You've hit on a complex issue with a lot of conflicting opinions. Let's break it down and try to give you a framework for thinking about this in your specific situation.

Here's a structured way to approach the question of soft starter ROI, especially when you're not penalized for momentary peak demand



1. Understanding the True Benefits Beyond Peak Demand Reduction (Which Is Irrelevant in Your Case)



Mechanical Stress Reduction

This is a HUGE factor, and often overlooked in pure energy cost calculations.

Belts, Gears, and Couplings

Across-the-line starting creates a massive torque surge. This shock load drastically shortens the life of belts, gears, couplings, and other mechanical components. Replacing these parts is costly, and downtime is even more so.

Motor Windings

The starting current can cause overheating and stress within the motor windings, leading to premature failure, especially with frequent starts and stops.

Driven Equipment

The shock can also damage the driven equipment (pumps, fans, conveyors, etc.). Imagine the stress on a pump impeller or a fan blade when it's suddenly wrenched into motion.

Pipe Hammer

Can cause damage over time.

Improved Motor Starting Characteristics



Adjustable Starting Torque

Soft starters allow you to tailor the starting torque to the specific load requirements. This can be critical for applications sensitive to sudden acceleration or deceleration.

Reduced Voltage Dip

While you're not penalized for peak demand, a large voltage dip during motor starting can still disrupt other equipment on your network. Sensitive electronics might trip offline. If you have other equipment tripping offline, that is a cost.

Process Control



Smoother Starts/Stops

For sensitive applications (e.g., conveyors carrying fragile items), a soft start/stop can be crucial to preventing product damage and downtime.

Reduced Wear and Tear on Motor Starters



Contactor Life

By passing a lower current through the motor starter's contacts during start-up, it may extend the life of the contactor.

Energy Savings during Ramp Time

While negligible compared to the initial inrush of current, soft starters use less energy during their ramp time than across-the-line starters do.

2. Quantifying the Costs



Soft Starter Purchase Price

Get actual quotes for the soft starters you'd need.

Installation Costs

Factor in labor and any necessary modifications to your electrical panels or wiring.

Programming and Commissioning

Soft starters need to be programmed correctly to match the motor and load characteristics.

Maintenance

While soft starters are generally reliable, they do have components that can fail. Factor in potential maintenance costs.

3. The Critical Question: What's the Cost of Failure?

This is where the real ROI calculation comes in. You need to assess the potential cost of equipment failure and downtime WITHOUT soft starters: What is the MTBF (Mean Time Between Failure) of your motors? Do you have historical data? If you're replacing motors every 5-7 years due to winding issues, a soft starter might extend that to 10-15 years. What's the cost of the motor and the labor to replace it? What is the MTBF of your belts, couplings, or gearboxes? Are you frequently replacing these components due to stress from across-the-line starting? What is the cost of unplanned downtime? This is the BIG one. Consider: Lost production time. Labor costs for troubleshooting and repair. Potential damage to other equipment due to a motor failure. Cost of restart.4. Motor Size Considerations

Your initial question about when to use soft starters based on motor size is a good one, but it's not a simple horsepower threshold. It depends on the application.

Smaller Motors (5-50 HP)

Across-the-line starting is generally acceptable IF the load is relatively light and starts are infrequent. If it's a critical motor driving a heavy load with frequent starts/stops, a soft starter might be worthwhile even at these lower horsepower ratings.

Mid-Size Motors (50-100 HP)

Here, the decision becomes more nuanced. The cost of a motor failure is higher, and the mechanical stress is more significant. This is where you really need to analyze the specific application.

Large Motors (100+ HP)

While you mention you've had no issues with 100HP motors, are you absolutely sure? Have you seen them fail earlier than expected, or have you replaced belts, gears, and couplings more frequently than you'd like? If the motor drives a critical piece of equipment or operates frequently, a soft starter is generally a good investment (even without peak demand charges).

5. Your Specific Energy Plan

The fact that you're not penalized for instantaneous peak demand makes the decision much less about energy savings. However, don't ignore the potential for reduced wear and tear and increased equipment lifespan.

6. A Practical Approach to Evaluation



Focus on Problem Areas

Identify the motors and applications where you're experiencing the most frequent failures or maintenance issues. These are the best candidates for soft starters.

Pilot Project

Install a soft starter on one or two of your most troublesome motors and carefully monitor its performance and the impact on maintenance costs. Compare the lifespan of the equipment and the costs versus not using a soft-starter.

Data Collection

Track motor failures, belt replacements, downtime events, etc. This data will be invaluable in making informed decisions about whether to use soft starters more widely.

Consider VFDs

Variable Frequency Drives can often do what a soft-starter does in addition to offer speed control of the motor. You'll need to determine which product works best for your situation.

Why Soft Starters Cost So Much



Complexity

Soft starters are sophisticated electronic devices with power semiconductors (thyristors or IGBTs), control circuitry, and protection features.

R&D and Manufacturing

The development and manufacturing of these components require significant investment.

Market Demand

While becoming more common, the market for soft starters is still smaller than for traditional motor starters, which affects pricing.

In conclusion

The decision to use soft starters in your situation comes down to weighing the cost of potential equipment failures and downtime against the cost of purchasing and installing the soft starters.

If you're not experiencing significant motor failures or mechanical issues, and downtime is not a major concern, the ROI of soft starters will be lower. If you're frequently replacing motors, belts, or couplings, or if downtime is costly, a soft starter is likely to be a worthwhile investment, even without peak demand charges.

Don't rely on simple rules of thumb like "use one above 100 HP." Focus on data, application-specific analysis, and a clear understanding of the potential costs of not using soft starters. Flag for review