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

Energy recovery - regen braking and storage

jeff_quality

Our servo press has regenerative braking and I'm trying to understand if we're actually recovering energy or just dumping it into resistors. How do I tell?

**How Regenerative Energy Works
**
During the return stroke (BDC to TDC), the servo motor decelerates the slide. This deceleration generates electrical energy that flows back into the DC bus of the drive.

This regenerative energy can be:
1. **Dissipated** in a braking resistor (wasted as heat)
2. **Shared** with other drives on the same DC bus
3. **Returned to the grid** via an active front end (AFE) unit
4. **Stored** in a capacitor bank or battery system

**DC Bus Sharing (Most Common)
**
If multiple servo axes share a common DC bus (typical in multi-axis presses), regenerative energy from one axis can be used by another axis that is accelerating simultaneously.

Example: On a 4-point servo press, when two axes are decelerating (returning), their regenerative energy powers the other two axes that are accelerating (forming). Net energy consumption is significantly reduced.

**Active Front End (AFE)
**
An AFE unit replaces the standard diode rectifier with an IGBT bridge that can both draw power from and return power to the AC supply.

Benefits:
- Returns regenerative energy to grid (reduces energy bill)
- Maintains near-unity power factor
- Reduces harmonic distortion

Cost: AFE units cost 30-50% more than standard rectifiers, but payback period is typically 2-4 years on high-SPM presses.

**Measuring Regenerative Energy**

To quantify regenerative energy on your press:
1. Install a bidirectional power meter on the press supply
2. Run press at production SPM for 1 hour
3. Record total energy consumed and total energy returned
4. Regenerative fraction = returned / (consumed + returned)

Typical values: 15-35% regenerative fraction for servo presses vs 0% for mechanical presses.

carlos_mx

Energy recovery efficiency varies a lot between press types. On our crank-type servo press, we recover about 15-20% of the forming energy during the return stroke. On our screw-drive press, recovery is 30-40% because the deceleration phase is longer. If energy cost is a major factor in your ROI calculation, the drive type matters more than most people realize.

mchen_servo

Energy recovery systems are becoming standard on modern servo presses. The payback period depends heavily on your energy rates and production volume. We calculated 18 months payback at our facility with a regen unit that feeds back to the plant bus.

Key metric: measure the deceleration energy per stroke. On a 200-ton press at 40 SPM, we were recovering about 1.8 kWh per hour. Over a year of 2-shift operation, that's significant savings.

toolndye_dave

Regenerative braking on our 400T servo press recovers about 18% of total energy consumption. The payback on the regen unit was 14 months. One thing to watch: the braking resistor is the backup for when the regen system cannot absorb all the energy. Make sure it is properly sized and ventilated. We had one overheat and trip the press because the ventilation louvers were blocked by cardboard.

anna_plc

Real talk on regen economics — the numbers people quote (15-20% recovery) are technically correct but can be misleading depending on your application.

What actually determines your recovery percentage:

The ratio of deceleration time to total cycle time is everything. A press running at 60 SPM with a short stroke has very little deceleration time relative to the forming work. You might recover 8-10% at best. Same press at 20 SPM with a long dwell at BDC? Now your return stroke is a bigger chunk of the cycle and recovery jumps to 25%+.

How to tell if you're actually recovering vs dumping to resistors:

On most modern drives (Siemens S120, Yaskawa D1000, Mitsubishi FR-A800), there's a parameter that shows regen energy in kWh. Compare that to your braking resistor duty cycle. If the resistor is getting hot, you're wasting energy. If it's barely warm, the regen unit is doing its job.

Quick test: put a clamp ammeter on the regen unit output (grid side). During the return stroke you should see current flowing BACK toward the transformer. If you see zero, your regen unit might be configured but not actually enabled — I've seen this twice where the installer wired it but forgot to set the control parameter.

The real ROI calculation most people miss:

Don't just calculate energy savings. Factor in the reduced cooling load on your braking resistor cabinet. We eliminated a 5kW cabinet cooler when we went full regen, which was another $800/year in energy plus no more filter changes. Also, regen reduces stress on the DC bus caps (less ripple current), which extends drive life. Hard to put a dollar figure on that but it's real.

For jeff_quality's specific question — if your drive has a braking resistor AND a regen unit, check which one is active. Some systems are configured with the resistor as primary and regen as backup (backwards from what you'd want). Look at the drive's power flow diagram in the manual and verify the priority setting.