[–] AnthraxAlex 0 points 7 points (+7|-0) ago  (edited ago)

P = I * V

You need to know the amp limit on the circuit in question.

5 amps at 12 volts works out too 60 watts continuous.

[–] bluefascist 0 points 2 points (+2|-0) ago 

It depends on the power source feeding the outlet, and the wire thickness feeding the outlet.

Usually if it is a car 12v plug it will be on a 15 or 20 amp circuit which may be shared with a few different devices.

try this calculator


120v and 2 amps gives 12v and 22.2 amps. This means that you are quite limited in the inverter. Most inverters give a wattage rating. In this case the 12v 22 amp converts to 240 watts.

If you installed your own circuit with larger diameter wire you could get a circuit that would be easily double that.

[–] 9-11 0 points 2 points (+2|-0) ago  (edited ago)

Your biggest load (from your comment below) is the microwave. Smallest ones are like 700W, but you can get specialty ones that are 500W. This is much too big for your cars cig-port to handle, dont try it. Watts=amp x 12V. You need like 60 amps, and the wires through that port aren't rated for more than 15 amps, maybe 20amps in some trucks, so I wouldn't plug any inverter bigger than 250W into that port without knowing specifics on your vehicle. If the fuse doesn't blow, those speaker wire thin wires will catch fire.

If this is a temporary solution, just use a 200W inverter through that port to power your laptop/phone and find another way to heat your food, like a gas station microwave, or tin foil+engine block, or a camp stove. There might be some food warmer plug in devices that could do the trick, there are plugin cooling devices too.

If you really want a microwave, and its semi permanent, you'll need a big ole inverter. Sizing it is iffy, 800w inverter might do it, might not, some ovens draw more than the rated cooking power. A 1,000W or 2,000W inverter probably would, but those are steadily getting pricier. So lets Say you got an 800w (remember it might not work!) inverter, you would have to hook it directly to the battery with a finger thick wires. Pencil thin wires will melt and ignite. If you had the 800w inverter straight hooked to you battery terminals, car running, it might get you a few minutes of microwave time before the battery drains... You see the alternator stock only puts out like 80-120 amps (trucks have beefier alternators), and only half of that capacity is available to accessories, so you got maybe 40-60 amps being put back into the battery. So eventually the draw exceeds the available and you'll drain the battery or the battery could blow up or the inverter pop a fuse or catch fire. You can get a 300 amp alternator installed if thats an option you need.

You could do like the car stereo guys and put in a 2,000W system with big fat wires, and maybe a second battery in parallel, but that's of course pricey. If you wanna try it and accept the risk of electrical fire get a 800w inverter, direct wire with thick cables to battery, plug in a 700w microwave, and nuke your dinner for like 60-90 seconds and give the system a recoup and do another round... I wouldn't put on 10 minutes like boiling water or potato cooking. Watch it carefully and get a fire extinguisher.

If you sounded like you knew what you were doing I wouldn't be using all the cautionary language, but go for it, YMMV.

[–] i_scream_trucks 0 points 0 points (+0|-0) ago 

Quick example for this wall of text (it's a good wall not knocking it)

I'm sitting in my garage with a portable air con unit. Its on a double adapter on an extension lead in a 20amp gpo.

When it was plugged in to a powerboard connected to the lead with the light, it would do its low power thing for a bit then the wotsit.... bit that evap... the evaporation unit... kicked in it would drop out the powerboard as its 15amp and didnt like the ac AND a light. Its happy parallel with the board in the adapter tho.

[–] spherical_cube 0 points 1 points (+1|-0) ago  (edited ago)

You can plug any size inverter you want into your car's DC outlet. It's what you plug into the inverter that you have to worry about. Car electricals are so finicky these days, even if it is fuse protected, you could cause secondary damage that will be very very hard to track down unless your mechanic is very very good. And most of them are good ol' boys that just know how to read codes and throw parts, that's it.

Look in your owner's manual, it should tell you the maximum wattage that each outlet can handle. Stick to it.

I'd also chime in and say if you need more wattage than say, what a laptop draws (100W), better to get a generator and run whatever off the generator instead. Generators are cheaper and easier to fix if you overload them.

[–] PM_ME_YOUR_BOOBS2 0 points 1 points (+1|-0) ago 

Wire that shit to the battery and depending on your alternator you could get away with 3000w

[–] zzyzzx 0 points 1 points (+1|-0) ago 

Do NOT attempt to run a microwave oven off of something that you plug into a car 12V power outlet.

[–] HarveyKlinger 0 points 1 points (+1|-0) ago 

Whatever draws less amps than the fuse that controls your cigarette lighter.

[–] spookybm 0 points 1 points (+1|-0) ago 

Depends on the AWG

[–] ToFat2Fish [S] 0 points 0 points (+0|-0) ago 

Not really sure what size they would be I suppose whatever is average for automobiles.

[–] spookybm 0 points 1 points (+1|-0) ago 

Check your manual then. Stay in spec with OEM, is this for an alternator?