Precision Backup Power, LiFePO4 Battery & Generator Sizing Engine
Naive watt calculators divide battery Watt-hours by running watts and strand homeowners in the dark. WattGrid Lab models Locked Rotor Amp (LRA) inductive motor surges, realistic compressor duty cycles, 85% inverter × 90% LiFePO4 depth-of-discharge losses, 120V/240V NEMA plug matching, and sub-freezing derating.
Interactive Load, Duty-Cycle & Runtime Simulator
Physics & Environment Parameters
Models all active items running while your heaviest motor kicks on: sum(runningWatts) + max(individualSurgeDelta).
Rec. Inverter: 1,462W (+20% NEC)
Draws ~10.2A @ 120V • Highest Plug: NEMA 5-15P
Spike Leader: 1/2 HP Submersible Sump Pump
+1,750W inductive LRA spike (staggered)
340 Wh/hr × 12h = 4,080 Wh net
Formula: 4,080 / (0.85 inv × 0.90 DoD)
Protects 1/2 HP Submersible Sump Pump from waveform damage.
Best Matched LiFePO4 Power Station
Zero fumes, <20ms UPS auto-switchover, safe for bedrooms, apartments & basements.
Bluetti Elite 200 V2
Ultra-Long 6,000-Cycle Home Fridge, Sump & Window AC
Runs your exact load for ~4.7 hrs — Expandable with solar/extra battery
Covers ~4.7h per charge; add solar panels or ~2 expansion pack(s) for full 12h autonomy.
- Automotive-grade prismatic LFP cells rated for 6,000+ cycles
- 2,600W continuous / 3,900W surge handles 3/4 HP pumps & 15A saws
EcoFlow DELTA 3 Plus
1/2 HP Sump Pumps, Kitchen Fridges & 2-Night CPAP
Runs your exact load for ~2.3 hrs — Expandable with solar/extra battery
Covers ~2.3h per charge; add solar panels or ~5 expansion pack(s) for full 12h autonomy.
- 3,600W pure sine surge easily clears 1/2 HP sump pump LRA
- Whisper-quiet 30 dB under 600W load + <10ms UPS switchover
Best Matched Dual-Fuel Inverter Generator
Unlimited runtime via stored propane or gasoline (operate 20+ ft outdoors only).
Champion 4500W Electric-Start Dual-Fuel Inverter
30A RV Rooftop AC, Mobile Detailing Vans & Jobsite Compressors
Est. 12h Fuel Burn: ~1.4 gal gas OR ~7.3 lbs propane (~0.4 × 20-lb BBQ tanks)
Modeled at ~10% average throttle (~0.12 gal/hr) based on your 340 Wh/hr duty-adjusted load.
- 4,500W starting surge handles factory 13,500 BTU RV ACs & 6-gal compressors
- Built-in NEMA TT-30R 30A RV outlet + push-button electric start
Westinghouse iGen4500df Remote-Start Dual-Fuel Inverter
Ultra-Quiet 52 dB RV Boondocking, Detailing & Heavy 120V Home Loads
Est. 12h Fuel Burn: ~1.6 gal gas OR ~8.3 lbs propane (~0.5 × 20-lb BBQ tanks)
Modeled at ~9% average throttle (~0.14 gal/hr) based on your 340 Wh/hr duty-adjusted load.
- Wireless key-fob remote start + electric choke for effortless winter cranking
- Oversized 3.4-gallon tank delivers up to 18 hours between refuels
Essential Hookup & Protection Kit (Auto-Matched to Your Load)
AC Compressor & Well Motor Soft-Start Capacitor Kit
Cuts your 1/2 HP Submersible Sump Pump startup spike (2,968W) by up to 65% so smaller inverters won't trip.
10-Gauge SJTW Heavy-Duty Lighted Generator Cord (25 ft)
Required for your 1,218W continuous / 2,968W surge stack to stop voltage sag on startup.
Heavy-Duty Storm-Proof Outdoor Generator Running Cover
Keeps outdoor dual-fuel generators running safely 20+ ft away from your house in driving storm rain or blizzard snow.
12 High-Intent Outage & Mobile Work-Rig Scenarios
Click any rig to open its pre-calibrated multi-appliance telemetry
Storm Basement Flood Defense + Kitchen Fridge
Pairs a high-surge 1/2 HP cast-iron submersible sump pump with a standard 18 cu. ft. kitchen refrigerator and emergency LED lighting to prevent flooded basements and food spoilage during 12-hour severe thunderstorm blackouts.
Winter Outage: Gas Furnace Heat + Fridge + Wi-Fi
Keeps central natural gas heat circulating through every room while preserving kitchen refrigeration, chest freezer storage, and fiber internet—taking advantage of freezing-weather battery derating math and neutral-ground bonding alerts.
Silent 2-Night CPAP + Humidifier Bedroom Backup
Models two full 8-hour nights (16 hours active runtime) for a CPAP running full heated humidification and ClimateLine heated tubing, plus a refrigerated biologic/insulin cooler beside the bed.
Mobile Detailing Van: Extractor, Vacuum, Pressure Washer & Polisher
High-amperage commercial mobile rig stack featuring a heated upholstery extractor, 15A wet/dry vacuum, 1800 PSI electric pressure washer, and dual-action polisher—demonstrating why staggered tool operation saves thousands in generator weight.
Rural 240V Well Pump + Chest Freezer + Lights
Solves the split-phase 240V challenge: powers a 1 HP deep-well submersible pump (5,200W LRA startup spike) alongside a 7 cu. ft. chest freezer and whole-floor LED lighting via NEMA L14-30P transfer switch.
30-Amp RV Boondocking with 13,500 BTU AC
Simulates a 30A travel trailer running a soft-start 13,500 BTU rooftop air conditioner, short microwave reheating bursts, and Starlink satellite internet without tripping shore-power breakers.
48-Hour Remote Work: Starlink + Laptop + Monitors
Sustains two full workdays of satellite broadband, 100W USB-C PD laptop charging, and local RAID NAS file access with <20ms pure sine wave EPS blackouts protection.
72-Hour Deep Freezer Meat & Food Protection
Protects thousands of dollars in frozen game and bulk groceries across both a 7 cu. ft. garage chest freezer and a 14 cu. ft. upright freezer over a 3-day storm recovery window.
Off-Grid Jobsite Air Compressor + Saw Rig
Combines a 6-gallon twin-stack air compressor, 12-inch sliding compound miter saw, and dual-port 20V rapid charger for full-shift off-grid trim and framing production.
No-Fumes Apartment Outage: Fridge + CPAP + Router
100% indoor-safe LiFePO4 sizing for apartment dwellers who cannot run fuel generators on balconies—covering a French door refrigerator, overnight CPAP, Fiber Wi-Fi 6E, and laptop charging.
Summer Heat Outage: 8,000 BTU Window AC + Refrigerator
Keeps one sleeping room cool and dry with an 8,000 BTU window air conditioner while maintaining a full-size kitchen refrigerator and emergency lighting overnight.
Home Security NVR + Garage Access Backup
Ensures continuous 24-hour recording on a 6-camera PoE NVR security rack, Fiber mesh internet alerts, and full 1/2 HP smart garage door opener breakaway surge support.
Browse Sizing Calculators by Electrical Category
High-LRA submersible pumps, 240V deep wells, and furnace blower electronics
- 1/3 HP Submersible Sump Pump800W / 2100W
- 1/2 HP Submersible Sump Pump1050W / 2800W
- 3/4 HP Cast-Iron Sump Pump1350W / 3600W
- 1/2 HP Sewage Ejector Pump1150W / 3200W
Compressor duty-cycle modeling for food preservation and emergency cooking
- Energy Star 18 cu. ft. Top-Freezer Fridge140W / 850W
- 26 cu. ft. French Door Refrigerator220W / 1200W
- 7 cu. ft. Chest Freezer110W / 750W
- 14 cu. ft. Upright Deep Freezer190W / 1050W
Zero-transfer-time silent indoor LiFePO4 sizing for CPAP, BiPAP & oxygen
- CPAP Machine (No Heated Humidifier)35W / 60W
- CPAP with Heated Humidifier & Heated Tube85W / 120W
- BiPAP / VPAP Machine105W / 150W
- 5 LPM Home Oxygen Concentrator360W / 750W
Universal brush motors, air compressors, detailing extractors & jobsite saws
- 15A Wet/Dry Shop Vacuum (6.5 Peak HP)1440W / 2900W
- Heated Carpet / Auto Upholstery Extractor1750W / 2600W
- 1800 PSI Electric Pressure Washer1550W / 3100W
- Dual-Action Car Polisher (15mm / 21mm)900W / 1350W
TT-30Pshore-power limits, rooftop AC soft-starts, mini-splits & space heaters
- 8,000 BTU Window Air Conditioner720W / 2100W
- 12,000 BTU Inverter Mini-Split Heat Pump950W / 1150W
- 13,500 BTU RV Rooftop AC (Standard)1450W / 3400W
- 13,500 BTU RV Rooftop AC (With Soft-Start)1420W / 1950W
Starlink snow-melt draw, Fiber ONT/Wi-Fi 6E uptime, workstations & PoE NVR
High-Priority Backup Appliance Wattage & Surge Preview
| Appliance | Running Watts | LRA Surge Watts | Duty Cycle | 8-Hr LiFePO4 Wh |
|---|---|---|---|---|
| 1/3 HP Submersible Sump Pump | 800W | 2,100W | 20% | 1,674 Wh |
| 1/2 HP Submersible Sump Pump | 1,050W | 2,800W | 25% | 2,746 Wh |
| 3/4 HP Cast-Iron Sump Pump | 1,350W | 3,600W | 25% | 3,530 Wh |
| 1/2 HP Sewage Ejector Pump | 1,150W | 3,200W | 15% | 1,804 Wh |
| 1/2 HP Deep Well Jet Pump (240V) | 1,100W | 2,900W | 20% | 2,301 Wh |
| 1 HP Submersible Well Pump (240V) | 1,900W | 5,200W | 15% | 2,981 Wh |
| Natural Gas Furnace Blower (1/2 HP PSC) | 650W | 1,600W | 45% | 3,059 Wh |
| Natural Gas Furnace (Variable-Speed ECM) | 420W | 650W | 55% | 2,416 Wh |
| Oil Boiler Burner & Hydronic Circulator | 480W | 1,150W | 45% | 2,259 Wh |
| Tankless Gas Water Heater (Igniter & Fan) | 140W | 260W | 25% | 367 Wh |
| 1/4 HP Garage Sump / Utility Transfer Pump | 460W | 1,200W | 50% | 2,406 Wh |
| Wood Pellet Stove (Igniter, Auger & Fan) | 450W | 550W | 45% | 2,118 Wh |
How WattGrid Lab Computes Surge & Battery Derating
Inspect our full electrical engineering equations—covering NEC Article 210 continuous load buffers, Locked Rotor Amp (LRA) inrush physics, 85% inverter conversion losses, and 90% LiFePO4 BMS depth-of-discharge.