Comparison Chart of 250VA power transformers using 3 different types of cores

Feature O-CORE TOROIDAL E-I CORE
Height 1.375" (34.9 mm) 2.2" (55.8 mm) 4.7" (119.4 mm)
OD/Width 4.5" (114.3 mm) 4.5" (114.3 mm) 3.9" (99.1 mm)
Depth -- -- 4.3"(109.2 mm)
Volume 22 cu.in.(361 cm3) 35 cu.in.(574 cm3) 78.8 cu.in.(1291 cm3)
Weight 3.6 Lb(1.63 Kg) 5 Lb (2.27 Kg) 10 Lb (4.54 Kg)
Mounting
Single Bolt Single Bolt bolts in four corners
Requirements
Through Center Through Center
Magnetizing
Current 16 mA 18.3 mA 160.0 mA
No-Load
Losses 1.7 W 1.7 W 20.5 W
Continuity
50% of grain
Of Magnetic 100% parallel grain orientation
Perpendicular Path
Causing higher Eddie
Currents
Magnetic
Optimized prior to winding and remain
Negatively impacted Properties Stable by clamping, welding Of Core or banding.
Coupling
Maximized by evenly distributed Limited by bobbin Factor winding on the core and close width and layers proximity to the actual core itself of windings.
Long-Term
In excess of 10 years
Performance
Reliability
Degradation over time, from thermal cycling and vibration.