What Size Capacitor Does a Boat Lift Motor Need?
Quick answer
The size printed on the old capacitor, matched in microfarads (µF) and at the same or higher voltage. Published boat lift motor start capacitors run from 465 µF to 800 µF at 165 VAC for 3/4 to 1 1/2 hp motors, but horsepower alone does not set the value: one 3/4 hp line uses 465 µF and another 700 µF. A generic store capacitor with the right µF is often a 125 V part, which is a downgrade.
On this page
A boat lift motor needs the start capacitor size printed on the one it came with: the same microfarad (µF) value, at the same voltage rating or higher. For the common 3/4 to 1 1/2 hp single-phase lift motors, the published values run from 465 µF to 800 µF, all at 165 VAC. Above 540-648 µF, the general-purpose capacitors in Cornell Dubilier's catalog are all 110/125 V parts.
The other answer you will see is one size per horsepower. It is wrong for lift motors. BH-USA lists 465 µF for a painted 3/4 to 1 hp motor and 700 µF for a stainless baseless 3/4 hp motor. It also notes that baseless 3/4 hp lift motors "often have start capacitors as low as" 600 µF. Same horsepower, three different values. Horsepower tells you the neighborhood. The label tells you the size.
- Published lift motor values: 465, 480, 650, 700 and 800 µF, all 165 VAC (BH-USA)
- Rule: same µF as the original, same or higher voltage, same bleed resistor if it had one
- Good reading on a meter: inside the range printed on the label; below the low number means replace
- Duty limit: 20 starts an hour of 3 seconds each (KEMET, 50 Hz), reduced by 20% at 60 Hz
- Does not apply to: 12 V and 24 V DC lift motors, which have no start capacitor
Safety: a start capacitor holds a charge after the power is off and can deliver a painful shock. Lock out the power, lower the lift empty or support the boat, and never stand, reach or swim under a raised boat while you work on the motor. Dock wiring belongs to a licensed electrician, on a GFCI-protected circuit (see boat lift electrical).
The published sizes, side by side
The clearest published set comes from BH-USA, which sells these capacitors for the painted and stainless lift motors it carries, including Elite motors. Where a motor listing gives the value too, it agrees.
| Motor | Capacitor | Voltage | Case |
|---|---|---|---|
| Painted 3/4 to 1 hp | 465 µF | 165 VAC | about 1 9/16 in across, 3.15 in long |
| Painted 1 hp heavy duty | 480 µF | 165 VAC | about 1 9/16 in across, 3.93 in long |
| Painted 1 to 1 1/2 hp | 650 µF | 165 VAC | about 1 9/16 in across, 3.15 in long |
| Stainless baseless 3/4 hp | 700 µF | 165 VAC | 3 3/8 x 1 13/16 in |
| Stainless baseless 1 to 1 1/2 hp | 800 µF | 165 VAC | 3 3/8 x 1 13/16 in |
| Baseless 3/4 hp (general note) | "as low as" 600 µF | not stated | not stated |
The motor side matches. BH-USA's 1 hp Heavy Duty Elite TENV motor lists a 480 µF capacitor, 13.0 A at 115 V (6.5 A at 230 V), 1,725 rpm, a 56 frame, a 1.25 service factor and a 15 minute time rating. Its Marathon 3/4 hp lift motor (model 5KC42JN0214, 11.4 A at 115 V, 15 minute rating) has a start capacitor, but the listing gives no µF value, which is why the old capacitor's label is the source that counts.
The painted-motor capacitors use 1/4 in quick-connect terminals, and BH-USA notes that replacing one does not require getting inside the motor: it sits under its own cover on the motor housing.
How to read the label
Capacitance is printed either as one number (465 µF, sometimes written MFD) or as a range (430-516 MFD). Start capacitors are made to a loose tolerance, and the range is that tolerance written out.
- Ranges: Cornell Dubilier's PSU series lists every part as a range whose top is about 20% above the bottom: 430-516, 460-552, 540-648, 590-708, 645-774, 708-850, 800-960 µF.
- Single values: KEMET's MS/MD start capacitors are made to either ±10% or -0% +25% of the number printed. A new capacitor of the -0% +25% type should never read below its label.
- Voltage: 110/125, 165, 220/250 or 330 VAC on the Cornell Dubilier range. This is the highest voltage the capacitor is built for, not the voltage it needs.
Pick a replacement whose range contains the original value: a 465 µF lift capacitor sits inside a 430-516 or 460-552 µF part.
Why a generic replacement is often the wrong part
Cross the lift values against a general-purpose catalog and two problems show up.
| Lift value (165 VAC) | PSU at 165 VAC | Smallest 165 VAC case | PSU at 110/125 VAC |
|---|---|---|---|
| 465 µF | 430-516 or 460-552 | 1 13/16 x 3 3/8 in | 430-516 in a 1 7/16 x 3 3/8 in case |
| 480 µF | 430-516 or 460-552 | 1 13/16 x 3 3/8 in | 430-516 or 460-552 |
| 650 µF | none (165 V parts stop at 540-648) | none | 590-708 or 645-774 |
| 700 µF | none | none | 590-708 or 645-774 |
| 800 µF | none | none | 708-850, 720-864 or 800-960 |
Voltage. In the Cornell Dubilier PSU series, the 165 VAC parts top out at 540-648 µF. Above that, everything is 110/125 VAC. So the part that matches a 650, 700 or 800 µF lift capacitor in µF is a 125 V part, which is a step down from 165 V. Temco's motor capacitor guidance is plain: choose a voltage rating "at or above the original capacitor," and going lower cuts its life severely.
Size. The BH-USA painted-motor capacitors are about 1 9/16 in across. The slimmest Cornell Dubilier 165 VAC part in the 430 to 552 µF ranges is 1 13/16 in across. The one that does fit in that diameter, 1 7/16 in, is again the 125 V part. A replacement that will not go under the motor's capacitor cover cannot be sealed in with the cover and gasket.
So buy the capacitor listed for your motor, or one that matches the label in µF, voltage and case size together. If all three cannot be matched, the lift-specific part is the right purchase. And treat a horsepower chart that gives one size per motor rating as a starting point only.
Why lift capacitors burn out
KEMET's data sheet says its start capacitors "are designed for intermittent duty only" and are "usually switched off automatically after starting." Its standard rating is "20 starts, each of three seconds duration per hour," 1.67% of the time. For 60 starts an hour, each start must drop to 1 second. Cornell Dubilier lists its PSU parts as meeting EIA RS-463 Type 2.
KEMET's duty figures are approved at 50 Hz. Under IEC 60252-2 the same capacitor is approved at 60 Hz, the U.S. supply, only if its operating time is cut by 20%: 1.67% becomes 1.36%.
Worked example: how much start time an hour allows
- At 60 Hz: 3,600 s x 1.36% = about 49 seconds of capacitor time per hour.
- A healthy motor reaching speed in about 1 second per start can start 40 or more times in that hour.
- A motor that hums and does not turn keeps the capacitor in circuit for as long as the switch is held. Three 15 second tries at a stalled lift is 45 seconds: nearly the whole hour, used up in under a minute.
Compare the motor: both BH-USA motors above are rated for 15 minutes of running at a time, about 18 times the capacitor's hourly allowance. (Running cost is a different matter, covered in how much electricity a boat lift uses.)
That points at the usual killers on a dock:
- Holding the button on a humming motor. Each second of hum is a second of start duty. Let go after a second or two and work through the motor troubleshooting guide.
- Low voltage at the motor. A long, thin run out the dock leaves the motor too little voltage to get up to speed quickly, so the start circuit stays in longer or the motor stalls. The troubleshooting guide works out a 120 V run that leaves about 70 V at start.
- A stuck starting switch. The centrifugal switch inside the motor takes the capacitor out of circuit. Temco notes that start capacitors fail when "left energized for too long due to a faulty starting circuit." A new capacitor that dies within days points at the switch.
- A dragging brake or a jam. A brake that does not release (see lift slipping or not holding) or a binding drum stalls the start. It looks like a capacitor problem and keeps killing capacitors until it is fixed.
- Jogging to level the boat. Each tap of the switch is a full start. At 60 starts an hour KEMET's rating allows 1 second per start, and 20% less at 60 Hz: about 0.8 second. A loaded motor that needs longer than that to get up to speed on every tap is past its rating, so pause between rounds of taps.
How to test one
You need a meter with a capacitance (µF) range and a resistor to discharge the capacitor first.
- Make it safe. Lift empty or boat supported, power locked out, nobody under the lift.
- Look first. Remove the capacitor cover. A bulged or split case, leaked electrolyte or a burned smell settles it without a meter.
- Discharge it. Hold a resistor across the two terminals with insulated pliers (see the worked example below), then confirm with the meter on volts that both AC and DC read near zero.
- Disconnect one lead so the motor winding is not part of the reading.
- Measure µF. A good capacitor reads inside the range on its label. On a single-value label, use the maker's tolerance: a KEMET -0% +25% part labeled 465 µF should read 465 to about 581 µF.
- Judge it. Below the low end of the range, an open reading, or a reading that will not settle all mean replace it. A reading in range, with the motor still humming, sends you back to voltage, the starting switch and the brake.
Worked example: how long to hold the discharge resistor
The motor troubleshooting guide suggests about 20,000 ohms at 2 W. On a 465 µF capacitor:
- Time constant: 20,000 ohm x 0.000465 F = 9.3 seconds.
- Worst case starting voltage is the peak of a 120 V supply, about 170 V.
- Getting from 170 V to under 10 V takes ln(170/10) = 2.83 time constants: 2.83 x 9.3 = about 26 seconds.
Hold it for at least 30 seconds, then check with the meter before you touch a terminal.
For comparison, under IEC 60252 a fitted bleed resistor must bring the capacitor below 50 V within 60 seconds; KEMET's approximation, R (kilohms) = 50,000 / µF at 120 V, gives about 108 kilohms or less for 465 µF.
Replacing it, step by step
- Photograph the label and wiring. Note µF, VAC, the case size, and whether a small bleed resistor is fitted across the terminals.
- Buy a capacitor whose µF value or range contains the original, at the same voltage or higher, that fits under the cover. If the original had a bleed resistor, the new one needs one too (Temco); KEMET recommends one wherever a motor has both start and run capacitors, to protect the run capacitor.
- With power locked out, discharge the old capacitor, move the leads across one at a time, and refit the cover and gasket.
- Test with the lift empty: a short run up and down with a clean start, then load the boat. Add the capacitor to the motor checks in your maintenance checklist.
If the motor still hums with a good capacitor, the starting switch, wiring or motor is next; replacing a boat lift motor covers matching the nameplate. If a failed motor has left a boat hanging, the methods in lowering a lift without power come first.
Where this page stops applying
- DC lift motors. 12 V and 24 V permanent magnet motors have no start capacitor. See AC vs DC boat lift motors and solar and battery problems.
- Run capacitors. Some single-phase motors carry a second, permanently connected run capacitor. It is a different part, with a much tighter tolerance (Temco gives ±5 to 10%), and it is never swapped with a start capacitor.
- Three-phase motors have no start capacitor.
- Other values. The table covers published 3/4 to 1 1/2 hp lift motors. A motor labeled differently is not wrong: follow its label.
A GFCI that trips only at motor start can share a cause with a failing capacitor; see why a lift keeps tripping the GFCI. For the rest of the motor, see boat lift motors, and for expected service life by water type, component lifespan.
Frequently asked questions
What size capacitor is on a 1 hp boat lift motor?
Published values for 1 hp lift motors are 465 µF (painted 3/4 to 1 hp), 480 µF (1 hp heavy duty), 650 µF (painted 1 to 1 1/2 hp) and 800 µF (stainless baseless 1 to 1 1/2 hp), all at 165 VAC. Which one yours takes depends on the motor line, so read the old capacitor's label.
Can I use a 125 V capacitor instead of a 165 V one on a boat lift?
Not as a lasting repair. Start capacitors should be replaced at the same voltage rating or higher, and a lower rating shortens their life. General-purpose 165 VAC capacitors stop at 540-648 µF in Cornell Dubilier's range, so for 650 to 800 µF lift motors buy the lift-specific capacitor.
How do I know if my boat lift capacitor is bad?
The motor hums but will not turn, or starts slowly. With power locked out and the capacitor discharged through a resistor, a meter reading below the label's range confirms it, as does a bulged case or leaked fluid. If it reads good, check voltage at the motor and the brake.
Why does my boat lift keep blowing capacitors?
Something keeps the capacitor in circuit past its few seconds of duty: a starting switch that does not open, voltage too low for the motor to reach speed, a brake or drum that stalls the start, or holding the switch while the motor hums. KEMET rates start capacitors for 20 starts of 3 seconds an hour at 50 Hz, less at 60 Hz.
Sources and further reading
- BH-USA, Painted Motor Start Capacitor: 465 µF (3/4 to 1 hp), 480 µF (1 hp HD), 650 µF (1 to 1 1/2 hp), 165 VAC, dimensions, 1/4 in terminals, fit to base, baseless and Elite motors (https://www.bh-usa.com/product/painted-motor-start-capacitor/)
- BH-USA, Stainless Baseless Motor Start Capacitor: 700 µF (3/4 hp) and 800 µF (1 to 1 1/2 hp) at 165 VAC; "as low as" 600 µF note for baseless 3/4 hp motors (https://www.bh-usa.com/product/stainless-baseless-motor-start-capacitor/)
- BH-USA, 1 HP Heavy Duty Elite TENV Wired Boat Lift Motor with Base: 480 µF capacitor, 13.0 A / 6.5 A, 1,725 rpm, 56 frame, 1.25 service factor, 15 minute rating (https://www.bh-usa.com/?p=470431)
- BH-USA, Marathon 3/4 HP Painted Wired Boat Lift Motor, model 5KC42JN0214: 11.4 A at 115 V, start capacitor, 15 minute rating (https://www.bh-usa.com/product/marathon-3-4-hp-painted-wired-boat-lift-motor/)
- Cornell Dubilier, Type PSU AC Motor Start Capacitors data sheet: ratings table by µF range, voltage and case size; EIA RS-463 Type 2; -40 to 65°C operating (https://www.cde.com/resources/catalogs/PSU.pdf)
- KEMET, AC Motor Start Aluminum Electrolytic Capacitors MS/MD data sheet A4041 (8/8/2023): intermittent duty, 20 starts of 3 seconds per hour, 60 Hz reduction under IEC 60252-2, tolerances, discharge resistor sizing (https://yageogroup.com/content/datasheet/asset/file/KEM_A4041_MS_MD)
- Temco Industrial, Motor Capacitor FAQ: matching capacitance, equal or higher voltage, bleed resistors, failure from a faulty starting circuit, run capacitor tolerance (https://temcoindustrial.com/product-guides/capacitors/motor-capacitor-faq)