My Car, the Generator
May 29, 2019 6:05 AM   Subscribe

Can I use my car during a hurricane to power a small window A/C unit?

I'm looking at buying this A/C unit and this inverter.

In the event of a bad hurricane, I'd like to be able to leave my car on for a couple of nights and power the A/C unit using the inverter.

Would this work?
posted by uncannyslacks to Science & Nature (21 answers total)
That air conditioner manual says it needs 15A 120V, over 1000W. You would be running the car's alternator at it's brief peak limit for days at a time. That seems likely to cause problems to the car very quickly.

Gas generators are designed for a longer active cycle and heavy current draw over a long period of time.
posted by nickggully at 6:18 AM on May 29, 2019 [2 favorites]

Almost definitely not. The power draw of this A/C is probably around 500 watts. A cigarette lighter is 20A, or 240 watts at 12V. You will just blow fuse after fuse. (Or, y'know, somebody who knows more about this stuff can come in and prove me wrong. I'm just a person who has tried to run lots of stuff off cigarette lighters.)
posted by nosila at 6:18 AM on May 29, 2019 [4 favorites]

It might work if the inverter is sufficiently large. The startup draw of the AC will spike high and then drop (see this thread). You'd have to stay clear of any adapters and connect the inverter directly to the battery. Even then you'd want to have a fuse on that connection and make sure the wires are heavy-gauge. Seconding the idea of a properly-sized portable generator if you can. The consequences of getting it wrong are a fire.
posted by jquinby at 6:23 AM on May 29, 2019

People have done this with some success on hybrids (see Prius or Volt), but it would not be recommended on a non-hybrid. Hybrids have a big battery that can supply full power at all times; conventional cars do not and power from the alternator is dependent on engine RPM. Generally idle is low enough that even if you hooked straight to the battery you would be running at a net loss and the 12V battery won't last long in that service.

The computer may be able to raise idle if voltage drops enough but do you really want to find out the hard way in a power outage?
posted by doomsey at 6:32 AM on May 29, 2019 [2 favorites]

Definitely not an expert here, but another way of thinking here: RVs, with their built in AC units, all require electrical hookups, a generator, or special large lithium batteries to run their ACs. Some newer RVs have under-the-hood generators that are effectively second alternators to recharge batteries, but this is not what you have. Knowing what I know about the RV space, I cannot see this working (but I'm not even close to an expert - if you are and I've butchered anything, please correct!)

Most people have generators for this use case for a reason. I wouldn't try and re-invent the wheel, never mind risk your car, when dealing with weather related emergencies.
posted by cgg at 6:35 AM on May 29, 2019 [3 favorites]

The Mitsubishi Outlander hybrid has AC outlets than can support up to 1500 watts, but it probably isn’t the best option.
posted by rockindata at 6:38 AM on May 29, 2019

Echoing doomsey -- at idle, a standard combustion vehicle is not going to be pumping out a kilowatt of extra electrical energy for you to siphon off. Get a good 4-stroke 1600W generator and keep it in repair for your hurricane power needs. Buy before the season starts (ideally) or at least before the TS watches go up.
posted by seanmpuckett at 6:38 AM on May 29, 2019 [1 favorite]

While generators can get stupid expensive, you can buy them for $300/400 thru Amazon or Costco if you plan in advance and aren't buying when the storm is bearing down. Also, keeping your fridge running and lights on will be probably be higher priority than AC.
posted by gnutron at 6:42 AM on May 29, 2019 [3 favorites]

Also, be sure you get a big enough one so that the startup surge won’t trip off the generator. We tried running a refrigerator off a small gas generator and while it could keep the fridge running, every time it started up it killed the generator. An AC unit probably has this feature in spades.

I’d treat this like doing computer backups: until it’s tested, it’s not a backup. So, try it for three days (or whatever your use case is) to make sure you won’t be disappointed.
posted by Gilgamesh's Chauffeur at 6:47 AM on May 29, 2019 [1 favorite]

SOME cars (well, trucks) can be safely used this way; my friend Danny used his Tahoe to power his home fridge after Harvey, for example. But a Tahoe has lots more oomph than most cars.

The right play for most folks is to buy a generator.
posted by uberchet at 7:16 AM on May 29, 2019

*** Run the generator OUTSIDE ***

Sorry to 'scream derail' but very very important. A small generator will cost vastly less than the harm to a car for that use case and there are solutions for the AC startup current spike but just wanted to add this for someone in the future.
posted by sammyo at 7:17 AM on May 29, 2019 [3 favorites]

you can buy [generators] for $300/400 thru Amazon or Costco

$200/300, with the offset for not buying the $100 inverter.
posted by Pig Tail Orchestra at 7:18 AM on May 29, 2019 [1 favorite]

SOME cars (well, trucks) can be safely used this way; my friend Danny used his Tahoe to power his home fridge after Harvey, for example. But a Tahoe has lots more oomph than most cars.

First off, keeping a fridge cold takes a lot less power than running an a/c unit.
Second, while the motor is much bigger, the alternator on a Tahoe isn't really all that much more powerful (150A at 12ish volts) than the rinky-dink one in my Del Sol (90 amp).

Back to the original question, it is possible to do this, but very inefficient. You would have to run your engine at 2500-3000 RPM for days on end, which would both use tons of gas and probably roast your engine due to no-load revving. Pretty much you'd have to *be* *in* the car the whole time, so you wouldn't be enjoying the meager a/c in the house, anyway!
posted by notsnot at 7:47 AM on May 29, 2019 [1 favorite]

A cigarette lighter is 20A, or 240 watts at 12V. You will just blow fuse after fuse.

Not just that. You'll be generating a lot of heat pulling that type of power through wiring that may not be designed for sustained high loads, possibly destroying the wire and/or starting a fire which you really don't want to be doing at night, in an area with limited emergency response, in the thing you might need to drive you out of there.

my friend Danny used his Tahoe to power his home fridge after Harvey

A fridge requires a lot less power than even a small air conditioner.

If you buy a generator, I recommend going for one that is propane based or dual source (gas and propane). It's a lot easier to deal with hooking up a propane tank than pouring in gas if you don't do it often and propane tanks are shelf stable unlike gas.

And yes, run it at least 15 (preferably at least 25) feet from any dwelling.
posted by Candleman at 7:57 AM on May 29, 2019 [1 favorite]

This is not really the way to go for a number of reasons. That specific combo is right at the edge of (or slightly below) specs which means it will probably not be able to supply the load at startup and the inverter will keep shutting down, or you will likely blow fuses. Even if you find the right combo of inverter and AC, your car is not designed to do this overnight. Also, it will burn a lot of gas. Having lived through a few major hurricanes, one of the immediate results is a gas shortage and possibly rationing, even if your area was not particularly hit. We were not directly hit by Hurricane Katrina, but it crippled our gasoline supply for several weeks. Even if gas supply was not an issue, your engine could be damaged by idling several nights in a row.
Also, unless you have a medical need for AC, your focus is probably better spent on preserving food.
Our hurricane aftermath prep is two generators. One is 7kw and will run pretty much anything in the house except the AC. Specifically for us, the washer, dryer and fridge during the day. For us this is important because we tend to have a lot of wet clothes and towels after a hurricane, but of course we ration it's use and try to run things concurrently when we do use it. For night time we have a cheap Sportsman inverter generator around 1000w to run box fans and lights with a network of extension chords. This uses a tiny amount of gas and is super quiet. A regular generator can be very loud at night. One like this would probably run your window unit more efficiently without damaging your car, but would recommend one with a higher wattage. It was around $150, so similar to your inverter.
Target has an 1800 W generator for a little over $200 (not inverter though.)
On preview, I agree with Candlemas that a dual fuel, or triple fuel generator if you have natural gas, is better. But it adds a little to the cost and they are usually only available for units starting around 3500W. It is easier to stockpile propane before a storm than gasoline.
posted by Short End Of A Wishbone at 8:05 AM on May 29, 2019 [2 favorites]

Also, if you must use your car for a generator, the keeping distance from the dwelling still applies. The car will be sitting there pumping out carbon monoxide. Regardless of whether you're using a car or a generator, a battery powered carbon monoxide detector in the house is advisable.
posted by Candleman at 8:18 AM on May 29, 2019 [1 favorite]

If you are going to power your AC, or other applications in your house, using your car then think about fuel. Here in Houston after Hurricane Ike, with power out for days for almost everyone, and then weeks for some, the gas stations were zoos. If the stations did not have electricity then no fuel was pumped. If they did not get deliveries from the refineries because of damage there or to the trucks, then fuel was not pumped. If word got out that the station was open and pumping, then the lines were blocks long, and needed police to keep things orderly.

So, when hurricane season arrives you should always have your cars at least half full. When a storm is 500 miles away, and might be targeting your part of the country, get your cars full no matter the hassle or expense. Premium gas might be your only option.

Finally, consider a fan rather than an AC unit. This will reduce the misery of summer without cooling, and will have a lower drain on your fuel.

Of course, the ultimate generator fuel option is natural gas. This will run you thousands of dollars, and is probably not a DIY task.
posted by Midnight Skulker at 8:36 AM on May 29, 2019

If I were going to give this a shot, I'd have the car power a fan in an improvised swamp cooler- much less power draw, and you're likely to have town water available in that circumstance.
posted by jenkinsEar at 9:41 AM on May 29, 2019 [1 favorite]

Electric motors can have a momentary startup draw of 5x the running current draw. Your AC is at heart a big motor running a pump(compressor) and a smaller motor running a fan. You may need 3500 to 5000 watts of generating or inverter power to handle the startup of just one AC rated for 10 amps (1200 watts) current draw.
posted by sol at 9:50 AM on May 29, 2019 [2 favorites]

Swamp coolers don't work in hurricane-prone regions, as a general rule, and especially not after a hurricane, when the ground is saturated with water and humidity is around 100% for days.
posted by seanmpuckett at 12:40 PM on May 29, 2019 [2 favorites]

Running the car at higher-than-idle-speed for extended periods is not an issue, always providing the cooling system, and especially the radiator fan, is in full working order. Running a big engine like a car engine to generate power through its alternator will be massively inefficient, and probably place more stress on the car's electrical wiring than it was designed for. Basically, not a good idea. Much better to get a properly matched generator-engine, sized for your load requirements.

I would not sweat the CO problem, just take basic precautions like running it in a well ventilated space (detached garage, or under some shelter) and be aware of where the wind might be blowing the exhaust gases - note that generators will be a target for passing thieves, don't make it easy for them.
posted by GeeEmm at 3:18 PM on May 29, 2019

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