What is a soft start and do I need one?
A soft start is a small device on your air conditioner that reduces the electrical surge when your compressor kicks on. It only applies to A/C systems, not heating.
This applies only to 25 kWh and 50 kWh battery systems. Soft starts are not provided for Base Core (our 39.2 kWh battery).
Base Core is sized to handle A/C startup surges on its own, so a soft start typically isn't needed.
If you have Base Core and want the extra buffer anyway, you can add a soft start at your own expense through a local HVAC contractor.
Do I need one?
It depends on your A/C unit's LRA (locked rotor amperage), the surge of current your compressor pulls the instant it starts, before it settles into a steady run. Think of it like a car engine: turning the key takes a bigger jolt than cruising at speed. Your A/C's LRA number is that jolt, measured in amps.
If your A/C's LRA is over 100, you need a soft start on a 25 kWh or 50 kWh system.
Here's why it matters: during an outage, your home switches from grid power to your Base battery. If your A/C compressor tries to restart at the same moment, without a soft start, that startup surge can be more than the battery can handle alongside the rest of your home's load. This can prevent the battery from turning on properly.
Where to find your LRA: it's usually printed on your A/C unit's nameplate (the metal tag on the outdoor condenser). If you can't locate it, Base will check this during your photo review, or our electricians will confirm it on-site during installation.
Note: Your home must be using 11 kW or less for the battery to turn on during an outage. If high-draw devices like electric heaters push usage higher, use the Base App to turn the battery on after reducing usage.
If you need a soft start, Base will let you know during setup, and our licensed HVAC partner will install it at no additional cost to you.
What happens next
Base determines if you need one, after reviewing your photo submission, or sometimes when our electricians are on-site during installation.
You'll get an email from Base once your battery installation is scheduled, letting you know a soft start is needed.
Our licensed HVAC partner will contact you directly by text or phone call to schedule the installation at a time that works for you.
Soft starts are typically installed after your battery system is set up, usually within a few weeks. In some cases, our licensed HVAC partner may be on-site before or during your battery installation instead.
If your soft start isn't installed yet
Your battery and A/C will still function normally day to day. But during an outage, before your soft start is installed, you may need to turn your A/C off to let the battery fully turn on. Your A/C may need to stay off for the rest of the outage until grid power returns.
Once our licensed HVAC partner installs your soft start, your A/C should run normally during outages without any action from you.
Startup delay after installation: some A/C units have a built-in compressor protection delay (often around 5 minutes) before restarting after a power interruption. This is standard behavior from the manufacturer, not an issue with your Base system or the soft start. If your A/C doesn't kick on right away during an outage, give it a few minutes.
Frequently asked questions
Do I have to pay extra for a soft start? No. If your home needs one, our licensed HVAC partner installs it as part of your setup at no additional charge.
Does a soft start change how my A/C runs day to day? No. A soft start only affects the moment your compressor starts up. It doesn't change your A/C's cooling performance or run-time efficiency outside of that startup moment.
What if I already have a soft start installed? Let our licensed HVAC partner know when they reach out. We'll check that your existing soft start is compatible with the Base battery system. If it meets our specifications, no new installation is needed.
What if I have a hard start instead of a soft start? A hard start and a soft start are different devices, and they can't both be installed on the same A/C unit. A hard start boosts the compressor at startup by drawing more power; a soft start reduces the startup surge, which is what the Base battery needs. If your unit has a hard start, our licensed HVAC partner will remove it and install a soft start in its place.
What if I have more than one A/C unit? Each unit is evaluated separately during your photo review or on-site installation. Some homes need a soft start on more than one unit. our licensed HVAC partner handles all installations in one visit, so you don't need to schedule separately for each unit.
Can I install my own soft start instead? Yes, but contact Base support before you do, so we can confirm compatibility and avoid a duplicate installation from our licensed HVAC partner.
What does Base cover if something goes wrong? Base and our licensed HVAC partner are responsible for the soft start device itself and its installation. Your existing A/C system, including the compressor, refrigerant, coils, and capacitors, remains your responsibility to maintain and repair, the same as before Base was involved. Repairs unrelated to the soft start installation are at your expense.
Does a soft start protect my A/C from power surges too? No. A soft start only manages the startup surge from your own compressor. It doesn't protect against outside voltage spikes on the grid, which Base can't control or prevent. If you want that kind of protection, a separate surge protector is a different device you'd need to install on your own.