Why Most Generator Wattage Charts Are Wrong (And Dangerous)

Search “generator wattage chart” and you will find dozens of tables listing appliances with a single wattage number next to each one. Refrigerator: 400-800W. Window AC: 1,200W. Air compressor: 3,000-4,000W. Sump pump: 800-1,300W. These charts appear on Amazon product pages, generator manufacturer websites, portable power station listings, and home improvement blogs. They look authoritative. They are often dangerously incomplete. And by “dangerous” we do not mean your power station will explode — we mean overheating extension cords, nuisance trips that spoil a freezer full of food, and unreliable backup for medical equipment when the grid is down.

In this article, “wattage charts” refers to the generic sizing tables published for both gas generators and portable power stations — because the failure mode is the same. Whether your power source uses gasoline or lithium batteries, an undersized inverter or alternator will trip on a startup surge it cannot handle. The physics do not care about the fuel source.

The problem is not that these numbers are fabricated. Most come from real industry averages. The problem is that a single number for a category of devices hides the exact information you need to size correctly: the startup surge of your specific model, the technology behind its motor, and the conditions under which it operates. When you buy based on a generic chart, you are gambling that your device happens to match an average that may not apply to it.

All data in this article comes from OEM-published specifications where available, or from NEC-derived estimates with conservative multipliers. We do not use manufacturer marketing figures or unverified industry averages. See our data source methodology for details.

Here are four specific ways generic wattage charts fail, with numbers from our database of 49 devices and 33 portable power stations.

1. Compressor Surge: The 3x Rule Is Dangerously Incomplete

Most wattage charts estimate motor startup surge at 3x running watts. This comes from NEC motor tables and works reasonably well for many motor types — fans, pumps running against low head pressure, and power tools starting under no load. But the actual surge ratio depends on motor type, compressor design, back-pressure, temperature, and cable length. The real range is roughly 2x to 7x, and for tank-based compressors, the 3x assumption is dangerously low.

The CRAFTSMAN CMEC6150 is one of the best-selling 6-gallon pancake compressors in the United States. CRAFTSMAN publishes both running and starting watts directly on their support page (per OEM spec):

• Running watts: 1,320W
• Starting watts: 6,800W
• Actual surge ratio: 5.15x

A generic wattage chart using the 3x rule would estimate this compressor’s surge at 1,320 × 3 = 3,960W. The actual OEM-published figure is 6,800W. That is a 2,840W underestimate — over 70% too low.

If you bought a power station rated at 4,000W surge based on a wattage chart, it would fail to start this compressor. The inverter would trip on the first startup attempt.

Why is the ratio so high? Because a compressor motor must overcome compressed air resistance in the tank on every restart. The motor stalls against back-pressure, drawing maximum inrush current for a longer duration than a motor starting against no load. This is fundamentally different from a fan or a drill spinning up freely.

2. Refrigerator “400-800W” Is Misleading

Generic charts typically list refrigerators at 400 to 800 watts as if that were the running power draw. This range conflates three different numbers — nameplate circuit rating, running watts, and startup surge — into a single misleading figure.

Here is what modern french door refrigerators actually draw. These figures are derived from ENERGY STAR annual energy data: divide kWh/year by 8,760 hours to get average watts, then divide by an estimated 40% compressor duty cycle to get running watts during active compressor operation.

These are approximate figures, not direct OEM-published wattage. The nameplate on these refrigerators says “15A” — but that is the minimum circuit requirement (the breaker size for safe installation), not the current the compressor draws during normal operation. Using 15A × 120V = 1,800W as your refrigerator’s running draw overestimates by roughly 9x.

So where does the “400-800W” chart number come from? Likely from older or commercial refrigerators, nameplate confusion, or lumping running watts with surge watts into a single range. For modern residential french door models, actual running draw is typically 195 to 207W with a startup surge of approximately 390 to 414W (conservative 2x estimate). Most power stations rated 500W or above can handle a refrigerator — the real constraint for multi-day outages is battery capacity, not inverter output.

3. Power Supply Rating Is Not Power Draw

This trap catches anyone sizing a power station for electronics. A gaming desktop with a 1,000W power supply does not draw 1,000 watts.

The power supply unit (PSU) is rated for its maximum output capacity — the ceiling it can deliver if every component simultaneously draws peak power. Actual system draw during intensive gaming is typically 40 to 80% of PSU rating:

A wattage chart listing “Gaming PC: 1,000W” based on PSU ratings will lead you to buy a power station twice as large as you actually need. The same trap applies to laptop chargers (a 130W charger does not mean 130W continuous draw) and phone chargers (a 65W GaN charger draws 65W only during fast-charge peaks).

For power station sizing, PSU rating is the safe worst-case ceiling. But if you want to know your actual draw, use a plug-in power meter (like a Kill-A-Watt) to measure wall draw under real load, or check OEM documentation for typical system power consumption. The difference between PSU rating and actual draw often determines whether a smaller, lighter, less expensive power station will work for your needs.

4. Window AC: One Number Hides a Nearly 2x Surge Difference

Generic charts list “Window AC (8,000 BTU)” as a single entry, typically around 1,200W. This hides the single most important variable: whether the unit has an inverter compressor or a traditional single-speed on/off compressor.

Same BTU rating. Similar running watts. But the Frigidaire surges to nearly twice the Midea’s peak draw at startup. A power station that handles the Midea comfortably will trip on the Frigidaire every time the compressor kicks in.

Inverter units use an electronic drive to ramp the compressor gradually — no hard inrush spike, no locked-rotor event. The surge is essentially a brief ramp-up to operating speed, typically 1.5x running watts.

Non-inverter single-speed units use a traditional compressor motor that draws high LRA (Locked Rotor Amps) on every startup. The motor is stationary, the windings act as a near-short-circuit for a fraction of a second, and the resulting surge can reach 3x running watts or more. In an 8-hour cooling session, that means dozens of separate surge events.

A wattage chart with one number for “8,000 BTU window AC” gives you no information about which technology your unit uses. For non-inverter units, a soft-start device can reduce the inrush to approximately 45% of the raw LRA — but you need to know the surge exists before you can address it. Our Window AC on Power Station guide covers the inverter vs. standard distinction in detail.

Why “Dangerous” Is Not an Exaggeration

When a power station’s inverter trips on a startup surge, the station shuts down to protect itself. That is the safe failure mode. The dangerous scenarios are subtler.

Voltage sag (brownout). When a generator or power station is overloaded but does not fully trip, it may deliver reduced voltage — for example, 95V instead of 120V. A motor receiving low voltage draws more current to compensate, which generates excess heat in the windings. Run a refrigerator compressor on sustained brownout power and you can permanently damage the motor. The generator did not trip. No alarm sounded. The compressor just quietly overheated and burned out. Replacing a compressor costs $500 to $1,500. Replacing the food inside costs more.

Medical device continuity. An oxygen concentrator or CPAP machine that loses power during the night because a surge tripped the power station creates a medical emergency. Charts that list CPAP machines at “400-600W” when actual draw is 40 to 56 watts lead to oversized purchases — but the reverse error (undersizing surge capacity for a device that shares a circuit with a cycling compressor) can cause nuisance trips that interrupt life-critical equipment.

Sump pump failure during flooding. A generic chart might list a 1/2 HP sump pump at 800 to 1,300 watts. The Zoeller M98 — one of the most widely installed residential sump pumps in the US — draws 1,081W running and surges to approximately 3,358W at every startup. A power station sized for “1,300W” based on a chart will fail on the first pump cycle. Your basement floods. Damage costs $10,000 to $50,000. The sump pump battery backup guide covers this scenario in depth.

Overheated extension cords. An undersized cord feeding a device that draws more than the chart suggested can overheat at the connection points. This is especially common with compressors and space heaters on lightweight indoor extension cords. The wattage chart said 1,200W. The actual draw is 1,800W. The 16-gauge cord rated for 1,300W gets warm. The connections fatigue over repeated overload cycles. This is a fire risk.

What to Do Instead: A 5-Step Checklist

Step 1: Check voltage

Is your device 120V or 240V? Look at the nameplate. If it says 240V (common for central AC, well pumps, clothes dryers, water heaters), most portable power stations cannot power it. This is a hard gate — no amount of wattage fixes a voltage mismatch. See our 120V vs 240V guide.

Step 2: Find running watts

Look for watts on the nameplate or OEM spec sheet. If only amps are listed, multiply by voltage: 120V × amps = running watts. Do not use the circuit requirement (breaker size) — look for rated amps or FLA (Full Load Amps).

Step 3: Estimate surge

If LRA (Locked Rotor Amps) is published on the nameplate, multiply by voltage for surge watts. If not, use a multiplier based on device type:

• Resistive loads (heaters, kettles): 1.0x (no surge)
• Electronic loads (laptops, TVs): 1.0 to 1.3x
• Motor loads (drills, fans): 3x typical, verify with OEM data
• Compressors (fridges, ACs, air compressors): 3x minimum, often 5x+ for tank-based

Our LRA to Surge Watts Calculator handles this math with built-in safety buffers.

Step 4: Add a safety buffer

Add 10 to 25% depending on load type. Resistive loads need minimal buffer (10%). Motor and compressor loads need more (15 to 25%) to account for voltage sag, cold starts, aging motors, and extension cord losses.

Step 5: Compare to your power station’s specs

Your power station must meet both requirements: continuous output must exceed buffered running watts, and peak/surge rating must exceed buffered surge watts. If either fails, the pairing will not work reliably. Our compatibility calculator checks both gates automatically for 33 power stations against 49 devices.

Recommended Reading

The How to Size a Portable Power Station guide walks through the complete sizing framework, including the 0.70 derate factor for real-world battery runtime.

The Surge Watts Explained guide covers the physics of motor startup and why surge capacity matters more than running watts.

Our compatibility calculator lets you check any power station and device pairing with model-specific data — not generic chart averages.

And the LRA to Surge Watts Calculator converts nameplate LRA into surge watts with adjustable safety buffers.