Buck / Boost Transformers

Buck-Boost Transformers are small single phase isolation transformers that will reduce (Buck) or raise (Boost) line voltage when connected as an Autotransformer. The most common application is Boosting 208 to 230v. Two or three may be banked for three phase application where the neutral is available from the input.

Much smaller transformers may be used in Buck - Boost applications, since the size of the transformer is roughly proportional to the change in voltage. I.E.: A 10KVA load at 240v can be increased to 264v, a 10% change can be achieved with a 1KVA transformer.

Rating Voltage Change Table Transformer Multiplier Table
A1 A2 B1 B2 C1 C2 D1 D2 A1 A2 B1 B2 C1 C2 D1 D2
120/240 X 12/24 1.10 .90 1.20 .80 1.05 .95 1.10 .90 .10 .11 .20 .24 .05 .05 .10 .11
120/240 X 16/32 1.13 .87 1.27 .77 1.07 .93 1.13 .87 .13 .15 .27 .34 .07 .07 .13 .15
240/480 X 24/48 1.10 .90 1.20 .80 1.05 .95 1.10 .90 .10 .11 .20 .24 .05 .05 .10 .11

  1. Multiply Input voltage by the appropriate number in Voltage Change Table for output voltage.

  2. Multiply Load by the appropriate number in Transformer Multiplier Table for approximate transformer size.

A1 Boosting A2 Buucking
A1: Boosting A2: Bucking
B1 Boosting B2 Bucking
B1: Boosting B2: Bucking
C1 Boosting C2 Bucking
C1: Boosting C2: Bucking
D1 Boosting D2 Bucking
D1: Boosting D2: Bucking