Transformer

[Kari Laine]

Hi,

I am playing around with a transformer. (I have enough experience to
make this probably safe...)

Anyway some facts about the transformer

1-phase 50-60 Hz
Type TBAE 30 and the manufacturer is Muuntosähkö.

There are two secondaries 12V/1.25A

On the transformer is 6 wires.
Two of them naturally for the 220V.

Now we have left 4 wires.
Transformer lists them as pairs

Red/Yellow
Green/Blue

My intention is to build controllable dual power supply +/-0 to +/-12V.
And the question is how to I know in which direction the windings are?
I think there is no middle point in the winding because there are four
wires - right?

I connected Green and Yellow together and meter showed dual the voltage
between Blue and red and the circuit breaker didn't blow..

Anyway is this right way to make a central tap, or should I get another
transformer? How about which of the wires to connect? Is there some kind
of phase shift depending which are connected and does it matter?

Then a question about regulators.
I would like to use switching regulators so that heat would not be a
problem. Do I need one positive switching regulator and other one
negative switching regulator or can one handle both situations?
Any part numbers?

Thanks beforehand.

And good links to dual power supplies would be nice. Either to buy or build.

Best Regards
Kari

--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[pimpom]

Kari Laine wrote:

Hi,

I am playing around with a transformer. (I have enough
experience to
make this probably safe...)

Anyway some facts about the transformer

1-phase 50-60 Hz
Type TBAE 30 and the manufacturer is Muuntosähkö.

There are two secondaries 12V/1.25A

On the transformer is 6 wires.
Two of them naturally for the 220V.

Now we have left 4 wires.
Transformer lists them as pairs

Red/Yellow
Green/Blue

My intention is to build controllable dual power supply +/-0 to
+/-12V.
And the question is how to I know in which direction the
windings are?
I think there is no middle point in the winding because there
are four
wires - right?

I connected Green and Yellow together and meter showed dual the
voltage between Blue and red and the circuit breaker didn't
blow..

Anyway is this right way to make a central tap, or should I get
another transformer? How about which of the wires to connect?
Is
there some kind
of phase shift depending which are connected and does it
matter?

It doesn't matter with your intended application. You've already
found the proper wire to connect together. This is because you
connected the two windings in series in the correct phase
combination so that the voltages add. You will get the same
effect if you connect Red and Blue. If, for example, you connect
the Green and Blue wires together, you will get little or no
voltage between the remaining two wires.

Then a question about regulators.
I would like to use switching regulators so that heat would not
be a
problem. Do I need one positive switching regulator and other
one
negative switching regulator or can one handle both situations?
Any part numbers?

There's more than one way to get what you want. You can tie Green
and Yellow together and use that as the common ground. Four
diodes will give you + and - outputs with respect to the common
ground. But the on-load outputs will be close to 12V, leaving
little head room for buck (step-down) regulators.

There are regulators with dual outputs and you can use separate
regulators for +ve and -ve. Many switching regulator ICs can be
configured for either positive or negative outputs from a
positive input. You could use a bridge rectifier to get 24V DC
(higher with a light load) from the series connected secondary
and use two regulators, one with +ve output and the other
with -ve output. I'll leave it to those with more experience
with switching regulators to recommend specific ICs.

One thing you should keep in mind is that switching regulators
generally have poorer regulation and noise characteristics than
linear types.

 

[Kari Laine]

pimpom wrote:

Kari Laine wrote:
Hi,

I am playing around with a transformer. (I have enough

It doesn't matter with your intended application. You've already
found the proper wire to connect together. This is because you
connected the two windings in series in the correct phase
combination so that the voltages add. You will get the same
effect if you connect Red and Blue. If, for example, you connect
the Green and Blue wires together, you will get little or no
voltage between the remaining two wires.
Thanks - so I got it right.

There are regulators with dual outputs and you can use separate
regulators for +ve and -ve. Many switching regulator ICs can be
configured for either positive or negative outputs from a
positive input. You could use a bridge rectifier to get 24V DC
(higher with a light load) from the series connected secondary
and use two regulators, one with +ve output and the other
with -ve output. I'll leave it to those with more experience
with switching regulators to recommend specific ICs.

Ok thanks for this info. I start fishing datasheets.

Any type codes highly appreciated. I think I try to use separate for +
and -, so that if I blow something it is easier to fix.

Have I understood right that regulators are current limiting so I don't
need extra circuit for it? I try to build it so that even if I short the
out the power supply it won't break.

One thing you should keep in mind is that switching regulators
generally have poorer regulation and noise characteristics than
linear types.
OK , I am thinking for switching variety because it does not require so

much cooling. Actually I might try with both because this is a learning
project.

Kari



--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[pimpom]

Kari Laine wrote:

Have I understood right that regulators are current limiting so
I
don't need extra circuit for it? I try to build it so that even
if I
short the out the power supply it won't break.

Most, if not all, modern regulators have current limiting as well
as thermal protection. In many cases, you can set the current
limit yourself with just a single resistor.

 

[Bob Masta]

On Sun, 14 Mar 2010 15:32:55 +0200, Kari Laine
<klaine8@gmail.com> wrote:

pimpom wrote:
Kari Laine wrote:
Hi,

I am playing around with a transformer. (I have enough

It doesn't matter with your intended application. You've already
found the proper wire to connect together. This is because you
connected the two windings in series in the correct phase
combination so that the voltages add. You will get the same
effect if you connect Red and Blue. If, for example, you connect
the Green and Blue wires together, you will get little or no
voltage between the remaining two wires.
Thanks - so I got it right.

There are regulators with dual outputs and you can use separate
regulators for +ve and -ve. Many switching regulator ICs can be
configured for either positive or negative outputs from a
positive input. You could use a bridge rectifier to get 24V DC
(higher with a light load) from the series connected secondary
and use two regulators, one with +ve output and the other
with -ve output. I'll leave it to those with more experience
with switching regulators to recommend specific ICs.

Ok thanks for this info. I start fishing datasheets.
Any type codes highly appreciated. I think I try to use separate for +
and -, so that if I blow something it is easier to fix.

Have I understood right that regulators are current limiting so I don't
need extra circuit for it? I try to build it so that even if I short the
out the power supply it won't break.

One thing you should keep in mind is that switching regulators
generally have poorer regulation and noise characteristics than
linear types.
OK , I am thinking for switching variety because it does not require so
much cooling. Actually I might try with both because this is a learning
project.

Kari

Hi, Kari!

I would encourage you to start out with simple
linear regulators and use heat sinks. But as
Pimpom notes, there probably won't be enough
headroom to get 12V DC, at least under much of a
load, from this transformer.

You can get an idea of the transformer's actual
regulation by measuring its output with a
resistive load. Better yet, you can build the
rectifier and filter stage (which you will need
with whatever transformer and regulator you end up
with), and measure the output voltage from that.

If you want to pull (say) 1 amp at 12 volts, then
the load resistor would be 12/1 = 12 ohms, and it
would have to withstand 12 * 1 = 12 watts. If you
don't have a 12 ohm, 12 watt resistor, try a
parallel combination of 10 x 120 ohms, etc. If you
only have 1/4 watt resistors, this would give only
10 * 1/4 = 2.5 watts. That's probably good enough
for a quick test. Have the meter reading the
unloaded output voltage, then momentarily shunt it
with the parallel array, read the meter, and
remove the shunt, all in a second or so. (Watch
your fingers... may get hot!) For a test like
this, you can increase the resistor power rating
enormously by submerging it in an oil bath. (At
these low voltages, a water bath would also work
fine, but I hesitate to suggest that... a water
bath on the benchtop is not a really good idea!)

If the loaded voltage will still give enough
headroom for your regulator, go for it! If you
want to try anyway, look for "low drop-out
voltage" regulators. (I don't have a part number,
sorry.) Or, you may want to test at (say) 0.5 A
and if that works you can at least get started
with the transformer you have.

Also, note that most linear regulators come with
current limiting as a standard feature.

Best regards,


Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

 

[Kari Laine]

Bob Masta wrote:

On Sun, 14 Mar 2010 15:32:55 +0200, Kari Laine
klaine8@gmail.com> wrote:

Hi, Kari!

I would encourage you to start out with simple
linear regulators and use heat sinks. But as
Pimpom notes, there probably won't be enough
headroom to get 12V DC, at least under much of a
load, from this transformer.
Ok I will do that. I have a look what the local supplier has.

You can get an idea of the transformer's actual
regulation by measuring its output with a
resistive load. Better yet, you can build the
rectifier and filter stage (which you will need
with whatever transformer and regulator you end up
with), and measure the output voltage from that.
Yep this is good advice.

If you want to pull (say) 1 amp at 12 volts, then
the load resistor would be 12/1 = 12 ohms, and it
would have to withstand 12 * 1 = 12 watts. If you
don't have a 12 ohm, 12 watt resistor, try a
parallel combination of 10 x 120 ohms, etc. If you
only have 1/4 watt resistors, this would give only
10 * 1/4 = 2.5 watts. That's probably good enough
for a quick test. Have the meter reading the
unloaded output voltage, then momentarily shunt it
with the parallel array, read the meter, and
remove the shunt, all in a second or so. (Watch
your fingers... may get hot!) For a test like
this, you can increase the resistor power rating
enormously by submerging it in an oil bath. (At
these low voltages, a water bath would also work
fine, but I hesitate to suggest that... a water
bath on the benchtop is not a really good idea!)
Ok thank you! This is how to make sure what the supplied voltage is at

certain current. I think I have those power resistors somewhere - will
have to dig...

If the loaded voltage will still give enough
headroom for your regulator, go for it! If you
want to try anyway, look for "low drop-out
voltage" regulators. (I don't have a part number,
sorry.) Or, you may want to test at (say) 0.5 A
and if that works you can at least get started
with the transformer you have.
Yep I got the transformer for free and I think those regulators are not

very expensive. I think the housing of the gadget will cost more.

Also, note that most linear regulators come with
current limiting as a standard feature.
Yep.

Thank you Bob, which reminds me that I will order the Daqarta now.
What I have had little look on it. It is very nice and the help is
superb! For everyone needing only audio frequencies price and quality
can't be exceeded. And for a hobbyist learning electronics it is nice
tool until one knows what kind of an "real" oscilloscope one needs later
on. It is great to learn what one can do with an oscilloscope. Schools
should be interested - it is quite a difference to blow up a $5 sound
card than $5000 tektronix

Or have I gotten something wrong ?

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)