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emergency power: Your car can be an effective generator - Printable Version

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emergency power: Your car can be an effective generator - Rob Tucker - 08-18-2026

I've been pondering 10's of thousands of local folks without power and not enough generators to go around.  Plus the fact that we have thousands of cars which are each more powerful than any Home Depot generator.

So I put it to Chatgpt.

Advise on adding a 110v inverter to a typical automobile sufficient to power a refrigerator and battery chargers. Cost and practical applicability.

Yes. Adding a 120V (nominally 110V) inverter to an ordinary automobile is quite practical for running a refrigerator and battery chargers, but I would design it somewhat differently from the typical inexpensive “plug into the cigarette lighter” inverter.
My recommended configuration
For what you describe, I would use:
Component
RecommendationInverter
1,500–2,000 W pure sine wave
Surge capability
3,000–4,000 W preferred
Input
12 V DC
Connection
Directly to battery with heavy cables, not cigarette lighter
Refrigerator
Normal household refrigerator
Battery chargers
Phones, laptops, power-tool batteries, etc.
Engine
Running while substantial loads are connected
Auxiliary battery
Optional, but worthwhile if refrigerator must operate with engine off
Approx. installed cost
$400–$900, depending on quality and auxiliary battery
The important point is not the refrigerator's running wattage—it is the compressor starting surge. A refrigerator that consumes only 100–250 W while running can momentarily require considerably more power when its compressor starts. Eaton specifically recommends accounting for refrigerator startup surge when sizing an inverter.
I would therefore not build the system around a 500–1,000 W bargain inverter, even though some refrigerators will work with one.
Why 1,500–2,000 W?
A typical refrigerator might look approximately like this:
  • Running: 100–250 W
  • Compressor startup: potentially 500–1,500+ W
  • Battery chargers: 50–300 W combined
  • Miscellaneous electronics: 50–100 W
A 1,500 W pure-sine inverter with substantial surge capability gives you a comfortable margin.
A 1,000 W inverter can work—there are 1,000 W units specifically marketed for refrigerators—but there is much less margin for an older refrigerator or simultaneous loads.
I particularly recommend pure sine wave, rather than modified sine wave. Modern refrigerator compressors and electronic chargers are much better suited to clean sine-wave power.
The bigger issue is the car's 12V electrical system
This is where the project becomes interesting.
At 1,000 W, a 12V inverter can draw roughly:
1,000 ÷ 12 ÷ 0.9 ≈ 93 amps
At 1,500 W:
≈ 139 amps
At 2,000 W:
≈ 185 amps
Those are substantial currents.
So I would not connect a 1,500–2,000 W inverter to the vehicle's 12V accessory outlet. The inverter should have its own appropriately sized cables and fuse connected directly to the battery. Eaton likewise recommends a direct battery connection rather than relying on a cigarette-lighter connection for higher-power applications.
The alternator is effectively your generator
With the engine running, the alternator supplies most of the energy while the battery acts as the electrical buffer.
That's why this arrangement works particularly well while driving.
For example, suppose the refrigerator averages 150 W and chargers consume another 150 W.
That's only about 300 W AC.
Allowing for inverter losses, the vehicle might be supplying roughly:
330–350 W DC
At 13.5 V that's approximately:
25 amps
That's quite manageable for many conventional vehicles.
The situation changes if you actually try to continuously draw 1,500–2,000 W. Then you're asking the vehicle electrical system for roughly 110–150+ amps continuously. That's a completely different proposition. An inverter should therefore be sized for starting/surge capacity, not because you intend to continuously consume 2,000 W.
I would actually build it this way
Option A — simplest and cheapest
Existing automobile battery + alternator


            ENGINE
                │
            ALTERNATOR
                │
                ▼
        ┌─────────────┐
        │ 12V BATTERY │
        └──────┬──────┘
                │
          heavy DC cable
                │
          fuse/breaker
                │
                ▼
      ┌─────────────────┐
      │ 1,500–2,000 W  │
      │ PURE SINE INVERTER│
      └────────┬────────┘
                │
            120 VAC
          ┌─────┴──────┐
          ▼            ▼
    Refrigerator  Battery
                    Chargers

Approximate cost:
  • Quality 1,500–2,000 W pure sine inverter: $250–$500
  • Heavy cable/fuse/disconnect: $75–$150
  • Installation: $100–$250
  • Total: approximately $425–$900
This is probably the best solution if the vehicle is primarily being used while traveling.
Option B — better system: auxiliary battery
If the purpose is emergency power, rather than merely powering things while driving, I'd add a second battery.
Something like:
Starting battery → isolator/DC-DC charger → auxiliary lithium battery → inverter
The refrigerator can then continue operating after the engine is turned off without risking the vehicle's starting battery.
A 100-Ah LiFePO₄ auxiliary battery contains approximately:
1.28 kWh nominal energy
Realistically, after inverter losses, you might have roughly 1.0–1.1 kWh of usable AC energy.
A refrigerator averaging 100 W could theoretically operate for around:
10 hours
although actual refrigerator consumption varies considerably with ambient temperature, door openings, compressor efficiency, etc.
This approach is considerably more useful for emergency preparedness.
An even better concept for a vehicle emergency system
If this is intended as a portable emergency-power system, I would consider putting the inverter and auxiliary battery into a small enclosure rather than permanently mounting everything into the automobile.
For example:
Vehicle alternator → DC-DC charger → 100–200 Ah LiFePO₄ battery → 2,000 W pure sine inverter
Then you have a portable power source that can:
  • run a refrigerator
  • charge cordless tools
  • charge phones
  • charge laptops
  • power lights
  • run small pumps
  • power medical/electronic equipment
  • recharge from the automobile while driving
That becomes substantially more capable than simply installing a wall outlet in the car.
One important distinction
There are really two different applications:
1. "I want 120V power while I'm driving."
Excellent application.
A 1,500–2,000 W inverter connected to the vehicle battery is quite practical.
You could run:
  • refrigerator
  • chargers
  • computers
  • TVs
  • small electronics
  • modest power tools


RE: emergency power: Your car can be an effective generator - punikahakaiferret - 08-18-2026

This is *insanely* detailed info but *SO USEFUL*! Mahalo nui loa, Rob!

Can't say much for anyone around here who never thought *they* would be affected...several people I just talked to (some in my own 'hood and others farther away) who "went looking for a generator to buy today" HAHAHAHAHAHAHA. Nope. My give a damn is busted.

Fail to plan is plan to fail. And fail...many are.

Sadly, one of those looking for a generator today bought on-grid in Ainaloa. ON CATCHMENT. And now is freaking out because they can't find a generator to buy to have water. Ummmmm.....?

My facepalm emoji is strong with these people.

RE: emergency power: Your car can be an effective generator - kalakoa - 08-18-2026

I forget the make/model but there are "two in one" batteries for this application -- they're designed to let the main lead/acid battery run flat, with a small lipo held in reserve so you can start the car again.

RE: emergency power: Your car can be an effective generator - randomq - 08-18-2026

Just a caution, as I have such a setup as a backup: Some cars will accelerate in idle to keep up with an inverter load, and some will not. My older vehicle could keep up with a 720w battery charger, but on my newer SUV it begins to drain the battery down below 12V, even with the alternator running! Keep an eye on the voltage and ensure it stays above 12.6 while running or you may kill your vehicle battery.

Powering a single fridge and charging phones may be more feasible, depending on the fridge!

RE: emergency power: Your car can be an effective generator - ironyak - 08-18-2026

Yeah, I was wondering if ChatGPT took into account issues like alternator outputting very low amps when idling / overall limiting the amps being sent to the battery, alternator max amps and damage considerations, the time it would take driving around / generating high enough RPMs to recharge that extra battery, etc... Lots of real world details to work through.

A handful of decades ago, we had a setup like this for road trips in the Datsun pickup truck, with a 12v chest cooler, and a spare marine battery on a charging harness. While driving, the 12v chest cooler was powered by the car and the spare battery was charging. When you get to the next campground, we'd swap the cooler to the battery, which would keep things cold overnight. Worked great until you wanted to spend more than a day or two at a particular state or national park, because without driving the spare battery would not get recharged (need those high RPMs for the alternator to put out enough amps).

Sources like r/vanlife has lots of these sorts of discussions, like this one for those who want to better understand these types of setups. While you can just put an 12v inverter on your car battery to run your house appliances, there may be larger and longer-term consequences to consider.

RE: emergency power: Your car can be an effective generator - HereOnThePrimalEdge - 08-18-2026

I’ve been running fans off my EV car’s 120 volt plugin. It uses very little power.  I checked to see if it could handle a fridge - - yes it can.  Uses about 3% of the battery per day, so can run a fridge for weeks.  Best to use a heavy duty extension cord, I have a few 10 gauge 15 amp cords for this type of use.

RE: emergency power: Your car can be an effective generator - BlackAkita - 08-18-2026

I've been leaning toward a lithium energy storage solution, as reviewed in Project Farm's video:

https://www.youtube.com/watch?v=qtFOSmIXvwg

In 2026, this is a viable off-grid solution. Battery Bill is a local equipment dealer in Honolulu and Hilo.

https://www.facebook.com/batterybills/


This is an alternative to gas-powered generators by Honda or Yamaha. I could not reconcile the idea of having a generator running during a rainstorm with horizontal rain slamming the underside and vent louvers of the power source. Especially overnight.

I do not recommend inverters attached to car batteries. When I moved to Hawaii from NY I had a Tripplite inverter I kept around for mainland hurricanes like Gloria. Keeping the front hood of a Jeep up during a raging storm is not advised. Even 12v outlets in the back of a SUV do not deal with the problem of running wires (AC or DC) out of the back of an auto.
(08-18-2026, 05:31 PM)HereOnThePrimalEdge Wrote: I’ve been running fans off my EV car’s 120 volt plugin. It uses very little power.  I checked to see if it could handle a fridge - - yes it can.

That sounds like a novel solution. What EV brand?

RE: emergency power: Your car can be an effective generator - HereOnThePrimalEdge - 08-19-2026

What EV brand?

I have a Kia. Here’s a list.

https://insideevs.com/features/769422/evs-with-ac-outlets-v2l-vehicle-to-load/