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.
Voltage Change Table
| Rating |
Reference Diagrams Below for Characteristics |
| A1 |
A2 |
B1 |
B2 |
C1 |
C2 |
D1 |
D2 |
| 120/240 X 12/24 |
1.10 |
0.90 |
1.20 |
0.80 |
1.05 |
0.95 |
1.10 |
0.90 |
| 120/240 X 16/32 |
1.13 |
0.87 |
1.27 |
0.77 |
1.07 |
0.93 |
1.13 |
0.87 |
| 240/480 X 24/48 |
1.10 |
0.90 |
1.20 |
0.80 |
1.05 |
0.95 |
1.10 |
0.90 |
Multiply Input voltage by the appropriate number in Voltage Change Table for output voltage.
Transformer Multiplier Table
| Rating |
Reference Diagrams Below for Characteristics |
| A1 |
A2 |
B1 |
B2 |
C1 |
C2 |
D1 |
D2 |
| 120/240 X 12/24 |
0.10 |
0.11 |
0.20 |
0.24 |
0.05 |
0.05 |
0.10 |
0.11 |
| 120/240 X 16/32 |
0.13 |
0.15 |
0.27 |
0.34 |
0.07 |
0.07 |
0.13 |
0.15 |
| 240/480 X 24/48 |
0.10 |
0.11 |
0.20 |
0.24 |
0.05 |
0.05 |
0.10 |
0.11 |
Multiply Load by the appropriate number in Transformer Multiplier Table for approximate transformer size.
Voltage Change Table
|
Reference Diagrams Below for Characteristics |
| Rating |
A1 |
A2 |
B1 |
B2 |
| 120/240 x 12/24 |
1.10 |
0.90 |
1.20 |
0.80 |
| 120/240 x 16/32 |
1.13 |
0.87 |
1.27 |
0.77 |
| 240/480 x 24/48 |
1.10 |
0.90 |
1.20 |
0.80 |
| Rating |
C1 |
C2 |
D1 |
D2 |
| 120/240 x 12/24 |
1.05 |
0.95 |
1.10 |
0.90 |
| 120/240 x 16/32 |
1.07 |
0.93 |
1.13 |
0.87 |
| 240/480 x 24/48 |
1.05 |
0.95 |
1.10 |
0.90 |
Multiply Input voltage by the appropriate number in Voltage Change Table for output voltage.
Transformer Multiplier Table
|
Reference Diagrams Below for Characteristics |
| Rating |
A1 |
A2 |
B1 |
B2 |
| 120/240 X 12/24 |
0.10 |
0.11 |
0.20 |
0.24 |
| 120/240 X 16/32 |
0.13 |
0.15 |
0.27 |
0.34 |
| 240/480 X 24/48 |
0.10 |
0.11 |
0.20 |
0.24 |
| Rating |
C1 |
C2 |
D1 |
D2 |
| 120/240 X 12/24 |
0.05 |
0.05 |
0.10 |
0.11 |
| 120/240 X 16/32 |
0.07 |
0.07 |
0.13 |
0.15 |
| 240/480 X 24/48 |
0.05 |
0.05 |
0.10 |
0.11 |
Multiply Load by the appropriate number in Transformer Multiplier Table for approximate transformer size.
Transformer Boosting Circuit Diagrams
A1: Boosting
B1: Boosting
C1: Boosting
D1: Boosting
Transformer Bucking Circuit Diagrams
A2: Bucking
B2: Bucking
C2: Bucking
D2: Bucking
Warning: When using this information to perform electrical work, call a licensed electrician or consult the NEC® for safety. All licensed
electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.