Transformer secondary winding question

[dakupoto@gmail.com]

Could some electronics guru please shed some light on
this. I am helping a colleague of mine wind a step down
transformer, as a weekend project. We have done all the
calculations, The secondary is center tapped, and my
understanding is that a "pig-tail" has to be created,
which serves as the center tap. The secondary coil
is made of two coils, such that the end terminal of
one coil is attached to the start terminal of the next
coil, -- the "end-start" connection being the center
tap. Is this correct ? Obviously the two coils making
up the secondary must have the same number of turns.
But the question is: suppose the output is 9 - 0 - 9
i.e., +/- 9 Volts with a center tap, for output of 18
Volts. Now would each secondary coil have the total
number of windings for 9 Volts ?
All hints. suggestions would be greatly appreciated.
Thanks in advance for your help.

 

[Robert Baer]

Could some electronics guru please shed some light on
this. I am helping a colleague of mine wind a step down
transformer, as a weekend project. We have done all the
calculations, The secondary is center tapped, and my
understanding is that a "pig-tail" has to be created,
which serves as the center tap. The secondary coil
is made of two coils, such that the end terminal of
one coil is attached to the start terminal of the next
coil, -- the "end-start" connection being the center
tap. Is this correct ? Obviously the two coils making

* -----YES-------^

up the secondary must have the same number of turns.
But the question is: suppose the output is 9 - 0 - 9
i.e., +/- 9 Volts with a center tap, for output of 18
Volts. Now would each secondary coil have the total
number of windings for 9 Volts ?

* Naturally, that is the original specification.

All hints. suggestions would be greatly appreciated.
Thanks in advance for your help.

Be advised that if a +/- DC supply is needed, that the RMS AC voltage
will different,depending on the type of filtering and regulation used.
Ripple actor and capacitor charging current must be taken into
consideration.

 

[Phil Allison]

Could some electronics guru please shed some light on
this. I am helping a colleague of mine wind a step down
transformer, as a weekend project. We have done all the
calculations, The secondary is centre tapped, and my
understanding is that a "pig-tail" has to be created,
which serves as the center tap. The secondary coil
is made of two coils, such that the end terminal of
one coil is attached to the start terminal of the next
coil, -- the "end-start" connection being the center
tap. Is this correct ? Obviously the two coils making
up the secondary must have the same number of turns.
But the question is: suppose the output is 9 - 0 - 9
i.e., +/- 9 Volts with a center tap, for output of 18
Volts. Now would each secondary coil have the total
number of windings for 9 Volts ?

** Yep.

All hints. suggestions would be greatly appreciated.
Thanks in advance for your help.

** AC supply transformers are a easy to design once you know and use the "
turns per volt " for the particular core being used.

This number depends on the supply frequency, grade of steel used in the
laminations and the cross sectional area of the centre limb for an e-core or
the wound ring for a toroidal. The larger the core, the less turns per volt
are needed.

Eg. Say you have a 1 square inch core section and the laminations are of
grain oriented silicon steel and the AC supply is 60Hz. Then you need to
wind about 4.5 turns for each volt - making the primary 540 turns.

Secondaries can be calculated the same way but you must allow extra turns to
compensate for the drop in voltage under load - called the regulation
factor.

Another rule is that the primary should occupy half of the available space
on the core and all secondaries the rest.

Calculating the wire gauges to use for best fit is the hard part and may
take a bit of cut and try.


.... Phil