What current should I use to lock the rotor?

Start at about 10 percent of rated current and increase slowly until the shaft locks firmly. Rarely more than 30 percent is needed.

Can I align an encoder by adjusting it until the motor runs smoothly?

It may run, but not at full torque, and it may overheat or run differently in each direction. Align to the measured rotor position.

Guide · 7 min read · Updated October 2026

How to check servo motor encoder alignment yourself

A misaligned encoder makes a healthy motor run hot, weak or rough, and it often looks like a winding or drive fault. You can check alignment on the bench with a current-limited DC supply, the encoder's own power supply and a meter or oscilloscope. Here is the method we use, simplified.

By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.

01Symptoms

Signs that point to alignment

High current at low load, or the motor heats up quickly
Torque is lower in one direction than the other
Overcurrent trips soon after enabling
The axis hunts, vibrates or growls at standstill
The problem started after a bearing change, encoder change or a repair elsewhere

02Tools

What you need

A DC bench supply with an adjustable current limit
A 5 V supply for the encoder, or the encoder's rated voltage
A multimeter, and ideally a two-channel oscilloscope
The motor's pole count and alignment reference from the datasheet
Brake supply, usually 24 V DC, if the motor has a holding brake

03Method

Step by step

Make it safe. Disconnect the motor from the drive and lock out the supply. Uncouple the motor from the machine. If the motor has a brake, release it with its rated voltage, usually 24 V DC.
Collect the data. From the nameplate or datasheet note the pole count, rated current and encoder type. Note the motor maker's alignment reference, for example U-phase edge or electrical angle at a stated lock position.
Power the encoder only. Supply the encoder at its rated voltage, usually 5 V, through its own connector. Do not power the drive.
Lock the rotor. From a current-limited DC supply, connect positive to U and negative to V and W joined together, or to the lock convention your maker gives. Set the current limit well below rated current, typically 10 to 30 percent, and raise it slowly until the shaft snaps to a position.
Read the position. For incremental encoders with UVW, check which commutation edge sits at the lock position with a meter or oscilloscope. For serial absolute encoders, read the electrical angle on the drive monitor or a tester.
Repeat at every pole pair. Turn the shaft to the next lock position. A healthy setup gives the same electrical reading at each one, within a few degrees. A reading that changes from position to position points to a slipped disc or the wrong pole count.
Check direction. Move the negative lead from V to W. The shaft should step in the direction your maker specifies, and the count should change in the expected direction.
Decide. If every reading matches the specification, alignment is fine and the fault lies elsewhere. If it is off, do not adjust without the maker's offset value; send the motor for alignment.

04Back-EMF check

A second check with an oscilloscope

With the motor disconnected, turn the shaft steadily by hand or with a drill at low speed. The motor generates a voltage on its windings. Put one scope channel on the U to V back-EMF and the other on the U commutation signal. On a correctly aligned motor the U edge falls at a fixed point of the back-EMF wave, often its zero crossing or 30° from it, depending on the maker.

05Safety

Keep it safe

Never apply more than rated current; the windings heat up quickly at standstill
The shaft can jump when the rotor locks; keep fingers and loose clothing clear
Never connect a DC supply while the drive is still wired to the motor
Large motors store energy in their magnets; turning them generates dangerous voltage on open terminals

06Help

When to send it to us

If the readings change from one pole position to the next, or you do not have the maker's offset, the encoder needs alignment on a proper test platform. Send the nameplate or WhatsApp +91 97866 22233. Related: encoder alignment service, encoder repair.

Free downloads for your maintenance file

Printable one-page sheets from our bench. More on the resources page.

Encoder alignment checklist

What to record before removing an encoder, the order of checks after refitting it, and the readings that tell you commutation is right before the motor goes back on the machine.

PDF · 1 page · 4 KB · free, no sign-up

Download PDF

Servo motor encoder quick reference

Encoder families, interfaces, counts per revolution and the motors they sit on: Fanuc pulsecoders (alpha A64, A1000), Mitsubishi OBA/OSA, Yaskawa UTOPH, Tamagawa, Heidenhain ECN/EQN/ERN and SICK SKS/SRS/SRM.

PDF · 2 pages · 8 KB · free, no sign-up