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Specify
a custom transformer design
Check
out our Transformer Facts Bulletins No.
1 & No.
2
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 Efficiency
| The
figure shows typical curves for efficiency as a function
of output power in relation to nominal output power
for different core sizes. |
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Duty Cycle |
| A
smaller transformer can be designed if the load is not
constant and the duty cycle is much shorter than the
transformer's thermal time constant (which has a magnitude
of hours). Note that the voltage drop increases linearly
with the instantaneous current. |
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Temperature Considerations |
| Operating
temperature is an important safety factor. Our transformers,
built for Class A (105°C) operation, are normally
calculated for a temperature rise of 60-65°C. Actual
increase will depend on how and where the transformer
is mounted and how well it is cooled. When higher temperature
ratings are needed, we offer UL recognized (UL1411 and
UL544) transformers to class B (130°C). Transformers
rated for class E (120°C), class F (150°C) and
class H (180°C) are also available. |
Using a larger core size will reduce temperature rise.
Due to the small core losses (in comparison with a laminated
core), the temperature rise will drop drastically when
the output power is reduced. At half the load the temperature
rise will only be about 25% of the rise at full load. |
The figure shows how temperature rise varies with the
actual output power (S out) in relation to nominal power
(S nom) for a given core size. |
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Voltage Drop |
| This
chart shows voltage drop at full load for standard cores
at 50/60Hz. The voltage drop is slightly higher for
a 60Hz transformers. A design with an oversized core
will reduce voltage drop and temperature rise. |
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| Static Shielding |
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Static
shielding may be required to minimize capacitive coupling
between primary and secondary winding when the transformer
is used in an extremely noisy environment. Since the
shield adds layers, a larger core size may be necessary
to provide adequate inside diameter for the shuttle
of the winding machine.
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| In-Rush Currents |
| A
consequence of the superior magnetic properties of a
toroidal transformer is that the transformer "remembers"
what polarity the primary voltage had immediately before
the power was last shut off. Whenever the voltage has
the same polarity when the transformer next is turned
on, the core will saturate for part of a half-cycle,
and a high in-rush current will flow in the primary
of the transformer. This in-rush current is larger than
the in-rush current in a conventional transformer, but
it is of very short duration, so it will not affect
slow-blow fuses or magnetic overload protectors with
thermal delay characteristic. (Some delayed magnetic
overload protectors act instantly if the current exceeds
a certain value. These cannot be used with large toroidal
transformers unless a current limiting resistor is used
as described below.)
For
very large transformers (1,500VA and up),it is common
to use a small current-limiting primary resistor to
reduce the magnitude of the in-rush current, and a
delayed by-pass relay to short out the resistor after
30-200 milli-seconds. This method eliminates external
voltage dips caused by the in-rush current, but slow-blow
fuses or delayed magnetic overload protectors must
still be used, as is the case for all types of transformers.
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| Size, Weight,
and No-Load Losses |
|
This
chart shows size, weight, no-load losses of our custom made
transformers from 20VA-10,000VA using our standard core sizes.
Other core configurations are available to meet your needs.
|
60Hz
Operation |
50/60Hz
Operation |
Approximate
Size |
Max.
Rated
Power
(VA) |
Max.
Rated
Power
(VA) |
No-load
Loss
(W) |
OD
x H
(Inches) |
Weight
(lbs.) |
| 23 |
17 |
.2 |
2.4x1.2 |
.7 |
| 38 |
30 |
.2 |
2.8x1.3 |
1.1 |
| 57 |
45 |
.4 |
2.8x1.8 |
1.4 |
| 90 |
72 |
.6 |
3.2x1.8 |
2.0 |
| 140 |
112 |
.7 |
3.7x1.9 |
2.6 |
| 190 |
152 |
1.0 |
3.9x2.1 |
3.5 |
| 220 |
176 |
1.0 |
4.5x1.9 |
3.8 |
| 345 |
276 |
1.5 |
4.5x2.5 |
5.5 |
| 550 |
440 |
2.3 |
5.5x2.5 |
8.1 |
| 950 |
760 |
3.5 |
6.4x2.6 |
12.4 |
| 1,400 |
1,120 |
4.7 |
7.1x2.9 |
18.0 |
| 2,000 |
1,650 |
6.7 |
8.2x3.3 |
24.2 |
| 2,750 |
2,200 |
..9.4 |
8.2x4.0 |
32.8 |
| 3,300 |
2,640 |
9.2 |
9.5x3.4 |
36.5 |
| 5,000 |
4,000 |
16.3 |
10.4x4.7 |
56.0 |
| 7,000 |
5,600 |
20.6 |
11.6x5.0 |
70.0 |
| 12,000 |
10,000 |
31.7 |
13.8x6.0 |
118.0 |
| Power
rating (VA) is determined by secondary RMS data. Physical
size may vary from above data depending on number of primary
and secondary windings. |
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Primary Winding Configuration |
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Rectifier Circuits |
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Termination of
Dual Primaries and Secondaries in Series and Parallel
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