What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Servo Press Encoder Battery: When to Replace and What Happens If It Dies

admin

**Question:** Our servo press manual says to replace the encoder battery every 3 years but we have never done it in 5 years. The press still works fine. Is this really necessary?

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**Answer:**

Replace it now. Here is what happens when the battery dies and why it matters.

## What the Encoder Battery Does

Servo presses use absolute encoders that remember the slide position even when power is off. The encoder has a small battery (typically CR2032 or similar lithium cell) that powers the position memory circuit when main power is off.

When the battery is good: power on the press, the controller immediately knows where the slide is. No homing required.

When the battery dies: the encoder loses its position memory. The controller does not know where the slide is.

## What Happens When the Battery Dies

**Best case**: the press displays an encoder battery alarm and refuses to run until you perform homing. You lose 30-60 minutes of production.

**Worst case**: the battery dies while the press is powered off with a die installed. When you power on, the controller thinks the slide is at TDC. An operator who does not notice the alarm jogs the press - and the slide crashes into the die at full speed.

Die crashes from lost position cost $5,000-$50,000 in die damage and press downtime. The battery costs $5.

## How to Check Battery Voltage

- Mitsubishi MR-J4: parameter display shows battery voltage directly
- Yaskawa: Un00F (encoder battery voltage)
- Siemens: check encoder module status in STARTER software

Replace when voltage drops below 3.2V (nominal is 3.6V for lithium cells).

## Replacement Procedure

**Never replace the encoder battery with the press powered off** - you will lose the position and need to perform homing.

1. Keep main power ON during battery replacement
2. Replace with the correct battery type (check the manual)
3. Verify the position reading has not changed after replacement
4. Log the replacement date

Replace every 2 years regardless of voltage reading.

anna_controls

Replace it. Now. A dead encoder battery means the absolute position is lost on the next power cycle. The press won't know where the slide is and you'll need to re-home —which on some presses requires a service technician. The battery costs $15. The service call costs $2,000+. Replace every 2 years regardless of voltage reading.

raj_maintenance

We learned this the hard way. Battery died on a Friday night, press lost home position. Couldn't run until Monday when the Yaskawa tech came out. Lost an entire weekend of production —about $45,000 in our case. Now we replace every battery in January, no exceptions. It's on the annual PM schedule in red.