
for sure.

The bandwidth of a transformer has little to do with the core and everything
to do with the arrangement of the windings - ie side by side on a divided
bobbin is the poorest.

The small ones I tested as pretty good as audio output
transformers, out to a few kilohertz were the side by side
(split bobbin) EI core type.

 

[Phil Allison]

"John Popelish"

The small ones I tested as pretty good as audio output transformers, out
to a few kilohertz were the side by side (split bobbin) EI core type.

** Not many consider a few kHz as "pretty good audio".

Even the cheapest 70 volt line transformers for BGM and voice PA are not
made that way.



........ Phil

 

[John Popelish]

"John Popelish"


** Not many consider a few kHz as "pretty good audio".

Fair enough. i meant their response was pretty good
(amplitude and phase shift) out to that audio frequency.

Even the cheapest 70 volt line transformers for BGM and voice PA are not
made that way.

Yes, of course.

 

[MooseFET]

I worked from the measurement I did. I found a bandwidth of about
4KHz on a transformer I used.


Agreed. Have you measured some numbers the OP can use?

Tranformer of unknown make: Numbers 19966624-41965DJ printed on the
top.
A little larger than typical wall wart xformer about 1.75 by 1.25"

6:1 ratio

Generator resistance: 8.6
Load resistance: 287

Freq Vp-p
100 2.0
1K 2.0
3K 1.80
5K 1.41
7K 1.30

 

[Phil Allison]

"MooseFET
"Phil Allison"

Tranformer of unknown make: Numbers 19966624-41965DJ printed on the
top.
A little larger than typical wall wart xformer about 1.75 by 1.25"

6:1 ratio

Generator resistance: 8.6
Load resistance: 287

Freq Vp-p
100 2.0
1K 2.0
3K 1.80
5K 1.41
7K 1.30

** Shame that is NOT an auto-transformer.


This is a typical multi-tapped tranny, with divided bobbin construction.

http://www.altronics.com.au/index.asp?area=item&id=M2155L

With the 0 volt used as common, the 7.5 volt terminal driven by an audio
power amp and the 15 volt terminal loaded with 16 ohms - response tested
flat from 15 Hz to 18kHz.

The -3dB point proved to be at 35 kHz.

QED.

Go away.



....... Phil

 

[Dr. Polemic]

"MooseFET
"Phil Allison"



** Shame that is NOT an auto-transformer.


This is a typical multi-tapped tranny, with divided bobbin construction.

http://www.altronics.com.au/index.asp?area=item&id=M2155L

With the 0 volt used as common, the 7.5 volt terminal driven by an audio
power amp and the 15 volt terminal loaded with 16 ohms - response tested
flat from 15 Hz to 18kHz.

You said in another post that "The bandwidth of a transformer has little
to do with the core...".

Just how little would the bandwidth be affected if your measurement were
repeated with the core removed?

 

[Phil Allison]

"Dr. Polemic Fucking Idiot "

You said in another post that "The bandwidth of a transformer has little
to do with the core...".

** So go find that other post, read it very carefully & take account of the
context.


Then go drop dead - you asinine prick.



......... Phil

 

[Dr. Polemic]

"Dr. Polemic Fucking Idiot "




** So go find that other post, read it very carefully & take account of the
context.


Then go drop dead - you asinine prick.



........ Phil

Your statement appears to be context free. You didn't say:

"The bandwidth of *an auto-transformer* has little to do with the core...".

or:

"The bandwidth of *a two-winding transformer* has little to do with the
core...".

You just said:

"The bandwidth of *a* transformer has little to do with the core...".

The word "transformer" was unqualified.

Anyway, you could just tell me what context you intended.

 

[Phil Allison]

"Dr. Polemic Fucking Idiot "

Your statement appears to be context free.

** You clearly appear to be a grossly autistic moron.

Spare the world from your congenital insanity - kindly top yourself now.





......... Phil