Delta VFD vs. Inverter Generators: What's the Real Difference for Your Backup Power Needs?

I get this question a lot, especially from folks who've seen the terms "inverter generator" and "VFD" thrown around in the same conversation. They’re looking at a 6000 watt inverter generator for backup power and a delta vfd-m for a motor in their shop, and they ask, "What's the difference between an inverter and a generator?"

The short answer? They do completely different jobs. But the confusion is understandable because both manage electrical power. In my role coordinating emergency power solutions for industrial clients, I've had to explain this distinction in high-stakes scenarios—like when a client's production line was down and they thought a portable generator could somehow act as a motor speed controller.

Let's clear up the confusion. We're comparing two distinct tools: a Delta VFD series drive (a variable frequency drive for motor control) versus a commercial generator (like a 6000 watt inverter generator for creating electrical power). This isn't about which is 'better.' It's about which tool matches your specific job.

Core Function: What Does Each Actually Do?

This is the fundamental misunderstanding. People think [the difference between an inverter and a generator is just size]. Actually, they convert power in opposite directions.

The Generator (e.g., 6000 watt inverter generator):

It converts mechanical energy (from an engine) into electrical energy. An 'inverter generator' is just a more sophisticated type that produces cleaner power (lower Total Harmonic Distortion, or THD) by converting DC to AC power electronically. In March 2024, I had to source a 6000 watt inverter generator for a client's mobile data center. The clean power was non-negotiable—standard generators with dirty power would have fried their sensitive electronics.

The Delta VFD (e.g., delta vfd-m):

A Variable Frequency Drive (VFD) takes incoming, fixed-frequency AC power (like from a wall outlet or generator) and converts it to a variable frequency and voltage to precisely control an AC motor's speed and torque. The delta vfd series is excellent for this. During our busiest season, when a food processing plant needed emergency repair on a conveyor drive, we used a Delta VFD-m to get the line running at partial speed in under 4 hours. A generator couldn't have done that job.

The most frustrating part of this confusion: clients spending $2,000 on a generator thinking it would solve a motor control problem. You'd think the name would be a clue, but when you're in a bind, you grab what you think works.

Application: Which Problem Are You Actually Solving?

The question to ask yourself is simple: Do you need to create power or control a motor?

When You Need a Commercial Generator:

• Your facility loses utility power and you need to run lights, computers, or a few standard appliances.
• You're working in a remote site with no access to the grid.
• You need clean, portable 120V/240V power for a specific event.
• Best guess? A standard 6000 watt generator will run a refrigerator, a few lights, and a sump pump, but not a motor with a high starting current.

When You Need a Delta VFD:

• You need to vary the speed of a 3-phase motor (fan, pump, conveyor, compressor).
• You want significant energy savings (up to 50%) from pumps and fans running at partial load.
• You need to reduce mechanical stress on your equipment during startup (soft-starting).
• I'm not 100% sure, but I'd say 70% of the pump failures I've seen were due to direct-on-line starting, which a VFD could have prevented.

The $500 generator quote turned into $1,200 after we accounted for the fact it couldn't power the motor it was bought for. The $650 all-inclusive cost of a properly sized Delta VFD for that same motor was actually cheaper in the long run. I now calculate TCO before comparing any two different pieces of equipment.

Total Cost of Ownership (TCO): Beyond the Price Tag

Looking back, I should have been more explicit in guiding clients on TCO. At the time, I just let them compare price tags. That was a mistake.

You're comparing two different cost structures.

Per FTC guidelines (ftc.gov), businesses must substantiate their claims. So here's the data:

• Generator Costs: Upfront cost (e.g., $1,200 for a 6000 watt inverter generator) + fuel ($2-5/hour at rated load) + oil changes + maintenance (spark plugs, air filters) + eventual replacement. According to USPS pricing effective January 2025, the cost to ship a 150lb generator is around $75-$150. Don't forget that.
• Delta VFD Costs: Upfront cost (e.g., $400 for a delta vfd-m to control a 5 HP motor) + installation (electrician needed) + no fuel costs + near-zero maintenance. The value it provides is energy savings and extended motor life, which directly impacts your operating bottom line.

The assumption is that a generator is cheaper because you can see its single purpose. The reality is a Delta VFD often pays for itself in energy savings within 18 months on a pump running 8 hours a day. The generator is a cost center; the VFD is a cost saver.

So, What's the Verdict? (Based on Your Scenario)

This isn't a simple "A is better than B" situation. It's about the tool for the job. Here's how I'd advise a client when they're stuck on this question.

1. You need backup power for the whole shop? Buy a commercial generator. Make sure you know the starting current (inrush) of your biggest motor. A standard 6000 watt inverter generator might not start a 3 HP motor. You'll need a much larger one, or a generator with good surge capacity.
2. You need to control the speed of a specific machine for efficiency? Buy a Delta VFD series drive. It's the only tool that does this job. Trying to use a generator for this shows a fundamental misunderstanding of the difference between an inverter and a generator.
3. You need to run a motor that's far from your main power source? This is the edge case. You might put a generator near the motor to provide 3-phase power, and use a Delta VFD right there to control its speed. I did exactly this for a large-scale project needed in 48 hours. The generator created the power, the VFD controlled the motor. They worked as a team.

Here's the thing: the confusion often comes from the word "inverter." Both use an inverter. The generator uses it to create clean power. The VFD uses it to control a motor's frequency. It's the same technology, but a completely different application.

After the third time a client tried to save $200 on a "cheap" generator instead of the correct VFD, I was ready to write this article. What finally helped was creating a simple flowchart for them: "Do you need to make electricity? Get a generator. Do you need to control a motor? Get a VFD. The two are not interchangeable."

See also Delta VFD Series: When It's the Right Choice (And When It's Not)

Standard print resolution requirements don't apply here, but the principle of clarity does. Industry-standard thinking is that these are competing products. The reality is they are complementary. Get the right tool for your actual problem, and you'll save time, money, and a massive headache.