single phase Motor capacitor calculator
Estimate single-phase motor run/start capacitor size from supply voltage, current, and frequency. Uses C≈k·I/V with 50/60 Hz factors and quick HP/kW rules.
single phase motor capacitor calculator
Starting capacitor This can be estimated very fast capacitor run (lF) = k(l) I(line)/V, where k = 2650 (50 Hz) or k = 3180 (60 Hz) In the case of cap-start motors select C start = 2-4 x C run; check the motor datasheet.
Formula & Table Summary:
Capacitor Sizing Formulas:
auxiliary winding capacitor
This Single Phase Motor Capacitor Calculator determines the large size capacitor (PSC) and star-t capacitor that it needs on single-phase induction motors. A common rule is based on the line current ( I ) of a motor (the motor must be in phase with the frequency), voltage ( V ) and frequency ( f ): In 50 Hz, 33 C run(micro F) =approximately equal to 2650I/V, in 60 Hz, 33 C run(micro F) =approximately equal to 3180I/V. Split-phase/cap-start motors have typical start capacitors that are 2or 4 times the run value. Shortcutting works, too: Run 10-20 1/HP (13-27 1/kW) at about 230 V and Start 40-80 1/HP (54-108 1/kW). Check each time on the nameplate of the motor and the manufacturer specifications; these guidelines are aimed at approximate phase shift and auxiliary-winding current typical designs PSC/cap-start). Final selection should be made based on voltage rating, temperature, and duty (continuous and intermittent) as well as surge.
50Hz capacitor calculator
| Freq | V (VAC) | I (A) | C_run (µF) | C_start (µF) |
|---|---|---|---|---|
| 50 Hz | 230 | 2.0 | 23.0 | 46–92 |
| 50 Hz | 230 | 4.0 | 46.1 | 92–184 |
| 60 Hz | 120 | 6.0 | 159.0 | 318–636 |
| 60 Hz | 240 | 3.0 | 39.8 | 80–160 |
| 50 Hz | 230 | — | 10–20 µF/HP | 40–80 µF/HP |
Frequently Asked Questions - single phase Motor capacitor calculator:
How do I estimate a run capacitor for a single-phase motor?
Use C_run(µF) ≈ k·I/V with k=2650 (50Hz) or 3180 (60Hz).
How large should the start capacitor be?
Typically 2–4× the run capacitor value, intermittent duty.
Can I size by horsepower instead of current?
Yes; run ≈10–20 µF/HP, start ≈40–80 µF/HP (verify against nameplate).
Does frequency change the capacitor size?
Yes. Use k=2650 for 50Hz and k=3180 for 60Hz in C≈k·I/V.
What voltage rating should I choose?
Select a capacitor with VAC rating ≥ supply; run caps often 370–450VAC.
Are these values exact?
No, they are practical estimates. Always confirm with the motor manufacturer.
Do PSC and cap-start motors use the same capacitor?
PSC uses a continuous-duty run cap; cap-start adds a larger start cap via a switch.
What if the motor overheats or hums after replacement?
Capacitance may be incorrect or the cap faulty; recheck value, rating, and wiring.
Can I parallel capacitors to reach a value?
Yes, parallel adds capacitance (C_total = C1+C2); ensure matching voltage ratings.
Is a higher µF always better?
No. Too high can raise current and heating; match the specified/estimated value.
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