VFD for a single-phase "Vodoley" pump: capacitor-free wiring

"Vodoley" is a pump brand, not a wiring method

"Vodoley" (Водолей) is a common brand of single-phase household centrifugal and peripheral pumps built on a 220 V single-phase motor. Such a motor has two windings — a main (run) winding and a start winding — with a phase-shifting capacitor wired between them. It is the capacitor that creates the phase shift the motor needs to start and run.

When an owner wants to "put a VFD on a Vodoley", they run into the physics: a conventional VFD is designed for a three-phase induction motor with three symmetrical windings. A single-phase motor with its capacitor does not fit that model — feeding it together with the capacitor from a VFD usually ends in an overheated capacitor or a protection fault.

Below we cover the working, field-proven approach — wiring the "Vodoley" motor without the capacitor, directly to the U-V-W outputs of the drive. Every parameter here is checked against the official manual of the Veichi AC01 drive, not quoted from memory.

Why fit a VFD to a "Vodoley" pump at all? Most often to hold steady system pressure without water hammer, to start the motor smoothly (less stress on the mechanics and on the grid), and to remove the typical pressure-switch clicks and voltage dips at start-up. Soft starting also markedly extends the pump's service life: the sharp current surge of a direct-on-line start is one of the causes of winding and bearing wear.

Before wiring, it pays to weigh both paths honestly.

• Option 1 — keep the single-phase motor with its capacitor. In practice this is unreliable: the drive delivers a pulse-width-modulated voltage at its output, and the capacitor in that circuit overheats and degrades. This is the most common cause of a "blown capacitor" after a VFD is connected.
• Option 2 — capacitor-free, i.e. driving the two windings directly from the three drive outputs. The capacitor is removed entirely, and the phase shift for starting and running is now created by the drive itself through its three-phase PWM. This is the method we describe.

An important detail that is sometimes left unsaid: to power such a pump from a 220 V supply you need a single-phase 1×220 V VFD. Single-phase drives are sensitive to input phasing — connect the supply strictly per the terminal markings (L/N), not at random. And if you have the option to fit a three-phase motor instead of a single-phase one, that is always the more reliable solution — we will return to it at the end.

If you are still selecting the drive itself, look at the Veichi VFD range: the AC01 series is a line of compact single-phase models aimed precisely at household pumps and small machinery.

Step 1. Identify the windings with a multimeter

A single-phase motor's terminal box usually has three or four leads. Until you know which winding is which, do not connect the drive — swapped leads will give you either no torque or reverse rotation with overload. Set a multimeter to resistance (Ω) and measure the leads in pairs.

• Common lead (Common). Shows electrical continuity to both other leads. This is the point where the windings are joined inside the motor.
• Main (run) winding. Has the lower resistance. It is rated for continuous current and does the main work.
• Start (auxiliary) winding. Has the higher resistance — wound with thinner wire and intended only to produce starting torque.

Write down the three readings: for example, A–B 4 Ω, A–C 7 Ω, B–C 11 Ω. The highest resistance (B–C) is the sum of the two windings through the common point, which means lead A is the common one. Of the remaining two, the lower resistance points to the main winding and the higher to the start winding. A small thing — but it is exactly where most first attempts go wrong.

A few practical notes. First, if the motor has four leads, two of them may already be joined internally or under the capacitor — first trace the old circuit and find where the capacitor "tails" ran. Second, cheap multimeters measure low resistances poorly (1–3 Ω): if the difference between the windings is small, ring out each pair several times and trust the stable ratio rather than a single random value. Third, label the leads immediately — it is very easy to mix them up once the capacitor is disconnected.

Step 2. The U-V-W wiring

Once the windings are identified, the wiring is simple. First, remove the start capacitor completely from the motor circuit. It is no longer needed and only does harm in a circuit with the drive.

Then connect the three motor leads to the drive's output power terminals:

• Common lead (Common) → terminal V;
• Main (run) winding → terminal U;
• Start (auxiliary) winding → terminal W.

So the common lead always goes to the middle phase V, while the two windings split to U and W. If the pump runs in the wrong direction after start-up, do not start tweaking parameters — simply swap the connections at U and W.

Before the first start, check and tighten every screw connection on the terminal block. A loose contact under vibration is a classic cause of power-module burnout. And one more thing from the field: if the old pump circuit had a mechanical thermal overload relay, remove it from the circuit after fitting the drive — the VFD has its own digital motor protection, which works more accurately.

Step 3. Veichi AC01 parameters

Now the key part — the settings. On a capacitor-free single-phase motor wired to U-V-W, the drive "sees" an unbalanced load and by default reads it as an output phase loss. So, besides choosing the control mode, you must deliberately disable the output phase-loss protection.

All codes below are taken from the official AC01 drive manual — pay attention to the column with the manual section.

Why F10.20 specifically, rather than some parameter in the F09 group? This is worth getting right: some materials and forum threads for single-phase motors quote "F09.13 = 0". There is no such parameter in the official AC01 manual — the F09 group handles auxiliary control, while phase-loss protection is owned by F10.20 in the F10 protection group. Disable the "wrong" parameter and the drive will still keep tripping. Always follow the manual for your exact series.

After the first start, watch the behaviour: the pump should ramp smoothly to the nominal 50 Hz with no jolts and no protection faults. We have covered the basic run/stop and frequency-source settings for the AC01 in a separate article — Veichi AC01 VFD setup.

One more tip from practice — do not push the pump above 50 Hz. The temptation to "add pressure" by ramping to 55–60 Hz ends in overheating for a capacitor-free single-phase motor: the start winding is not rated for continuous operation under raised voltage. Keep the working range within 30–50 Hz and adjust the required pressure by pump selection and settings, not by "over-revving" the frequency. If the motor hums noticeably at low speed, that is normal for V/F mode; a sharp metallic whine can be removed by slightly raising the PWM carrier frequency in the relevant parameter group.

When this method should not be used

Honestly: capacitor-free does not suit every single-phase motor. There is a limit beyond which it makes no sense to push.

After start-up, measure the motor's running current and compare it with the rated value on the nameplate. The rule of thumb is simple:

• Current within the rated value — the motor is compatible and can be put into service.
• Running current exceeds the rated value by more than twice (>2×) — stop operating it. This means the winding design of this motor performs poorly without the capacitor; it will overheat and fail. Such a motor must be replaced with a three-phase one.

This is not a "shortcoming of the VFD" — it is simply that some household single-phase motors are physically not meant to run without their phase-shifting capacitor. In that case the most reliable path is to fit a three-phase pump (or three-phase motor) and feed it from an ordinary single-phase VFD. We have explained how that works here: connecting a three-phase motor to a single-phase supply. And to decide on the drive type in the first place, this article helps: single-phase and three-phase frequency converters.

A separate word on sizing the drive by current. On a capacitor-free single-phase motor the current splits unevenly between the windings, so the VFD should be chosen with a margin — base it not on the nameplate power in kW but on the drive's rated current, which should cover the motor's running current by at least 25–30%. A drive sized "to the limit" by power easily trips on over-current at start-up under such a load. If the motor is, say, 0.75 kW with a running current of about 5 A, choose a drive with a rated output current of 6–7 A or higher.

Frequently asked questions

Can I control a "Vodoley" with a VFD without removing the capacitor?

No. A capacitor in a circuit with the VFD's PWM output overheats and fails quickly. To run with a drive the capacitor is removed completely, and the phase shift is created by the drive itself through the U-V-W connection.

Which VFD do I need for a single-phase 220 V pump?

A single-phase drive with a 1×220 V input — for example the Veichi AC01 series. See the single-phase 220 V VFD category. Pay attention to the drive's rated current: it must cover the motor's running current with a margin.

Why does the VFD trip on phase loss immediately?

Because a single-phase motor on U-V-W is an unbalanced load, and the protection reads it as an output phase loss (faults of the E.oLF type). On the AC01 this is fixed with parameter F10.20 = 20, which disables output phase detection.

The pump runs the wrong way — what do I do?

Swap two wires at terminals U and W. The direction of rotation changes with no parameter changes needed.

Does this method work for a borehole (submersible) pump?

The principle is the same, but a borehole adds its own factors — a long cable, voltage drop, dry-run protection. That is a separate topic: Veichi VFD for a borehole pump.

If you are unsure about the compatibility of a specific motor or about sizing the drive by current, send us the pump nameplate and we will suggest a model and safe settings for your case.