Soft Starter Inrush & Inverter Sizer
Calculate inrush reduction for rooftop air conditioning compressors with an electronic soft starter (Micro-Air, SoftStartRV). Verify inverter surge headroom and battery DC discharge amps.
Enter the values above and click Calculate to view recommendations and engineering specifications.
How Electronic Soft Starters Enable Battery-Powered A/C
Calculation Assumptions
- Microcontroller soft-starters (e.g. Micro-Air EasyStart) ramp motor winding current, cutting peak inrush by 65%–70%.
- Maintains compressor starting torque while eliminating peak locked-rotor spike.
Engineering Limitations
- Requires 3 to 5 learning starts on utility shore power to map the motor starting curve.
A 13,500 BTU compressor with 50A LRA (6,000W surge) is reduced by an active soft starter to ~16A surge (1,920W), allowing a 2000W pure sine wave inverter to start the air conditioner on battery.
Standard RV air conditioners use single-phase permanent split capacitor (PSC) or capacitor-start induction-run (CSIR) compressor motors. Without modification, the raw starting current spike causes inverter voltage sag and triggers instant overload shutdowns.
- Dual-Ramp Microprocessor Control: A quality soft starter (such as a Micro-Air EasyStart 364 or SoftStartRV) uses a microprocessor to learn the compressor's specific mechanical characteristics over 4 to 5 learning cycles. It then injects power precisely across the AC sine wave, providing smooth rotational acceleration rather than an abrupt mechanical slam.
- Battery Bank Requirements: While a soft starter solves the momentary starting spike, running an air conditioner continuously on batteries requires substantial energy. A 1,500W load draws approximately 135A to 145A DC continuously from a 12V lithium bank. Ensure your battery BMS continuous discharge rating can support this load.
Frequently Asked Questions
What does an RV AC soft starter do?
An RV AC soft starter (such as Micro-Air EasyStart) is a microprocessor-controlled device that ramps up voltage to the air conditioner compressor over 100-300 milliseconds using advanced current-limiting algorithms. This slashes peak starting Locked Rotor Amps (LRA) by 65% to 75% without reducing cooling capacity.
Can I run a 15,000 BTU RV air conditioner on a 2000W generator or inverter?
Without a soft starter, a 15k BTU rooftop AC has a starting surge of 50A to 60A (exceeding 6,000W), instantly stalling a 2000W generator or tripping an inverter on overload. With a soft starter installed, starting inrush drops to approximately 16A to 18A, allowing smooth operation on a small 2000W-2200W inverter generator (Honda EU2200i) or a 2000W lithium-backed inverter.
What is the difference between a hard start capacitor and an electronic soft starter?
A hard start kit is simply a large start capacitor and potential relay that increases starting torque and shortens startup duration, but actually INCREASES peak starting inrush current. A true electronic soft starter actively controls motor winding current to SLOWLY accelerate the rotor, slashing peak surge amperage.
Does a soft starter damage the air conditioner compressor?
No. In fact, soft starters significantly extend compressor mechanical life by eliminating violent mechanical torque shock, reducing thermal stress on motor windings, and preventing line voltage collapse during startup.