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AuTO/iSOlATiON TRANSFORMERS
Step-Down, Step-Up and Isolation Transformers
Style C
Style A
GENERAL INFORMATION
Standard length of the input and output cords:
• Input Cord = 5
1
/
2
Feet minimum
• Output Cord = 8 Inches minimum
Auto/Isolation Transformers can be used in most countries by using
an input adapter plug. See page 40 for STANCOR’s high quality line of
International Adapter Plugs.
WHy & WHERE AUTO & ISOLATION
TRANSFORMERS ARE USED
Stancor’s stock Auto Transformers are connected for either step-down or
step-up applications involving line voltages of 115 or 230 Volts., 50/60 Hertz.
When isolation between the primary and secondary circuits is not necessary,
and a direct connection between them is permissible, the Auto Transformer
offers the advantages of smaller size, less weight, and lower cost.
This type of unit is generally used in applications involving American appli-
ances used abroad where our standard 115 Volt equipment must operate from
a 230 Volt source. It is also used for foreign appliances designed for 230 Volt
operation, which are to be used on our 115 Volt circuits. Our catalog items
are designed for continuous rated output on either 50 or 60 Hertz.
It is important to bear in mind that the Auto/Isolation
Transformers change only the voltage levels and do not change
the frequency from 50 to 60 Hertz or vice versa. In appliances
using synchronous motors, such as clocks or phonograph record
changers and players, the speed will be different when using them
on a frequency which differs from the frequency they were origi-
nally designed. In these cases the manufacturer of the appliance
should be consulted to obtain the proper motor.
The VA rating is equivalent to a Wattage rating where a resistive load and/
or unity power factor exists. When inductive loads such as motors are used
(as in a motor driven appliance) the power factor is not unity and to be accu-
rate the output is expressed in VA, which is the product of the output voltage
and the output current (Amps).
When selecting one of these items for use with an appliance which
includes a motor, allowance should be made for the starting current of the
motor which is somewhat higher than the running current. This information
is generally available from the appliance manufacturer. Information pertaining
to the AC Wattage or current required by an appliance is generally marked
on the item by the manufacturer and should be observed. It is much better to
buy a transformer with a larger VA rating than you will actually need because
of larger motor starting currents and variations in the line voltage and/or fre-
quency in some locations, which could cause overheating.
Isolation Transformers
Used where a direct connection between primary and secondary circuits is
not desired and the circuits must be isolated. This results in a larger, heavier
and more costly item for a given power rating. However, in addition to the
isolating advantages, an electrostatic shield is generally added to minimize
capacitive coupling between primary and secondary circuits. This helps to
minimize the transfer of unwanted power line transients and interference
from other sources connected to the power line by capacitive coupling to the
secondary circuit. The standard insulation test voltage rating between wind-
ings and between each winding and the core is 1,500 Volts R.M.S. This is
normally sufficient for 115 and 230 Volt operation.
The VA rating should be selected for each specific application, with allow-
ance for any abnormal load or environmental conditions. All catalog items
have an operating temperature of 105 Degrees C. (Designed for a 65 Degrees
C. maximum temperature rise above a maximum ambient temperature for 40
Degrees C., with unrestricted free air ventilation.) V-A/Amps output ratings are
for continuous operation from the specified input voltage and frequency.
General Information
All of these items have Class “A” insulation and are rated to have a maximum
operating temperature of 105 Degrees C. These units may be used with
rectifiers but the form factor as explained elsewhere in this catalog should
be observed for various combinations of rectifier circuits and types of load
following the rectifier.
These items are made with our standard N.E.M.A. plugs and receptacles,
primarily for use in this country. However, if used overseas where different
types of plugs are necessary, an adapter plug should be used or our plug
removed and a foreign plug attached to the end of the line cord.
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