Cincinnati, Ohio Ferroresonant transformers from Foster Transformer provide a stable power output (typically ±3%) for input voltages that vary as much as ±15%. The standard square wave output requires less filtering than linear transformers for DC applications, said the company.
These devices can be used in battery chargers, medical equipment, inverter and UPS systems, line voltage stabilizers, industrial automation, machine tools, and other applications that require a stable output with a high degree of isolation from line disturbances.
The ferroresonant transformers are available for 50 Hz, 60 Hz, and 50/60 Hz, with output ratings from 50 VA to 5.0 kVA. They feature vacuum and pressure impregnation with specialty formulated epoxy resin for low acoustic noise. Typical operating efficiencies exceed 85%.
The transformers can be designed to operate continuously with a direct short applied across the output terminals. An optional sine wave output reduces total harmonic distortion to typically <5%. UL Recognized insulation is available from class 130 (B) through class 220 (R).
Since these are typically custom devices, prices will vary. For example, pricing begins at $30.00 each in quantities of 100 for a 50 VA transformer with a standard square wave output. Sizes larger than 150 VA typically are priced at $0.20 to $0.25 per VA (W) with a square wave output, and $0.30 to $0.35 per output VA (W) with a reduced harmonic sine wave output. Delivery is typically six to eight weeks.
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