70053K Datasheet, PDF (16/28 Pages) List of Unclassifed Manufacturers – THE ADVANTAGES AND BENEFITS OF USING AMVECO TOROIDAL TRANSFORMERS

CONSIDERATIONS WHEN USING TOROIDAL POWER TRANSFORMERS
Substantial benefits may be derived from the use of toroids as long as
thought is given to their application. The following two considerations
are important.
A) Shorted Turn Condition
A completed path by any conductor passing through the center hole of
the toroid around the outside constitutes a short circuited turn. As with
any short circuit, this condition will result in high circulating currents and,
more importantly, high heat.
B) Inrush Currents
The excellent magnetic properties of the toroidal transformer and the
high remanence of the grain-oriented silicon steel, under certain circum-
stances, occasionally leads to high inrush current at turn-on.
To prevent nuisance interruptions due to blown fuses or supply breakers,
some simple precautions should be considered. As the power rating of
the transformer increases, the potential effect of the inrush current
becomes greater. The following table suggests different types of circuit
protection according to the toroid’s power rating.
Our standard mounting options utilize either a single bolt and large washer
(disk mount) with no outside structure to act as a conductor, completing
the circuit; or two metal flanges (flange mount) which clamp the toroidal
like a sandwich with four bolts at the outer periphery, but nothing
through the center. The L-Bracket and Clamping Bracket described are
both designed to avoid a shorted turn condition.
In addition, in those applications where an even lower in-rush
current is desired, AMVECO has developed several proprietary
construction techniques. Without added circuitry, both the peak value
and the duration of the in-rush current can be reduced. As a matter of
fact, AMVECO has manufactured toroidal transformers without any in-
rush current at all. In these cases, AMVECO works closely with the cus-
tomer to meet the specific requirements of the application. A slight
increase in the overall size of the transformer is sometimes necessary to
facilitate the lower in-rush current.
TRANSFORMER RATING SUGGESTED PROTECTION
• 15 to 300VA
None
• 300VA to 1.0kVA
Slow-blow fuse in primary circuit
• 1.0 to 2.0kVA
Small value resistor in series with
primary circuit
• 2.0kVA and up
Relay momentarily inserts resistor in
primary circuit at start-up, or NTC
Thermistors
15
AMVECO Magnetics, Inc. • 10401 Westoffice Dr. • Houston, TX 77042 • [phone] • [phone] • Fax: [phone] • Email: [e-mail] • www.amveco.com