AIM Manual

Motor Application » Single-Phase Motors (Page 15)

Auxiliary Running Capacitors

Added capacitors must be connected across “Red” and “Black” control box terminals, in parallel with any existing running capacitors. The additional capacitor(s) should be mounted in an auxiliary box. The values of additional running capacitors most likely to reduce noise are given below. The tabulation gives the max. S.F. amps normally in each lead with the added capacitor.

Although motor amps decrease when auxiliary run capacitance is added, the load on the motor does not. If a motor is overloaded with normal capacitance, it will still be overloaded with auxiliary run capacitance, even though motor amps may be within nameplate values.

Table 15 Auxiliary Capacitor Sizing
MOTOR RATINGNORMAL RUNNING
CAPACITOR(S)
AUXILIARY RUNNING CAPACITORS FOR
NOISE REDUCTION
MAXIMUM AMPS WITH RUN CAMP
HPVOLTSMFDMFDMIN. VOLTSFRANKLIN PARTYELLOWBLACKRED
1/2115060(1)370TWO 1553271018.474
1/2230015(1)370ONE 1553281014.23.52
3/4020(1)370ONE 1553281035.852.5
1025(1)370ONE EA. 155328101
155328102
7.15.63.4
1.51020370ONE 1553281039.37.54.4
22010370ONE 15532810211.29.23.8
345None3701712.66
580None37027.519.110.8
7.54545370ONE EA. 155327101
155328101
373211.3
107030370ONE 155327101494213
15135NONE7562.516.9
  • (1) Do not add running capacitors to 1/3 through 1 hp control boxes, which use solid state switches or QD relays. Adding capacitors will cause switch failure. If the control box is converted to use a voltage relay, the specified running capacitance can be added.

Buck-Boost Transformers

When the available power supply voltage is not within the proper range, a buck-boost transformer is often used to adjust voltage to match the motor. The most common usage on submersible motors is boosting a 208 volt supply to use a standard 230 volt single-phase submersible motor and control. While tables to give a wide range of voltage boost or buck are published by transformer manufacturers, the following table shows Franklin’s recommendations. The table, based on boosting the voltage 10%, shows the minimum rated transformer kVA needed and the common standard transformer kVA.

Table 15A Buck-Boost Transformer Sizing
MOTOR HP1/31/23/411.52357.51015
LOAD KVA1.021.361.842.212.653.043.916.339.6611.716.6
MINIMUM XFMR KVA0.110.140.190.220.270.310.40.640.971.21.7
STANDARD XFMR KVA0.250.250.250.250.50.50.50.7511.52
  • Buck-Boost transformers are power transformers, not control transformers. They may also be used to lower voltage when the available power supply voltage is too high.